How does barrel length affect accuracy?


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sammass
May 8, 2013, 02:53 AM
I have a new bolt rifle, a Ruger Gunsite Scout. It has a 6 groove,16.5" 308 Win barrel with a 1-10" RH twist. I am sure those of you in Hi-Power or Benchrest competition are wondering why I am posting here. I figure you folks are well versed on the intricasies of barrel length, speed of twist, and cartridge components to optimize your competive scores.

I realize that 16.5 is rather short for a service rifle. Have no idea what is normal for Benchrest. If ya'll have experience eeking out the best of a short stick, would appreciate your thoughts. Been into the Nosler 6 Guide to start to understand the reloading factor but sorting out the effective range for accuracy is still beyond my knowledge.

Thanks in advance.

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jr_roosa
May 8, 2013, 04:23 AM
Barrel length doesn't directly affect accuracy per se. However you may find it harder to shoot a 16.5" rifle as well as a 24" rifle for a few different reasons.

"Service rifle" barrels are longer, but that's just because NRA rules arbitrarily dictate 20" ARs, 22" M14/M1As, and 24" Garands as "Service Rifles" as opposed to "Match Rifles" for highpower matches. Arguably, the 20" AR is the most accurate rifle in the bunch, but that doesn't have much to do with the 20" barrel length.

Lighter guns have heavier recoil, which makes learning to shoot accurately more difficult. Long, heavy barrels soak up a lot of recoil and make it easier to develop good technique.

Longer sight radius when using iron sights can make it easier to shoot more accurately, which is easier to do with a longer barrel. Scopes don't care how long the barrel is.

A rifle with a long, heavy barrel wobbles slower than a short rifle, making it a little easier to shoot accurately, especially from unsupported positions.

Keeping the bullet above Mach 1.2 before it gets to your target results in better accuracy. To get a .308 to stay that fast to 1000 yards requires a crazy long Palma rifle barrel and slow powders to really drive the bullet fast when it leaves the barrel. Forget that sort of performance out of a 16.5" rifle. 600 to 800 yards should be within reach.

Barrel quality plays a MUCH bigger role in accuracy than length, and I don't know how good your barrel is. It might be awesome, or it might be a dog. Likely it falls somewhere in between.

The biggest factor in accuracy is your shooting technique. Shooters with good technique can compensate for some pretty substandard equipment.

The next biggest factor is probably the quality of the trigger...bad triggers are really hard to shoot accurately. Next comes the rifle itself: barrel quality, uniform barrel crown, stock fit/bedding, how the rifle fits you, etc. Next would be finding a load your rifle likes. Then optics. Then maybe barrel length.

I'd say find some federal match .308 ammo and see what you and your rifle can do with that. Try a bunch of other brands and see if some are good and some are bad, and keep good notes. Don't do this with 3 shot groups. 5 or 10 shot groups will give you much better info. When you find something your rifle likes, try to replicate that with your handloads as a starting point for load development. Right now is a terrible time to start reloading because there aren't a whole lot of components to be found for .308, but that will probably get better in a few months.

Good luck!

-J.

1911Tuner
May 8, 2013, 08:28 AM
You can actually get better intrinsic accuracy by shortening a barrel.

Barrels vibrate much like a tuning fork when the gun is fired. The longer the barrel, the greater the amount of deflection. Between two barrels of identical profile, the shorter barrel will be stiffer and less prone to "whipping" than the longer barrel.

Think about it. If long barrels equated to accuracy, the benchrest competitors' rifles would all be sporting 32-inch barrels.

Pete D.
May 8, 2013, 08:52 AM
Very interesting points made here about accuracy. I like that comment about bench rest guns and bbl length.
I have read that barrel length itself has little effect on mechanical accuracy. The length may effect other elements of the shot - like velocity carried over long distances - but in many cases that can be accommodated by adjusting the sight...especially at shorter ranges...under 600 yards.
For a shooter who is shooting with iron sights from unsupported positions or positions less stable than a bench rest, barrel length makes a difference to both precise use of the sights and the stability of the hold. There is a reason why one does not see short barrels on the line at High Power matches.

kludge
May 8, 2013, 12:14 PM
One test showed something like 21-3/4" to be the most inherently accurate length for rifle barrels. (don't quote me on that)

I think it had something to do with the speed of sound in steel.

There are two modes of vibration in a rifle barrel, longitudinal and transverse. The bending is the transverse wave; there are also harmonics of the this wave - but only the odd harmonics. The longitudinal is where the impulse from the burning powder (the sound wave) which travels down the length of the barrel and back (and back and forth and back and forth until the energy is gone.)

http://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html

Mike Kerr
May 8, 2013, 12:15 PM
Interesting points in the replies posted so far. A longer sight radius with irons is aften confused with accuracy, when intrinsic accuracy has other determinants.

regards,

:):):)

Howard Roark
May 8, 2013, 11:03 PM
I've shot NRA Highpower for many years across the course and long range. Short barrels may have some sort of accuracy advantage due to stiffness. Is there data to confirm this? I don't know.

I do know that length most often allows for higher velocities which means less wind drift. When a person has to deal with changing conditions at MR and LR every bit of speed counts to have the smallest amount of wind drift. If one person has a slow tack driver but misses a wind call and gets blown out for a 9 or worse, then they are screwed. Another person with a fast high BC bullet has less drift in a given condition so their wind call is not as criticle and may still hang a ten.

This is why the .308 gave way to higher BC and faster calibers like the .243, .260. Tubb told a friend of mine years ago that a .223 would never win the nationals again. My friend went on to win two 2nd places. He now admits that David was right.

Edited to add:
There are reasons to weigh speed vs. accuracy vs. weight for position shooting. A long sight radius as you know reduces sight alignment error. This is why to manage weight we use shorter barrels with a bloop tube. I shoot a .243 with a 26" barrel with a 5" bloop tube. Prone shooters let their sling carry the weight so a longer barrel (30" or so) producing higher velocities are typically used.

sammass
May 9, 2013, 03:36 AM
Folks...

Thanks so much for your thoughtful information. I appreciate it. The GSR is already to the riflesmith for inspection and anticipate the trigger, crown, lug work with internal polishing will be next. The smith wonders if the rifle was made on Mon, Wed, or Friday? :-) The GSR does have a bit of handicap due to the barrel length, but it has to shoot better than my eyesight. I was anticipating the 2-300 yd range with glass, but the 6-800 concept is a wow bonus.

Thank you all again!

Sam

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