Sunday, September 14, 2014

Barrel Length and .45ACP

Tam has started posting again. Here's a range report on .45ACP and the effect of different barrel lengths on bullet velocity.

It's good to see the posts, but she has turned off comments. Even though I understand the reasons, it takes something away from a blog to not have the interaction that comments create.

You can load .45ACP specifically with a longer barrel in mind and see some increase in velocity, although it is not going to be that great. The case size is also a limit on how much pressure you can develop as the powder begins to burn.

The volume in a larger case, like a rifle cartridge, allows the pressure generated to have some place to begin it's expansion before the bullet has moved. Once the bullet is moving, the ongoing burn continues to generate pressure behind the bullet so that it continues to accelerate. In handgun cases, that volume isn't there. Trying to generate an ongoing pressure behind the bullet to take advantage of a longer barrel results in a dangerously high pressure in the early moments when the volume is limited.

This is what limits carbines in .45ACP to lower velocities even though they may have barrels of 16 or 18 inches. In some cases, the bullet velocity peaks in the barrel and begins to slow down before it exits, the powder having been consumed and no additional pressure being created. Here's a link to ballistic tables for various commercial .45ACP loads in barrels from 18" down to 2". It's the same sort of testing Tam was doing, taken to 11.

Ballistics by the Inch is a great resource on the effects of barrel length on handgun ammo and I am adding it to the sidebar.


Tam said...

Ballistics by the inch is an interesting site, alright, and the scope of the project there is staggering.

I just like seeing my loads in my guns with my chrono with my eyes. The process is half the fun, you know, moreso since it involves shooting. :D

Overload in Colorado said...

As a counterexample, there's a huge fireball when I fire .30 Carbine out of a 6" barrel. The round was loaded for a 18" barrel carbine. I would assume the same back in the day when .44-40 was fired out of the Colt Frontier. OTOH, that was black powder, so maybe not?

This reminds me of the idea of getting a carbine and pistol in the same caliber. If the base ammo is pistol based, the carbine won't extract much more performance, while the other way around there's a bunch of unused potential in the pistol.

Old NFO said...

Thanks, that is really interesting...

ASM826 said...


There are a couple of cartridges I would consider for a pistol/carbine pair. .45Colt and .357 Magnum come to mind. Even there, the ammo might be different loads to try to gain the performance from the carbine.

You're right about fireballs when there's unburnt powder. Some of the TC Contenders are chambered in rifle calibers and they put on quite a show.

Overload in Colorado said...

I've considered those, as well as .44 mag, as well as guns that can default down to these rounds (e.g. .454 Casull revolver will chamber .45 Colt and .45 Schofield rounds). However, I want to try this in a semi auto pistol and rifle. Right now, .460 Roland is the leading contender for caliber. These guns can default to .45ACP if needed.

Tam said...

Can hardly wait to chrono the .243 out of my Encore. :)

aurictech said...

I ought to start reloading someday, if for no other reason than to optimize a 9x19mm load for my Beretta Cx4 Storm carbine. My first mad-scientist thoughts on the idea involve using a light bullet intended for .380 ACP, combined with a powder intended for carbine-length barrels. I would expect the muzzle velocity to be wicked fast*! ;-)

*Unfortunately, for loads using JHP bullets, it would probably be too fast for proper expansion at short-to-medium range. Perhaps using a 124-grain JHP bullet that is designed for use in +P cartridges (if such bullets exist**) would work better for this application. That way, I would be using a bullet that's already designed to move out smartly from a pistol barrel, while using a slower-burning powder to take advantage of a 16" barrel, adding just a modest velocity boost at the muzzle over what a +P cartridge would normally achieve from a pistol barrel.


**If such bullets exist, what about 124-grain 9mm bullets designed for use in +P+ cartridges? Would they work even better in carbine-optimized cartridges?

R.K. Brumbelow said...

A few comments:

I have not been to the afore mentioned site as I am trying to get our store online and if I jump down that rabbit hole my partner will kill me. That being said:

External ballistics are one thing, Internal ballistic is deep magic and transition ballistics is dark magic. I hope they are taking everything into account or at the least limiting one variable at a time.

An interesting but expensive experiment would be to start with a 32 inch barrel and take a thousandth off of the length each time. However, wear would be a major factor after 32,000 rounds so you compromise and take the longest barrel a machine can make and make a bunch of barrels with it. Even then you have to compensate for load variables, atmospheric conditions, temperature and a whole bunch of other factors.

OK next issue is twist rate, twist rate I believe has as much to do with accuracy and the initial exbal values as anything else. total energy of a round after transition is going to be rotational + forward momentums.

Third, why not the FN 5.7x28 as a pistol and carbine matched pair? The pistols are still in allocation, but I can get a PS90 tomorrow (if I had the cash)

Overload in Colorado said...

I seem to remember, about 20 years ago, there was some hot 9 mm ammo available, specifically for carbines. The problem was, if you used it in a pistol, it was over maximum pressure, or was damaging older 9mm pistols, or something.
I assume Michael, Tam, or someone else remembers better than I.

