Miscellaneous Questions #16

This section contains brief 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 and 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.

Check back frequently as new topics are always being added.

On this page:

What are the qualification tests for Federal Sky Marshals?
What is "subdued" or "dim" tracer ammunition?
Is the super hot 9 mm submachinegun ammunition dangerous to use in pistols?
What does leading in pistols or revolvers tell you about your loads?
How effective was the ancient sling compared to a firearm?
How do the various .38 cal/9 mm duty rounds compare to each other?
Why are some cartridges loading to a lower pressure than others when the same gun is chambered for both high and low pressure rounds?
Why are there so many different cartridges with effectively the same performance?
How effective is the P90 "submachinegun" used on Stargate?
At what point is the bullet traveling the fastest?
What were the ballistics of the pistol cartridges commonly used in the "wild west?"

Q. What are the qualification tests for Federal Sky Marshals?

A. There have been 2 tests.  The first was so difficult that few could pass it.  The newer one is easier but the original qualification standards are still strived for.

Q. What is  "subdued" or "dim" tracer ammunition?

A. Subdued tracer ammunition gives a lower level of visible trace for the first 75 to 100 yards of flight to avoid giving away the shooter's position.  "Dim" tracers,  give a very low level of trace for the entire flight and are almost invisible unless viewed through night vision equipment.  Standard tracers are identified by a red tip, subdued tracers by an orange tip, and dim by a violet tip.

Q. Is the "super hot" 9 mm submachine gun ammunition dangerous to use in pistols?

A. The myth of the super hot 9 x 19 mm submachine gun ammunition seems to resurrect itself every couple of years.  The NRA did some testing and found several things.  First, the higher than normal velocity specification were based on lighter than normal bullets--typically 90 - 100 grs, and the velocity specs were derived from longer test barrels (nominally 8" - 12") that typified SMGs. Second, the usually very loud muzzle blast that occurred when fired in pistols was due to the use of slower powders optimized for long SMG barrels.  Velocity and pressure testing gave pressures within what we call "standard" to +P ammunition and lower than expected velocities from a pistol barrel with 115 - 124 gr bullets.   Some of the mid-90 gr projectiles ran around 1400 fs from a P-38 pistol with a 4 7/8" bbl which is typical pistol velocities for such a light bullet.  One reason for the "SMG Only" warnings on some ammunition is that it is either steel cased rather than brass cased (like some WWII German ammunition) which could give extraction problems in many pistols, or that it is loaded with extremely hard primers.  While "SMG Only" ammunition may be unpleasant to shoot in pistols because of its muzzle blast it is safe to use in any modern pistol chambered for the 9 x 19 mm. 

The international CIP specification for commercial 9 x 19 mm ammunition is 34,083 psi with proof at 44,300.  No +P specification is indicated.

Note that the new US M1152/53 9 mm ammunition runs at very high pressures and gives velocities of 1326 and 962 fs respectively from a 4.7" barrel.

Q. What does leading in pistols or revolvers tell you about your loads?
A. Generally, leading that occurs towards the muzzle end of the barrel indicates too high a velocity for the alloy or lack of lube issue. Leading that occurs towards the chamber or cylinder can indicate several things. First, if the bullets are undersized compared to the throat diameter of the cylinder, they may be entering the barrel slightly off center which can cause leading. Second, if the alloy used is too hard to obdurate (or upset the bullet base) gas can leak past the bullet base and cause leading. Third, too light a load can also create this same situation because it does not produce enough pressure to upset the base of the bullet. It is commonly believed that a harder alloy is the answer to stopping leading, but at times a softer alloy can actually help.

Q. How effective was the ancient sling compared to a firearm?

A. Some literature suggests that the sling was capable of accurate use to several hundred yards by an expert slinger but there doesn't seem to be any information to confirm this.  There are several historical drawings showing slings being used to take birds in flight.  Typical projectiles range from an almond shaped "sling shot," to cast round lead balls, and simple stones. There were also long dart-like projectiles used but I have no further information on them.  Slings ranged in length from about 4 to 5 feet in length on the average.

1.4 oz slingshot (1.5" x .8" x .6")

Several years ago some different types of projectiles were tested for distance by an admittedly "non-expert"  and the results are given below.  For the typical loop sling used the table below shows the ranges obtained with different weight projectiles in this test.  Interestingly, velocity in all cases was between 100 and 125 f/s.  At those velocities the 1.4 oz  (612 gr) .75 caliber lead ball would have about 14 ft/lbs of kinetic energy, the 3.5 oz (1530 gr) 1" caliber lead ball would have about 35 ft/lb of kinetic energy, and the 5.6 oz (6560 gr) stone (probably about 2") would have about 146 ft/lb of kinetic energy.

