The Care and Feeding of the AR/M16 Platform Rifles
(How to live happily with your AR platform fighting rifle, as well as some arcane technical info)

The Armalite AR-15/M16 series of rifles has become one of the most popular military rifles ever but there are some tips and tricks that have been learned over the years that make owning and using them easier.  This document has been prepared with input from numerous sources including Pat Rogers, Ed Harris, Colt Firearms, the Gunsite Alumni List, and various professional armorers, and trainers too numerous to mention.  I make no claim that these are absolutes and or that I have discovered anything myself.  You can ignore these suggestions, but you do so at your own peril.

Before we continue....

According to some "experts" the AR/M16 is the worst military firearm ever fielded (with perhaps the exception of the horrendous French Chauchat light machine gun of WW I).  While it is not the wonder design some claim it is not a useless piece of crap and it has been in continuous service around the world for close to 50 years now so it must have something going for it. Just like the vaunted M1 Garand, M14, and the 1903 Springfield rifles (how sone people forget) it had some initial teething problems.

First, as originally introduced to the market the AR-15 had a conventional 1:14 twist barrel as that was the twist used in commercial .22 centerfire barrels.  Unfortunately with this twist the longer M193 FMJ-BT bullet was barely stable at normal temperatures and completely unstable below about 40 degrees F.  In spite of the manufacturer's hype to the contrary at low temperature most rounds would not stay on target at 100 yards.  It took publication of tests by the NRA to get this noticed and the rifling was then changed to 1:12 and stability problems ceased.  The rifling twist change DID NOT affect the lethality of the cartridge, contrary to the rumor mills.

Second, it was claimed that the rifle did not need to be cleaned and in fact cleaning supplies and lubricants were not even issued at first.   (Folks forget that the training and manuals issued with the vaunted M1 Garand, M14, and 1903 Springfield recommended daily cleaning and lubrication. 

Third, the barrel and chamber were bare steel and while that might suffice in dry areas, in the the humidity of Vietnam rust and corrosion resulted and were exacerbated by the small diameter of the bore and chamber.  (Refer to the "no cleaning" above.)

Fourth, the rifle was designed around a non-canister IMR (stick) powder, 8208M, which operated the action properly and at the correct design pressures.  In an effort to make high speed ammunition manufacturing easier the military, without checking with the designer, changed to a non-canister ball powder, WW846.  While it met chamber pressure and velocity specifications the port pressure (gas system) was much higher than the design specs called for, resulting in much faster and more violent cycling of the action, which caused extraction and wear issues.  In addition it was found that the new 846 powder generated very high levels of fouling to the point that it clogged the gas tube and fouled the bore and chamber.

To correct these problems cleaning and lubrication supplies were issued and training started.  The barrel and chamber were hard chrome plated to resist rust and corrosion, and a change was made to the buffer system to reduce cycling speed.  However, the fouling problem continued.  Further investigation by Frankford Arsenal, documented in their report Report R1936, M16 Rifle Gas Tube Fouling - Composition, Properties, and Means of Elimination, by L. Stiefel & B. Brodman, August 1969, determined that the level of calcium carbonate (CaCO₃) used in the powder manufacturing process was way too high (up to 0.9 percent of the components).  Calcium carbonate was used as a stabilizer and as a storage life enhancer.  When the calcium carbonate was lowered to, or below, 0.25 percent the fouling issue disappeared without adversely affecting the stability or life of the powder or its other characteristics. (Winchester/Olin subsequently reduced the CaCO₃ content of their ball powders across the board.)

These changes turned the M16 into a much more reliable rifle.  Interestingly the military, ever obsessed with white glove cleanliness insisted that only minimal lubrication should be used.  It began to be noticed that in dry dusty environments and for that matter in normal use that reliability was still not what was desired.    Numerous independent tests and combat/range experience over the years showed that the M16 can run just fine when quite dirty if heavily lubed rather than dry, even in dusty conditions.  The "heavy lube" idea was recently (July 2010) acknowledged by the military.  Tests showed that heavily lubricated M4s and M16 have 94% fewer stoppages than lightly lubricated ones even in dusty conditions. 

