Tested in a variety of locations and temperature on three different days.
65-70 degrees, 1000-2800 feet MSL
Method: For the initial testing I loaded 3 shots for each load and averaged the data, then did some minor smoothing of the data based on some outliers. Second and third round testing was simply "around the edges" to verify my previous findings. Numbers are in FPS. Loads not listed were either below what I thought would reliably cycle the gun or above what I thought would reliably stay under the sound barrier.
All loads shown reliably cycled the gun listed below. I did not test if the last round would reliably hold the bolt open. All shots were made suppressed.
Yes, Accurate 1680 is a superior powder for cycling ARs subsonic!
Part of this testing was to see if the A1680 actually produces more volume of gas than the others to help in cycling subsonic rounds. I think the test results show this is true. I was a bit surprised I could even make a 155 grain load that would cycle reliably. None of the others could come close.
Reloader 7 is a good solid reliable powder for cycling subsonic ARs with consistent results.
A5744 gives the most consistent speeds but the most inconsistent cycling of the gun. This may result in the best accuracy if you can find a load that reliably cycles your gun. This powder was the most likely to cause a hickup near the lower loads.
Another surprising finding is that the flat tail 180g Winchester Power Point clearly worked better and gave a wider window of operation than the boat tail bullets. Comparing this to a similar weight 180g HPBT I would expect superior results in at least the area of more likely to use the gas more efficiently.
COAL 2.13"
Gun: DDM4 V7 300 aac. 16" barrel
Gas: Carbine Length
Suppressor: SAS Arbiter
H buffer and regular spring
