I posted this over in the gunsmithing forum but have not received much feed back so i figured i would post here as well.
I have late 1970s Olympic Arms M16 Lower. Unfortunately the top deck is out of spec, it is too high and all mil-spec uppers make contact with the top deck. I have to force the upper into place and literally hammer the rear take down pin into position.
I would like to remove a small amount of the top deck, probably around 1/100 of a inch.
What would be the best method of doing this?
My first thought was to use a sanding block/stone to remove the small amount of material plus keep a square edge, i believe a file might remove to much material and leave a uneven surface. For reference im an Engineer and have access to a machine shop and plenty of tools. I understand the standard response when dealing with a machine gun is "send it to a gunsmith" and i thank everyone for their concern but i would really prefer to do the work myself. I understand the risks and i still want to proceed.
This is what i am trying to accomplish and i think will resolve the issue im having. The picture is of an identical lower (same make and model) which the owner had a gunsmith remove some of the top deck, rear radius and material in between the front face between the take down pin lugs.
Overview of the gap between the upper and lower receiver. This is how close they get without applying force to close the gap and alight the rear pin holes.
Close up of the gap. Notice how the pin holes do not come close to lining up.
You can see where the upper and lower are making contact, especially near the front of the mag well near the front take down pin. This wear was visible when i bought the rifle.
Contact area between the front take down pin lugs. Does not seem to be rubbing on the BCM upper though.
On the left side you can see wear marks on the upper from the lower. Its a new upper btw.
I def feel the top deck is out of spec and needs to be milled/sanded down. Obviously this is a touchy issue when it comes to transferable machine guns. But since this is not a colt i dont see how performing gun smithing that will bring the lower into spec a negative thing. Sure it will remove the original finish on the upper deck but IMO thats a small price to pay to have any mil spec upper fit the lower properly.
The other option would be to sand the lower deck of the upper receiver. This will avoid damaging the lower but i loose the convenience of being able to put any upper on it. I will be limited to uppers which i have specifically sanded/milled to fit the lower.
All thoughts and suggestions are welcomed.
Thanks
~S