When NATO standardized on the steel penetrator SS109/M855 ammunition with its even longer bullet (about .93" for the M855 vs. .75" for the M193) the twist rate was further increased to 1:7 mainly to adequately stabilize the even longer (1.12") tracer round.  While the M855 is stabilized in a 1:9 twist the 1:7 twist was adopted to insure proper performance with either round.  Again, the rifling twist change DID NOT have any significant effect on the lethality of the cartridge, contrary to the rumor mills.

The current 14.5" barreled M4 carbines run at quite high port pressures because of the shortened gas tube which brings back the fast cycling problem.  To counter this a different, heavier buffer and action spring are used.  A stronger extractor spring is fitted along with the use of a rubber insert and a rubber doughnut to increase extractor tension.  The short gas tube also leads to gas port erosion in heavy use guns..

While the direct impingement gas system can lead to overheating of the bolt and receiver and fouling, proper maintenance procedures will prevent problems.  No firearm is perfect.  Even the vaunted AK-47 and Glock pistols malfunction with great regularity if not cared for.

Leaving aside arguments over it's cartridge's suitability I would have no qualms about carrying one in combat again, although if I could, I'd like to have a gas piston version in 6.8SPC.  

Like any firearm the AR/M16 platform has its quirks and idiosyncrasies.  If you learn about them (as you should with any tool you use) you won't have any problem.

I assume that you know how to completely field strip your rifle.

So now, pay attention!

CLEANING
While having a clean gun is never bad, you don’t have to put up with the white glove nonsense with the AR platform.  While there are a couple of gun writers and other idiots who seem to brag about the fact that they've never cleaned their guns (any gun), the question is WHY would you do that rather than clean them.  Sure, maybe they still (for now) work, but what happens if that "one more little spec of gunk" seizes things up just as the cape buff or VCA (violent criminal actor) take a bead on you.

Field strip the rifle and remove the bolt carrier and charging handle from the receiver.  With the sights on top (to keep cleaner out of the gas tube) swab the barrel and chamber out with a patch wetted with your favorite bore cleaner, and allow it to soak while you continue. 

Remove the bolt from the bolt carrier assembly.  Clean the bolt carrier assembly and be sure to remove any carbon from the bolt cam pin slot, the inside of the bolt carrier (that chrome lined hole where the bolt goes), the smaller hole that goes through the carrier, the bottom of the bolt carrier itself, the firing pin, and the inside of the carrier key.  You can use a stripper clip to run a patch down inside of the bolt hole in the carrier, or a worn 20 ga brush.  A .25 caliber bore brush or a worn .30 caliber bore brush can be used to clean the firing pin hole inside of the carrier,  and a cleaner wetted pipe cleaner or a worn .22 caliber bore brush  to clean the inside of the bolt carrier key. (A new 17 cal brush is ideal.)  

However, do not put anything inside of the gas tube- it is unnecessary, and you will only stick debris in there that can do no good.

 Use your toothbrush to clean the bolt body. 

At this point you can run a wet bore brush through the bore.  Then attach the chamber brush to your cleaning rod and scrub out the chamber. Using a worn chamber brush, wrap a wet patch around it and insert it in the chamber and turn it a few times.  Clean out the locking lug recesses of the barrel extension with cotton swabs.  Run several dry patches through the bore and chamber, insuring that the chamber is dry.  Note that there are also dedicated  locking lug recess cleaning star shaped felt pads that hook onto your bore brush (Brownells #100002057) and an upper receiver cleaning kit with purpose shaped brushes (Brownells # 084000028) that are available to make life easier if you want.

Then wipe/blow out any gunk in the lower receiver.

Disassemble your magazines and blow or wipe out any dirt.  Do not lubricate the insides.

INSPECTION
Before reassembling, check your bolt gas rings for any damage.  To check for serviceability insert the bolt fully into the bolt carrier and suspend the assembly by the rear of the carrier (preferably over something soft).  If the bolt drops out on its own, you need to change the gas rings immediately.   Next, hold the assembly by just the bolt head.  If the carrier falls of the bolt of its own weight the rings are starting to wear and will need replacement shortly.  If it passes these tests, you are good to go. (While the Colt Armorer's School instructors state emphatically that the gun will run with one good ring so there is probably no need to get paranoid about having the slots in the gas rings misaligned,  it is probably a good idea to do so—just in case.  An improvement in the gas rings is the one piece McFarland type ring and if you replace your gas rings replace with one of these.

