long barrel ballistics with pistol calibers

[Cousin Pat]

I'm thinking about replica rifles for cowboy action shooting, etc., chambered for 357M and 45LC. Some of this have barrels out to 24". When I look at the ballisticsbytheinch website, it seems to flat line for these calibers at about 16". Do you start to actually lose velocity at >20", i.e. the bullet/barrel friction starts to offset the extra push time?

[jmr40]

You'd have to have a pretty long barrel before you start losing velocity. I've heard that it's possible in 22's fired from some of the longer production barrels, but doubt any centerfire is long enough to actually do that.

You may reach a point where gains are so small that it is certainly not worth the longer barrel. Id say somewhere around 16-20 would be as long as I'd want a pistol caliber rifle.

[Brian Pfleuger]

I set up QuickLoad to include barrel friction and asked for a max .45LC load in a 10" barrel. It says RL-7 gets me about max speed with reasonable case fill. I then looked at a 24" barrel with and without barrel friction. It still thinks Rl-7 is the powder to do it.

It says that speed would max out at 1,358fps at 15.8", remain roughly flat until 17.5" and then drop to 1,296fps at 24"

[Cousin Pat]

wow - not sure I understand some of the terms you used, but interesting stuff. My conclusion is that barrel length > about 15" out to 24" lead to a 5% velocity LOSS = about a 10% muzzle energy loss. Thus these longer barrels are a negative not a positive in pistol calibers. Am I thinking about this correctly? thanks - tom

[Jimro]

Longer barrel equals better sight radius.

So even if you lose some velocity, it might shoot better for you.

Jimro

[skizzums]

that is interesting, on ballistics by the inch in 357 mag, it seems 16inch to be the optimal length with all but one ammuntion, i just bought a 20 inch because i figured that would be the highest powered, reckon i figured wrong

can anyone tell why this is the case? seems to be the opposite with rifles, although i rarely have seen ballstics on barrel length over 24in

is it because at the point when all the powder is burnt, then you just have the friction of the barrel causing drag?

[Pathfinder45]

The BBTI charts for 45 Colt don't mean much to me since all the bullets listed are are lighter than standard. I use 250-300 grain bullets for the most part. When I had a chronograph I compared a number of hand-loads in a 4-5/8" Vaquero versus a 24" Marlin. What I found was the faster burning powders like Red-Dot or W-231 would gain about 200 fps in the longer barreled rifle; while the slower burning propellants like 4227 would gain 400 fps. The powders in the midrange could be closely predicted for velocity gain relative to where they ranked in burn rate. It may be, perhaps, that a 20" barrel might launch a 250 grain bullet faster than a 24" barrel with the faster burning powders but not by much. 6 grains of Red-Dot is going to run out of steam a lot sooner than 24 grains of 4227. I think the 4227 load will still be gaining velocity in the longer barrel. Probably the only way to know for sure would be to test the longer barrel, cut it shorter, then retest with the same loads on the same location, date and temperature. Try it with your own rifle if you like, but leave mine alone. I think the difference will not be noticed by the game animals or targets.

[Art Eatman]

For no more loss than Brian's data shows, I'd have to agree quite readily with Jimro.

Pathfinder45's comments about slower powders giving different results seem quite valid. They pretty much fit my own notions about burn rates and pressure curves within barrels.

[Brian Pfleuger]

Originally Posted by Cousin Pat

wow - not sure I understand some of the terms you used, but interesting stuff. My conclusion is that barrel length > about 15" out to 24" lead to a 5% velocity LOSS = about a 10% muzzle energy loss. Thus these longer barrels are a negative not a positive in pistol calibers. Am I thinking about this correctly? thanks - tom

QuickLoad is a program that calculates internal ballistics. Pressure, velocity, all kinds of "stuff".

The precision it gives with straight-walled cartridges like 45LC is a little iffy but the basic concept is certainly correct. It might be at 14" or 17", but somewhere in there the velocity starts to go down.

From a pure velocity/energy perspective a long barrel is worse than a shorter barrel. There might be other considerations though, such as the mentioned sight radius. Accuracy trumps power, every time.

Originally Posted by skizzums

can anyone tell why this is the case? seems to be the opposite with rifles, although i rarely have seen ballstics on barrel length over 24in

Modern, high-power rifle cartridges typically have much greater case capacities, operate at much higher pressures and have much smaller expansion ratios. Expansion ratio is basically the amount of space the powder gases have to fill as the bullet moves forward. Because of those factors, the powder continues to burn and produce/maintain pressure in much longer barrels.

Even rifles will start to lose velocity eventually though. For example, a 55gr 5.556NATO round can get to about 3,135fps in 16", up to 3,431 in 24" but gains only another 120 at 30", for 3,550, and only another 60 at 35". By 40", it's losing speed.

