This section continues the discussions of various ballistics and shooting related topics as requested by correspondents. If you have a question you have been trying to find an answer to (keep 'em ballistics or shooting related--see your minister for the mysteries of life) email me by clicking here and I'll do my best to find the answer for you and if it is of general interest, publish it here. If you can contribute additional input to one of the answers I'd would appreciate hearing from you too.
On this page:
What spare parts would you
recommend for my (supply your own brand name) gun?
How effective are those "laser" sights seen in all the movies?
How do they get blank ammunition to work the action of semi and fully
automatic firearms?
Just what is a "Scout Rifle?
Won't having a more accurate firearm make me a better shot?
Won't using a higher power "scope" make me more accurate?
What are "mils" and "minutes of angle?"
What commercial cleaning, preserving, and lubricating
products do you recommend?
How long will ammunition last in storage?
What affect does screen spacing have in using a chronograph?
What is the difference between "Boxer" and "Berdan"
primers other than their size.
What are the "standard conditions" used
in ballistic computations?
What are the differences between the various cartridge case base designs
What are "magnum primers" and when are they
needed?
Q. What spare parts would you recommend for my (supply your own brand name) gun?
A. A precise answer for this would depend on whether the particular firearm has a known history of parts breakage or not. However, a good compromise would be to have a spare set of all critical pins and/or screws, any small springs, and a spare extractor, ejector, and firing pin. Don't forget any small parts that could be dropped or lost. (This could be a critical issue with some modern designs that have a bunch of tiny springs and pins.) Such a kit should keep you set for all eventualities. You would also want to include in this kit the appropriate screw drivers, allen wrenches, or other special tools needed to disassemble the firearm.
Q. How effective are those "laser" sights seen in all the movies?
A. The fact that they are used in the movies should pretty well answer that question! In practical use they are not all that effective. With pistols, the dot is much harder to pick up quickly than aligning traditional sights and the normal jiggling of the dot on target makes it difficult to hold it steady on a target, since any movement by the shooter is magnified by the distance. Some testing seems to indicate that they are best for very short range encounters where you are forced to basically point-shoot. Even on rifles they are not all that effective although some nifty shooting tricks can be accomplished by sitting cross-legged and resting the rifle on your legs. For tactical use the same limitation as with the pistol apply. However, they do have a very high intimidation effect in a static situation when the target is illuminated by the red dot. Some folks whose eyes have "matured" and who have difficulty picking up the front sight, especially in dim light do report that with a bit of practice the laser pistol sights work OK but that they aren't as fast as traditional sights.
The one place that laser sights do work well is for night combat using night vision equipment. Night vision equipment can't be used with iron or reflex sights but a laser spot shows up very well in the night vision device.. The laser used in the military for this purpose are infrared, rather than visible light (meaning that the beam or spot cannot be seen with the naked eye). Used with third and fourth generation night vision devices the laser spot can be seen up to about 200 meters and hits obtained under previously unshootable conditions.
Thanks to Spc. Ian Van Harper for reminding me of the IR laser designators.
Q. How do they get blank ammunition to work the action of semi and fully automatic firearms?
A. Because there is no bullet to offer resistance to the burning powder and create pressure and/or recoil, blank ammunition will not normally cycle the actions of self loading firearms. (Contrary to what is sometimes portrayed in the movies.) In gas operated firearms a "blank firing adapter" which constricts the muzzle opening, thus building up gas pressures to an operating level is used. For military firearms these devices attach to the muzzle or flash hider of the firearm. In the movies they are often permanently installed in the bore so the firearm looks normal.
In a recoil operated firearms the blank firing adapter is attached to the barrel jacket in such a manor that the resulting gas pressure acts upon the face of the muzzle, simulating recoil. Another method, useable only with recoil operated firearms never intended to be used again with live ammunition, is to modify them to operate using blowback alone. This is usually done with semi automatic pistols used in the movies.