Inspect the firing pin, bolt cam pin, locking lugs, and extractor for cracks and chips and replace if any are found.  Pay particular attention to the area around the cam pin hole in the bolt and the locking lugs, especially next to the extractor cutout.

LUBRICATION
There are a great number of myths that surround the AR platform, and many of these have taken on the status of urban legends. One very prominent one is that it must be kept white glove clean and other is that the gun runs better dry (lightly lubed) than wet (heavily lubed)--a myth perpetuated in the military manuals and schools. Both of these myths are incorrect.  Numerous independent tests and combat/range experience have proven that the AR platform can run just fine when quite dirty and that it runs significantly better heavily lubed than dry, even in dusty conditions.  The "heavy lube" idea was recently (July 2010) acknowledged by the military.  Tests showed that heavily lubricated M4s and M16 had 94% fewer stoppages than lightly lubricated ones even in dusty conditions. 

A totally dry gun will usually only run 100-200 rds before seeing problems. A properly lubed gun in good condition should go well over 1000. [In my own experience I have watched a test firing involving 3 guns involving some 4700 rounds fired out each over the course of 3 days  where the only "lube" and cleaning done, after the initial startup clean and lube, was to put a couple of drops of oil in the 2 holes on the bolt carrier hole and the bolt head. Not a single stoppage occurred. - Fr. Frog]  Note, however, that using a suppressor will cut down the round count drastically, as will firing multiple rapid fire strings or firing with the selector switch on “high volume” but this can be mitigated by proper and frequent lubrication as mentioned above

The bolt rings function just like the piston rings in your car engine.  Keep in mind that when shooting hundreds rounds at a time, the bolt and bolt rings will get blown dry. How long do you think your car would last without lube??  However, note that it is not the brand or amount of lube used, but the placement of the lube that is critical.  

There are certain wear points in the AR platform that need special attention, and failure to lubricate them can cause a stoppage. A good rule of thumb is to look for shiny marks, which indicates metal to metal contact. If it shines, get it lubricated.  Note the shiny areas on the bottom and sides of the bolt carrier. These are wear points. The slot that the bolt cam pin rides in is another wear point, as is the chromed hole in the bolt carrier that the bolt rides in. The entire bolt carrier should get a coat of lube, but pay particular attention to those shinny areas and put a drop of lubricant down the bolt carrier key. The bolt itself requires a coating of lubricant, paying particular attention to the bolt gas rings and the lugs.  Put a drop of lube on the hammer and sear contact points and on their pins.  Finally, lubricate the sides and bottom of the charging handle and put a little lubricant on the trigger and hammer pins and the sear nose, hammer notch in the lower receiver, lightly lube the face of he hammer where it rubs on the bolt carrier.

The type of lube you use is something else that is full of myths and sprinkled with a little fact. While the military still uses CLP there are now better choices.  Synthetic, rather than petroleum based lubricants are preferred. The general preferences these days are Slip 2000 EWL or MilComm MC-2500 a.k.a.TW25B oil.  A close runner up is 5W20 or 5W30  synthetic motor oil like Mobil 1 or synthetic ATF fluid.  For grease on larger bearing areas like the inside of the upper receiver and charging handle) the grease of choice is Slip EWG or MilComm TW25B.  While you can use EWG or TW25B on the hammer and sear points, either a little generic automotive moly bearing grease or Brownells Action Lube Plus does wonders for these high pressure points.

However, in an emergency just about anything slippery will work as a lubricant.  Ed's Red is particularly good (especially if you leave out the acetone which most folks do) and in fact has tested better than the issue "CLP."  WD-40, 3 in 1 oil, suntan lotion, butter, and even KY and Vagisil (don’t laugh), can all keep you running.  You wouldn’t want to use any of these odd ones for the long run, except for possibly Ed's Red, but for a quick fix they beat having a non functioning gun.

A gun like any other machine must be properly maintained. That does not mean being paranoid about the process but rather to take care of those particular areas that affect functioning.  A good idea is to keep a gun book and annotate it with a round count so that you can figure out when certain parts--extractor springs, gas rings, bolts and barrels need replacing. Keep it lubed to reduce friction and understand that the more you use it, the more parts may need to be replaced.

