Miscellaneous Questions #4

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.

This is a fairly long page and may be slow to load.  MS Front Page says 54 seconds at 28.8.

On this page:

Are oils and solvents dangerous to ammunition?
How much power do I really need in a telescopic sight?
What is the best reticle to use?
What are some good general tests of someone's shooting skills?
At what range should I zero my (supply your own caliber) rifle?
How do changing various components affect chamber pressure and velocity?
Are the 7.62 x 51 mm NATO rounds and the .308 Winchester really the same round?
Are the 5.56 mm NATO rounds (and M193 types) and the .223 Remington really the same round?
What was the largest gun in history?
Can you recommend any "homemade" gun cleaning solutions?

Q. Are oils and solvents dangerous to ammunition?

A. Absolutely! One of the characteristics of gun oils and cleaning solvents is their great penetrating capability. This allows them to seep into places that one wouldn't expect. This can lead to the deactivating of primers and powder which will result in an embarrassing click (or maybe a "Pfffftt!") when you expect a bang. In one test, ammunition was deactivated or substantially degraded in performance in as little as 4 hours after being sprayed lightly with a well known lubricants.

In addition, any lubrication on a cartridge case can cause excessive back pressure on the bolt because the case will be unable to grip the chamber walls, not to mention the attraction of dirt..

Keep ammunition well away from any solvents and lubricants and ensure that your ammunition and chamber are dry prior to firing, and remember--when lubricating your firearm use the minimum amount of lube possible.  You want it lubricated and not an oil field.

Q. How much power do I really need in a telescopic sight?

A. Before we can discuss this topic we have to first understand that a telescopic sight doesn't make for a more accurate firearm. Nor does higher magnification lead to greater accuracy. A telescopic sight simply allows the user to more easily pick out a target from the background. In addition, while higher magnification can reveal greater detail it also magnifies vibration and can actually make a target harder to hit because the shooter subconsciously tries to "beat" the motion.

For general field use somewhere between 2x and 4x is probably the most useful with 6x possibly of use for extended ranges. Beyond these, holding under field conditions becomes difficult and visible mirage can cause additional problems. Keep in mind that 95 percent of all shots in the field are under 200 yards with the majority of them under 100 yards (despite what the gunshop cowboys may claim). With a scope of too high a power it can actually become difficult to hit close in targets, especially quickly, because of their highly magnified image.

A variable power scope can provide the best of both worlds, but keep in mind that the field of view for variables is less than for fixed power scopes, and while modern variable power scopes are very reliable they can exhibit a change of point of impact when changing magnification. If you choose this kind of sight verify that the point of impact remains the same when changing settings.

Some folks recommend variable power scopes because they claim can scan for a target with the higher magnification and then switch to a lower setting for the shot (or some say the other way around). However, doing this violate a primary rule of firearms safety--Never point your firearm at anything you don't intend to shoot. Binoculars should be used for searching. 

Q. What is the best reticle to use?

A. The choice of reticle to use is one of those things "you gotta try yourself" as personal preferences vary greatly. My preference is for what is known as a "duplex" reticle which tends to lead the eye to the center because of its thicker outer legs yet which offers a fine aim point when needed. See the illustrations below of some common reticles and comments about them and the draw your own conclusions. If I could design my own reticle it would be similar to the heavy duplex for the outside legs but the inner wires would be as fine as the standard duplex as shown I have shown.

Standard Crosshair		Duplex Crosshair		Heavy Duplex		MilDot
Gives precision aim point but is hard to see in dim light or to pick up quickly		Gives precision aim point and aim point can be seen in dim light. Faster aim point pick up then standard.		Aim point is not as precise for target use but extremely fast to use under field conditions.		Used for ranging purposes and growing in popularity

German #4		German #1		Post & Duplex
A European reticle that provides fast acquisition with a fine aim point		A European reticle that provides fast acquisition. Popular in the military.		Similar to the German #4 but offering a more open view

Fr. Frog #1

This would give very fast pickup under all conditions yet provide for a precise aim point when needed. This design would probably require an etched glass reticle as current wire technology may not permit this design. A "post & duplex" version would also be acceptable. Asked to provide dimensions I'd say a thick section of about 3 or 4 moa and a thin section of .7 moa. For the spacing between the ends of the thick sections between 18 and 24 moa tip to tip would probably be good.

