Well it was a breakthrough for me anyway. First off my expectations. I already have a nice built lower that is setup just the way I like for 5.56. In that rifle, I have the M16A2 buffer spring and heavier buffer, and national match bolt carrier, which is an extra ounce vs the standard bolt carrier. Neither of these features are necessarily a good thing on the subsonic .300 blackout, but those are the parts I had so that is what I wanted to use.
My expectations were simple in concept, use the same parts which perform so well with 5.56, powder that will meter well for progressive reloading, temperature stability, cycle my AR reliably, and accuracy. Well this proved to be more difficult than expected. 1680, the go to powder, was just dirty, and with the heavier spring, buffer and carrier still did not cycle reliably with loads that were subsonic.
For the upper I have a 16" satern 8 twist with a carbine length port (fyi even with a 16" I recommend still going with a pistol length port, will save alot of troubles). My first step to improve cycling reliability with the 1680 was to open up my gas hole. I did that as little as I could until the rifle seemed to run subsonic with suppressor. My load development was early this spring, with colder temperatures, so the next time I took it to the range in an attempt to really test it, the warmer weather made my 1050fps @60 degrees go supersonic. I didn't have the chrono with me at this point to see the exact velocity. by the time I reworked some loads back to subsonic for the higher temps, my gun wouldn't cycle.
Now for the breakthrough. I got to speaking with the gunsmiths at Vestals in Abingdon (excalibur and col kurtz here on the hide) and they said to just try going on up to a slower powder and see what happened. That makes sorta obvious sense, but everything I had read about this round steered back to 1680 type powders. Well I go home and see what I have that's a little slower and found some vihtavuori n530 that I wasn't using for anything else. I decided to load up a few rounds with it and see what happened.
I started with 10 grains behind a nosler 190 custom competition (the cheapest heavyish bullet I could find) and the round went super, but cycled well. I incrementally went down and behold it appears I might just have found the answer. I have it cycling beautifully subsonic, temperature wise it should be stable, it meters as well as could be expected for a smaller grain stick powder. It is raining so I couldn't chrony for exact numbers or shoot any groups, but I have rounds loaded up from 9-9.5 grains that should all run subsonic. Again this is with a 190 bullet and heavier spring, buffer, and carrier, so stepping up to the 200 weight bullets, as well as standard parts should only improve chances of finding a good sub load.
I should be back to the range over the weekend and have full report on accuracy and velocity!
hope this helps someone and remember your setup may be different so work up loads safely and accordingly!
My expectations were simple in concept, use the same parts which perform so well with 5.56, powder that will meter well for progressive reloading, temperature stability, cycle my AR reliably, and accuracy. Well this proved to be more difficult than expected. 1680, the go to powder, was just dirty, and with the heavier spring, buffer and carrier still did not cycle reliably with loads that were subsonic.
For the upper I have a 16" satern 8 twist with a carbine length port (fyi even with a 16" I recommend still going with a pistol length port, will save alot of troubles). My first step to improve cycling reliability with the 1680 was to open up my gas hole. I did that as little as I could until the rifle seemed to run subsonic with suppressor. My load development was early this spring, with colder temperatures, so the next time I took it to the range in an attempt to really test it, the warmer weather made my 1050fps @60 degrees go supersonic. I didn't have the chrono with me at this point to see the exact velocity. by the time I reworked some loads back to subsonic for the higher temps, my gun wouldn't cycle.
Now for the breakthrough. I got to speaking with the gunsmiths at Vestals in Abingdon (excalibur and col kurtz here on the hide) and they said to just try going on up to a slower powder and see what happened. That makes sorta obvious sense, but everything I had read about this round steered back to 1680 type powders. Well I go home and see what I have that's a little slower and found some vihtavuori n530 that I wasn't using for anything else. I decided to load up a few rounds with it and see what happened.
I started with 10 grains behind a nosler 190 custom competition (the cheapest heavyish bullet I could find) and the round went super, but cycled well. I incrementally went down and behold it appears I might just have found the answer. I have it cycling beautifully subsonic, temperature wise it should be stable, it meters as well as could be expected for a smaller grain stick powder. It is raining so I couldn't chrony for exact numbers or shoot any groups, but I have rounds loaded up from 9-9.5 grains that should all run subsonic. Again this is with a 190 bullet and heavier spring, buffer, and carrier, so stepping up to the 200 weight bullets, as well as standard parts should only improve chances of finding a good sub load.
I should be back to the range over the weekend and have full report on accuracy and velocity!
hope this helps someone and remember your setup may be different so work up loads safely and accordingly!
