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Best powder for short barreled 308

 
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  #15  
Old 04-19-2013, 09:12 AM
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Re: Best powder for short barreled 308

I've seen shorter barrels do better with faster powders at times than long barrels. My brother had a 243 with a 24" barrel and I had one with a 14" barrel. My pistol did it's best velocity with vit 540; I was getting 2800 fps with a 100 grain bullet with vit but rl22 or 7828 would only get to 2600 fps. His rifle would top 3100 fps with 7828 with a 100 grain but wasn't any faster than that with vit 540.
It is the total amount of available energy that you can actually harness that nets you your muzzle velocity, and if the barrel is short enough you may need to use a slightly faster powder and possibly get the fire moving a bit quicker with a magnum primer to actually get most of the burn finished by the time the bullet exits the barrel.
With a 20" barrel you don't need to worry nearly as much about powder choice and such as a 14" barrel though; you can most likely do nearly as well with the same powder you would have used in the longer barrel.
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  #16  
Old 04-19-2013, 11:29 AM
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Re: Best powder for short barreled 308

"I've seen shorter barrels do better with faster powders at times than long barrels."

Not at the same peak pressure you didn't.

At the same pressure, all a faster powder can effectively do is burn more of the charge before bullet exit. The amount of energy available to drive the bullet is totally dependant on the peak pressure AND the total area under the time:pressure curve prior to bullet exit so where the bullet exits along that curve doesn't matter to the optimum energy transfer. A too fast powder peaks and declines too rapidly for optimum exit speed in any barrel length and a too slow powder will never achieve optimum peak pressure no matter the barrel length.

Rifle pressure peaks when the bullet is about 3" down the bore and then it rapidly falls so we really aren't trying to fine tune a pressure peak to occur some 16-24" down the bore; no powder we have burns that slow! Given that the peak pressure is supposed to be fixed, it's the pressure that remains AFTER it has peaked that has most effect on muzzle velocity. Thus, whatever works "best" in a long barrel rifle (again, at the same peak pressure) will work best in a shorter barrel; it's pure physics. (Well, unless the barrel is shortened to less than 3" ... and that's not legal.)

Last edited by boomtube; 04-19-2013 at 12:10 PM.
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  #17  
Old 04-19-2013, 11:47 AM
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Re: Best powder for short barreled 308

Quickload has h4895 listed in the top 10-15 powders to try with that barrel length, also with imr 3031, imr4895, rl15, rl17. I think if you have h4895 laying around go with it.
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  #18  
Old 04-19-2013, 03:43 PM
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Re: Best powder for short barreled 308

Yes boomtube, I've worked with strain guage equipement and seen the curves so I'm at least wet behind the ears on this one( btw, my sendero 7mm stw was still at 12 kpsi at the end of the barrel). If the barrel is capable of burning the powder that produced higher velocity then said powder will always be faster. I'm talking about barrels that are short enough in a given caliber that you CAN NOT burn a full charge completely.
The 308 will burn a full charge- even a compressed charge-- nearly completely even in a 14" pistol barrel, so I don't think he'll see more than a 100 fps difference between a 20" and a 26" barrel-- chicken feed.
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  #19  
Old 04-19-2013, 07:54 PM
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Re: Best powder for short barreled 308

I have a 20" Scout rifle in .308 and use IMR4198 w/ 110gr bullets for coyotes.
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  #20  
Old 04-19-2013, 08:22 PM
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Re: Best powder for short barreled 308

Quote:
Originally Posted by Bob L. View Post
Quickload has h4895 listed in the top 10-15 powders to try with that barrel length, also with imr 3031, imr4895, rl15, rl17. I think if you have h4895 laying around go with it.
A few of these powders you mention have been run past me a day ago via private message by a members screen name that I'll keep to myself. I'll have to try them out for sure. Like I said before, I'm not saying anyone is wrong. I just feel that this is something that needs to be tested and witnessed for oneself. There are to many variables to account for, for anyone to say make an absolute statement that the same powder that produces best velocity in a long barrel will do the same in a short barrel. I'm going to reread "Understanding Firearm Ballistics" By Robert A. Rinker and go out and actually test these powders with my rifle. I have yet to find any load data or "unscientific" tests done with a 308 and a 16.5 barrel. This might be a hard pill for some people to swallow but anyone can learn something from anyone. Regardless of credentials or post count.
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  #21  
Old 04-19-2013, 08:28 PM
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Re: Best powder for short barreled 308

" I've worked with strain guage equipement and seen the curves so I'm at least wet behind the ears on this one... I'm talking about barrels that are short enough in a given caliber that you CAN NOT burn a full charge completely."

I am too; it doesn't matter where on the optimum pressure curve the bullet exits nor if all the powder has burned, which is rare for any length of barrel. A bullet has no idea of how much powder remains unburned anyway, it just runs down the barrel until it's suddenly free! I know the powder burn facts and am simply responding to the OP's rational question in view of the often suggested - including here - but incorrect web info of using a faster powder in a short barrel by explaining why the optimum speed rifle powder choice is irrelivant to barrel length.

I have no idea how wet your ears are, I never addressed velocity and care not what your 7STW muzzle pressure is because none of that is relivant to the question. Nor have I any personal interest in competing with you for being perceived as the resident site guru. Thus, you may happily post any opposing views you feel you need; I'll just laugh.

Aramarine6, your post count is fine and you should indeed do the experiments as you plan. BUT, you should recognise up front that what I said would require you to first test the long barrel for speed and then cut it to test the short version of the same barrel and chamber with the same load. It's not uncommon for 'identical' factory hunting rifles to vary a couple hundred fps with the same load! Simply testing different powders in one length can only give you the results from that specific barrel, there's no way to compare the results to another rig and say the barrel length is what caused any differences you may see.
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