Because of the inherent dangers, never attempt to make your own blank firing adapters. Also, never use grenade launching "blank" ammunition (usually identified by a rosette crimped case mouth) or blanks with plastic or wood "bullets" with a blank firing adapter. Never attempt to launch grenades using standard blank ammunition. Serious damage to the firearm or personal injury could result because the powder used in blank ammunition intended to simulate firing is usually very fast burning and could generate extreme pressures if used to launch a heavy projectile like a grenade. Conversely, grenade launching cartridges usually have large charges of slow burning powder which could cause disastrous pressures if restricted with a muzzle device, and wooden or plastic bulleted blanks could jam in the restricted opening of the blank firing adapter causing a blow up.
Q. Just what is a "Scout Rifle?"
A. By the definition of the Scout Rifle Conferences held under the auspices of Jeff Cooper in 1983 the scout rifle has been defined as a light weight, handy, general purpose rifle suitable for taking targets of up to 400 kg (880 pounds) at ranges to the limit of the shooters visibility (nominally 300 meters) that meets the following criteria:
Weight-sighted and slung: 3 kilograms (6.6
lb). This has been set as the ideal weight but the maximum has been stated as being 3.5 kg
(7.7 pounds ).
Length: 1 meter (39 inches)
Barrel length: .48 meter (19 inches) 19" - 20" acceptable
Sighting system: Forward mounted (ahead of the action opening) long eye
relief telescope of between 1x and 3x. Reserve iron sights desirable but not necessary.
It can also be fitted with just iron sights or a low power conventional scope
(the 1X - 5X compact variables are very popular) and still be considered a scout.
Action: Magazine fed bolt action with short length receiver. Detachable
box magazine or stripper clip charging is desirable but not necessary as is a magazine
cut-off or provision to prevent magazine feeding.
Sling: Fast loop-up type, i.e. Ching or CW style.
Caliber: Nominally .308 Winchester (7.62 x 51 mm) because of
its compactness, versatility, and availability. However, 7 mm - 08 Remington (7 x 51 mm), .260 Remington (6.5 x 51 mm), and .243 Winchester (6 x 51 mm)
would be useable for frail individuals or where "military" calibers are
proscribed.
Built-in bipod: Desirable but not mandatory.
Accuracy: Should be capable of shooting into 2 minutes of angle or less
at 200 yards/meters (3 shot groups).
Rifles that do not meet all of these specifications are technically not "scout rifles." Thus rifles of this general design in calibers other than those stated above are not true scout rifles but actually "pseudo-scouts." Note, however, even though Steyr Mannlicher (and now Savage) are making production rifles of this type (as well as some wild variations) they are under no legal obligation not to call their variations "scouts" as a marketing tool. Thus the Steyr .376 Scout also known as (and probably better referred to as the ".376 Dragoon" although Jeff dislikes the term) nor the .223 variation are true scout rifles. For that matter neither are the custom made scout-like rifles made up in .30-06, .375 H&H, or what ever caliber. However, there are many parts of the scout design concept that can be handily used on non-scout or "scout type" rifles.
Q. Won't having a more accurate firearm make me a better shot?
A. Not really. It is the shooters ability that really makes the difference and not the ability of the firearm. (Despite what the advertising folks would have you believe.) The intrinsic accuracy of most firearms is much better that that of the vast majority of shooters--probably better than 98 percent of them. I have seen many, many, times an excellent shot hit everything he could see with a pedestrian 3 to 4 minute rifle while duffers with incredible tack drivers missed the proverbial barn less than 100 yards away.
Look at the drawing below. The large circle represents the "group" size (let's say 6" for this example.) that a particular shooter might be able to hold his point of aim to in the field--not off the bench. (That is, his actual point of impact would be somewhere in that circle with the proverbial "one hole" rifle.) With a rifle capable of shooting into 4 MOA off the bench the actual point of bullet impact in the field will be within a 2" radius of the shooter's actual point of aim somewhere within that 6" circle, giving an possible 10" group. (6" + 2" in either direction = 6+2+2=10.) With a 1.5" MOA (just a little more than 1/3 of the 4" group size capable rifle), the resulting actual shooting group would be 7.5" which is not all that much better, and surely not enough to magically guarantee hits in the field for the average shooter. We can't count on the random chance that the error will be towards the center of the target. Until the shooter is capable of holding much closer than the intrinsic accuracy of the firearm, the firearm's accuracy doesn't count for much. While "accurate rifles" are interesting (with apologies to Townsand Wheelen) money and effort spent on learning to shoot well will be much more rewarding than that spent than on trying to build a tack driver.
