Change in bullet speed verses barrel length

[wboggs]

A little bird told me there was a discussion on this Forum about bullet speed verses barrel length (with the same load obviously).

I Googled the subject and found what is probably a wonderful calculation if you're a ballistic scientist and can work the calculation.

My question; is there a reasonably accurate rule of thumb as to the increase in velocity verses the increase in barrel length or a calculation that you dont need a PhD to use?

OR since my answer is probably there along with other wonderful stuff i would like to know; can someone familiar enough with this forum post the URL to that discussion?

...and incidentally, this forum looks like a great place to get lots of good Cowboy shooting information which is a new venue for me. I've been a target shooter for some 45 years; mostly trap and handguns. I love action shooting which is what drew me to Cowboy. My Cowboy guns are Ruger Blackhawk .45 Long Colt and Marlin 1894 chambered in .45 Long Colt. I need more stuff to be official but having fun with the guns shooting different targets.

[RP]

I have heard that a number per inch added to speed but it was not backed up by any data just someones thinking. Myself I think it would be real hard to have a simple short cut because of the differents in powder burn speeds. What iam thinking a fast burner is out of push and a slow in a short barrel burns up in the barrel flash not making any speed. But just my thinking which most of the time is off.

[Piedmont]

In general for rifle calibers and legal barrel lengths it is about 25-35 fps per inch of barrel. Something like your .45 Colt in a rifle will be less.

John Barsness wrote a good article in Handloader before he left on this citing his own experiments and the incredibly extensive experiments of Phil Sharpe. The bottom line is you really can't count on anything. While cutting the same barrel there were times where velocities stayed the same and I believe even increased with a barrel cut. The conclusion of the article was to go with the barrel length you like and don't worry about the ballistics.

[deltaenterprizes]

Some loads actually slow down with increased barrel length increases. There was an article in one gun mag where the author took a 10'' Ruger Super Blackhawk and cut off one inch of the barrel incrementally and recorded the velocities drop. The results were only good for that gun on that day and your mileage may differ with a different gun and load.

[TCLouis]

here is a link to the site with the information:

http://www.ballisticsbytheinch.com/ .

It is really a good thing I captured the link yesterday as I am not sure where I saw it now, and would have lost the info for my use also.

[missionary5155]

Good morning
Overe the years there have been several Reports in the mags. One I remenber was started with a 36 " barrel and taken down to 1 ".
But as stated above.. it has alot to do with fast or slow powder burn rates.
Remove half a foot off a weatherby 26 " barrel and shoot factory loads and there will be a HUGE loss plus the most magnificient fireball I have seen since tank gunnery. But a good dose of faster rifle powder can restore some of that lost fps but not all.
To me the question is always " Purpose". Pistols calibers are a near no loss situation going shorter in carbines. But revolvers... I figure about 40 fps per inch but that also is a variable dependent on powder and bloolit weight.
The dan Wesson barrel system gives a reloader the place to easily change 2 " of barrel length. On a 357 10" to 8 " innot a whole lot.. but reduce 2" more to 6 " barrel and a stout load of 296 just went way down. But take that same 180 grgc boolit with 7 grains Unique and volocity goes up by removing the 10" and using a 6" barrel.
Works the same in 41 mag.. powder is the real variable.

[45 2.1]

Somewhere in the past an article was published showing velocities from a barrel who started about 26" long and was shortened an inch at a time. All jacketed ammo was from the same lot. Velocity will vary with the load intensity also. What cast will do.................?

[bigdog454]

I have a SRH 454 with a 9 1/2 in barrel and a model 92 rossi with a 20 in barrel and the difference in velocity with the same load and bullet is ~225 fps.

[shooter93]

It's basically guess work or so so rule of thumb. I do think case capcity and bore size are factors. The last caliber we played the game with was a 416/284. Started at 26 and cut back to 21 inches an inch at a time and looking at all the different loads we tried at each length there was no real difference. There SEEMS to be a trend that bigger calibers tend to lose the least. again....given case capcity and bore size.

