Standard CAR buffer will run fine.

H buffer as well. I run both in carbine gas and middy, issue free.

A heavier buffer softens the recoil impulse.

Standard Carbine buffers will run under the absolute worst conditions... filthy firearms, questionable ammo ( low powered) horrible field conditions etc...

A heavier buffer slightly slows the cyclic action ( milliseconds ) .. and allows the BCG to open at slightly lower pressures because of that slower opening.

You will find that the AR15 is very tolerant of different buffer weights... ( and depending on your gas port size, / gas system length, ammo selection. )

Ultimately, you can "tune" your carbine / rifle's cyclic speed ( recoil impulse ) .... changes include, brass ejection position, the speed of extraction while under pressure ( heavier buffer is easier on the extraction and the brass ) , staying on target is typically easier, since the BCG isn't moving as abruptly  ( "softer" milliseconds slower recoil impulse ), easier on the parts ... stuff like that.


IMHO, using a good recoil spring ( Tubbs Flatwire ) and a heavier buffer can make your carbine / rifle far more enjoyable to shoot.

Lots of people will say "the recoil of a .223 / 5.56 isn't that bad..." and that is true... but you can tame the recoil even more with a heavier buffer, so why not ?


If you buy another weight buffer.... consider this one... it is fully configurable through all the carbine buffer weights possible... from LtWt - HyWt. ... it is easy to adjust and use.

That way to can see for your self what works best with your specific carbine... it is hard to suggest a single buffer weight because, again, gas port sizes are different from darn near all the different barrel makers and the gas system length .

On a side note, a middie length gas system accomplishes the same thing... using pressure from the barrel at a point that is lower pressured but with ample volume of gas ... ( milliseconds thing again ) ... = "softer" recoil.

https://www.kakindustry.com/shockwave/ar15-buffer-system