It is a good idea during a break in firing, whether in a class or in combat, to put a few drops of oil into the two gas ports on the right side of the bolt carrier. The lube will get into the gas rings and keep your gun running smoothly.  Also, while not really lubrication related, when not shooting you should close the action dust cover and keep a magazine in the mag well to help keep crud out of the action.  Every little bit helps.

REASSEMBLY

Reassemble the rifle and check for proper functioning.  Check for proper functioning of the safety/selector, and trigger reset. One of the most common reassembly "goofs" is to not have the firing pin fully seated before inserting the retaining pin, which will prevent the rifle from firing.  You can check for proper firing pin function as follows.  Cock the weapon. Then drop a section of an old aluminum .22 cal cleaning rod (with the ends cut off flush to provide a flat face) down the barrel and then holding the rifle vertical, pull the trigger.  The rod should come out of the barrel. 

SPARE PARTS
If you are a heavy user of an AR platform the following are the recommended spare parts you should have available. Note that some of them are simply commonly lost parts.

AR15/M16 TOOLS 
This list includes the major tools needed to do “depot level” maintenance.  Specialty item have their Brownells stock number listed when available. 

While removing the standard handguards can be done (with great effort) by hand, it generally requires 2 people with the physique of the Incredible Hulk to depress the "delta ring" enough to remove the handguards..  There are commercial tools that you can get that make it easy, but they run about $25.  Some years ago instructions were posted on the web on how to make a handguard removal tool for just a couple of dollars and minimal effort using 1/4" steel rod and a MAPP or propane torch..  The instructions are difficult to locate these days  so I contacted the author, Doug Paul, and have received permission to make his instructions available on my site.  Click here to download a 560k  MS Word version of the instructions.

CLEANING & LUBRICATING SUPPLIES
The following are cleaning and lubricating products. While not the only possible choices these are the most commonly recommended

HIGHLY RECOMMENDED AFTER MARKET ACCESSORIES
The following are some after market accessories that are very popular for the serious AR Platform.  While they may not be right for you lots of folks like them.

MAGAZINES
Magazines are the critical part of the rifle.  You should  inspect all your magazines for cracked or bent feed lips and discard any such magazines if found and pull from service any magazine that generates a malfunction. You should also mark each of your magazines with an identifying mark so bad ones can be easily identified.

Don't buy junk or unknown manufacturer's magazines.  The reasonably priced Brownells "GI" magazines are getting very high marks as are the polymer MagPul "P-Mags," and there are several other excellent brands out there.   Ensure that all your 30 round magazines have the gray Gen III or GI tan followers.  While the Gen II green followers are useable they should be replaced with the newer followers at your earliest convenience.  In my testing the MagPul gray Gen III followers are superior to the new GI tan followers. The MagPul followers have 2% Teflon in their material and are noticeably smoother and more stable in operation.  In addition, because of the change in geometry, the tan followers are not compatible with existing springs.

M16 30 Rd Magazine Followers
Shinny metal	Original design
Dull metal	Vietnam era
Black plastic	Early improved USGI.  Used now in 20 rd mags.
Green plastic	Current USGI follower through 2010
Gray Plastic	MagPul Gen III anti-tilt follower.  Considered by most to be the best follower available
Tan plastic	Latest US military anti-tilt.  Considered by many inferior to the MagPul.  For some strange reason they moved the bullet shaped hump to the opposite side from other followers thus screwing up the "touch" of most magazines

Front view of followers.  New GI on right.  Note change in position of the "hump."	Top view of followers.  New GI on top

The feed lips are a critical part of the magazine.  Out of spec or damaged lips will cause malfunctions.  There seem to be several different specs for the width between the feed lips.  The table below gives three that I know of.  The US Military drawing is #8448674 but so far I haven't been able to get a copy.

