.308's and barrel length - accuracy comparison?


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MyRoad
January 18, 2010, 03:59 PM
I'm wondering if anyone here, or anywhere on the net there are actual figures for .308's in relation to barrel length. I understand that at some point (and what point would that be?) you lose a certain amount of foot-pounds of energy for each inch of barrel you remove. But I'm more concerned with accuracy than energy, since I don't shoot past 300 yards anyway.

I'm wondering about accuracy at comparative distances. For instance, Remington makes a 700P with a 26" barrel. I'm wondering how the groups would be affected at say 100 and 300 yards, if you compared that gun side-by-side with the same gun, but after having the barrel cut down to 22", or 20", or 18"?

I suppose a more straight forward comparison might be the 26" model and the "LTR" - which has the 20" barrel - if anyone has any experience with that.

From another angle: I don't see a reason to go down to 16", but I'm wondering what is gained (other than ft.-lbs.) with every inch over 18"?

Also, do some bullet weights respond better to longer barrels?

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jmr40
January 18, 2010, 04:06 PM
Google "velocity and barrel length". You will be reading for a while. Short version. Shorter barrels have almost no effect on accuracy, and in fact if everything is equal should be stiffer and thus more accurate than a longer barrel. Velocity is somewhat less, but much less than most people think. Going from a 20" barrel to a 26" barrel will probably gain around 120 extra fps or so. Probably less. At 300 yards it is not a problem. For the guys who want to shoot at 1000 yards they need every tiny bit of extra performance they can get.

MyRoad
January 18, 2010, 04:16 PM
That's what I thought -- but I see so many rifles with long barrels that I was wondering if I'm missing some information.

rcmodel
January 18, 2010, 04:19 PM
All a shorter barrel will have any effect on is less velocity, and more muzzle blast closer to your ears.

rc

conhntr
January 18, 2010, 04:30 PM
id rather carry around a 22" barrel and not go deaf; anything shorter is too loud for me...

benzy2
January 18, 2010, 04:31 PM
A shorter barrel of the same design would be stiffer. All things equal, stiffer is more accurate. Then we have the real world where velocity sheds as the barrel length shrinks. Often it isn't much difference in velocity though. This drop in velocity means a given strength of wind will push the bullet farther than it used to. For long range shooters it also means the distance at which the bullet becomes trans sonic is closer, which if it becomes shorter than the range the shooter is shooting, it is a bad thing. For most of us I think the two forces of a stiffer barrel and a slightly slower bullet basically cancel out and you don't notice any difference in accuracy, given everything else equal.

Now this is all assuming you are shooting with a scope. If you shoot with iron sights the extra length becomes important in that it increases the distance between your two sights and this makes them easier to be more accurate. Its the same reason why short barreled pistols tend to be inaccurate, not so much that the pistol is in accurate, just that accurate aiming becomes difficult.

The situation you are describing is one where if done 20 times(26" barrel to start then cut down to 20") I don't think you would see a significant trend one way or another.

Boba Fett
January 18, 2010, 05:19 PM
Here's a good read I found a while back:

http://www.sniperschool.com/sniper-rifle-barrel-length/

js2013
January 18, 2010, 05:28 PM
If you want to find the most accurate length of any given barrel, slug it. The tighest point in the barrel is where the barrel should be cut. For example if the barrel is 26" but the tighest point of the barrel is at 23", then that barrel will shoot best at 23". If the barrel's tighest point is 26" then 26" is the best length.

MyRoad
January 18, 2010, 05:34 PM
Great article Boba Fett, that's exactly my thinking.

MyRoad
January 18, 2010, 05:35 PM
If you want to find the most accurate length of any given barrel, slug it.

