Cutting magnum barrel revisited, read some surprising data ...

[Snakum]

I've always read that I'd lose X amount of velocity if I cut the barrel of a 7mm mag rifle. Estimates ranged from 30fps/inch to over 100fps/inch. But today I read that Tac Ops magazine and a California Sheriff's dept. both independently tested this theory in 308 and 300 mag bolt guns. IIRC, they found that going from 24" to 18" on a .308 saw a total decrease of something like 34fps. And cutting a 300 Win Mag from 26" to 22' saw NO decrease in velocity, though it was expected that below this the velocity would certainly drop off. IIRC the rounds used for both were Sierra MatchKings at 168gr for the 308 and 220gr for the 300WM.

So my question is ...

Are there other variables that might have affected their tests?

If I went to 22" on my 7mm Rem Mag might I see minimal velocity loss as they did with the 300?

Have you guys ever cut a mag barrel down before while measuring the effect on velocity with a known load and a chrono?

 

[DRYHUMOR]

I never measured the effect, but I did cut a M70 Laredo 7mm down to 22.5". It was a very accurate rifle both before and after, but balanced better after.

 

[Oyeboten]

I believe that Bullet velocity/FPS loss or gain owing to Barrel Length in Rifles ends up being a question of with what propellent, how much of it the Cartridge has or will be given, and, how this relates to the Bullet particulars.


One can cut a Rifle Barrel and gain FPS, for that matter...( even if usually that is not the case ).

Ideally, the Cartridge Loading particulars for a given Bullet, would be tailored to match the Barrel length one has, or, prefers.


Off the Shelf Ammunition of course, for better or worse, guesses to a sort of average Rifle perameter for the Cartridge.

 

[Snakum]

Thanks for the info.

Ideally, the Cartridge Loading particulars for a given Bullet, would be tailored to match the Barrel length one has, or, prefers.

How would one do that for say, a .308? I've been looking thru loads while preparing to get my first kit, and I can't tell which loads are good for shorter barrels; ie. I know I can't look in the Lyman book and find .... "Here's a very accurate and still relatively fast handload for a .308 from a 19" barrel"/ How can I find good SBR loads for a 308 bolt gun?

 

[Oyeboten]

You could start a Thread asking for people's favorite .308 Loads, Factory or Hand-Load, and, once begun, ask others about what Barrel Lengths they were using these Loads in...and go from there.

 

[GaryL]

It depends a lot on the pressure curve generated by the powder.

Change powders & bullets & seating depth and you could easily see the losses predicted.