I have the Colt 6400C which has a 1/7" twist 16" heavy barrel designed for the long tracer rounds and 62G M855 used in the military today...ive heard talk/read on the ammo oracle that it can overstabalize the 55g M193 ammo because of the high velocity and overstabalization caused by the super fast twist rate.

Ive shot 62G and 55G ammo, and the 62G did seem to be much more accurate, but it was also the Swiss GP90, as opposed to XM193, which is renound for its accuracy/consistency.

What have you guys with the 1/7 twist found out at 2-300+ yards with the 55G surplus ammo? Should I stick to the 62G ammo?

Just my opinion, but all the talk of " overstabilisation " is not really applicable to 223 firearms especially 16" ones.

I have fired 40gr. loads through my 20' 1/8 twist with no apparent loss in accuracy.

I have heard of this problem in 220 Swift and 22/250 rifles, but they drive em a little faster than we do. The centrifical force actually causes the bullet to lose it's structural integrity and occasionally disintegrate before it reaches the target, or in lesser cases become unbalanced and innacurate.

The only sure way to find out is to try some and see what they do in your rifle, though results with one load may not be conclusive that your rifle won't shoot that weight of bullet.

Good luck

Travis F.

M193 shoots just fine at 300 yds thru 1:7 twist . Remember though that GI ball ammo is not MATCH AMMO ! some lots shoot really well and some don't ..

The Swiss GP90 is much more consistant than XM193. The 1\7 twist was designed for the tracer round because it's much heavier than the 62 gr SS109 bullet. Unless you're going to be shooting a match, don't worry too much about the ammo. XM193, Q3131a, and GP90 are all good rounds. Your rifle will probably be more accurite with one particular round, mine is the GP90.

One note on M855, also missidentified as SS109. The penetrator core in the SS109 bullet is not a match grade part. The placement of the penetrator in the bullet isn't always dead center. I've noticed that regardless of the size of the group, SS109 has always given me a football shaped grouping. All other rounds give me round groupings.

The M856 tracer actually weighs [i]slightly[/i] less than the M855 (61gr or 61.7gr, depending on sources).  Twist rate really depends on the length of the bullet, and the M856 is a REALLY long bullet...thus the reason for the fast twist.  Weight is really only a factor because longer bullets weigh more [i]usually[/i].  Not the case with the tracer, as the tracer compund weighs far less than lead.


Back to the original question.  You'll be fine shooting 55gr on up.  100gr 5.56 will still even stabilize in the 1/7 twist barrels.