Originally Posted by PathFinder

What I found was the faster burning powders like Red-Dot or W-231 would gain about 200 fps in the longer barreled rifle; while the slower burning propellants like 4227 would gain 400 fps.

Generally speaking, whatever powder produces the fastest velocity in a long barrel will also produce the fastest velocity in a short barrel. There's a point where this is no longer true, depending on the specifics. Within reason, say going from 24" to 20" or even 16" in most cases, whatever was fastest at 24" will also be fastest at 16.

Going from short towards long, you'll find what you mention, that at some length (usually that would be considered very long for a handgun but much too short for a rifle, 10 or 12" , or so) the fast powder will be over-taken by the slow one. For every length up from there, the slower powder will be better velocity.

[B.L.E.]

I compared .38 special loads shot out of a 5.5 inch revolver and a 24 inch rifle barrel. My chronogragh indicated a mere 150-200 fps gain with the long barrel over the revolver, and that includes the advantage of no cylinder gap leakage.
The fact that shooting .38 special loads out of the 24 inch rifle is easy on the old eardrums tells me that the pressure is largely gone by the time the bullet exits the barrel, the last few inches of barrel essentially just guides the bullet to the target.
.357 magnum loads using slow burning powder might gain more with the rifle barrel but I haven't tested that yet.

[zxcvbob]

I've only skimmed all the replies here, not read them slowly, so sorry if this has been covered already. If you want to shoot pistol cartridges in a rifle barrel, use lead bullets instead of jacketed. The difference in friction becomes very significant past about 12 inches.

[44 AMP]

I'd like to point out that even the best computer models do not, and cannot accurately predict what happens in the real world 100% of the time.

General trends are one thing, but detailed specifics about what is going to happen in your gun, with your ammo can only come from direct observation and measurement.

There are exceptions to every "rule" and when it comes to velocity, your gun and ammo could be the exception, or could follow the rule, (flip a coin for those odds), but the only way to know is to measure what is actually in your hands.

Barrels vary. Bullets vary. EVERYTHING varies. Sometimes, its enough to be significant. I have seen the same ammo, fired in 3 different guns (same barrel length) yield as much as 100fps difference.

I have seen a certain 4" barrel and a certain load deliver higher measured velocity (if only slightly) than a certain 8" barrel with the same ammo.

Most of the time things follow the usual pattern, but when it is an exception, almost anything is possible.

Yes, there is a point at which all the powder is burned, and there is no longer any increase in pressure. And there is a point (much earlier) where the rate of velocity increase per inch of barrel drops a lot.

And this will vary, as well, with the specific combinations of ammo and barrel that are possible. Pistol rounds generally reach this somewhere between 16 and 20 inches, BUT, even if that last 4 inches only nets you a 1% increase, its still an increase.

Choose your barrel length based on what feels and handles best to you. The velocity will be what it will be.

[B.L.E.]

I've only skimmed all the replies here, not read them slowly, so sorry if this has been covered already. If you want to shoot pistol cartridges in a rifle barrel, use lead bullets instead of jacketed. The difference in friction becomes very significant past about 12 inches.

The velocity difference between rifle vs revolver .38 special loads measured by me was done with hard lead bullets, Lasercast 158 grain RNFP.

I remember in some old loading manuals warnings not to load half jacketed bullets below a certain velocity because of the danger of the jacket becoming stuck in the barrel while the core separated and went on to the target.

I got a jacketed bullet stuck in the middle of a revolver barrel once while trying to work up a load using some shotgun powder for which there was no published pistol data. It was a real job to get that bullet out. Luckily, because of no target impact sound and no recoil, I checked for a barrel obstruction before shooting the next round.
On that particular load, you can definitely make a case for the fact that the maximum velocity was achieved before the point where the bullet stuck.

[PawPaw]

I don't normally shoot jacketed in the .357 magnum, preferring hard cast bullets in that caliber.

I have one load in .357 magnum (180 RF gas-checked bullet) that gives me 1200 fps from my Model 28 and 1600 fps from my Marlin 1894C. Plenty good deer medicine there under 100 yards.

My standard .38 Special plinking load is a 158 grain SWC over 4.3 grains of Unique. That gives me 780 fps from my Model 28, and 970 from the Marlin Carbine. It's a good little load for lots of things, and it's long been my favorite load for the .38 Special. Very accurate in my revolvers. Good small game load.

The standard .38 special target load is a 148 grain wadcutter over 2.7 grains of Bullseye. That load gives me 660 fps from my Model 28, but slowed to just a tad under 600 fps when I shot it from the Marlin 1894. I speculated that barrel friction was slowing the bullet after the powder had run out of push.

