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Posted: 7/9/2006 10:52:34 PM EDT
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This question is for other Bushmaster owners. I understand that not all 1/9 barrels are created equal with regards to twist rate. Some may be a bit faster and some slower. For those who have Bushmasters, what is the heaviest bullet you have shot, and with what results? Thanks! |
1-9 is the twist rate, period. With out splitting hairs, all 1-9 barrels should be equal and perform the same. The differences come into play between the twists rates them selves: 1-12, 1-9, 1-7 ect. |
Just to see what it could do, I took my Bushmaster 1/9 20" Govt profile out one day and from a rest, shot ten shot groups of XM-193, Black Hills 68gr., Federal 69gr., BH 75gr., and BH 77gr. At 100 yards, the 75gr. shot the best with nearly 1" groups, the 68gr. shot the worst with like a 4-5" group. The 77gr was only slightly less accurate than XM-193, somewhere around 3" IIRC. Certainly good enough for social work out to 100 yards at least. This rifle has always amazed me with it's inherent accuracy. 
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They should be the same, but sometimes they are not. Pull buttoned barrels (what Bushmaster uses) vary in twist rate as the button sometimes slips in its shaft going down the barrel, or the rifling machine fails to maintain a constant velocity. It's just your standard mass production variation. The only way to get exactly the twist rate is to buy a cheap, hammer forged barrel (which are useless for accuracy work no matter how well stress relieved they may be) or an expensive, cut-rifled barrel (Krieger, Obermeyer, Broughton). So while 1 in 9 may the nominal rate of twist, it is sometimes more or less. That's why the occasional 1/9 barrel fails to stabilize 75 grain bullets. |
The heavest bullet I have shot out of my Bushmaster 1-9" is a 69 grain Sierra MK. The best ever 5 shot group at 100 yards was 0.46" But most of the 5 shot groups are around 1" And the best ever 10 shot group at 100 yards was 1.58" These groups were done with the 69gr. Sierra MK. HPBT and Varget powder. |
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I've shot 77gr Nosler OTMs and 75gr Hornady OTMs (the Hornady's being slighlty longer than the Noslers). My 20", 16", and one of my 14.5" barrels would shoot them to around 2" (+/- 0.2") @100y; the other of my 14.5" Bushy's shoots the 75gr to 4" at 100y . Note if the first 14.5" is really copper fouled it won't shoot the 75's at all (they will keyhole), if it's clean it can shoot a 2.25" group. |
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I shot my M16A1 with a Bushy 11½ at a target 200 yards away last year. Using straight Iron Sights and shooting only semi-auto my groups were almost the same as if I had used my 20 inch upper. I wish I still had the Threads address. It was a very fine day shooting at the range. In other words: Unless you are shooting very heavy bullets there should be no problems. |
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