Leupold & Stevens has a wide variety of reticles that they will install in their scope for a charge of about $47 and Premiere Reticles has an even larger selection for Leupold scopes. Leupold's web site is at: http://www.leupold.com and Premiere Reticles web site is at http://www.premierreticles.com.

Q. What are some good general tests of someone's shooting skills?

A. There are a lot of folks out there who claim to be incredible shots. So how can you find out the truth? First, we need to establish that in the context of my web site we are talking about the practical use of firearm and not gun games. Second, it's not what someone did once, but what they can consistently do on demand time after time that counts. With these things in mind there are several fairly easy to set up tests that will show whether or not the claimer is as good as they claim to be.

Anyone who does consistently well at any of them is probably a pretty good shot with their firearm. And remember, it's not what you did once but rather what you can do on demand that counts. Click here for information on these courses of fire.

Q. At what range should I zero my (supply your own caliber) rifle?

A. Most folks zero their rifles at too close a range. While most shots in the field are taken at fairly short range, zeroing too closely limits (or at least makes more difficult) hitting targets of opportunity at longer ranges. Ideally you want to zero your rifle at the longest range that the bullets path does not rise above half of your target's vital zone. That way you can hold dead on out to a much longer distance than if you simply zero for say, 100 yards.

If we assume, as many people do, a vital zone size of 6 inches, we want a zero such that the bullet's path does not rise more than 3" above the line of sight. A good general rule of thumb is to zero cartridges with a velocity of 2100 to 2300 f/s at about 180 yards, those with a velocity of 2400 - 2900 f/s at 225 yards, and those with a velocity of 3000 f/s and over at 250 yards.

To obtain an good approximation of these zeros, adjust your point of impact to be between 2.75 and 3 inches high at 100 yards (the lower figure for the lower velocities and the higher figure for the higher velocities) and you will be in the ball park. With the proper zero you will be able to hold dead center for ranges from up close to about 40 yards past your zero range (where the bullet drops more than 3 inches). You should, of course, confirm things by actually firing at different ranges. (By the way, the .22 rim fire because of its smaller normal targets is probably best set for about an 80 yard zero which puts the bullet ¾ inches high at 25 yards, 1.5 inches high at 50 yards, and about 2.5 low at 100 yards.) Of course it goes without saying that you should verify you zero at the actual ranges.

If you have ballistics software you can refine these calculations for your particular load.

If you are interested in a more in depth discussion of zeroing visit the "Zeroing" link on my "ballistics" pages by clicking here.

Q. How do changing various components affect chamber pressure and velocity?

A. Changing components can definitely affect things as the tables below show for the .308 Winchester cartridge. As you can see from the data, a change of almost 8,000 cup or more is possible simply by changing one component. If multiple changes occurred the effect could be even greater, and if the initial load was at or near maximum one could easily get into dangerous territory. This is especially true of small capacity cases in high intensity rounds like the 9 x 19 mm where case capacity can vary greatly. Note: These results were typical under the conditions tested. Your firearm and ammunition may behave differently so don't use this as loading data.

Data courtesy NRA.

Most reloaders standardize on a particular brand primer and bullet for a given load and the factor most likely to change is the cartridge case since most shooters will pick up anything that looks like brass. To give you an idea of how things can vary look at the difference in case weights for representative cartridge cases that I have measured.  The weights are based upon the average of 10  fired, cleaned, and unprimed (but otherwise unmodified) cases.  Your cases may differ with different lots so don't count on these figures.  (If you can supply data on other cases I'd greatly appreciate it

In the 9 mm cases the difference in case weights translate to tremendous difference in case capacity. There is an old rule of thumb that for equivalent pressure, charge weight varies by about 12 percent of the difference in case weight. While this rule of thumb is based upon  .308/.30-06 size cases it hold true fairly closely for other case sizes and can at least keep you out of major trouble.