Brownells offers an magazine check gage (#080000744) that can be used to check magazines.  It is a copy of the US military gage, part no. 13023560 "magazine feed lips wear tool."  The gauge seems to be based on "drawing #2" and is made with a slight taper with .454" at the bottom and .476" at the top..  To use it remove magazine follower and spring or push the follower down away from the feed lips.  Slide the slotted portion of the lower leg down the back of the magazine from the top of the magazine. The upper portion of the gauge has a very slight taper and should stop just as the gauge has entered the magazine (a "Go" measurement of .454").  If it does not enter the feed lips the magazine should be rejected.  The wide part of the gage ("No-Go") is .475"  If it enters the fed lips to the top of the gage or if the gage goes completely through the feed lips the magazine should be rejected. 

If the magazine is rejected the feed lips can be adjusted with a  Brownells Magazine Feed Lip Tool (#080000314).  However,  if you repair a magazine I would STRONGLY recommend that repaired magazine NOT be used for critical applications and relegated to training use only.  With "plastic" polymer other composite materials magazines the magazines will need to be scrapped or relegated to training use only. Such magazines should be prominently marked to prevent them from being used in critical applications.

Brownells Gage	Military Gage

Also check your magazine springs for strength and any damage or corrosion.  You can check spring strength by comparing the springs force with a new magazine's.

SLINGS
Everyone has their own preference for slinging their rifle.   The best single point sling in my opinion is the Magpul "Multi-mission Sling" which is available in a kit that also contains their ASAP (Ambidextrous Sling Attachment Point) adapter plate lot which allows easy shoulder switching (Brownell #100005695).  This sling has the advantage that it will quickly convert to a 2 point sling if desired using the Magpul  rail sling attachment (Brownells #100-006-197) or other side mount ring type sling adapter up front.  Because it is a quick detachable sling in either configuration the best rail front attachment for it (2 point configuration) is probably Magpul's "RSA" rail sling attachment (Brownells #100006197).

For a dedicated 2 point sling a lot of folks like the Viking Tactics VTAC slings  which can be adjusted to hold the rifle in tight while negotiating obstacles or looser to allow mounting the rifle.  They come in a padded (Brownells #100002868) and unpadded (Brownells #100000669) versions and while the padded version is much more comfortable it seems to have a minor drawback, when used on short AR carbines.  Unless you remove the second buckle on the butt end and make the butt end portion of the sling as short as possible the adjusting strap at the front will be way past the front swivel and the keeper won't work.  You'll probably have to trim and re-burn the ends of the nylon strapping to get rid of the flapping extras.  VTAC offer a "quick release buckle adapter but it is fairly long and might not fit properly with a short rifle and the padded sling.  If you have a railed fore end a good arrangement is probably the Midwest Industry's MCTAR-08 Swivel Mount Adapter  (Brownells #100001993) which has a button release.

ZEROING INFORMATION
There are all sorts of zeroing philosophies for the AR platform.  The most efficient zeroing distance seems to be between 250 - 275 yards.  For a comparison of zeroing strategies click here.  For a set of iron sight and red dot sight zeroing targets, in zipped MS Word format you can click here.

SUB-CALIBER TRAINERS
If you like to shoot your AR a lot or do extensive training with it you may want to look into getting a .22 rim fire conversion unit, or even better, getting (or building) a dedicated .22 rim fire upper.  The conversion units consist of a bolt assembly, magazines, and a .22 RF chamber adapter that allows you to shoot rim fire ammo through your 5.56 mm.  They work quite well and accuracy is good enough for training, although some combinations show excellent accuracy.  The downside of the conversions is that you are shooting lead .222" bullets down a .224" barrel which tends to induce leading and you can block your gas tube with lead shavings although a couple of rounds of ball should blow things clean.  I personally just don't like to crud up a working gun and take a chance with reliability.  The conversion I like the best is the one made by CMMG and sold by them and also marketed by Brownells under their own brand name.  The Brownells unit is available in a package with 3 10rd or 3 26 rd magazines.  [Without going into details DO NOT buy the Ceiner brand conversion.  You will eventually be sorry if you do.  Note as of Nov. 2011 Ceiner is out of business and in legal trouble.]  Note that all these conversions like high velocity ammunition with plated bullets, exclusively.

CMMG /Brownells Conversion Unit (shown with magazines)

The thing I like the best is to build or buy a dedicated .22 RF upper using a barrel designed for 22 RF.  CMMG make a dedicated barrel and adapter that works with their (and Brownells) conversion unit.  Added to a dedicated inexpensive upper receiver topped with an inexpensive red dot optic it will give you hours of enjoyment and practice on the cheap. CMMG and others also offer complete .22RF uppers but it is more fun to build your own. 

