Posted: Oct 28th 2009, 10:54 PM
I am a fairly new AR-10 owner and I recently stumbled across some interesting information about my lower receiver from
CMMG. Apparently
CMMG intentionally designed their 7.62 lower receivers with the forward takedown pin outer diameter slightly thicker than a standard lower receiver. The added thickness was designed to prevent the upper and lower from pivoting at the front takedown pin more than about 10 degrees.
CMMG added this feature to prevent damage to the hand guard and the takedown pin holes in the lower receiver. Apparently the barrel weight would cause the upper to swing down with enough force to dent the hand guard and rip the takedown pins right out of the lower receiver takedown pin holes.
However, The way the
CMMG lower receiver is designed, the added thickness to the outer diameter of the takedown holes would damage my
DPMS .308 upper receiver by creating excessive pressure at the takedown pin holes of the upper receiver.
I think the intentions of
CMMG are good, but I like the convenience of being able to pivot the lower and upper enough to remove the charging handle and bolt carrier group for bore sighting at the range. I did some grinding on the takedown pin holes outer diameter to give the upper and lower enough space to rotate freely. I used Rust-oleum flat black high temperature spray paint on the exposed metal. When I put it back together it worked great, just like an AR-15. The paint job looks pretty good, not exactly like the factory paint, but pretty close.
I am not sure if the restricted pivoting at the forward takedown pin is a normal conditions for AR-10's, but I found it to be more of hassle then a benefit. Did anyone else run into this problem? I figure my AR-10 is a custom build, and I can always just replace the lower receiver if I decide I don't like it, or if it breaks.