For example, a load developed in 9 mm Winchester brass listed above would have to be reduced by about 1 gr in Remington cases and a whopping 1.3 gr to maintain the same pressure in TZ cases. In a cartridge like the 9 mm where typical powder charges run 5 to 6 grains that's a big 22 percent change.  In the .308 examples above the change incurred from the lightest to heaviest cases would be about 4 grains. With a typical 45 grain charge weight that's about an 8 percent change. It should be noted that average case weight can vary from lot to lot (usually no more than about 2 gr) within a particular brand of rifle cases.  With .308 size cases differences in average weights of about 1.5 gr can probably be ignored safely.  In 5.56 the charge difference can be around .6 gr which with an average charge of powder (27 gr) would about a 2 percent change. The .40 S&W has similar issues.

You should also be aware of the fact that the burning rate of your powder can change slightly from lot to lot. Although the lot to lot consistency these days is quite remarkable there is still the chance that things can change. (This is one reason why big-time match shooters buy large quantities of a single lot of powder).

No wonder the reloading manuals caution you to drop at least 10 percent from any maximum charge data and slowly work up. A good rule of thumb for the amount of an increment to use when working up from a starting load is to fill the case to the base of the neck with the powder you are using, dump and weight the powder, and to then use 1 percent of that weight as an increment. As an example, if your case would hold 55 grains of the powder you are using a good "increment" would be .5 (5/10) of a grain. Once you get "in the ball park" for accuracy (see the article on load development) you could then cut that increment to about half (say to .2 gr in this case) to fine tune things.

Remember. Play it safe. If you change anything drop your load 10 percent and slowly work back up.

A special warning!  Seating depth, especially in small capacity high pressure cases, like the 9 mm and .40 S&W, has a major effect on pressure.  Tests have shown a 20 - 25 percent change in pressures with as little as .05" in seating depth in these cartridges.  A chart for the .40 S&W changing seating depth with the same charge and brand of cases is shown below.  If you couple a change from a thin case to a thicker case with less volume and a change in seating depth it become clear that you can get in big trouble very fast.  This is especially true if you are using cases that have been reloaded a lot and a pistol that has poor case head support.

Pressure changes interpolated from data supplied by Ramshot Powders.

Q. Are the 7.62 x 51 mm NATO rounds and the .308 Winchester really the same round?

A. Well, er, ah, umm--kinda. The cartridge cases themselves are effectively identical with the exception that the NATO specification rounds (those marked with the NATO "cross in circle" mark) have substantially thicker cases than the commercial variety and slightly different tolerances on some dimensions . They are thus able to withstand stretching better when fired in loose chambered military weapons (done for reliability purposes).  There is a pressure specification difference though.  

Thus commercial ammunition may over stress military firearms and their gas systems and coupled with the thinner commercial brass and the larger GI chamber may result in case rupture. 

The NATO specs for the cartridge case dimensions reference different datum points for some measurements but these can be interpolated. Base diameter specifications .2" from the base of the rim are approximately .4706" - .006" for NATO specifications and .4703" -.008" for SAAMI.  The specifications for the diameter at the shoulder of the case is difficult to compute as it is at the intersection of two datum lines but would probably be slightly larger (.4543"  -.006 by my interpolation) than the SAAMI specification of  .4540" +/- 0  at 1.450" from the base of the case.  SAAMI gives the case to shoulder length from the base to the .400" datum on the shoulder as 1.627" - 1.634" while the NATO spec is 1.628" - 1.634".  However, I have gauged many military rounds as being well under the minimum specification, especially non-US military surplus.  (After all it was surplused for a reason.)

The GI .7.62 mm chamber has a larger diameter neck (.3445" +.020 vs. .3442" +.020 SAAMI), a different shaped and dimensioned bullet seat and throat, and more generous diameter tolerances, (.4730 + .002 (interpolated at the .200 reference line) compared to .4714 + .002 for SAAMI.  I am working on obtaining drawings for both the cartridges and the chambers and will post them when available which will show the differences more clearly.

The headspacing requirements for the NATO chamber is much more generous than that of the SAAMI commercial (.308 Winchester) specifications as can be seen in the table below. (All dimensions are from the breech face to the .400" datum point at the shoulder and are taken from SAAMI or US government specification sheets.)

