I was running A5H4 in my full auto 6991 as well. Good results. I am now running KAK 10oz w/standard Carbine spring. From my experience is shots softer and slowed the cyclic rate of fire just enough. I can do 3 round bursts with ease and the casings aren’t as dirty which tells me the bolt is staying home longer. I have tried everything and the kak 10oz is the best I’ve tried. Your miles May very.
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