Re: 5.7x28 in matched pair. I want a pairing that can chamber easy to get ( and hopefully cheap) ammo, and that has ballistics better than .22 magnum.

Can a 10mm gun shoot .40 S&W?

R.K. Brumbelow said...

22wmr from a 4.3 barrel
Barrel Velocity: 1230 fps
Barrel Energy : 134.40 ft/lbs

5.7x28 from a 4.75 barrel
Barrel Velocity:2009 fps
Barrel Energy :358.57 ft/lbs

Cost to reload a box of 5.7x28: about 6-8 bucks

As to the 10mm vs .40 S&W:
They are not the same, they are similar. Kind of like you can fire a 50MMG out of a 12ga but it is - ahem- sub optimal.

Case length is more than 1/8th different, sine this directly affects headspacing in both weapons you will get some real nastiness firing a .40 S&W.

Tam said...

5.7 info:

R.K. Brumbelow said...

@tam Wow there is so much crap in that article with few sources.

In all honesty I can find a negative review of any calibre out there. However, the 5.7x28 is in use by over 40 countries asw well as the USSS and we are specifically talking about rounds that will work in both a carbine and pistol.

So tell me what about the 5.7x28 is it that you really dislike?

R.K. Brumbelow said...

I will simply respond with the following discussion about the 5.7x28 by laymen advocates and critics alike and let people draw their own conclusions

Tam said...

R.K. Brumbelow,

Your opinion of the linked piece speaks volumes about your subject matter knowledge.

When it comes to opinions on the terminal effectiveness of a round, I'm going to trust one of the foremost wound ballistic experts, several people in JSOC, and SWAT officers who've used the round over Some Dude on the internet. Absolutely nothing personal intended; you're free to love or hate whatever cartridges you want.

As far as "disliking" 5.7, I really don't feel any emotion of that sort towards cartridges. That'd be like having a favorite octane rating or a preferred voltage.

Tam said...

Sorry to stir this kerfuffle in your comments, Borepatch; I'll bow out.

Borepatch said...

Tam, it's not a discussion on ammunition performance without some kerfuffle. ;-)

008894ba-3378-11e4-a94e-8feb39834159 said...

89 octane kicks @$$.

R.K. Brumbelow said...

@0089 Shut your mouth! If its not AVGas blue its crap!

Geodkyt said...

Yeah, there's a reason the Secret Service jumped all over the 5.7, and it *wasn't* to replace either their pistols *or* their carbines.

They had a very specific role on mind. They needed a reasonably concealable shoulder weapon that could deliver rapid, *highly controlled* fire, penetrate body armor up close, incapacitate with head shots, yet minimized the danger to persons downrange. The P90 and 5.7x28mm seemed to offer all that, and certainly has advantages (in the very specific niche USSS needed to occupy) over it's predecessor - the P90 has better penetration, better controllability, better concealbility (and no need to unfold a stock to get maximum controllability), and reduced down range hazard than the full sized Uzi SMG. Plus, Presidential Detail agents train to be better shots than the average bear...

That's a *really* limited niche, in the hands of very atypical users. And from what I understand, USSS isn't entirely happy with the P90, because its performance on COM hits isn't what they'd like it to be...

Me, I like it for plinking, and small, reasonably close range varmints. From what I've seen, it approximates decent .22 Hornet from a carbine.

As for the "it's a glorified .22WMR!"...

According to the guys who actually shot the P90, with the ammo the cops would use (I.e., the AP stuff, because *that's* the best reason to use one), the *wound tracks* in calivrated FBI protocol gelatine were " indistinguishable from those made by .22 Magnum hits" (that's a quote). You can have wildly different energies, velocities, etc, that produce similar wound tracks - for example, ball 7.62x39mm M43 and ball 9x19mm NATO produce wound tracks on gelatine that are practically indistinguishable, despite the M43 going a HELL of a lot faster with an equal weight bullet (of course, if the M43 hits a bone en route, totally different story). Likewise, performance AFTER you pass 12-18" of tissue is rarely relevant, unless you're shooting Jabba the Hurt.

Don M said...

Twist rate is important. The M-1 Abrams gun is rifled at the throat, and smooth bore further down to give a higher velocity, and to permit lower pressure as the round exits, which reduces the need for muzzle brakes or blast deflectors. An interesting shot gun design was the paradox system, that used smooth bore at the start and a rifled bit at the end. That was intended to permit using shot with little decrease in effectiveness, or solid slugs, with the benefit of rifling, perhaps even mixing loads in the magazine.

The energy from propellant combustion can go to
(1) heat,
(2) 1/2 mv^2 kinetic energy of projectile (and propellant gasses), and
(3) 1/2 I w^2 angular kinetic energy of projectile

m is the mass of the round
v is the velocity of the round (and propellant gases)
w is the angular velocity of the round
I is the moment of inertia around the axis of rotation

Matt G said...

There are some very specific posts here on the color of the sky.

I usually will note who reported that the sky was red or green or yellow with some interest. But not for the reasons that they would think.