Best powder for short barreled 308

[Lefty7mmstw]

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.

 

[boomtube]

"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 timeressure 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.)

 

[Bob L.]

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.

 

[Lefty7mmstw]

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.

 

[Kevin Rohrer]

I have a 20" Scout rifle in .308 and use IMR4198 w/ 110gr bullets for coyotes.

 

[aramarine6]

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.

 

[boomtube]

" 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.

 

[aramarine6]

"Generally, the faster powder, at equal charge weights, will produce faster velocities. This is because a lot of the slower powder's energy is wasted in heat transfer to the barrel and escaped gas and heat at the muzzle." Understanding Firearm Ballistics. Pg. 25 Robert A. Rinker.

So please explain how a slower burning powder "Varget, will produce better velocity in a 16.5 inch barrel than say 4895 or 3031. Both are faster burning powders.

 

[Buttermilk]

As already mentioned, the same powder that gives highest velocity in a rifle will normally give the highest velocity in a short barrel.

I used Varget in a 15" barrel .308 Win with great success.

Without getting into a debate on fast vs slow powders in short barrels, I've shot a lot of different powders thru short barrels (currently don't own a rifle and shoot only 15" to 16.5" T/C Encore and XP100).

In my experience, the same powders listed as giving highest FPS in rifles also give the highest FPS in shorter barrels. There are some exceptions. But typically that's the case.

In my 280AI 16.5" long IMR7828ssc gave me the fastest FPS when compared to some faster burning powders. That's just one example. I've chrono'd nearly all my loads at the range, and as I've said, that's typical, though there are some exceptions.

In most cases, maximum peak pressure occurs within the first three inches of the barrel. This is why even in short barrels, the same powder type produces the highest FPS in both short and long barrels. The longer barrel simply contains the solid state matter converted to a gaseous state for a longer period allowing it to push on the base of the bullet for a longer time thus producing more FPS in the longer barrel. Short barrels do tend to display more muzzle flash due to the burning gases exiting a shorter barrel.

Check out some loading manuals that have a handgun section that includes loads for the 308, 7-08, etc.

I'd load some Varget and go have some fun.



Regards
Rog

 

[Lefty7mmstw]

Deleting subscription to thread; why bother.... It doesn't matter a dang bit anyway. Heck, I just deleted subscriptions to all threads!!

 

[boomtube]

"So please explain how a slower burning powder "Varget, will produce better velocity in a 16.5 inch barrel than say 4895 or 3031. Both are faster burning powders."

.Ara, I make no prediction on what powder will be ideal for your rig.

I know what I said is counter intuitive but intuitive in this case is based on incorrect "conventional wisdom". I've already explained that the powder which produces the highest speed in a 24" barrel will do so in your 16" barrel; the bullet's acceleration is solely dependent on the timeressure curve, it matters not at what part of that curve the bullet exits, fastest in one length will be will be fastest in the other. That's all there is to it. I won't argue with your author but I will question him on this point. I'm sure Mr. Rinker is a smart and quite knowledgable man and I would love to have his book for study but he is not the first author to write something which sounds right but isn't entirely correct in application.

Think of how little heat energy can possibly be transfered to a bore surface in the 2-3 milliseconds it has to do so. Certainly heat (energy) IS transferred or the barrel wouldn't get hot but that's because the burn temp is quite high, hot enough to melt the steel if it were maintained longer. IF barrel temp mattered very much we could reasonably expect the last round fired would always be fastest but...not really! Thus, Mr. Rinker's equating a measurable velocity difference based on heat exchange to the barrel because of powder burn rate is quite a stretch of both physics and logic! The actual bore time of bullets at say 2,500 fps and 2,800 fps isn't much no matter what powder is used so the end difference in energy transfer will be infintesmal no matter the burn rate.

We reloaders make a lot of noise about "fast" and "slow" powders because it matters to us but the real world time differences are quite tiny. We're only moving the instance of peak pressure small fractions of a millisecond and changing the duration of that pressure peak just a little longer.

 

[trigger puller]

I agree with boomtube I have had a 26" barreled 308 that I would get 2775 with varget and 175 smk I now have a scapel with a 22" barrel that is running 2730 with varget. I also have a 19" 308 that will shoot 2700 with the same load 45fps is not going to make that much differance. The barrels are in order a Shilen,Krieger and Broughton. It does not matter how fast it is going as long as you do your part. Good luck and if you have 4895 try it and see what you think. I am always trying something different but always end up with Varget for my 308s.

 

[Lefty7mmstw]

Deleting subscription to thread; why bother.... It doesn't matter a dang bit anyway. Heck, I just deleted subscriptions to all threads!!

I've gotta stop playing around here half asleep...I suppose apologies to the o.p are in order....

Boomtube has valid point. I have seen plenty of short barrels that can be made to shoot at almost the same speed as a longer barrel with the right powder and primer choice. Most of these loads would be screamers in a longer barrel too though.

 

[Brian21785]

Digging up an old thread. I have a savage 10fp xplea chambered in 308. It came with a 25" barrel. I reload on a dillon 550 with dillon digital scales. I use 7.62 nato brass. Hornady sst 180gr. And h380 powder with Winchester large rifle magnum primers.
My experience
With the 25" barrel I got 2780-2800 fps
I cut the barrel down to 18.5" and turned in a lathe to a buttoned 11degree crown
And now I get 2675-2700fps and typically shoot .200-.250 groups at 100yds
The load is 48grs of h380 compressed with Winchester magnum primers. Brass trimmed to 2.05 and a coal of 2.80.
This is a compressed load. I worked up to this load in half grain increments and it shows no over pressure signs. The magnum primers help with the ball powder.
This year during deer season I shot a doe at 775yds. With a balistic calculator I'm not a mathematician lol. Perfect heart shot and bullet still passed completely through. That's good enough for me.