"55 grain m193 ball was the standard military load for many years, with the original M16 twist rate of 1:14 not surviving long due to lack of long range accuracy, and the M16a1 twist rate of 1:12 being the standard until the introduction of the M16a2 at 1:7. Along with the tighter 1:7 rate came the 63 grain M885 steel penetrator ball, along with new tracer ball compatible with the impact point of the M855.
1:7 probably overstabilizes 55 grain bullets. :shrug: 1:12 won't properly stabilize anything heavier than about 55 grain bullets, and you will get keyholing by 100 meters if you use heavier bullets. 1:7 stabilizes sufficiently for 75-80 grain SMK rounds, which are what is generally used in heavy sniper rounds, and long range target rounds. There may be even heavier bullets used for special purposes.
Most commercial AR barrels I've seen are 1:9 or 1:7. If you're not shooting any of the heavy target/sniper stuff, the 1:9 will work fine.
For a dedicated varmint rifle that only sees 45-55 grain bullets, the 1:12 is still fine."
Well said Sixgunner! My 1:9's shoot very well with anything from 50 gains to 69 grains.
Rifleman, yes the M193 is the military designation for the 55 FMJ used prior to the adaption of the M855/SS109 62 grain loadings. When you see companies advertise as M193 it means that they are attempting to duplicate the military specification for that round. It does not mean that this always happens however or they are a military contractor.
There are a bunch of good deals for .223/5.56 out right now but I have already expressed my preference for the PRIV Partisan M193 from Wideners at $73/200. Shipping will usually be around $10 generally so that puts you at over $80 unless you buy in more bulk. Price breaks are usually at the 500 and 1000 round quantities.
That said, I would not hesitate to pick up some Federal XM193 (good brass for the reloader) for the same price. I may be tempted at the $90 you mentioned. I just won't pay elevated prices for it.
Hope this helps, Bill.
