Why is the .45 ACP more accurate than other duty calibers?

[DocGKR]

Again, we are not talking about any particular pistol, barrel, or other hardware; only about ammo testing using SAAMI test barrels and fixtures.

[SLG]

A while ago, in the 1911forum:

Quoted from Joe Chambers:
I've built a couple of .45's that will shoot 1" or slightly less for 10 shots out of my Ransom Rest. They are RARE. On average I'm getting 1.35" or a tad better and I use either ASYM or my own hand loads when testing .45's. With the 9mm and .38super now, that is a different story as those guns have shown, with the proper loads, to shoot under 1" consistently. But still, I have not found anyone that can capitalize on that potential by shooting one handed.

Quoted from Jerry Keefer:
Most of the military teams, and a number of high end bullseye builders have and use barrel testers.. Barrel testers are a robust device that receives the barrel and secures it in a solid, very rigid, immobile state. The tester is mounted to a massive steel/concrete structure. This allows for a very precise evaluation of the performance a particular barrel is capable of. It is rare, very, very rare, as in almost impossible, to find a .45 barrel that will shoot into an inch or less group. 9mm is a different animal. Contrary to popular myth, all barrels are not created equal.. Generally, when installed in the 1911 frame/slide, by a skilled smith, the group will expand by 1/4 inch + . 1-1/2 inch guns do exist, but not in the numbers commonly believed..and, not all ammo is capable of one inch groups..Jerry

I'm not totally sure what he's saying, but it sounds like he has found that using actual pistol barrels in a fixture, shows 9mm to be more accurate. At what distance? What type of barrels - i.. 1911, Beretta, etc.

Using test barrels, not actual barrels (test barrels probably have a better name, but I don't know it) is how the tests I'm aware of were conducted. Other tests may well show other things. Test barrels are like 10 pounds or something, and look like extreme bull barrel rifle barrels. They are single shot only, and not capable of fitting on any gun known to man.

Either way, my info on this is definitely a bit dated, like 10 years or so, but if Doc agrees with it, I'm pretty confident in it.

[Wheeler]

Yes, the .38spl and .357mag are straight walled cases, but they are revolver cartridges meant for being loaded into a full supported cylinder and head space off of the case rim. The case mouths of both cartridges are relatively thin, allowing for a tight gas seal. Auto cartridge head space off of the case mouth, and thus they are beefed up to allow for good support for proper spacing.....the downside is that that thicker case mouth has more trouble sealing gas. Also.......the .38spl is again a low pressure cartridge. I do agree with you that heavier bullets "can" be more accurate, provided that pressures do not spike as a result of pushing that longer, heavier bullet out of the barrel. High pressure cartridges have a tendency to cause those longer bullets to keyhole if the wrong reloading powder and primer combination are used. Backing off on the powder burn rate can actually increase accuracy(delaying peak pressure) on the .40 and .357 even though the slower burn rate load has the same chronographed velocity as the higher burn rate load.

As for the 10mm, its larger case space delays peak pressure until the bullet has travelled further down the barrel. This puts less stress on the bullet. The .40S&W has a very small case volume relative to the caliber size, this causes the pressure to spike much earlier in the discharge and stresses the bullet more. The .40S&W can come close to 9mm or .45 accuracy, but a bullet resistant to deformation like solid copper needs to be used. Don't believe me, ask Tom Givens who is a .40 aficionado.

It's not a question of believing you or picking up Tom's name from where you dropped it, rotation and stabilization are a thing and usually the biggest thing to affect accuracy. The 180 grain .40 caliber loadings as offered by the ammo companies are less stable than the 165's, because they aren't spinning fast enough and don't stabilize. I have no doubt all the other things you mentioned are true, I just don't feel as if they are as relevant.

[TiroFijo]

I'm not totally sure what he's saying, but it sounds like he has found that using actual pistol barrels in a fixture, shows 9mm to be more accurate. At what distance? What type of barrels - i.. 1911, Beretta, etc.