At this point I am sure that someone is asking, "OK. Just how accurate a rifle do I really need?" While tighter the group size the "better," most authorities feel that if your rifle is capable of 2.5 - 3 MOA 5-shot groups out to 200 to 300 yards that you have more than enough accuracy. That standard is easily achieved by just about any rifle that is properly bedded and shooting decent ammunition. Anything better is just icing on the cake. (By the way, the accuracy standard for US Military rifles is 3.5 moa.)
"Gunnery, gunnery, gunnery. All else is twaddle." - Admiral "Jackie" Fisher (father of HMS Dreadnought)
Q. Won't using a higher power "scope" make me more accurate?
A. Nope! That's another myth. All that a telescopic sight does is to allow the shooter to more easily discern the target against the background but it does not make the shooter mechanically more accurate. The shooter induced error (discussed above) is still present. In fact using too much magnification can actually cause misses for the untrained shooter as any motion is exaggerated and the novice shooter tries to compensate for it, causing even greater errors.
(Refer to Fisher's quote above.) The best investment any shooter can make is to take a good class in practical marksmanship.
Q. What are "mils" and "minutes of angle" (MOA)?
A. The "mil" is a unit of measurement used in military fire control. A mil is the angle whose tangent is 1/1000. That is, the angle subtended by 1 unit at a distance of 1000 units, i.e. 1 yard at 1000 yards. This works out so that there are 6283 mils in a complete circle. As this number is not divisible into whole fractions the mil was changed to give 6400 mils in a complete circle and this became known as "the artillery mil" which is now in standard usage for ranging purposes and scope reticles.
A "minute of angle" is literally the distance described by 1 minute of arc (1/60 degree) at a given range. It is approximately 1.044 inches at 100 yards so for all practical purposes it is 1 inch per hundred yards of range. Thus 3 inches at 300 yards is 1 MOA as is 1/2 inch at 50 yards, or 10 inches at 1000 yards. Minutes of angle are commonly used to describe the grouping ability of a firearm.
| 1 artillery mil = .05625 degrees | 1 degree = 17.778 artillery mils |
| 1 "real" mil = .05729 degrees | 1 degree = 17.453 "real mils |
To convert "artillery" mils to MOA multiply by 3.375 and to convert MOA to artillery mils multiply by .2963.
Q. What commercial cleaning, preserving, and lubricating products do you recommend?
A. This is another one of those dangerous topics as everyone has something they swear by. However, the following products get good reviews from lots of people. (Listed in no particular order.) I have personally been very impressed with Mil-Comm'sTW25B as a commercial lubricating product and either Boeshield or Eezox for long term storage, but I use the homebrew Ed's Red for bore and general cleaning, and either a homemade copper solvent, KG12, or Shooters Choice Copper Solvent for copper fouling, depending on what I grab off the shelf first..
Bore Cleaners: Shooter's Choice
MC-7 (Formerly
Marksman's Choice)
Hoppe's No. 9 (If you don't smell like Hoppe's you ain't a shooter!)
J-B Non-Embedding Bore Cleaning Paste (for tough fouling problems)
Simple Green (A commercial household cleaner excellent for black powder guns.)
Copper Solvents: KG Coating's KG12 (non ammonia based), Sweets 7.62, Barnes CR-10, Shooters Choice Copper Solvent
General Cleaning: Generic automotive brake cleaner (Just as good as
the "gun" products and cheaper.) Just remember that this stuff
removes ALL lubricants and protectants so be sure to re-oil to prevent rust
Preservatives: Boeshield
T-9 (Long term storage)
Eezox
Corrosion X*
Sentry Tuf-Cloth wiper (short term storage)
Lubricants:
TW25B
MC3000 (liquid TW25B)
Lubriplate
130-A (general moderate-temperature lubrication use)
FP-10
Miltech
Tetra Gun G grease
Tetra Gun L oil (Shake well before use.)
