Just as Jaxman discovered in his experience, don't underestimate the importance of polishing the bearing surfaces of the Bolt Carrier. You'd be shocked the role that friction plays. Phosphate on rough anodized aluminum is gritty. Try polishing those areas as proscribed in other threads and then using the H4. You might be surprised.
Mtdawg, have you polished the bearing surfaces on the BC as mentioned above?

Originally Posted by
ROK
Just my data point...
Colt 6920LE
16" Colt carbine gas length barrel, M4 profile
LMT enhanced carrier+enhanced bolt
Vltor A5 RE (short rail)+Vltor A5H4 buffer+Sprinco Green action spring
Griffin Armament M4SDII comp
Geissele SSA-E trigger
I went down this path looking to take some of the "jump" away from the 16" carbine after shooting my 18" mid-length gas upper. The carbine was almost
over caffeinated compared to the nicer manners of the 18" upper.
Results->
The Colt 6920LE is now a completely different animal. Little to no harshness. A word used a lot to how it handles is "smooth". I would have to agree. Second, third and forth shots very fast and on target. Where the improvement really shows is shooting on the move. The dot moves much less.
Very happy with this upgrade to the Colt 6920LE carbine.
I liked it so much, I picked up another lower (Colt 6920SP) to give the 18" mid length upper a home.
Rainier Arms Select MedCon 18" barrel
Another A5 RE (7 hole)+Green Sprinco+A5H4
A1 flash hider
Geissele SSA-E
Colt BCG
This upper is much more outside temperature sensitive with the heavy A5H4 buffer. I use Lake City xm193, IMI, and xm193 PPU almost exclusively.
With cold temperatures <32*, I started to see short stroking, bolt failure to hold back. I made a A5H3 from a std A5H2 and a donor tungsten weight from a H carbine buffer. The H3 in cold weather worked in a cleaned gun, lubed with Fireclean. Shot as cold as -6* F w/o issues. 400 rounds tells me this works. I plan to swap back to the A5H4 once the weather breaks and see what happens. Stay tuned.
The 18" mid length saw a dramatic example, to me, of how buffer weight affects reliability. My range bag now has an A5H2 and A2H4 in it.
Last edited by BufordTJustice; 03-13-14 at 15:41.
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