M193 and M855 out of a 1-7" twist barrel

[jmoore]

I don't know why the rumor persists that 55gr bullets won't shoot at all accurately out of a fast twist barrel. Just recently, a fellow at work was all concerned that his proposed build might suffer if he gets a "too fast" twist barrel.

So, here is a quick demonstration of the two standard milsurp types out of a "Government profile" chrome lined 20" Colt barrel of not spectacular accuracy. Since errors tend to compound, I figured this combo would be most apt to produce poor results without the introduction of substandard components.

Ammo:


Good quality and to spec.

Rifle:

"A4ish" build but no A2 stock- was gonna do it, but the SOPMOD's too useful. Colt receiver and parts,mostly. Geisselle FCG (it's USMC approved!).

'80s vintage barrel

TA31RCO-A4 Bad photo, sorry. Actual target used. (And yes, it's patched up from previous range trips.)



10rds M855 off bench at 100yds, no bags, just handheld with a little impromptu support. Getting fancy won't help- this is as expected, and is "good enough"! ~2 1/2 MOA


10rds M193 as above. Zero shift, but not much enlargement. In "match grade" barrels it does do better, but this was a test for gross accuracy loss- I don't see it, do you? Again, about 2 1/2" MOA. As noted above this barrel's not hugely accurate, but it's consistant!

BTW, just for giggles, 18rds Prvi and 2 rds Twin Cities (circa 1970) M193 were then fired standing at 200yds w/ no zero corrections (note that the RH and low shift is also present like on the 100yd target). Given how "off" I've been doing this exercise lately, the results were actually pretty pleasing- the low rounds were all called, only the high hit was a bit unexpected. Too bad you can't get a "skilled" tester!




Oh, now if your lightweight bullets are "substandard" (a recent lot of PMC Bronze 55gr FMJ comes to mind), then the fast twist WILL show the faults more than an "optimized" twist rate- but still no keyholing or other such evilness. Poor bullet jacket concentricity is the real villain here, not a too fast twist.

Anybody else have any actual results along these lines they would like to share?

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