went to the range today to experiment with a couple things and fire-form some brass.....
the last changes made to the chamber reamer seemed to work out pretty good...pushing a 125 TNT at a consistant 2,650fps out of the 20" with 26.5gr of accurate 1680....with a combination of a few tweaks the 20" now cycles very positive and reliable....
a pic of the revised round in a line-up (left to right: 300-221, 7.62x39Russian, 7.62x39USA, 5.56x45)...revised round is approaching 7.62x40mm
also got a few of the 20 round pmags for shooting prone....modified them using a 11/16" bedding tool....disassemble the mag, hold the mag body vertical insert and pull down the bedding tool a few times and it cuts out both ribs at the same time....works great on the 20 and 30 round pmags....
a pic of the revised round in the pmag....
after a few requests from the AR-15.com forum I am probably going to chamber a couple more barrels this week...most are interested in the 16" but I'm kinda starting to favor the 20"....going to start next week on another 20" with a mid-length gas system, may be a little easier to tune...