While not very impressive by shooting standards, a hit to an unprotected body part, especially the head or upper torso, could be quite damaging if not fatal.  A rain of shot from massed slingers (who could each launch 4 to 6 balls a minute) would not be something to take lightly even at some distance.  The modern world distance (not accuracy) record by a modern expert slinger is1450 feet for a oval projectile and 1550 feet for a dart shaped projectile so it is possible that trained slingers of old could be a serious concern at 300 to 500 yards.  Interestingly, slings have been used in modern combat to throw grenades although I'm not sure I'd want to be whirling a grenade about with the pin pulled and the fuse burning.

Q. How do the various .38 cal/9 mm duty rounds compare to each other?

A. The table below summarizes the performance of the  9 x 19 mm (9 mm Luger), .38 Spl +P, .38 Super ACP, 9 x 23 mm, .357 Magnum, and .357 SIG, with two commonly used bullet weights.  Data is the advertised ballistics from various factory tables.  There is some discrepancy between manufacturers as to the velocities obtainable with +P and +P+ loads but this table gives a fairly accurate portrayal of the differences.

And while we're on the subject, you can see from the above table, that despite all the hype in the media the 9 mm Parabellum is not some kind of a magical super deadly round.  

Q. Why are some cartridges loading to a lower pressure than others when the same gun is chambered for both high and low pressure rounds?

A. Several reasons for this.  First, way back when, steel and powders weren't what they are today so they set max avg pressures to what were believed to be safe levels, and the standards just stuck. As an extreme example take the .30-40 Krag which is limited to about 40 k cup. In the guns of the day, including the Krag, going to 42 k cup started cracking locking lugs. Same thing with the .45-70 which was limited to 28 k cup. Both of these rounds can be loaded way up in modern rifles--the .45-70 is routinely loaded to over 35 k for use in modern lever guns. In a modern action with new brass I've seen the .30-40 loaded to about 55 k psi which would pretty much take a Krag apart. (But then, since one can easily take anything that walks in North America with the standard Krag load, why bother.)

Second, there are a lot of older firearms around that won't stand much above the original lower pressure loadings and the ammo companies run in fear of a lawsuit should someone stick a hot load in an old firearm. This is the reason that the .357 and .44 mag have cases longer than their parent cases to prevent chambering in a firearm not rated for their pressures as you can run a .38 or 44 Spl case at mag levels easily, and that's why lots of older rounds that could safely be run hotter, are not.  Modern cartridges that were never chambered in "old" guns are produced with higher pressures.

Third, the cartridge case also plays a big part in the pressure limits. Some designs are not very thick in the base and head area. The generally accepted pressure limit for brass cartridge cases is about 70 K, assuming good tight headspacing and chamber dimensions. Using specially designed steel cases in a .30-06, apparently safe operations have been done at 80 k+ pressure levels--but velocities only went up about 300 f/s and muzzle blast and barrel wear were drastically increased.

As an  interesting aside. SAAMI is pretty much a paper organization of good ol boys. Cartridge designers tell SAAMI what the specs will be and SAAMI's test procedures are archaic to say the least. The rest of the world follows CIP standards which are much more detailed and meaningful. Due to their different measuring protocols pressures are slightly different than SAAMI. As an example for the .308 Win SAAMI max avg is 62 k psi (piezo), 52 k cup (copper crusher) and CIP's standard is 60,190 k psi (piezo). Currently the highest official operating pressure in a commercial cartridge as listed by CIP as 68,200 k psi (.338 Lapua, and a couple of other esoteric rounds) which is just about at the brass limit.  

Q. Why are there so many different cartridges with effectively the same performance?

A. Ah! The plethora of similar cartridges.  As a friend says, "What are they for? Why to SELL, you silly goose!" Ballisticly it takes about a 200 f/s change in velocity to make a truly noticeable effect on performance. Of course nobody cares about that fact since most folk forget that marksmanship and not gadgets or trick ammo is what counts.  They think that a new trick cartridge will automatically make them a better shooter.  Besides, if you don't use the latest razzle-dazzle .337 Super Slam Bam cartridge you just aren't "in."

Sometimes new cartridges come about in an effort to get big cartridge performance from a smaller case. The Winchester short, and super short magnums are a good examples. However, such things come with a price. The WSM and WSSM run at quite high pressures and have very short necks. They are VERY hard on barrel throats--the .300 WSM has been reported to burn out throats in as little as 500 rds.