Additional problems can arise when commercial .308 ammunition is fired in military specification chambers since the minimum military chamber is .0015" longer than the SAAMI maximum chamber. Since commercial ammunition is generally dimensioned to fit in a minimum sized SAAMI chamber, the thinner commercial brass can be stretched to the failure point when fired in maximum sized military chambers, while minimum spec military brass is thick enough to stand the stretching.. In addition, military chambers may also be cut on the "generous" size diameter-wise to allow for functioning with dirty chambers. In the other direction, some military ammo may fail to chamber properly in very tight commercial chambers, although it appears that military ammunition is generally on the minimum side of specifications.  

While reports of catastrophic failures seem to be almost unheard of, it is prudent to keep in mind that there IS a difference and to use commercial .308 ammunition only in firearms marked as .308 Winchester. Military ammunition that fits SAAMI chambers properly is considered safe to use in non-military arms.  The headspacing "problem" with military chambers can be taken care of for a particular rifle and reloads by careful adjustment of your sizing die. Most "commercial" rechamberings are done with SAAMI spec chambers. If in doubt or really paranoid do a chamber cast.

... and the .30-06.  For all intents and purposes the cartridges and chambers are the same.  However, US military ammunition is loaded to a specification of 50 -  54 Kpsi average (depending on the particular type of round) while the current commercial .30-06 ammunition is loaded to 62 Kpsi average.  In bolt action rifles this isn't a major thing but in the M1 Garand use of commercial ammunition can lead to battering and the bending of the operating rod.

Q. Are the 5.56 mm NATO rounds (and M193 types) and the .223 Remington really the same round?

A. This is another of those "Well, er, ah, umm--kinda" items. 

There is a slight difference between .223 Remington and 5.56 x 45 mm military ammunition.   While the  cartridge cases themselves are identical (although some dimensions are referenced to different datum points), 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, again,  measured to different datum points 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" that is much longer than the normal field gage to reject rifles.

The chamber 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 similar and it is also loaded hotter than M193..  When military specification ammunition is fired in a SAAMI specification chamber chamber pressure can increase dramatically--M193 typically goes up 3 - 5K psi (from a nominal 55K, while M855 goes up about 10K from a nominal 58K). 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 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.    

*NATO 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.  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 piezo pressure specifications for SAAMI, M193, M855, and CIP (European standards) ammunition are given below.  Keep in mind that the SAAMI pressures are taken in a SAAMI spec test barrel and measured 32 mm from the base of the case.  Military pressures are taken in a mil-spec barrel and chamber and are measured at the case mouth.  CIP pressures are measured in a CIP standard chamber and are taken 25 mm from the case base.

Q. What was the largest gun in history?

A. The largest gun ever used in combat is generally accepted to be the German "Gustav Gun" (and its sister canon "Dora") built in 1941 by the Krupp company. It had an 80 cm bore (31.5") and fired either a 10,500 lb HE projectile (which made a crater 30 feet wide and 30 feet deep) or a 16,500 lb concrete piercing projectile (which would penetrate 264 feet(!) of reinforced concrete). The typical powder charge was about 3000 lb of powder. The range was between 23 and 29 miles and the muzzle velocity was about 2700 f/s. The gun weighed 1344 tons and had a crew of 500 men.  It was used by the German's during the siege at Sevestapol in April 1942. 

One round from Gustav destroyed a Russian ammunition dump 100 feet below Severnaya Bay and covered by 10 meters of concrete, and a near miss capsized a large ship in the harbor. Gustav fired 300 rounds during the siege wearing out the original barrel in the process. A second gun, called "Dora" was set up west of Stalingrad in mid-August. It was hurriedly withdrawn in September to avoid capture and never saw action. Gustav next appeared outside Warsaw, Poland, where it fired 30 rounds into Warsaw Ghetto during the 1944 uprising. 

Late in WW II the US developed a "mortar" called the Little David  which fired a 36 inch (92.5 cm), 3700 pound shell containing about 3/4 ton of explosives about 10,000 yards. Intended for use during the invasion of the Japanese homeland, it was never fired in combat. It required 2 tractors to transport the base and the tube separately.

Mortar in place	36" projectile	Loading projectile

Q. Can you recommend any "homemade" gun cleaning or lubricating solutions?

A. Due to the amount of information this section has been moved to its own page.  Click here to visit it.

Please email comments to Fr. Frog by clicking here.

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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 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 2020-02-29