CMMG Barrel and adapter

AMMUNITION SPECIFICATIONS
There IS a difference between .223 Remington and 5.56 x 45 mm military ammunition.   While the  cartridge cases themselves are effectively identical with the exception that military and/or NATO specification rounds (those marked with the NATO "cross in circle" mark) may have thicker cases and are thus able to withstand stretching better when fired in loose chambered military weapons (done for reliability purposes). From the data I have seen the headspace specifications are identical for SAAMI and military ammunition although measured to different datums and the dimensions of the cartridge cases are the same.  While the standard .223 and 5.56 NATO use the same headspace gauges, the Colt factory uses a special "maximum field gauge."

The chamber throat dimensions are where big differences are.  While there are just minor dimensional and tolerance differences in the body area, the big differences are in the throat areas.

There are actually 3 standard chambers, SAAMI, US GI "NATO," and FN NATO.  Commercial SAAMI specification .223 chambers have a much shorter throat, a smaller diameter bullet seat, and less freebore than the US GI  military chamber and the NATO chambers. This typically results in the ogive of the M193 Ball bullet touching the ball seat of the SAAMI chamber. The profile of the M855 bullet is different and doesn't cause this condition.  When military specification ammunition is fired in a SAAMI specification chamber chamber pressure can increase dramatically--sometimes up to 10,000 psi. While this should not cause any problems in modern well made rifles it should give one pause. Conversely, SAAMI specification commercial ammunition when fired in a military chamber gives significantly lower pressures and velocities.   

The reason the big difference in the FN NATO chamber is that the  deeper intrusion of the M856 tracer bullet into the powder space was found under some conditions to cause riveting of the bullet, which gave a steep pressure spike. (This has also been seen with 77 gr and 80 gr match bullets.)  Thus the FN NATO 5.56mm chamber has an intermediate 11 degree, 30 minute cone transitioning between the case shoulder and the case neck to help eliminate this problem. as marked with the red dot on the drawing below.  This chamber is primarily used on the M249 SAW.  The US "NATO" chamber used in the M16 rifles does not have this double shoulder but otherwise they are identical.

The data below shows the dimensional differences between the US GI NATO and SAAMI chambers.    

FN NATO STANAG dual angle detail

It must also be noted that all 5.56 x 45 mm NATO ammunition (such as US M855) requires a 1:9" twist or faster rifling to stabilize the long 62 gr ball bullet and a 1:7" twist to stabilize the extremely long tracer variation and the 77 gr OTM bullets.  The standard twist used for .223 Remington commercial chamberings is 1:12" or 1:14" neither of which will stabilize the NATO type ammunition.  There does seem to be a recent push to standardize the 1:9 twist for .223 though.  The NATO ball ammunition is easily identified by its green bullet tip.

The pressure specifications for SAAMI, M193, and M855 ammunition are given below.  Keep in mind that the military pressures are taken in a mil-spec chamber and have a different pressure reading point (at the case mouth) than SAAMI chambers (mid-case).

The data below on the  M193 and M855 are from ATK Product Manual and are based on a full length (20") M16 test barrel..  The MK262/362 data is based on published sources and assume an 18" M16 SPR type barrel..   Pressure and velocity specifications are based on the NATO 5.56 mm chamber (not SAAMI .223). In practice the charge weight is lot adjusted to meet velocity and pressure spec.  

M193 Ball
56 gr - 2 gr; Vel =3250 +/- 40 @ 15' SD 40
Pressure 55 Kpsi (piezo), or Avg + 3 SD <= 61 Kpsi
Port Pressure (M16) = 14.4 +/- 2 Kpsi (piezo)
Propellant WC846 28.5 gr or CMR170 26.6 gr (adjusted to give spec performance)

M855 Ball
61.8 gr +/- 1.5 gr; Vel 3020+/- 40 @15' SD<= 40
Pressure 58.7 Kpsi (piezo), or Avg + 3 SD <=64.7 Kpsi
Port pressure Avg +5 SD >=15.3 Kpsi
Propellant WCC844 27 gr or WCR845 27 gr (adjusted to give spec performance)

