Gunsmithing Looking for ar10 upper receiver truing /laping tool

[Luky]

I have seen several inexpensive laping tools to true the receiver for the barrel extension for AR15 receivers, but I am not finding a cheap one for a large frame AR. Is there a place I can rent one? I only need it to do one receiver... I just got a new BHW .260 barrel that I am going to install on my Franken-SASS LR308 and figured I would do this while I have it apart. It is a DPMS upper receiver with a Lilja heavy barrel on it now.

 

[LRI]

Most "good" AR upper/lower receivers are forgings made from 7075 AL. -Good chit. Harder and stronger than other grades and very dense. That being said it's still aluminium. "Good" upper and lowers are also Type III anodized.

What you have is a hard boiled egg. That few .001's of 'ano' is what saves your bacon because it's hard as woodpecker lips. Lapping with an AO or silicon carbide abrasive is going to remove this. What your left with is the egg minus the shell.

AR's often don't respond well to this. This topic makes me think back to the summer of 1990 when I was a recruit at MCRD. M-16A2's with lord knows how many rounds, cleaning rods, Q Tips, etc run through them. The Upper Receiver bores were still in amazing shape considering... Never forget: A recruit or Lance Corporal can feck up a bowling ball, lol. Yet the guns seem to tolerate it.

At one time I did a great deal of AR work for the USMC Reserve Shooting Team. Col Hoham and CWO Karcher were the HMFIC's. Those guns ran great at Perry, Karcher taking a National Championship in 2002. -Not a single lapping or "truing" tool used on any of em.

Just a thought.

 

[Luky]

Thanks for the feedback. I pulled the barrel today and the DPMS upper receiver looks pretty clean/square. I had mounted the previous barrel with rocksett on the extension because I thought it fit a bit loose when I originally assembled it but it was really a minimal layer that was there. (But it was held together pretty solid as I had to heat it with a torch a bit and use a wooden dowel and mallet to get it out). The rifle was shooting .5-.75 MOA @ 200 yds with 155 palma SMK and 175 grain SMK .308 loads when I was working on it (then lost interest when I started shooting a .260 Surgeon).

I remember the M16A1's we had in Basic at Ft Knox back in '85. They were totally worn out and trashed from all the cleaning/shooting. It was the only time I didn't score expert when I was in the military...