Springs and buffers AR 40's Results are in

[Albroswift]

Back from the range, final results in:

16" Carbine Sprinco red spring / 10 oz KVP tungsten buffer chewed through 180 gr plinkers, 180 gr major loads, and 155 gr  1500 fps+ with ease. Good "back on target" split times.

4.5" pistol Ditto above except for didn't run any of the lawman 155's 

From several trips to the range with various combinations, it seems to me a 10 oz buffer will run with several different spring weights, both pistol/ carbine, but a 7.5 oz buffer will only run in the pistol even with the EA1095 spring

Slower cycling makes cheap mags work better, and factory mags work flawlessly.

Springs I used from light to heavy

KVP Extra Power 308 carbine

Sprinco Red

EA1095

Buffers: 

KVP 7.5 and 10 oz

Just my opinion, but it seems possible to over buffer to the point that rounds will feed but bolt travel is insufficient to engage the disconnector, resulting in burst mode

Also my opinion, it seems possible to under buffer to the point that the bolt speed is fast enough  that either a. parts are moving so fast that the disconnector doesn't grab, or b. the effect of slamming into the "end of travel" jars the disconnector enough that it does not grab. Whatever the mechanics involved the results can be a bit bloody, out of battery slam fires and such, highly recommended to avoid at all costs! 

 

[sketch]

Thank you for the results!