For M193 and M855 equivalent handloads BL-(C)2 748, H335, H4895, TAC, and Benchmark are suitable powders

MK262 Mod 0/Mod 1 (These are believed to be the actual specifications)
77 gr Sierra MatchKing (Mod 1 is cannalured lightly); Velocity 2780+/- 40 @15' SD<= 30
Pressure 58.7 Kpsi (piezo), or Avg + 3 SD <=64.7 Kpsi
Port pressure Avg -3 SD >= 15.3 Kpsi
Propellant RL 15 (chrg unk) or non-canister TAC 24 - 25.5 gr (adjusted to give spec performance)

MK362 Mod 0/ Mod 1 (Currently experimental - works in 1:9 twist bbls)
75 gr Hornady BTHP (Mod 1 is cannalured lightly); Velocity 2800+/- 40 @15' SD<= 30
Pressure 58.7 Kpsi (piezo), or Avg + 3 SD <=64.7 Kpsi
Port pressure Avg - 3 SD >= 15.3 Kpsi
Propellant RL 15 (chrg unk) or non-canister TAC 24 - 25.5 gr (adjusted to give spec performance)

For the MK262/362  equivalent handloads TAC, RL15, AA2230, H335, and H4895 appear suitable with TAC looking the best.

Load notes:  With the Hornady 75 gr BTHP (#2279) seated to 2.26" OAL, using 24.5 to 24.6 gr of TAC, in LC08 cases weighing 92.5 gr avg, UNPRIMED,  and Federal small rifle primers your will get 2760 f/s in a 16" 5.56 mm NATO chambered barrel at the same pressures as the GI issue MK 262 ammunition.  If you use cases of a different weight you will need to adjust the charge weight by 12% of the difference in case weight.  If you use different primers, start at 24 gr and work up in 1/10 gr increments.

The use of CCI #41 primers is highly recommended.

As to velocity loss for standard 5.56 mm ammunition from different barrel length it is hard to give a definitive answer.  I have seen a fairly large variance in data.  From barrels from 20 inches down to about 12 inches the velocity loss runs approximately 50-60 f/s per inch.  Under 12 inches it is about 100 f/s per inch.  "Your mileage may vary."

BARREL WEAR AND TEAR
Because the 5.56/.233 is a fairly high intensity round, barrel throat wear can be an issue, especially with heavily used rifles or those fired extensively on full auto.  As the throat wears accuracy and velocity will decrease.  While throat wear is best examined with an optical bore scope a good indication of wear can be measured with a bore rod.  This is simply a rode of a specific diameter that is inserted into the throat and the depth of penetration is measured by guide marks along the rod.  The military has such rods specifically for the M16 but they are not easy to come by.

If you start with a known new barrel you can make your own by turning a 13"  piece of .250" steel rod to exactly .219" for about for about an inch. The measuring tip should have a clean and fairly sharp but smooth edge.  Remove the bolt and carrier and gently insert the gauge into the chamber until it goes into the throat.  With the rod centered in the upper receiver carefully put a mark on the rod even with the rear edge of the receiver.  This is your starting point. As the throat wears the rod will go further and further into the throat. When it goes more than about an inch or inch-and-a-half it is time to start thinking about replacing the barrel.

The other area of concern is the gas port, especially with the shorter barreled M4 carbines which operate at a higher port pressure than the longer M16 rifles.  The area at the front edge of the port in the bore will begin to erode causing a lose of gas system pressure.  This wear is not detectable with a gage and must be inspected with a bore scope.

ACCURACY TEST LOAD
If you want to test the accuracy of your AR there is a simple, consistent load that originated with Wally Hart of benchrest fame that can be used to test with. Use the Sierra 52-gr. or 53-gr. benchrest bullet and 22 grs. of H4198 or IMR4198; or alternately 23.5 grs. of H322, and anybody's match primer, in whatever brass you have, but sorted by make or arsenal and year. Seat to 2.26" OAL.  DO NOT exceed this charge with 4198, as this is a fairly fast burning powder for this case. As for the H322, this surplus powder varies from batch to batch, and while the 23.5 gr. charge suggested to me was a mild load with the lot I used, others may run faster, so please be careful.

