I just recently completed my first build: Spikes lower, complete Spikes mid-length upper.  I used a regular carbine buffer.  When I went to go shoot it the first time, I noticed that the recoil was a lot harsher than on my other AR, an M&P Sport.  I used the same .223 ammo I usually use.  With the heavier mid-length I expected the opposite.  Is it the buffer? spring?  Everything functioned perfectly otherwise.  Any input is appreciated.  Thanks.

Someone can diagnos but that is backwards. Your intuition is correct

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H or H2 buffer if that doesn't help Wolff XP spring try carbine, H, H2 again one of those combos should be perfect

Ok thanks guys.