Understand, I don't use Quickload, but instead push these loads over my chronograph, through my barrels. YMMV, etc.

[Jimro]

All powder has essentially the same chemistry within its class, either single, double, or triple base.

For maximum energy transfer you want all the powder to be turned into gas before the bullet leaves the muzzle. For a 2" stubby revolver, that should logically be a different choice than a 20" carbine barrel.

But, since the chemistry is essentially the same, that means that the more powder you use, the more gas is produced, so the longer your barrel the you have, the slower the powder you want. In reality you don't get to different powders until you get to the extremes in barrel length differences, but there is a transition point.

What that does is change the pressure curve in the firearm. Fast powder peak quicker, and slower powders are more gradual. But when you calculate the area under the curve, the powder that produces the largest area before the bullet leaves the muzzle should perform best in that barrel length.

The ultra fast pressure spike is perfect for that snubby revolver. Possibly a heavy load of the slowest appropriate powder is what you want for a carbine.

For what it is worth, you can check out some heavy Alliant 2400 loads by searching for them. The caveat is always that the firearm needs to be strong enough (sometimes called "Ruger loads").

Jimro

[Deja vu]

Long ago I was working on a Subsonic Jacketed load for my 45-70. I was shooting Hornady DGS 500 grain bullets set really deep to function from the marlin action. A developed a trail boss load that was hitting about 900 FPS from my BFR (10 inch 45-70 revolver) but only getting about 700 FPS from my marlin. That told be the bullet was slowing down. These bullets are jacketed and very long so they have a lot of drag. I feel I am lucky I did not stick on in the barrel.

[B.L.E.]

Long ago I was working on a Subsonic Jacketed load for my 45-70. I was shooting Hornady DGS 500 grain bullets set really deep to function from the marlin action. A developed a trail boss load that was hitting about 900 FPS from my BFR (10 inch 45-70 revolver) but only getting about 700 FPS from my marlin. That told be the bullet was slowing down. These bullets are jacketed and very long so they have a lot of drag. I feel I am lucky I did not stick on in the barrel.

That's 898.4 ft-lb of energy verses 543.5 ft-lb of kinetic energy. Almost 355 ft-lb of energy lost in the longer barrel, which means if that rifle barrel is one foot longer than the pistol barrel, it takes about 355 pounds of force on the base of the bullet just to maintain velocity. The friction is probably higher since there most likely was still some pressure in the barrel.

With lead bullets, once started in the rifling, you can easily push the bullet through the bore with a ramrod. Get a jacketed bullet stuck in the bore and you'll need a hammer to get it out.

[Jimro]

A developed a trail boss load that was hitting about 900 FPS from my BFR (10 inch 45-70 revolver) but only getting about 700 FPS from my marlin. That told be the bullet was slowing down.

That assumption is only true if the coefficient of friction between the two barrels is exactly the same. Considering how much variation in velocity there is between even barrels of the same length, that is not a valid assumption.

An alternate explanation is that the bullet simply didn't speed up as much due to having a higher friction bore in the Marlin.

Another alternate explanation is that the Marlin had a poor gas seal and lost more energy before the bullet was fully engaged in the rifling.

Jimro

[44 AMP]

We had quite a discussion in another thread a little while back about jacketed vs lead bullets, and the force required to get them through the barrel.

And interestingly, while it does take less force to drive a lead slug than a copper one, lead bullets usually get to max pressure with less powder than jacketed ones.

One theory was that pressure on the base of a lead bullet forces it to press harder on the barrel than a jacketed one. According to that, while lead is softer than copper, it actually has MORE friction in the bore.

"Can't say its true, and I won't say its not, but there's been talk...."

(extra bonus points if you can ID that quote, )

[SHR970]

"Can't say its true, and I won't say its not, but there's been talk...."

The Quiet Man.

Father Lonergan to Will Danaher before the race.

The heck with points...I want PINTS

[Cary]

I have a Winchester Trapper M94AE in 357mag that I really like. It has the 16" barrel and shoots hard cast bullets just great. My favorite loads use a SAECO 180 gr RNF checked bullet I cast. They are pushed with either H110 or Alliant 2400 to ~1500fps. Plenty accurate and fun to shoot with no leading.
Cary

[pathdoc]

I suspect the important thing for most rifle shooters of pistol calibres is that they gain velocity over their revolver load. Sure, in a perfect world they might get more energy out of a sixteen rather than a twenty inch rifle barrel, but when your rear sight is forward of the breech, those extra four inches to the front sight matter to some people.

[Unlicensed Dremel]

Radius, schmadius..... Get a Trijicon RMR-DI & an SBR stamp & cut those leverguns to 12", or even with the tube mag, whichever is longer!

[Pathfinder45]

Naw.... I'll restrain myself a little....