.308 what gained by 30" bbl
- Thread starter onegun2
- Start date
At 30" the velocity is probably going to drag down a bit.
Some of the long range "Leech Cup" shooters use long barrels to get the front sight out as far as possible. It's not for velocity, but for sight radius.
Another approach is to use a shorter barrel with a “bloop tube” over it. The tube is nothing more than a front sight extender.
Some of the long range "Leech Cup" shooters use long barrels to get the front sight out as far as possible. It's not for velocity, but for sight radius.
Another approach is to use a shorter barrel with a “bloop tube” over it. The tube is nothing more than a front sight extender.
Most who choose the longer 30" barrels are using them for long range target shooting. Most are using the heavier bullet for caliber and want to make sure they are keeping them supersonic out to 1000yds for top accuracy.
If your not expecting to get into this sort of thing where ranges aren't out past 600yds, then you should be fine with anything one side or the other of the 24" area depending on just what your goals are.
My only .308 came with a 16.5" barrel and I use it for what I purchased it for, hunting thick stuff or just having a light weight rifle to go on a walk about with. It's the little Ruger Compact and only weighs in at 6.5# ready to hunt. It isn't a takc driver, but I have reached out with it on several occasions to around the 425yd mark and put some nice feral hogs in the freezer with it.
(Edit) - Danged I hate it when I read what is posted them forget what I just read. Since you ARE looking to get out to 1K with it, you might research Palma shooting and see what is said about getting into it. While you might not get into that sort of thing, some of the same principles apply to the rifle and barrel.
If your not expecting to get into this sort of thing where ranges aren't out past 600yds, then you should be fine with anything one side or the other of the 24" area depending on just what your goals are.
My only .308 came with a 16.5" barrel and I use it for what I purchased it for, hunting thick stuff or just having a light weight rifle to go on a walk about with. It's the little Ruger Compact and only weighs in at 6.5# ready to hunt. It isn't a takc driver, but I have reached out with it on several occasions to around the 425yd mark and put some nice feral hogs in the freezer with it.
(Edit) - Danged I hate it when I read what is posted them forget what I just read. Since you ARE looking to get out to 1K with it, you might research Palma shooting and see what is said about getting into it. While you might not get into that sort of thing, some of the same principles apply to the rifle and barrel.
You don't gain much per inch beyond about 24", but it won't be slower. And even if you're only getting an additional 10-15 fps/inch, that could be 50-100 extra fps, over a 24" barrel. For a hunting rifle that is irrelevant, but it might help if shooting right on the edges of a rounds abilities.
With heavier bullets you will likely do better with a different powder. Barrel length is not an issue. The load you find that is fastest from a 30" barrel will still be the fastest from a 20" barrel.
With heavier bullets you will likely do better with a different powder. Barrel length is not an issue. The load you find that is fastest from a 30" barrel will still be the fastest from a 20" barrel.
Unlicensed Dremel
Moderator
No sir - in a bottlenecked "full power" round, drag doesn't overcome gas expansion / acceleration until approx. the 10 FEET worth of barrel range, if an optimal powder is chosen - somewhere in there. You do definitely gain velocity from a long barrel like this.
But rapidly-diminishing returns to be sure, past 24" or so. Especially when considering how the bbl has to get thicker WHILE getting longer, to maintain same stiffness.
Brian Pfleuger
Moderator Emeritus
Unlicensed Dremel said:
QuickLoad disagrees with that assumption.
Given a 178gr Hornady Match in .308, QuickLoad says that N550, W760, H414 and Rl-17 would produce the highest speeds at almost any barrel length. I checked from 20" up to 10 feet.
Friction matches gas pressure at approximately 45", producing a speed of 2,947fps at that length, only 4fps faster than a 40" barrel and 91fps faster than a 30" barrel.
Speed declines from 47" on.
Unlicensed Dremel
Moderator
Hmm, thanks. My bad. OK, 4 feet; not 10 feet. If the program is right, which I'm sure it is. I had read years ago that it was 8 to 10 feet for a "full power" bottlenecked smokeless round, unlike say, .22lr, which is sometimes purported to be in the neighborhood of 12 to 14" before that point is crossed, although it's actually in the 16-20" range for most types of ammo.
This shows gains are present to 33" (at least):
http://bulletin.accurateshooter.com/2011/12/barrel-length-and-velocity-barrel-cut-down-tests/
This shows gains are present to 33" (at least):
http://bulletin.accurateshooter.com/2011/12/barrel-length-and-velocity-barrel-cut-down-tests/
Brian Pfleuger
Moderator Emeritus
I wouldn't doubt that that was the going assumption. Really, aside from someone actually getting a 10 foot barrel, there would be no way to know except for QuickLoad's estimates. "They" may well have simply made a guesstimate that prevailed until better data was available.
QuickLoad's numbers are no sure bet but I would bet that the general implications are true. It might be 42" or 45" or maybe even 5 feet but I'd bet it's in there somewhere close.
I'm most curious about 22LR. Have you ever seen Ballistics By The Inch? I don't know how many shots they took at each length and with each ammo but the stuff doesn't behave very well at all, losing speed for several inches in a row before suddenly jumping to a higher speed than it was 3" ago.