This is not a high velocity load, about 2950 fps in the full length AR-15, but it is HIGHLY accurate. It shoots well in 7" to 12" twist barrels. If a .223 rifle will not group with this load, it will not group with ANYTHING! (In a full blown benchrest rifle, using GI cases assembled on a Dillon loader, with no benchrest tricks whatever, this ammo averaged 1.39" for twenty-five consecutive 10-shot groups at 200 meters fired the same day, running a round-robin on five different makes of primers.) Primer seem to make no difference either! The CCI450 and Federal 205 seem best , but Winchester WSR is also very good if priced competitively.

AMMUNITION TYPES
This is a fairly up to date listing of US Military 5.56 ammunition

MISCELLANEOUS INFORMATION

RECEIVER MANUFACTURERS

The following is a listing of who machines the raw receiver forgings for whom

Aero Precision Aero Precision Continental Machine Tool Stag     Used by early S&W Rock River Arms High Standard Noveske Century (New) Global Tactical CLE S&W MGI Wilson Tactical Grenadier Precision Colt JVP Double Star LRB Charles Daly LAR Manufacturing LAR Bushmaster Ameetec DPMS CMMG Double Star Fulton Armory Spike's Tactical American Spirit American Spirit

Lewis Machine & Tool LMT Lauer DS Arms PWA Eagle Armalite Knights Armament Barrett Mega Machine Shop Mega GSE Dalphon POF Alexander Arms Olympic Olympic SGW Tromix Palmetto Dalphon Frankford Century (Old) S&W S&W (Current) Stubborn Mule Outdoor Supply LaRue Sun Devil Sun Devil forged billet receivers Superior Superior Arms Lauer (New)

CHAMBERINGS

The following is a listing of known commercial chamberings on the "standard" AR platform.

MANUALS
I have available a CD that contains the following manuals and files of interest for AR/M16 owners.  If you own an AR you should have this CD.  Note that this CD can not be shipped outside of the United States.

• TM 9-1005-319-10 -  Operators Manual for M16A2, A3, A4, and M4, M4A1

• TM 9-1005-319-23P - Unit and Direct Support Maintenance Manual (Including repair Parts and Special Tools List) for M16A2, A3, A4, and M4, M4A1

• TM 9-1005-249-10 -  Operators Manual for M16 and M16A1

• TM 9-1005-249-23P - Unit and Direct Support Maintenance Manual (Including repair Parts and Special Tools List) for M16 and M16A1 

• TM 9-1005-309-10 - Operators Manual for M231 Port Firing Weapon

• TM 9-1005-309-23P - Unit and Direct Support Maintenance Manual (Including repair Parts and Special Tools List) for M231 Port Firing Weapon

• FM 3-23-9 C3 - Marksmanship

• Change 4 to FM 9-3-23

• M16 Armorer's Checklist

• MIL-R 63997B (M16A2 specs)

• MIL-C 71186 (M4A1 specs)

• MIL-C 70599A (M4 Specs)

• GI M16A2 and M4 Zeroing targets

• MCRP 301A - Marine Rifle Marksmanship

• Zipped Archive of special zeroing targets.

• MEUSOC Qualification Course

• M16/M4 Malfunctions, Corrections, & Drills

• A PDF version of this web page

• STANAG4172 5.56 x 45 mm NATO Ammunition

• Zeroing the AR-15/M16/M4

• Canadian C7 Rifle and C8 Carbine manual

• SOPMOD Program Presentation

• Making a Handguard Tool

If you would like a copy of this information shipped via 1st class mail, send $12 in cash, check, or MO to

John Schaefer
1365 S. Saddleback Dr.
Cottonwood, AZ 86326

If you have other relevant AR/M16 manuals in PDF format that you think should be included on this CD, if you send them to me, by clicking here, I will send you a free CD with your addition included.

Please email comments or questions to Fr. Frog by clicking here.

| Back to Fr. Frog's Homepage |

Disclaimer

As far as I know all the information presented above is correct and I have attempted to ensure that it is. However, I am not responsible for any errors, omissions, or damages resulting from the use or misuse of this information, nor for you doing something stupid with it. (Don't you hate these disclaimers? So do I, but there are people out there who refuse to be responsible for their own actions and who will sue anybody to make a buck.)

Updated 2012-01-15