Is there a rule of thumb for velocity loss as a barrel is shortened? My PH in Namibia is thinking about shortening his barrel and was wondering how much velocity he would loose if he took 2" off his .458 win.

I experimmented with that issue and found a very consistent loss or gain of 20 fps per inch of barrel length change.

465H&H

Thanks for the information.

The loss of velocity varies considerably by cartridge, powder, initial barrel length etc. Slow burning powders usually show much more loss than faster burning ones..Expected losses are usually in the 35fps range for most calibers.-Rob

quote:

Originally posted by Lhook7:
Is there a rule of thumb for velocity loss as a barrel is shortened? My PH in Namibia is thinking about shortening his barrel and was wondering how much velocity he would loose if he took 2" off his .458 win.

I understand from a top end custom gunmaker that the 458 Win Mag is fine down to 19 inches. Below that velocity starts falling off quickly. But keep in mind that the ability of a barrel to burn powder is related to total volume of air within the barrel, when you have a .458" hole the air volume is pretty big even at a stubby 19 inches.

The gunmaker found this out by starting with a 26" barrel and progressively cutting off 1" of length and re-chronographing his ammo.

For the .505 gibbs, the magic length was 21 inches.

quote:

Originally posted by Robgunbuilder:
The loss of velocity varies considerably by cartridge, powder, initial barrel length etc. Slow burning powders usually show much more loss than faster burning ones..Expected losses are usually in the 35fps range for most calibers.-Rob

My information was for the 458 Win with 5 different factory loads and 4 different powders with handloads.

465H&H

Remingtons website used to have (may still have) a good estimator for velocity loss per barrel length.If memory serves (I'm not at home and don't have access to my hard copy)they base the standard on 24" and loss is for above and below that length. Their figures are based on velocity ranges ie; 1500-2000,2000-2500 etc. Loss is minimal per inch of length. I can't see how powder burning rate has any effect unless barrel is cut below length where all powder is burned which is quite short I understand. There have been MANY test run over the years actually cutting barrels and checking velocity and the census seemed to be to me it's insignificant as to the effectivness of the round. I don't have a chronograph and am not hung up on velocity. If it shoots accurately and the animal is killed it's fine by me. My favorite 375 and 416Rigby have 21" barrels and none of the game including Elephant has complained the bullet was under velocity when it hit them.

I wouldn't hesitate to chop 2" off a .458. I shortened my .416 Rem. Mag from 24 1/2' to 22" and my 300 gr X bullet load lost 50 fps. Thats with Rel. 15. The 458 should loose less per inch.

I shoot a 458 Lott with a 21inch barrel and with factory Hornady ammo I am getting 2240fps through my Oehler chrono. With faster burning powder you do not loose much, there are other variables involved but 20-35fps is a good conservative range.

When I took 2" off a Zastava 458WM barrel the chronograph actually showed a 30fps increase! For all intents and purposes I dont think there will be much of a change. When I get another 458WM built on an M17 action ... I'll be looking at a 20"-22" barrel.
Cheers...
Con

I just finished chronographing my Savage 116 FSS with Sierra 300 grain GameKing soft point bullets with 70.0 grains of Reloader 15. It has a 20 inch barrel. I also shot my CZ 550 Safari Magnum, 25 inch barrel. I was surprised at the results. Average velocity was only 36 fps difference for a five inch barrel length difference in the .375 H&H. The bore and cartridge volume to cartridge volume ratio gives a good indicator of velocity loss to expect. The ratio for the .375 H&H is greater than the .458 Win Mag so the .458 Win Mag should loose even less velocity per inch. An average of 25 fps for each inch for 3000 fps cartridges and 20 fps per inch for 2500 fps cartridges seems to work pretty well for me. A 100 fps isn't going to make any differnce as long as terminal velocity is high enough to insure expansion for soft points. The Barnes tech rep Ty Herring says 1900 fps is their lowest expected velocity for expansion. With a .458 Win Mag, Barnes lists 2391 fps as maximum muzzle velocity from a 24 inch barrel with a 400 grain XFB bullet. At 2291 fps muzzel velocity the bullet is still at 1898 fps at 230 yards. Four or five inches less barrel won't hurt a thing performance wise, unless you shoot dangerous game past 200 yards. A 500 grain solid at 2200 fps, Barnes' listed maximum with 24 inch barrel, has 4000 ft-lbs at 150 yards. At 2100 fps it still has 4000 ft-lb at 100 yards. How many elephants are shot at 100 yards these days? I heard factory Winchester ammunition was near 1900 fps in the days before chronographs and honesty in advertising, and it still worked when fresh from the factory.

I can tell you that Federal factory .470 Nitro Express cartridges, with a nominal velocity of 2150 fps printed on the box, chronographs at 2060 fps out of a 16-inch (yes, sixteen)barrel.