Rem Oil (Shake well before use.)
Break-Free CLP (Shake well before use and Do Not use as a bore cleaner!!)
Weapons Shield
Keep in mind that no matter what
lubricant you use, you should use
the minimum amount of lube possible.
You want it lubricated and not an oil
field. All lubricants seem to work best if initially applied to surfaces
that are cleaned and degreased of other old lubricants.
All of the above are available from Brownells or at most gunshops. Simple Green is available from your local supermarket. Automotive brake cleaner is available at any auto store. The caveat about not using Break-Free or Tri-Flow (or for that matter any Teflon containing product) as a bore cleaner is based upon advice from a noted long range shooter who reports that Teflon usage in the bore usually leads to degraded and erratic accuracy. For alternative homemade products click here.
Q. How long will ammunition last in storage?
A. Properly stored ammunition can last at least 40 years or more without any problems. However, the caveat here is "proper storage."
The method the military and ammunition industry use for long-term storage of ammunition is very old and very simple. Make a concrete bunker with walls about a foot thick. Then cover the whole thing about a yard deep with dirt. This construction is called an "igloo". The igloo produces a remarkably constancy in temperature and humidity inside, requiring neither power nor adjustment. Using this technique, modern small arms ammo may be stored for 40 or more years with no material degradation. Conversely, ammo "stored" in a hot car trunk may be dead as a mackerel, or wildly inconsistent in a single summer. However, not all of us have an "igloo" handy. Given even moderately consistent conditions most modern ammunition components are fairly resistant to degradation in the short run, say 10-15 years, absent high temperatures and/or constant temperature fluctuations.
To hit the high points of home storage very generally
1. In general, it is the PRIMER that you are worried about. Absent excessive high temperature and/or humidity, modern smokeless powder is very resistant to degradation in storage. As an interesting aside, corrosive priming compounds that use to be commonly in use have longer storage lives and are more resistant to degradation than comparable non-corrosive priming compounds.
2. No matter where you store ensure there is "dunnage" (i.e. 2x4 wood) under and between each layer stacked. Also ensure there is air space between stacked cases on the same layer. These provide air circulation which is crucial.
3. Humidity--Drier is better, but in sealed cans will make little difference if dunnage and air space are maintained. The ammunition should be packed with a desiccant. You can purchase a commercial product or go the "do-it-yourself" route. Go to any construction site and ask the straw boss if there are are any broken sheet rock boards around or some wallboard scraps. There will usually be. Sheet rock is gypsum and hydroscopic. Get a few pieces and cut them to about the size of a deck of cards square. Cook them in the oven at about 200 degrees for a few hours to drive the moisture out of them, then put one in each of your ammo cans. The piece will absorb what little moisture there may be in your ammo can can giving you a nice dry environment.
4. Temperature--This is a big one with lots of details. Good ammo is like good wine. Both like a constant, even temperature around 65 degrees F. The constancy of temperature is more important than the temperature itself. (This is a dandy excuse to build a wine cellar to store both.), And, as a wise man once said, "you can never have too much of either."
For short-term storage of general-usage ammunition, the most important factor is to keep the ammo out of excessive heat--say over 85 degrees. Excessive heat degrades ammunition. Ammo stored in car trunks is the most common victim here. Low temperatures do not harm ammunition per se. What degradation may occur is caused more by repeated temperature fluctuation than by the cold. (As an aside, double base powders can perform erratically when USED in very cold temperatures, but this is not a function of storage.)
At this point we probably should explain what we mean by "degradation" If you're storing MG ammo or "rattle battle" ammo, for a few years, the garage should suffice nicely, given the constraints above. The standard deviation of the velocity may go up slightly, but I suspect you will not notice a thing. On the other hand, if you are storing match ammunition, I'd recommend keeping the stuff in a place with a more even temperature. The bedroom closet, where the temperature stays nice all year, for instance. With something as precise as match ammunition even a little degradation could be of consequence.