[Piedmont]

Another rule of thumb, and this is for full jacketed loads is if you cut your barrel and want to maintain as much speed as possible, is to use heavy bullets and slow burning powders. For some reason they retain the most of what they had. So if you cut your .308 from 22" to 18", load something like a 180 gr. with IMR 4350, if you want the most performance.

[wboggs]

OK got the chronometer and went to the range today. My load was 200 gr. LSWC, CCI 300 primer, 5.2 gr. Unique. The weapons; Kimber Tactical Ultra (3”); Kimber Pro Carry II (4”); Kimber Custom Target II (5”).

3” average 856 FPS
4” average 900 FPS
5” average 943 FPS

So we’re looking at about 50 FPS per inch of barrel. A real SWAG

[flounderman]

at one time there was a barrel maker in montana that would make any length barrel you wanted. he told me that the velocity had increased with barrel length up to the longest barrel they had tested. supposedly, the 22 rimfire reaches its maximum in a 16 inch barrel. I haven't chronographed it to test this theory. a ballpark figure on most centerfire rifles seems to be in the 40 to 50 fps per inch in the 18 to 28 inch barrel length

[wboggs]

at one time there was a barrel maker in montana that would make any length barrel you wanted. he told me that the velocity had increased with barrel length up to the longest barrel they had tested. supposedly, the 22 rimfire reaches its maximum in a 16 inch barrel. I haven't chronographed it to test this theory. a ballpark figure on most centerfire rifles seems to be in the 40 to 50 fps per inch in the 18 to 28 inch barrel length

That makes sense since eventually the length will become a deterrent to speed.

[JIMinPHX]

It varies with the type of powder that you use. The increase in speed is non-linear & after a certain point, more barrel length does less. In revolvers, the size of the forcing cone gap makes a huge difference. A snub nosed revolver with a tight gap can shoot the same ammo at higher speeds than a 4" with a loose gap.

All that aside, I've had a 1250fps load in a 4" revolver come out of a carbine at roughly 1700fps. I've also had a Super Calibri .22 rimfire round come out of a pistol faster than it came out of a rifle.

[wboggs]

It varies with the type of powder that you use. The increase in speed is non-linear & after a certain point, more barrel length does less. In revolvers, the size of the forcing cone gap makes a huge difference. A snub nosed revolver with a tight gap can shoot the same ammo at higher speeds than a 4" with a loose gap.

All that aside, I've had a 1250fps load in a 4" revolver come out of a carbine at roughly 1700fps. I've also had a Super Calibri .22 rimfire round come out of a pistol faster than it came out of a rifle.

Understand that the post of my results are not to be taken and an exact "science" to every situation, but simply as an example that firing the exact same cartridge from three guns being the same in every way except barrel length are likely to have similar results to mine. If, like myself, you want scientific facts, buy a chronograph and run the same test as I did.

Of course different powders will produce different results which is true more so because different powder characteristics make it impossible to replicate same results. But my hunch is that except for nit-picking, given the same criteria as my example, the results wont be notably different. But then since powders have characteristics that have a fit to certain loads, comparing powders verses the results of an ideal powder is more a situation of arguing for the sake of arguing. I happen to be am Alliant Powder fan so I use the highly suited Bullseye for me .45 ACP loads (which is the subject of my study) where I would use the slow burning 2400 in Magnum loads; neither having anything to do with the other situation.

So if I can routinely fire one hole groups with my Bullseye loads, why would I concern myself with the performance of other powders?

[yarro]

Varies, but here are my notes on .223/5.56.

Barrel Win.55g Mil.62g Win.55g Mil.62g
fps fps Ft. lbs. Ft. lbs.

10" 2739 2627 918 950
11 1/2" 2872 2738 1007 1032
14 1/2" 3064 2907 1146 1163
16" 3132 2989 1198 1230
20" 3259 3095 1297 1318
24" 3315 3158 1342 1373
26" 3391 3231 1404 1437

-yarro

[Oyeboten]

FPS vis a vie Barrel Length - it will definitely depend on the Power type and charge, loading density, and Bullet to Barrel fit and other details...