Whats the best buffer for an M4?

[crusader377]

I have always run H or H2 buffers on my carbines 14.5" and 16". I prefer the slightly less recoil of the H2 but both work fine and 100% reliable.

[Iraqgunz]

I have it run it in that configuration as well. I opted for the H3 as the compromise set up.

I got ahold of a new 6920 and it ran A5H4 with Sprinco Green and still ejected kinda 3ish, IIRC. Whored my lower out at the range one day, lol! Nothing choked with that setup, even middy's running Monarch Academy steel case 55gr fodder.

[tom12.7]

A cold and fouled 6920/6921 may suffer in a combination of the A5H4 then a combination of the A5H3.
Warm, wet with oil, and relatively clean would be preferred with an A5H4. Cold, dry, and fouled could be better with a A5H3 in operation. Even more worse circumstances could cycle better with the A5H2. The preferred choice may depend on where you fall into these circumstances.

[squid8286]

I have a 16" carbine upper and a couple of 14.5s. I use regular old BCM carbine springs with all of them. I use H buffers on the 14.5, and an H2 on the 16.

[MistWolf]

The real answer is a balance of gas porting, reciprocating mass, spring rate and ammo

[samuse]

For any normal application a standard Colt or LMT spring and an H2 will work and work very well. Don't over think it.

I think the lighter buffers have a quicker, flatter recoil impulse than the heavies. I tested a KAC SR15 a couple weeks ago with 69gr .223 with a CAR, H, H2, and H6 buffers and the CAR felt the lightest to my shoulder. I run the H2 because I think it's a better fit.

[tom12.7]

The real answer is a balance of gas porting, reciprocating mass, spring rate and ammo

That is a better answer than most others provided. Maybe not complete or 100%, but better, as operation is a balance that includes required work with time all the way down to other timed events like round presentation via bolt over travel in time dwell. There is a lot going on, many simple answers aren't so simple. Without some specific test in mind, most would do well with a common rifle action spring type action, higher loadings in springs is a double edged sword. Can they work? Yes, but is it really the better compromise?