Invest in a "min/max" thermometer that shows both the minimum and maximum temperature recorded. They run 10 bucks or so. Check your storage area monthly for signs of excessive temperature (check the min/max) or other degradation (rust on cans, etc.). There are no magic procedures. Just remember that equipment respected is equipment that will be reliable.
{As an example of what is possible, some years ago I fired some 60+ year old GI .45ACP ammo (FA 18 headstamp) that had been found in a military storage bunker. Of 40 rounds fired every one went off and 5 rounds over a chronograph averaged 788 f/s. -- FF}
Thanks to John Nichols for supplying this information--courtesy his stint with Uncle Sam.
Q. What affect does screen spacing have in using a chronograph?
A. With a chronograph, velocity is determined by dividing distance between two detection "screens" by the time it takes the bullet to pass through both screens. (Originally the "screens" were just that, a screen of fine wire or a circuit path printed on a sheet of paper that was broken by the bullet. Modern chronographs use optical sensors to detect the bullet's passage, but the term "screen" has stuck.) The timing is done with high frequency counters ("clocks") to measure time precisely and modern chronographs with their extremely fast clocks theoretically allow the use of shorter inter-screen distances since time is measured more precisely due to there being more "counts" per second. If a clock is erratic or is off its designed frequency errors will result, but modern clocks are remarkably accurate and consistent .
The greatest source of chronographing error is inaccurate screen spacing. If the inter-screen distance (the distance between the first and second screens) as set into the chronograph is 4 feet and the distance is mis-measured by one-half inch, the inter-screen distance is off by about 1 percent. At a velocity of 3000 f/s this introduces an error of about 30 f/s. With a 10 foot screen spacing a similar half inch error would cause about a .42 percent error or about 12 f/s. It can be seen from this that the shorter the screen spacing the greater the potential velocity error for a given inter-screen distance error. Granted, these errors seem small but such errors can lead to discrepancies between measured data if you are not consistent each time you set things up. Use the greatest inter-screen distance you can conveniently use. I consider 4 feet to be the minimum safe spacing with modern high clock speed chronographs, but with a good unit 2feet will work fine.
Some of the newer 1-piece or unitized chronographs have use a 1 foot spacing and a 1/16th inch error in spacing can cause a .52 percent error or about a 15 f/s error at 3000 f/s. While the one piece units are usually carefully adjusted at the factory there is the potential for misalignment if the units are dropped or subjected to shock. Treat chronographs like the precision instruments they are.
Also, the screen sensors must be pointed up at 90 degrees to the mounting rail. If one of the screens is tipped either toward or away from the muzzle of the gun the inter screen distance will be different that what is set into the chronograph since the bullet path is some inches above the sensors.
 |
|
If the sensor head is tilted (red line) the effective inter-screen distance will be different than what you think. Keep in mind that a tilt of 6 degrees is the angle 1 minute makes on a clock face |
If the bullets path is 9" above the sensor a 3 degree cant of the sensor base will change the effective screen spacing by .47 inch, which will induce an error of about 1 percent or 30 f/s at 3000 f/s with a 4' screen spacing. If one of your sensor head can wobble back and forth by 3 degrees each direction there is the possibility of a 60 f/s total error.
(bullet height above sensor) * (tangent of the angle of cant) = error
Tangent of 3 degrees = .0524 (from Trig tables)
9" * .0524 = .47"
The other "spacing" issue involves the distance from the firearm's muzzle to the mid point between the screens which determines the distance at which the velocity is actually measured. It is common industry practice to set this distance to 15 feet from the muzzle although many handloaders use a more convenient 10 feet for this distance, and the military historically uses either 53 or 78 feet. The actual distance used is not as important as not being too close because it is possible for the muzzle blast to affect a screen's detection of the bullet's passing if sub-sonic projectiles are being measured.
