[buffetdestroyer]

I tried doing .5 grain incremental drops from the loads that I posted here and I found that within 1 grain of my subsonic load, I lose the oomph necessary to reliably cycle my action.

For example if my load is 7.9 grains of 2400 with 175 grain Matchking, I can't reliably cycle at or below 6.9 grains and the velocity becomes highly erratic as the cycling starts to get finicky.

I may be able to get a little more reliable cycling with lower power loads by getting an AR15 BCG (instead of the slightly heavier M16 carrier in there now) and if I lighten the buffer spring.

However, I have found that with smaller lighter bullets like 150's you have a lot less friction (due to less surface area of the bullet touching the barrel) to overcome and can get loads down into the 800's fps where it still cycles consistently (some shots were down into the high 6's so be careful). The accuracy and velocity left a lot to be desired, but it functioned (for the 10 rounds I loaded) and was pretty quiet! The load was with military FMJ bullets and 7.5 grains of 2400 in my 10.5" barrel. The Standard Deviation was very high so use caution that it doesn't squib if you try this load in your gun. Breaking down the the upper to inspect the barrel for obstructions only takes 30 seconds and can save you the cost of a replacement barrel!

It has taken me about a year to find two subsonic loads that I am really happy with (one with 220's and one with 175's). There is a ton of info on supersonic loads, but that defeats my reason for building my upper and I have other rifles that will perform ballistically the same as a supersonic .300 WTF (my 7.62 AK's for example - cheaper and less hassle since I don't have to reload for it). I agree that having a compiled document or thread would be beneficial since I seriously doubt I will ever buy 300 BLK subsonic ammo because of cost and I doubt it will shoot subsonic in my rifle based on the load & velocity rsilvers posted (the one with 1680 powder) - mine shoots about 150 fps faster than his and I had to drop almost 2.0 grains off his load to find a 1050 fps load. Subsonic WTF loads are very sensitive between not cycling/squibbing and going supersonic and that happy spot is sometimes blurred and takes a lot of load development and trips to the range in order to find one that is consistent in the middle of both of those across varying external conditions.