Just about all barrel contour include Palma heavy,standard and light barrel contours cut 30"
http://www.shilen.com/contours.html
http://www.kriegerbarrels.com/Contours-c1246-wp3382.htm
http://www.shilen.com/contours.html
http://www.kriegerbarrels.com/Contours-c1246-wp3382.htm
Ballistically you don't gain much past 24 with a 308. Folks have been shooting 1k with 22" M1As and 20" AR-10s for quite a while now.
But if you are stuck with a certain projectile do to the rules of the game, say the 155gr Palma, then a 30 inch barrel makes a lot more sense.
Also the added sight radius never hurt anything either.
Jimro
But if you are stuck with a certain projectile do to the rules of the game, say the 155gr Palma, then a 30 inch barrel makes a lot more sense.
Also the added sight radius never hurt anything either.
Jimro
Jim Watson
New member
At 1000 yds "a few fps" is not trivial.
I haven't seen WINNING F Class or any-any shooters with those "short, stiff" barrels that are successful in short range benchrest. They are using scopes so sight radius is not a factor.
And the barrel length of a Service Rifle is a limitation.
I haven't seen WINNING F Class or any-any shooters with those "short, stiff" barrels that are successful in short range benchrest. They are using scopes so sight radius is not a factor.
And the barrel length of a Service Rifle is a limitation.
Not at all! Quite the opposite actually. More velocity, which is good. You're likely seeing a lot of long range .308's with 30'' tubes because it helps keep bullets from going trans and sub-sonic, which will throw off accuracy. Having a higher velocity helps increase that range that projectiles can travel before they start going transonic.
I remember reading, back in the 70s, where some wag calculated the barrel length needed for efficiency, if you necked the .50 BMG down to .30 caliber.
And it was done using the canister powders available then (before the super slow ones came out for the .50BMG). Their calculations (best guess) was that it would take a barrel length of 100 inches for full combustion.
Not a .308, by any means, but still a bit short of 10 feet.
Am always amused with those who think the barrel can be long enough to actually slow a bullet down. Sure, its possible. ITs possible to make a barrel long enough that the bullet will actually slow down and stop inside, but neither you nor I are going to be carrying that around, even just to the range.
What you get is not a slowing down but a decrease in the rate of increase. But its still an increase.
And it was done using the canister powders available then (before the super slow ones came out for the .50BMG). Their calculations (best guess) was that it would take a barrel length of 100 inches for full combustion.
Not a .308, by any means, but still a bit short of 10 feet.
Am always amused with those who think the barrel can be long enough to actually slow a bullet down. Sure, its possible. ITs possible to make a barrel long enough that the bullet will actually slow down and stop inside, but neither you nor I are going to be carrying that around, even just to the range.
What you get is not a slowing down but a decrease in the rate of increase. But its still an increase.
I use a .308 with a 24'' barrel with no issues. 30 seems excessive unless using irons.
With a 24'' barrel, McMillian A5 stock.. and a 5-20x56mm with 35mm tube scope, on high rings with a 20MOA base, Bipod.... the gun is already pretty big and hefty for a .308, I wouldn't wan't 6 more inches of barrel to gain a little FPS.
With a 24'' barrel, McMillian A5 stock.. and a 5-20x56mm with 35mm tube scope, on high rings with a 20MOA base, Bipod.... the gun is already pretty big and hefty for a .308, I wouldn't wan't 6 more inches of barrel to gain a little FPS.
Just to clarify, there is more than just "F Class" even in F Class.
The most winningest F/TR Class shooter I personally know who routinely shoots at 1k uses a 28" Bartlein barrel on his 308 rifle. I don't really pay too much attention to what the F-Open shooters are using as I shoot service rifle whenever I compete F/TR. No, I don't win with a service rifle, but it keeps me shooting when I can't get to a cross the course match.
As far as Palma shooters, who are restricted to iron sights, that sight radius thing really comes in handy...
Jimro
Most 1000 yard matches actually consist of 4 Matches.
Any Rifle Any Sight
Any Rifle Iron Sight
Service Rifle
Team Match.
Most people use the same rifle for the Any sight/Iron sight matches.
As to velocity you don't need more then 22 inches for a 308 at 1000 yards (My best 1000 yard scores were in the service rifle matches, using a M14 or M1A).
Where the longer 30 inch barrel has the advantage over the shorter barrels is the Longer Sight Radius for the Iron Sight Match.
Since you aren't carrying the rifle through the brush, the 30 inch barrel isn't really a disadvantage.
Any Rifle Any Sight
Any Rifle Iron Sight
Service Rifle
Team Match.
Most people use the same rifle for the Any sight/Iron sight matches.
As to velocity you don't need more then 22 inches for a 308 at 1000 yards (My best 1000 yard scores were in the service rifle matches, using a M14 or M1A).
Where the longer 30 inch barrel has the advantage over the shorter barrels is the Longer Sight Radius for the Iron Sight Match.
Since you aren't carrying the rifle through the brush, the 30 inch barrel isn't really a disadvantage.
No you don't need super velocity to get a 308 to shoot. The 308 seems to get its best accuracy about 2200 fps ( as discovered by the International 300 Meter 3 Position shooting).
How ever you do need to keep the bullet super sonic at 1000 yards. 41.5-42 grns of 4895 or 4064 (med. burning powder) @ 2550-2600 FPS is super sonic at 1000 yards using 175 SMKs or 178 Hornady bullets.
I shoot 308s at 1000 out of my M1A and M-70 Win Tgt. using the above load and according to the BC programs I'm getting about 1200 fps remaining velocity at 1000.
If you want hyper velocity, use a 300 WM.
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