I need help building a lighter weight 3 gun/SPR style 5.56/223 AR.
I’m looking to do 18”/rifle gas with rifle buffer, although I have lowers available with the full gamut of carbine/A5/rifle receiver extensions. I want to stay with full weight m16 BCG, fixed gas block and factory brass case (no steel), both 223 and 5.56 in primarily 55/77gr variety. The full weight/fixed gas block part seems outside the normal for most 3 gun types, and as a result I’m struggling with finding gas port sizing info for 18” barrels. Research so far has shown people reporting ports from .089 to .108, but very little is said about BCG/buffer weight or adjustable gas blocks. While I want reliable, I would prefer to stay on the conservative end of gas drive.
My thought was that .093 as Colt spec for a 20” SP1 was a starting place and given 2” less barrel after the port, the 18” will likely need a bit more port size, but how much more I can’t seem to figure out. Anyone able to help?