I'm not familiar with this -- how do you "slug" a barrel?

greg531mi
January 19, 2010, 01:02 AM
You hammer a pure lead slug through the barrel and then get a good 0-1. mic
and measure the lands and grooves....
The length of the barrel is less important than the stiffness of the barrel....
A bull (Thick) barrel, is stiffer than a light (narrow) sporter barrel....and usually more accurate.....

benzy2
January 19, 2010, 01:31 AM
When you slug you tend to find a spot in the barrel that the slug has the most tension to push through. This is the tight spot and where you want the bullet to be leaving the barrel. If the tight spot is before the end of the barrel you have the bullet compress to the tightest area of the bore and then when the bore opens up the bullet isn't as tight of a fit as it was which hurts accuracy. I know of a lot of rimfire guys who will cut a barrel to whatever length is tightest. That article was a good example that length isn't the be all end all to accuracy but I'm not so sure you can jump to the conclusion that a 8" barrel cut is going to drop group sizes in half. His conclusion that it was the extra stiffness from the shorter barrel is one idea, just not a lot of data to show the stiffness is what made the difference and not the removal of either a looser last 8" or a section with a flaw or a bad crown that now is cut right or a world of other reasons. I will say though that it does show short barrels don't have to be inaccurate and long barrels don't have to be accurate (or outstandingly accurate).

Boba Fett
January 19, 2010, 02:09 AM
His conclusion that it was the extra stiffness from the shorter barrel is one idea, just not a lot of data to show the stiffness is what made the difference and not the removal of either a looser last 8" or a section with a flaw or a bad crown that now is cut right or a world of other reasons.

There is another article on that site from someone else who has done it too:

http://www.sniperschool.com/barrel-length-revisited/



And a few pics of the rifles:
http://www.sniperschool.com/wp-content/uploads/2008/06/18inchbarrel02.jpg


I don't think I could watch them do that to my rifle. Even though I plan to cut mine down, I couldn't watch.
http://www.sniperschool.com/wp-content/uploads/2008/06/18inchbarrelcut.jpg

benzy2
January 19, 2010, 03:38 AM
I see that article but I didn't see any comments to if this increased or decreased group size for these before and after rifles. Again I hate to make assumptions as to why a given or a given few rifles shot better or worse based on strictly cutting the barrel down. There are multiple variables in these situations that could cause rifles to act differently. I do applaud them for going out and doing it rather than talking about it, I just hate to jump to conclusions based on a handful of barrels. I guess I deal with studies a lot and sample size is something we pay close attention to. These test, at least to me, prove there is no generic correct answer that can be applied to all barrels and lengths. That's about it.

blackops
January 19, 2010, 04:21 AM
All a shorter barrel is going to do is give you a little less velocity.

Bobarino
January 19, 2010, 04:46 AM
shorter barrels do have a slight advantage with being stiffer and less prone to variances due to barrel harmonics. longer barrels have the advantage with velocity but in my opinion, doesn't give up enough in harmonics to make up for the lost velocity. if you never shoot past 600 yards, 18 or 20 inches is probably just fine. if you plan to reach out to 1,000 yards or beyond, i'd take the longer barrel and extra velocity to keep the bullet supersonic out to that range.

that said, i just built a long range gun with a Rem 700 SPS Varmint .308 with a 26" barrel in a Choate stock and posted this group first time out with Hornady 155 grain Amax.

it's 7 rounds, 300 yards, 1 3/16"

http://img8.imageshack.us/img8/795/dscf1090i.jpg


and here's 1 3/4" group at 300 yards with 168 grain Federal Gold Medal Match, 5 rounds

http://img33.imageshack.us/img33/2746/dscf1091r.jpg

Jim Watson
January 19, 2010, 10:54 AM
One of the sources in the famous Houston Warehouse experiments said the optimium barrel length was 21.75". That for the medium sized .22 and 6mm cartridges firing flatbase spitzers at 100-300 yards in the most common formats of benchrest competition. Does it apply to a .308? I dunno, but if you are setting up a gun to shoot small groups at moderate range, it would be something to try. At worst no different from 18, 20, or 22 inches.

As said, a longer barrel gets you some free velocity and moves the blast farther away from your head. It also gives longer sight radius for those dinosaurs shooting iron sights in formal target competition. Those are worth more at 600-1000 yards than a smidgen smaller group at short range.

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