Q. How effective is the P90 "submachinegun" used on Stargate?

A. Despite all the manufacturer's hype and Hollywood glitz The P90 "Personal Defense Weapon" (not "submachine gun") is not as effective as they want you to believe.  It weighs about 6.5 pounds with a loaded 50 rd magazine.  It is a blowback operated firearm.  It was originally designed as a "personal defense weapon" for rear echelon troops and vehicle crew members that would be smaller than a rifle, easier to to shoot effectively than a handgun, have a large magazine capacity, and that would penetrate most infantry body armor out to 100-200 yards.  The general trend is to use small, high velocity cartridges l.

The 5.7 mmSS190 ball penetrates between 10 and 11 inches of gelatin, but the wound resulting from this projectile is a relatively small.  The permanent cavity at its largest is either a .22 cal hole or simply a . 22 caliber flat slit the length of the projectile (2.1 cm) caused by the projectile tumbling.  

Although the 5.7 x 28 mm SS190 round penetrates soft body armor, its wound trauma incapacitation potential is at best like a .17 HMR or .22 Magnum. Even 9mm NATO FMJ makes a larger wound--and I'm sure you know of the awe inspiring incapacitation potential of M882 FMJ 9 mm ball from the M9.  While it's stated "effective" range is listed as 200 meters this is pushing things a bit.  While it can deliver a severe wound at that range, even up close it lacks the "stopping" ability of most regular pistol rounds and that is what you want when you shoot someone.  There are some special purpose "Secret Service only" AP loads that will defeat level IIIA body armor with ease but their solid projectiles do no not make a very large permanent cavity.

Also consider this.  The reputation of the  5.56 NATO rifle round either M193 or M855 is marginal.  If a 55 gr at 3200 or a 62 gr at 3030 s considered "marginal" how can a 30 gr projectile at 2300 fs (much less from the 4.8" Five-seveN pistol) be such a magical stopper?  DUH!  Yet people continue to talk  like the 5.7 rd is the hammer of Thor.  It may work OK but it's far from magic.

The "civilian" 40 gr softpoint 5.7 mm rounds may be a bit more effective in creating a permanent cavity but penetration would be reduced. I haven't seen any tests of this round and wound profiles are not in evidence but they too will reportedly penetrate some body armor.  But we're still talking about a .22WRM rifle performance round.

The P90 is also available in a semiautomatic civilian version with a 16" barrel as opposed to the 10" military version.  The 16" barrel gives about 140 f/s greater velocity with the SS197 ammunition.  Below is a table of known ammunition variants.  Only the now discontinued SS196 and the SS197 variants are available on the civilian market.

The problem with the 5.7 x 28 is that in order to get the desired penetration in armor they have to use a very light, non-deforming bullet and for any kind of acceptable performance they have to load to extreme pressures.  The "high performance" ammo available to "official users" runs so hot the cases are deformed on ejection.  (I always wondered why they didn't use slightly larger diameter case or a locked breach design like the MP7. They could have achieved better ballistics at the same pressure.  Even the .221 Rem Fireball could have been used  and easily gives a 40 gr bullet 2700 f/s from a 10" barrel.  With a steel core 40 gr bullet it would defeat most soft armor easily and magazine capacity would only be reduced to 35 or so rounds.  In a 10" Contender barrel you can get slightly over 2800 f/s.  The 7.62 x 25 necked down would have worked too.  Even in it's conventional form some loads reach close to 1900 in short barrels.

Now if they'd just chamber the P90 for the 10 mm ACP cartridge....and its little known of "penetrator" round. (Not holding my breath.)

Better options than the P90 are, in my opinion, the gas operated H&K MP7 and the Brügger & Thomet recoil operated MP9 The  MP7 is a gas piston, locked breach design.  It is limited by it's 4.6 x 30 mm round which leaves a bit to be desired, in power but it could be adapted to other rounds running at pressures not useable in a blowback arm  It has a 7" barrel.  The MP9 is a "locked blowback" that uses either the 9 x 19 mm or 6.5x25 mm round that features a 4 mm saboted tungsten projectile and provides rather good WTI and excellent hard target penetration. In 9 x 19 it's just another SMG. The MP7's 4.6 runs a 31 gr .18 caliber projectile at about 2350 f/s from the 7" barrel of the MP7 while the 6.5 x 25 runs a saboted tungsten 4mm, 31 gr projectile at about 2400 fs from the 5" MP9 barrel. There is a variant ammo that uses a penetrator with a spoon shaped cutout that provides better WTI while only slightly reducing hard target effectiveness.  The MP9 is available with either a 5" or 7" barrel. One of the advantages of the 6.5 x 25 is that with a simple barrel swap it will function in weapons chambered in 9 x 19 so conversions are easy. 

