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9/22/2017 12:11:25 AM
Posted: 12/15/2003 3:57:15 AM EDT
I've built up (2) AR15s using MEGA recievers without any problem.... until now.

I have a new MEGA Lower that will not fit-up to a DPMS 16" Bull upper. The same MEGA lower mates up perfectly with my Bushmaster M4 Upper. Also, the 16" DPMS upper mates up fine on my Oly preban lower.

With the front pivot pin in, the upper will rotate down and very nearly seat properly for the rear pin to go in... but it's about 1/16" from seating low enough on the lower for the pin to go in.

I've disassembled this thing and tried everyway that I know how to figure out where the binding is taking place, but no cigar. It doesn't appear to be binding between the rear of the upper and the face of the lower where they come together. It's almost like the rear lug on the upper is either too long under the pin hole.

Anybody come across this before? Again, it's a MEGA lower (worked fine on my Bushmaster Varmiter upper and my Bushmaster M4 upper) and the DMPS 16" upper mates fine with my Oly preban lower?

Any comments would be greatly appreciated (please email me at jshep@mindspring.com).

Many Thanks,
Link Posted: 12/15/2003 4:04:42 AM EDT
Suspect either, as you suggested, the DPMS rear takedown notch is too long or that the rear shelf on the inside of the Mega lower is too shallow. FWIW, both could be outta spec just enough to cause your problem, sounds like it's time to break out the Dremel tool...... Mike
Link Posted: 12/15/2003 5:56:02 AM EDT
Hi Mike, That's the way I'm leaning on this - gonna do some more checkin' tonight and will probably relieve a little out of the MEGA receiver. Thanks again, Jim
Link Posted: 12/15/2003 6:25:10 AM EDT
FWIW, I had the same problem building a rifle for a buddy of mine, using a DPMS upper and a RRA lower. Took a lot of pressure and much cursing to get the receiver halves together and get the rear pin in. Looks like there's some binding/dragging on one edge of the rear lug; we might lightly bevel this edge if it doesn't loosen up with use. Interesting to note that even this tight, the gun has shown flawless reliability.
Link Posted: 12/16/2003 3:16:53 PM EDT
Guys for what it's worth i just built my first ever using a Mega lower and a DPMS 20" 7.62x39 upper and it went together in an instant.
Link Posted: 12/16/2003 5:04:05 PM EDT
I had a DPMS lower and none of my Colt uppers would fit exactly right, and neither would the Bushmaster upper that I'd originally intended to use. I finally just gave up and bought a DPMS upper, which fit perfectly. QED, if the DPMS lower wouldn't take any other upper, there must be something different about the DPMS upper, too. Hate to say it, but you might be better off just using a different upper and selling the DPMS on eBay.
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