See my post from 2-28-2011. I now have a Delta 10.3" 300 Blackout upper. I found 13.8gr H110 to be most accurate in it. It was also accurate in my 16" AR upper, so that is now my standard frangible load. I also reduced the oal to 2.2" and now rarely have a broken bullet tip while shooting. It gives 1711fps in my shorter upper. Actually, the Delta 10.3" bbl shoots more accurate than the Model 1 Sales upper. No problems with cycling with either upper. Matter of fact, I just got back from shooting the Delta upper today.
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