What would be VERY nifty would be the MP7 in a 6.5 x 28  (or whatever case length that gave you an oal equal to the 4.5 x30  round based on a stretched 9 x 19 case, or perhaps the 9 x 23 round, either as is or sub-calibered like the 6.5 x 25.  This would fit the MP7 nicely and give even better performance at an estimated 26-2700 fs with the 31 gr saboted projectile, and could use either load with a bbl switch..

HK MP7 PDW

B&T MP9 PDW

Left to right:  5.7 x 28, 4.6 x 30, 9 x 19, 6.5 x 25

The .300 Blackout round has possibilities and can use standard M16 magazines but it currently lacks an effective AP round.  Perhaps a 5.56 or 6 mm, 60 gr saboted hard projectile might do the job here and even without the AP round it would be more effective on soft targets than the smaller "pistol-like" cartridges.  In a 9" barrel the .300  will run a 110 gr projectile at 2300±, so a saboted  60 gr projectile should get close to 2700 fs.  In a piston gun with a folding stock this would be nifty. The discussion is open!

Long range battle carbines they are not, but they make sense for vehicle crews or REMFs.

Thoughts on the PDW concept

The issue is what are the requirements for a PDW?

The original idea was to provide a light weight, compact, easy to carry and shoot, firearm for military personnel not directly in combat on the front lines.  It would be able to defeat body armor out to 100-150 meters.  For non-militray use the body-armor requirement might be dropped and something in say 10 mm ACP might suffice

The most portable "PDW" would be a pistol, but pistols are generally lacking in penetration (especially armored opponents that the .mil folks would likely be facing, and they are not easy to shoot accurately for semi-trained people, and lack the range necessary. Adding some kind of shoulder stock simply makes them easier to shoot without addressing the effectiveness issue.  Same with a conventional SMG.  The other end of the spectrum would simply be a short barreled version of the standard battle rifle, but these are not really that compact nor handy when you are engaged in something other than combat.

The US recently adopted a new SMG, the B&T 9APC.  While billed as a close protection weapon it will probably be cross purposed as a PDW, with all the armor defeating limitations of the 9 x 19 mm cartridge.

B&T 9APC

The specifications for a good PDW might be something like:

• Weight: 6 pounds or less
• OAL: 24" extended, 18" or less folded/compacted. Able to be fired in folded/compact mode
• Magazine capacity: 20 - 30 rds
• Effective range: 200 yards
• Sighting system: Long life red dot
• Caliber: Must be effective against common body armor to 150-200 yards, and provide sufficient WTI to take the person shot out of the fight within the effective range.

But then nobody listens to me.

Q. At what point is the bullet traveling the fastest?

A. One would assume that the bullet is traveling it's fastest at the moment it exits the muzzle and begins to shed velocity immediately, and for all practical purposes this is true.  But for nit-pickers there is more of a story.

As the bullet exits the muzzle the expanding powder gases continue to exert some force on the base of the bullet until the gas has dispersed enough so that the force on the bullet's base dissipates.  This occurs, according to researchers at Aberdeen Proving Ground, at a distance of between 6 inches and 1 foot from the muzzle of a rifle.  The velocity increase is very small--being only a couple of f/s.  However, there is also another effect.  Powder gases have a velocity of between 3,000 and 5,000 f/s on their own and the gas cloud actually passes the bullet and creates a cavitation effect which lowers the drag of the bullet while the bullet is in the gas cloud.  (Similar to the ultra high speed torpedoes that envelop themselves is a cloud of bubbles.)  Past the 1 foot max velocity distance from the muzzle the bullet actually has very little, if any, drop in velocity out to about 3 - 6 feet or so at the muzzle where the gas cloud has dissipated and thinned sufficiently that air drag can have an effect on the bullet.

Many shooters create an interesting fallacy whereby they attempt to "correct" the velocity readings from a chronograph (usually done at 10 feet) back to "muzzle velocity" simply by means of using the velocity loss computed from the bullet's BC.  While this has little, if any effect on ballistics calculations, the premise is wrong.

Does all this really matter down range?  Nope!  Do your nits a favor and instead of picking them let them sleep, while you practice your marksmanship.

A sleeping "nit."

Q. What were the ballistics of the pistol cartridges commonly used in the "wild west?"

A. The table below lists the characteristics of some of the more common pistol cartridges of that era.  Note that published data on the early versions of these cartridges varies greatly.  If you can supply any updated data for these or any other common cartridges of the era please let me know by clicking here.  With the exceptions of the light .36 cap& ball, .32-20 and .38 Colt all were serious fight stoppers.

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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 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 2019-06-03