barrel length vs case capasity

[Steve-W]

the parent case is 7 Rem mag blown out to .01 taper from belt .513 to .503 shoulder 40 degree shoulder neck shoulder junction will remain same length 2.229
what i am looking for is the correct length
of barrel or close too that will give me the best effiecient use of the powder charge to burn all powder
the powders used will either be h1000
or h4831sc or something in that burn rate category this is a long range project shooting 168 berger vld
has anyone played with a version of this cartrige in a barrel length around 34 or so inches will this barrel length burn all powder or does it need to be longer or shorter
Thanks Steve

 

[Guest]

Alot of guys shooting 300 Ackleys and other big overbore rifles use 30" tubes , I would think that 34" would be plenty if not to much if your going for some sort of tapered barrel.
i know a guy that had a 32" #5 weight barrel that woulden't shoot to good at all , he cut it back to 28" and it closed the groups and he only lost about 100fps , this was with a 300 RUM
better to have a slower hit than a faster miss

 

[Guest]

If you like, you can go by expansion ratio, compare your case capacity to other common rounds' ER.
But I'd say that case would know what to do with 30" of barrel, but the longer you go, the more harmonics are involved (barrel whip) which is mitigated by a heavy barrel or possibly BOSS-type contraption.
Strictly speaking about powder burn, I think you'd need to get into the 40" or longer before you'd actually start losing velocity.
To give you a comparison, I think I read the 22LR needs something like 16" of barrel before you start introducing more friction than the powder burn will overcome, and that little case holds something like 6g!

[edited to add:]
Get the longest barrel you can stand. It's easy to cut back if you're not happy.
EASY.

[ 02-01-2004: Message edited by: youngun ]

 

[Steve-W]

Well actually it will be barrel blocked so a 34" barrel would only be hanging around 25 inches with a 9" block or so as far as taper what i was planning to do was 1-1/2" dia straight thru barrel block and tapering it to 1-1/4 at muzzle in a solid aluminum stock reciever will be a Rem 700 blue printed and bolt sleeved havent decided on glass yet pobly leupold something this isnt a carry gun by no means hoping it will work to around 1200 or so that all im after anyway
thanks for the help
Steve

 

[daveosok]

This is an interesting subject.
A few years back I had a nice dicussion with Dan Lilja over this very point. In the conversation (about a 7mm stw) I had asked what length barrel to get a full or 95% or better powder burn would I need.
His response was 34 inches, and actually he had said if your case holds 70 grains or more you need 34 inches or better to get a full powder burn.
Maybe this will help you.
Dave

 

[Steve-W]

thanks Dave I appreciate the info if anyone else has any more imput it wold be appreciated
Steve