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Posted: 1/25/2014 6:06:21 PM EDT
[Last Edit: 1/25/2014 6:11:49 PM EDT by usp45aac]
i have an 18 and was thinking of cutting it to 16 so it would  stick out 1" from my hand guard, would i be loosing much taking 2 inches off ?

EDIT:

forgot to mention, the build is a "precision or dmr" style build
Link Posted: 1/25/2014 6:17:23 PM EDT
[Last Edit: 1/25/2014 6:19:46 PM EDT by sanausnol]
You would lose anywhere from 70-120 fps dependent on the type of ammo your are using.  The standard is 50 fps for every inch you lose.

ETA:  Forgot to add that the 16" barrel may actually give you better accuracy as it will be stiffer and will reduce harmonics although from my own shooting I have found very little difference between my 18" .308 rifles and my 14.5" .308 rifles.  The weight savings is very nice and I shoot with the same accuracy out to 500 yards (don't shoot any further than this).
Link Posted: 1/25/2014 6:19:31 PM EDT
From all the research I've read you wont lose much.  How far do you typically shoot?  I've got a 16in and love it.
Link Posted: 1/25/2014 6:46:25 PM EDT
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Originally Posted By JonLSU:
From all the research I've read you wont lose much.  How far do you typically shoot?  I've got a 16in and love it.
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well i havent got to shooting yet honest, i have an 18" gun with 20 rounds threw the thing just to function test it.... hmm wonder if i should cut and thread it ?
Link Posted: 1/25/2014 8:50:37 PM EDT
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Originally Posted By sanausnol:
ETA:  Forgot to add that the 16" barrel may actually give you better accuracy as it will be stiffer and will reduce harmonics although from my own shooting I have found very little difference between my 18" .308 rifles and my 14.5" .308 rifles.
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Speaking to Ed Shilen on the matter, he says it's mostly a myth. Properly timed reloads will exit the barrel at roughly the same point, harmonically, and thus making them accurate. Properly timed rounds have more to do with it than barrel flex. Otherwise 32" barrels wouldn't ever hit a damn thing.
Link Posted: 1/26/2014 7:26:58 AM EDT
I think 18 is a happy medium. My old 16 did fine out to 300 easy. I never shot past that though.

AL
Link Posted: 1/26/2014 9:09:08 AM EDT
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Originally Posted By ZX10dencies:

Speaking to Ed Shilen on the matter, he says it's mostly a myth. Properly timed reloads will exit the barrel at roughly the same point, harmonically, and thus making them accurate. Properly timed rounds have more to do with it than barrel flex. Otherwise 32" barrels wouldn't ever hit a damn thing.
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Originally Posted By ZX10dencies:
Originally Posted By sanausnol:
ETA:  Forgot to add that the 16" barrel may actually give you better accuracy as it will be stiffer and will reduce harmonics although from my own shooting I have found very little difference between my 18" .308 rifles and my 14.5" .308 rifles.

Speaking to Ed Shilen on the matter, he says it's mostly a myth. Properly timed reloads will exit the barrel at roughly the same point, harmonically, and thus making them accurate. Properly timed rounds have more to do with it than barrel flex. Otherwise 32" barrels wouldn't ever hit a damn thing.


"Properly timed reloads" would mean I assume working with reloads until you reach the best accuracy from your particular barrel.  Personally I believe the shorter stiffer barrels will "generally" be more accurate than a longer barrel of the same diameter.  You'll find long barrel on varmint rifles or maximum velocity, but most top level bench rifles will have shorter barrels to maximize accuracy. Of course those guys are concerned about ten-thousands of an inch improvements.  Nothing most of use would care about or even notice.
Link Posted: 1/26/2014 10:06:41 AM EDT
Forgive me for not being exact, as it's been a bit on a materials engineering principal I had to learn to grasp the conversation. But basically the understanding is that rule of thumb, reverb energy moves through barrels at roughly 18,000fps and with minor variations, it's relatively consistent with the materials that are suitable for barrel construction.

That said, the barrel primarily flexes in an up and downward motion. The goal of the "timed reload," is to exit the barrel on the pauses. That is, think of a teeter totter, when the transition occurs from the up to downward pause there is a momentary pause, motion stops as momentum switches from the upward to downward flex cycle. Another pause, of course, occurs at the down to up transition. The goal is for the projectile to exit the barrel at this pause, as more or less the barrel is in the "same," location. Where as, by firing whilst the barrel is in motion you have the inconsistency of powder charges, projectile shape, case weight, etc (commonly expected issues that effect even the most perfect bench rest rifles of course) as well as the fact that the barrel is in motion, which transitions some of the momentum into a "flinging," effect. While firing on the pauses, the barrels energy of motion isn't transferred to the projectile, because the barrel is no longer in motion.

The goal is to fire on the upward pause, though the lower pause will also work for accuracy. But you may as we'll take advantage of the extra elevation if for no other reason. So as Ed explained, the barrel length matters less, as they'll all flex, it's just about finding a projectile that fires on your particular pause. This is the reason why your load may shoot lights out in your rifle, and shoot like utter crap in your buddies relatively similar setup.
Link Posted: 1/26/2014 11:51:11 AM EDT
[Last Edit: 1/26/2014 11:53:00 AM EDT by jtb1967]
Some competitive shooters also feel a shorter barrel reacts less to shooter movement since the bullet spends less time in the barrel. I know many feel the shorter barrels balance better in the bags as well.  There are guys who shoot fantastic groups with longer barrels, but 22" to 24" barrels seem to be far more common in serious competitive shooting compared to longer barrels.  But then we're talking about 16" vs 18" or 20" unlike the bolt rifles.

Dan Lilja has an interesting article on barrel rigidity
http://www.riflebarrels.com/articles/barrel_making/rigidity_benchrest_rifles.htm
Link Posted: 1/26/2014 6:40:44 PM EDT
I recently helped a friend test .308 ammo from Southwest Ammo for velocity and standard deviation. We tested 7 different loadings with bullets from 150g to 185g in 16", 18", 20", and 24" barrels. We found very consistently 28-30 fps gains for each inch of barrel length. We also found that as velocity went up (longer barrels) standard deviation lowered.

So roughly 60 fps is lost between 18" and 16". It's not a substantial loss unless you need the velocity. I'm happy with my 20" running 120 fps faster than a 16". Run the numbers through a ballistics calculator and see if you value the difference. Lowered standard deviation may contribute to better accuracy but probably less than a lot of other factors relating to the barrel.
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