Hunting Washington Forum

Equipment & Gear => Guns and Ammo => Topic started by: jdb on February 02, 2010, 06:23:40 PM

Title: optimum velocity
Post by: jdb on February 02, 2010, 06:23:40 PM: so velocity goes up as barrel length gets longer right but at some point it will have to start going down. but what is the optimum length for a givin cartridge? like say my .270 has a 22" barrel and I can buy an encore barrel up to 28" long is the 28" still going to be gaining velocity?
Title: Re: optimum velocity
Post by: Curly on February 02, 2010, 06:30:17 PM: If you used real slow burning powder like Rotumbo, the 28" barrel might be of benefit. But I doubt the minimal gain in velocity would be much benefit.......
Title: Re: optimum velocity
Post by: elkaholic123 on February 02, 2010, 06:32:34 PM: I think 28 in a standard .270 would be too long but on a.270 WSM or even better yet a .270 Weatherby mag should be about right!Jerry
Title: Re: optimum velocity
Post by: elkaholic123 on February 02, 2010, 06:35:16 PM: Reloading manuals usually state if test barrel length is 24" and you have a 26" it is usually 50 fps per in
over the test barrel length!
Title: Re: optimum velocity
Post by: Bofire on February 02, 2010, 06:35:37 PM: :)There are a lot of sites about this. Mike Bellum has done soem work. basicaly it is what you think. slow powder = long barrel, to a point. I think Mike B did a 204 and it came out at about 23 inch for max efficency. do some searchs lots of folks started witha long barrel and cut cut cut! I read a sub sonic 22 is 6 inch?, I think 22LR is baout 16.
Carl
Title: Re: optimum velocity
Post by: high country on February 03, 2010, 05:44:11 AM: really going to depend on the cartridge. a 45acp might get stuck in a 28" tube.....lol.
Title: Re: optimum velocity
Post by: Big10gauge on February 03, 2010, 06:43:11 AM: I asked the same question a few days ago on PM but really didn't get a answer.
the amount of powder and burn rate seem to be the 2 most important factors with bore diameter and bullet weight also a factor. I can't find any formula that calculates this. I'm e-mailing Hodgon hoping they have some info.

http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=1506754&gonew=1#UNREAD (http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=1506754&gonew=1#UNREAD)
Title: Re: optimum velocity
Post by: Curly on February 03, 2010, 07:25:11 AM: I think that if you can find someone with reloading software like "Quickload" then they could run some scenarios with different powder/bullet combos and different barrel lengths to figure out what is likely the optimum barrel length for your cartridge.
Title: Re: optimum velocity
Post by: Bob33 on February 03, 2010, 07:49:58 AM: Most modern centerfire cartridges have burned all the powder within 26 to 28 inches. At that point there are more compelling factors to consider such as gun weight and balance.
Title: Re: optimum velocity
Post by: Intruder on February 03, 2010, 07:56:42 AM: Quote from: Big10gauge on February 03, 2010, 06:43:11 AM
I asked the same question a few days ago on PM but really didn't get a answer.
the amount of powder and burn rate seem to be the 2 most important factors with bore diameter and bullet weight also a factor.

You've pretty much hit it from what I've read/experienced.... powder burn rate and amount are the biggest influences when it comes to how much effect barrel length will have on velocity. Things like the bullet weight and diameter may be a factor but probably more so because larger/heavier bullets often require more, slower burning powders to push em. The faster the burn rate and the less the powder charge means the less barrel length will make a difference. Casings actually make a difference too. Some casing designs (short/fat) seem to burn powder more efficiently. As a rule of thumb, it's usually safe to assume that unless you're talking some kind of mag cartridge an inch or 2 in barrel length doesn't buy you much. Where you reach a point of diminishing returns though, I don't know.
Title: Re: optimum velocity
Post by: high country on February 03, 2010, 06:30:06 PM: there are also the accuracy losses to deal with due to long tubes. sometimes wringing out 100 more fps is not worth giving up .2moa........like at 500yds.
Title: Re: optimum velocity
Post by: .Forty_One on February 03, 2010, 07:16:04 PM: You'll need to know case capacity as measured in grains of water and a couple of other odd specs, but the Powley computer will estimate velocity as well as recommend a powder.
Powders are in the IMR series only, but you should be able to compare different barrel lengths here.

http://kwk.us/powley.html (http://kwk.us/powley.html)

In my tinkering with it the results have varied between 20 and 50 Ft/s per inch of barrel length, usually toward the lower end of that. To my thinking it makes long barrels hard to justify for most calibers in sporting rifles...
Title: Re: optimum velocity
Post by: Huntbear on February 03, 2010, 07:23:07 PM: The only thing I have noticed when shooting the same caliber from 2 guns with diff. barrel lengths is muzzle blast. A hot load from a shorter barrel has much more muzzle blast (noise to the ears) in my opinion. My .257 AI with the loads I have found work best, sounds like a magnum going off, with a 22 1/2 in. barrel, especially under a tin roof on a range.
Title: Re: optimum velocity
Post by: 44 Flattop on February 04, 2010, 08:52:57 AM: Heh!

Optimum velocity for my 26" barreled '86 in 45-70 with a 420gr cast bullet seems to be 1500fps as it drives plumb through every elk I've shot with it........ :IBCOOL:

44
Title: Re: optimum velocity
Post by: Bofire on February 04, 2010, 09:02:30 AM: http://www.accuratereloading.com/223sb.html (http://www.accuratereloading.com/223sb.html)

here is a link to one test, there are lots if you look. many people have done this, no calculation needed, cut the barrel shoot the gun thru the chrono.
Mike Bellum at the custom TC site has done this.
Carl