caliber/pressure and service life

General Firearms Reloading & Ammunition
1

I am curious about how/why caliber affects the service life of a handgun. This question is not so much about real-world relevance (I understand that I will never shoot this volume of ammo out of a single weapon, and that if I did, I could certainly afford a replacement.) This is more to increase my understanding of firearms and their function.

  1. This is NOT another “stopping power” question about terminal ballistics or a caliber debate for carry.

  2. I tried searching several sources and did not gain a clear understanding. If I missed something, I apologize, and could someone please direct me to the appropriate source?

H&K has reported a USP .45 with over 297,000 rounds, and Chuck Taylor’s Gen. 2 Glock 17 is reported to be around 300,000. It seems to be fairly well accepted that an identical .40 S&W will not have the service life that a 9x19mm or .45 ACP weapon will. I have always heard that the higher pressure of the .40 round is harder on guns, and therefore accelerates wear. However, I’m confused: max SAAMI chamber pressure for both the 9mm and .40 is 35,000 PSI. Why then, does .40 accelerate wear over 9mm or .45? Do we see this so frequently because the commonly-mentioned Glocks were designed around the 9mm round, with the under-sprung .40 as an afterthought? Do we not see more high round counts in .45 pistols because of the cost of the ammo/the physical toll the higher recoil on the shooter? Or because the round is harder on those guns?

Going back to the calibers that seem to show the highest round counts, between similar 9mm and .45 handguns (i.e. USP 9/USP 45; Glock 17/21, M&P 9/45), can we expect a longer service life out of the 9mm (lower recoil) or the .45 (lower chamber pressure) model, assuming all else is equal? Or do the variables between models make it impossible to determine this? If so, what about an identical 9mm vs. .45 1911 (with the appropriate spring weights, etc.)?

Thank you in advance for explaining some of the physics behind how caliber affects weapons.

2

Base diameter of a 9mm case = .391" - pressure 35,000 psi, load on the locking lugs = 4200 pounds

Base diameter of a .40 S&W = .424" - pressure 35,000 psi, load on the locking lugs = 4950 pounds

Base diameter of a .45 ACP = .476" - pressure 21,000 psi, load on the locking lugs = 3700 pounds

You can also compare the recoil forces for the typical loads, which are based on momentum so the projectile weight is just as important as velocity.

3

You are quoting “approximate” bolt thrust or the pressure applied to the bolt face “AND” not all firearms have the same amount of locking lugs. On top of this just one of the reasons military rifles have “longer” headspace settings is because it reduces bolt thrust and dwell time the rear of the cartridge is in contact with the bolt face. And why bolt thrust figures are approximate pressure figures.

To the OP, this is why racing engines do not last as long as the standard engine in car you bought off the dealers lot. The more horsepower (chamber pressure) you develop the more strain and wear on the engine.

lystander gave the correct theoretical answer but how many lugs does a .45 acp pistol have and how many lugs does a Glock have. So it boils down to how hot you load your firearms, and the Speer manual has .40 S&W 165 grain law enforcement loads or .40 lite loads that develop less “horsepower”.

And “WHY” they have lite practice loads that put less strain on your brass and firearm for increased service life.

And I do not spend all day shooting magnum loads of 296 out of my 5 inch model 29.

Below my .40 Glock and very light loads with plated bullets.

Make Right With a “.40 Lite”
http://www.handgunsmag.com/ammo/ammunition_40lite_091806/

And I will die and pass on my firearms to my sons before my pistols and rifles wear out with smart reloading. :wink:

So quit worrying and do what a Brit said in another forum “Just shoot the bloody thing”.

4

Thanks for the answers so far–this is quite informative!

Don’t a G17 and a G21 have the same number of lugs? And I’m not worried–in my original post I said this was solely to increase my understanding firearms, specifically the wear and battering associated with different calibers, than any real-world decision. I am a shooter, and my weapons are tools that serve a real-world purpose. If I’m fortunate enough to shoot enough to wear one out, I will replace it. But I’m also a gun enthusiast, and am curious about the mechanics and physics that go with firearms.

5

+1 to the “.40 Lite.”

