Well guys, here we go
I picked up my AR10A4 upper yesterday (A2 handguards, lightweight stainless barrel with bare muzzle and target crown, .243 WIN) and of course couldnt wait to get it home from the office and start tinkering
First observation: the front pivot lug was extremely tight so I ended up taking some 600 grit wet/dry paper and smooting off each side of the lug (just smooth, not through the anodizing), it now fits but is still tight enough to take effort to install. Once this was done the upper dropped into place and everything lined up.
Second observation: The front pivot pin would only go approximatley 1/3rd of the way into the hole in the lug, upon observation I could see where the hole tapered from outside to inside on each end with the center having a distinctive ring and smaller diameter which precluded the pin from passing through, a few moments (gently!) with a cylindrical diamond imbedded tool on the Dremel and then smoothing with 600 gritt wet/dry paper and it works, tight again but that is ok at least for now. The rear pin pushed through with zero resistance and now this puppy is mounted
I believe this uppers front lug was at the extreme for tolerance and maybe missed some CQ, by the way, this is a bran spanking new upper that has never been mounted.
Okay, now its mounted and its time to try the bolt/carrier group and charging handle. Being cheap and on a shoestring gun hobby budget
I purchased this sans B/C and C/H after reading from different RKI's (resonably knowledgable individuals
) that the DPMS B/C group would work but I had to hold my breath on the charging handle. Much to my surprise and distinct pleasure BOTH fit and function perfectly in this upper (although my carrier does not have a cuttout for the port door hoever it will work when the bolt is locked back and opens with aplumb
).
Next came a big issue HEADSPACE
Lacking a set of gauges I resorted to an old trick that I learned from the Gunplumber (AKA Mark Graham) from the FAL Files, this isnt truly scientific but is a good and acceptable WECSOG technique that will work in a pinch, the secret to WECSOG headspace measurement? MASKING TAPE!
Gunplumber opines that a good quality factory unfired round (keep the upper off the lower for this one or things may happen
) with a single layer of standard masking tape on the rear will tell you if your headspace is close enough to be safe, so I tok the plunge and taped it up and the result? The bolt would not even begin to close with this single layer of tap on the cartridge (I cant remember how thick the tape is but I THINK it is on the order of 5 - 10 thousandths). So, I would have to say that the headspace is tight and safe on this arangement
Well, so far so good, or is it?
Third observation: Now I am ready to try a mag and see how things line up in anticipation of getting some ammo for function and accuracy testing. Much to my chagrin the mags (3 steel and 1 plastic) would NOT seat and lock
Close observation discovered 2 little shelves at the front of the mag well opening in the upper receiver that prevented the mags from seating, if these were cut off or relieved by 50 thousandths everthing would be hunky dory, what to do?
I can seat the plastic mag in the receiver with the upper pivoted up and close it as the plastic gives enough but that precludes normal operation and is most definitely a hinderance to enjoying my new upper
Before I cut, grind and swear at these small protruberances I need to ascertain for certain whether removing or altering them will cause this upper to NOT work with a standar AR10 lower receiver, does anyone here (Randall?) if these help to stabilize the M14 style mag? Hopefully not. If need be I can alter the plastic DPMS mag for now but I would rather not.
Observation four: There are 2 somewhat crescent moon gaps that are left at the rear of the receiver, I highly doubt they will ever be an issue outside of aesthetics but I may tyr to make some filler pieces in the future that I can attach to the upper in a secure but non-permenant way.
Overall this upper is light and feels great! It should be perfect for deer hunting and also woodchucks and maybe coyotes with lighter bullets, it is a MUCH lighter package than the 24" DPMS bull upper that weighs in at better than 14 pounds with scope, bipod and loaded mag
Someday I might pick up and AR10 lower but I wanted to try this so as to increase the options for my DPMS and not have to spend a lot more money on a different feed system, I like my DPMS and think this will increase my care for it by a greater margin. If anyone else wants to try this just keep in mind the points I have raised, it will take some minor tinkering but nothing that cannot be done in an hour or so (that is if the shelves can be removed without making this upper unuseable on an AR10 lower, if you dont care about that then just grind away
).
I have pictures below and will post again once I make the mods for the magazine to insert (after getting definitive information first) and firs this puppy for function.
Thanks for reading, any input will be gladly accepted but not necessarily heeded
Jeff