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Posted: 4/3/2005 2:52:23 PM EDT
| I have an 11.5 pencil barrel that gets about 5" at 100 yards. What kinds of groups are people getting at 100 yards with sub M4 length barrels? I'm looking for info on barrels int he 8" to 12" range, profile non specific. Please include ammo type info as well. I'm not looking to start a debate on SHTF gear, just looking for general data. |
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Well, I can play in this topic truthfully. 7.5" DPMS 1x9... 1 1/2" at 100 with cheap 3-9x40 Tasco, 52gr HP Hornady in WCC cases and 748 powder. 11.5" Bushmaster 1x9 (1989 barrel), same ammo/results as above. 12" SS DPMS 1x9 bull barrel cut from a 16" bull, have not even messed with it. |
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DPMS 11.5" 1-9 non-chromed bore - 2" groups @100 yards with LC XM193 and Aimpoint ML2 DPMS 11.5" 1-9 non-chromed bore - 1.75" groups @100 yards with Radway Green 62 gr (British milsurp) Aimpoint ML2 DPMS 11.5" 1-9 non-chromed bore - 4" groups@100 yards with Wolf 62 gr FMJ. Aimpoint ML2 |
+1 these guys shoot a hell of a lot more than i do. i'm lucky to pull those groups with my 20" a2! |
You're partially correct here. Remember that a bullets are designed to stabilize out of a barrel at a specific velocity. A perfect example of this is the 230 FMJ bullet I'm required to use to shoot CMP 'leg' matches. Many shooters load a very light .45 wadcutter round for better controlability in bullseye, but the 230 FMJ just dosen't fly well unless it's loaded close to maximum pressure and velocity. The 1.5" group guarantee is usually only good with some very specific (and sometimes only one) load. My target AR shoots different sized groups depending on the specific ammo, and if I shorten the barrel on a given load I will change the velocity, thereby changing the accuracy. In a rifle, barrel whip has some effect here which is why I suspect that an H-bar profile will get better accuracy. I'm just trying to find out.
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That was just an example - Barrel length has NOTHING to do with accuracy, no matter what caliber. |
| I'm aware of one experiment where a revolver had it's barrel shortened 2" and recrowned between strings of shots. The result was that the 2" barrel shot as well as whatever the barrel length was to begin with. I think Guns and Ammo did the test. My question now is, has anyone done the same thing with a rifle? This would be fairly easy to do with a bolt gun, but a semi auto would pose problems. Because of the different factors in rifle accuracy, I would like to see some data before I make up my mind. |
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While I would agree that barrel length has no direct correlation to accuracy, there are several indirect effects, mostly at longer ranges. For example:
Before we can arbitrarily wave off barrel length, we need to talk about the amount of accuracy degredation tolerated at a given range. For the average Ar15 at 50yds, you just won't notice. |
While I agree, it would still be amusing to see a bench rifle with a barrel as long as the scope. Oh wait, that's called an XP100 
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Ok, here's the chart. The test was conducted at Thunder Ranch by Pete Nantirux. The rifle was a Robar SR60-2 300 Win Mag. They used a Lilja bbl and the bbl work (cutting and crowning) was done by Robbie Barrkman of Robar Inc. The rifle was topped off with a Leupold model 54680 Long Range M1 6.5x20.
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The above chart basically shows what I expect. However... 300 Win Mag is damn near a 1,000yd cartridge, and 300yds is the very close end of its effective range. The effects of the shorter barrel are going to be seen at the far end of the effective range, and will move closer as the barrel is shortened. If you want a good example of this, run the trajectory of your favorite cartridge on a ballistic calculation program. Now change the velocity by 25fps and repeat. You'll notice that the while the near range trajectory changes only slightly, the far range effects start to stack up. What's missing from the above chart is how the muzzle velocity variation is growing. Again, barrel length effect on accuracy depends on the definition of "accuracy" and the range at which one expects to wield it. |
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