As for correction from "instrumental" velocity to "muzzle velocity the correction is very small at a 10 foot or less distance to the center of the screens--on the order of 5 - 10 f/s for typical rifle bullets and velocities--and this falls well within the standard deviation of most loads. If you consistently use the same muzzle to screen pair distance you really don't need to worry about this correction.
[One other thing to consider about chronographs is their inherent standard deviation error--that is the random error that would occur if a projectile of exactly a given velocity was measured several times. This is a function of its circuit design, clock frequency, and clock stability. The best units in this respect are the current CED Millenium and the Oehlers.]
(NOTE: As of November, 2005, Oehler has announced that it is ending sales of consumer chronographs and is no longer going to ship M35 and M35P chronographs. They will continue to support units in the field for the foreseeable future.)
One other thing to pay attention to is the sturdiness of your mounting of your chronograph screens. Loose, wobbly screens can give errors or false readings. If your screen setup mounts on a tripod, get a sturdy one and not an el-cheapo unit as furnished by many chronograph makers.
Q. What is the difference between "Boxer" and "Berdan" primers other than their size.
A. The two primer types differ in their internal construction. With Berdan primers the primer cup contains only the priming mixture and the anvil is part of the cartridge case. With Boxer primers the anvil is an integral part of the primer assembly. Berdan primers, because of the fact that the flash holes are not centered in the case's base, require special tools to remove them easily and Berdan primed cases are not generally reloaded.
Q. What are the "standard conditions" used in ballistic computations?
A. The "standard conditions" refer to an assumed set of meteorological conditions used to standardize computations. There are actually two "standards." The older one, is known as "Standard Metro" or "Army Standard". The more modern "standard" is called the International Civil Aviation Organization (ICAO) standard. The characteristics of these two "standards" are listed below.
| Standard Metro | ICAO | |
| Altitude | Sea level (0') | Sea level (0') |
| Temperature | 59° F | 59° F |
| Barometric pressure | 29.5275" Hg | 29.9213" Hg |
| Humidity | 78% | 0% |
While they are similar, the different parameters do have a slight affect on calculations and in effect change the standard atmospheric density by about 1.8 percent. Under ICAO conditions the speed of sound 1116.5 f/s and under Standard Metro conditions it is 1120.27 f/s.
Since a quoted ballistic coefficient depends on atmospheric density, the same bullet has two different BCs depending on the conditions used. If a quoted BC based upon the "Standard Metro" conditions is used in a ballistics program based upon the ICAO standard the BC needs to be modified by multiplying it by .982. Conversely, ICAO based BCs need to be multiplied by 1.018. While this is a very small change and has little effect at short (under 600 yards) range it does have an effect at long ranges
Q. What are the differences between the various cartridge case base designs?
A. There are 5 basic base (rim) designs used as shown below.
The rimmed design was the earliest and provides for easy extraction and headspacing. However, it is not well suited for feeding from box magazines. The rimless design allows smooth feeding from magazines but depends upon accurate case length or a shoulder to insure headspacing. The semi-rimmed case was an attempt to combine the advantages of the rimmed and rimless designs but it was never very popular. The 6.5 x 50 Japanese cartridge and the .220 Swift are examples, although the Swift actually headspaces on the case shoulder. The belted case was designed to provide positive headspacing and allow magazine feeding. The rebated rimmed case was designed to allow a large diameter case while being able to use a smaller (more standard sized bolt face. The .284 Winchester and .40 S&W are examples of this design.
Q. What are "magnum primers" and when are they needed?
A. "Magnum primers" simply contain more priming compound and give a longer and hotter flame than standard primers. Magnum rifle primers are recommended for use with some "ball" powders and large charges of slow burning powders in large capacity cases . Magnum pistol primers are recommend for full power loads using slow burning, hard to ignite powders. While many people have no problem with standard primers under these conditions, if you find that you are getting very high standard deviations in velocity with slow burning powders or large charges try the magnum primers.
As always, when changing components, drop your load a bit and work back up.
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Disclaimer
As far as I know all the information presented above is correct and I have attempted to insure 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 your 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 2007-09-28