Really easy, and the 77gr ammo uses a slower burning powder than say 55gr ammo (even through both have the same over all working pressure), which pushes the spike dwell of the gun powder burn closer to the gas port, which raises the gas pressure to the B/C-has the bolt unlocking a touch to soon while the residual pressure in the bore is to high for a clean case pull.  Hence we are trying to get the residual bore pressures back down to normal when the bolt does unlock.
Note, to tell that a bolt is unlocking too soon, will either rip the extractor off the rim, or if the extractor has a strong enough spring, spent case rims will be bent back from the harder than normal pull.


So in the graph, the slower the burn the powder, the farther to the right the spike will be, which also raises the gas port pressure; even through the over all working pressure of the round has not changed/increased instead.


So to slow the bolt back down to normal unlock times with the heaver ammo using slower burning powder, so the bore residual pressure can drop the normal level to allow the extractor to cleanly pull the case without popping off the spent case rim, a heaver buffer is required.  With a H2 in play, may need to go to a H3 or even heaver carbine buffer.  I prefer buffer swaps when using different ammo, but there is also adjustable gas blocks and carrier keys if you want to stay with the same buffer and just adjust the gas pressure to the B/C instead.

Also, on the extractor spring (even with the bolt unlock slowed down), it needs to be replaced with a Extra tension spring as well.  I prefer the Colt M-4 extra tension springs since they have a marker to tell you that its an  actual  M-4 Spring (its gold), but there are other places that sell extra tension extractor springs as well.  Until you get a extra tension extractor spring, you can use a #60 O ring around a standard tension spring for now to increase the extractor spring tension.



As for extractor, check it for burs on the end of the grabbing claw that may need to be cleaned up, as well as the sides of the rim relief channel just below the claw that may not be allowing the extractor to get a full bite on the rim during the pull.  If needed, small jewelers file make quick work of cleaning up the burs.

So edge of claw burs cleaned up,


Sides of rim relief channel burs cleaned up,


And Bob's your uncle with some cold bluing.


As for lube, switch over to BreakfreeCLP in the large spray can.  Short of the bore that needs to be cleaned with a good copper solvent like Sweets, the rest of the rifle will be first cleaned with CLP (including scrubbing the chamber with chamber brush by hand with some CLP.  Once rifle parts are cleaned, then removed the fouled CLP, and apply just a light coat of CLP to the upper bearing surfaces.  Hence coat the inside and outside of the B/C with CLP, install the lubed B/C in the upper and empty cycle the action a few times to transfer the CLP off the B/C , to the upper receiver bearing areas.

BreakfreeCLP has a cleaning agent in it, and think of cleaning the rig as just change the lube in the rig instead. Hence what you miss during a cleaning, the cleaning agent in the CLP will disolve before you shoot the rig again.

Also, when cleaning barrel, bore first with Something like sweets to start, push clean patches out until they are no longer Blue.  Switch over to chamber brush and CLP by hand to clean/scrub the chamber, and when you push the fouled CLP from the chamber to muzzle with patches, even through the chamber and bore will look dry, there will be enough CLP lube still on the surfaces for short term storage of the rig to prevent rusting.