Using test barrels, not actual barrels (test barrels probably have a better name, but I don't know it) is how the tests I'm aware of were conducted. Other tests may well show other things. Test barrels are like 10 pounds or something, and look like extreme bull barrel rifle barrels. They are single shot only, and not capable of fitting on any gun known to man.

Either way, my info on this is definitely a bit dated, like 10 years or so, but if Doc agrees with it, I'm pretty confident in it.

The gunsmiths were talking about custom 1911s built for extreme precisión, and the barrels they are talking about are top notch custom 1911 barrels. They test these barrels (before fitting to the gun) in very solid fixtures to select them for accuracy. They are two of the best bullseye/pure accuracy gunsmiths in USA.

These are not the massive test barrels that are often used in ammo factories (that look like a thick bull barrel fitted to a floating bolt action, and very rigidly anchored to the test device). Theoretically, the rigidity of these test barrels (if they are kept in optimun condition, they start as match grade barrels) makes them the ideal, nonbiased, test device to compare loads, bullets, and the inherent accuracy of a cartridge, independently of the gun.

[BehindBlueI's]

It has a lot to do with propellant burn rates, pressure curves, and gyroscopic stability.

Thanks, that's what I was looking for. I realize this is a big ask to put into layman's terms, and realizing the limitations of any expertise tailored to the understanding of the novice, why?

[noylj]

There is the "hand-waving" of 9x19 accuracy--yes, if you spend at least $1000 getting your gun customized, most likely with a 30:1 twist rate and you carefully work up the loads, you "might" be as accurate as a .45 Auto. If your 9x19 is as accurate as a .45 at 25 yards, it might be more accurate at 50 yards (faster rounds drop less--reason folks don't shoot .45-70s at 800+ yards compared to .300 Win Mag).
Load development? .45 Auto loads used today in Bullseye were generally developed in the '40s and '50s. The top shooters don't sort cases or any thing else.
Why? I have no idea. I would say that NO cartridge is inherently accurate, but:
I know that of my twelve guns in 9x19, NONE of them will consistently give me groups under 4" at 25 yards (I get some groups under 1", but not consistently). Of fifteen guns in .45 Auto, NONE of them will give me groups OVER 4" at 25 yards with decent ammo if I do my part. My three .40s are close to my .45s.
It should be a matter of barrel and build quality.
I also don't care what gunsmiths say, I want to see Bullseye competition scores showing 9x19 is out-shooting .45.

[LtDave]

I've got a couple 9mm service pistols that will do less than 1" at 20 yards off the bench with Winchester white box 115 grain fmj and handloads. Lots more that easily shoot under 2" with a wide variety of ammo. If one of my 9mm's was only shooting 4" groups, it wouldn't be mine for long. My .45's shoot pretty good too, but the smallest groups I've shot have been out of my 9mm's.

[farscott]

The accuracy I was referring to had to do with absolute accuracy, from a test barrel, at AMU. I'm glad some of you don't see a difference with your guns (very scientific, I'm sure), but when guys who shoot bullseye and such for a living want to know about accuracy, they ask AMU for a test.

The last discussion I had about this with David Sams suggested that the 9x19 absolute accuracy was better than .45 ACP, now that there is a focus on match accurate 9x19 guns and loads. The way that groups are counted for score in Bullseye gives the edge to .45 as an impact in the same point can cut a higher scoring ring with the .45, but not with the 9x19.

[SLG]

The last discussion I had about this with David Sams suggested that the 9x19 absolute accuracy was better than .45 ACP, now that there is a focus on match accurate 9x19 guns and loads. The way that groups are counted for score in Bullseye gives the edge to .45 as an impact in the same point can cut a higher scoring ring with the .45, but not with the 9x19.

Maybe things have reversed themselves now, iDK. I'll see if I can find out more.

[psalms144.1]

This. Has nothing to do with triggers, JMB, or "shootability". It has a lot to do with propellant burn rates, pressure curves, and gyroscopic stability.

And 'Mericuh, dammit! We are talking about the .45 American Communist Perforator here, have some respect. I'll just leave this here (again)...



I will now return to fondling my G19, and my 9mm P2000, and my VP9, and...