I load 155gr lead SWCs over 4.5gr of Unique. That gets me about 850-875fps (depends on barrel length), and my Glocks cycle fine. I tried even lighter loads (less powder) and had stovepipe failures.

FWIW, that’s about 250-275 ft-lbs of energy, which is about half of what a premium factory .40 load (155gr Gold Dot or 155gr Hydra-Shok) makes at 1,200-1,225fps (500+ ft-lbs).

I can only think that it’s a lot less wear and tear on the gun, my brass seems to last forever, and it’s definitely less wear and tear on me (the difference in recoil is huge).

6

More lugs in the same space means smaller lugs and lower load on each lug. The stress on the steel will be the same. More lugs in a bigger space means more recoiling mass which means more stress on the other parts…

The bolt thrust has to be handled by the pistol as a whole, whether by one lug or fifteen.

Bold - bolt thrust is bolt thrust - chamber pressure times the area the pressure acts on. Changing the headspace will not change the bolt thrust.

7

When the rear of the case stretches to meet the bolt face, the case acts like a shock absorber, meaning the further away from the bolt face the case is the more it reduces bolt thrust. This was told to me by the senior armourer in the UK Captain Peter Laidler and Enfield author in a Enfield forum.

The British used the base crusher system using a hollow copper crusher and measuring chamber pressure at the base of the case.

Cartridge Pressure Standards
http://kwk.us/pressures.html

“In Britain, a third set of crusher standards were developed, using a “base” crusher. The crusher was a short, thick tube placed behind a piston at the base of the cartridge, and the firing pin passed through the center. The cartridge case was well oiled before firing, to minimize cling to the chamber walls (if not oiled, the indicated pressures were about 25% lower). To prevent case rupture on set back of the base, the crusher was first deformed in a press to a pressure a bit lower than that expected in firing. The units were generally stated in British long tons per square inch, or tsi. Pressures indicated by this method run 10 to 20% below those indicated by radial crushers. Kynamco in England still rates their production cartridges with this method.”

Below is from the 1929 British “Text Book of Small Arms” in reference to the base crusher system.

Below is from the Sierra manual and “WHY” they tell you to remove all grease or oil from the chamber before firing.

Simply put your bolt thrust calculations are purely theoretical and not actual pressure measurements taken at the bolt face. To this day the British use two oiled proof pressure cartridges to proof military small arms and if the firearm headspace increases over two to three thousandths the firearm fails proof testing. Meaning the extra oiled bolt thrust cause lug setback and increased headspace.

So your bolt face pressure figures are purely theoretical and a dry case delivers less bolt thrust, and increased headspace delivers less bolt thrust with less dwell time contact with the bolt face because the case must stretch to meet the bolt face.

Below the longer the headspace setting (the head clearance or air space between the bolt face and the rear of the case) the “LESS” bolt thrust is delivered to the bolt face and its dwell time.

I’m not trying to start a pissing contest but I collected the Enfield rifle for half a lifetime and can tell you this. The Enfield rifle was made from lower grade steels and had a replaceable bolt heads, this would compensate for bolt wear and lug setback when firing under combat conditions. Meaning oil and water in the chamber and increased bolt thust that the British actually measured at the rear of the case and not theoretical pressures generated by a computer program.

The bolt thrust figures you posted are not actual pressure readings and are nothing more than chamber pressure and the surface area of the case this pressure can act on. And it has nothing to do with case stretching, dryness and condition of the chamber nor dwell time.

So do not tell me headspace settings or head clearance has no effect on bolt thrust because this was proven with actual British bolt thrust reading well over 100 years ago and their base crusher system which is still used today in Britain in their older proof houses.

8

Nice read, as stated the harder you run any machine the faster the damage.
I shoot 9mm and .45… The .40 is just a bit much it reminds me of a .357. If iam gona do that iam gona shoot a .41 or .44…

I just dont like the recoil impulse on a .40 seems way to stiff. Maybe outa a 1911 frame , something heavier than a poly frame would be better. I like the 10mm on the 1911 frame colt made,the delta 10mm. I remember it still packed a punch though.