I have been to a couple of gunsmiths and 1 machine shop about what can be done. They all said they do not have the proper bits to reach the required depth.

I need to have the 12 o'clock channel bored out to about 7/16". The upper channel steps downward, not allowing the spring bushing to seat on the barrel nut. I can not bore it from the back due to the locking collar threads would be drilled out. Bushing lies just slihgtly over top of the threads. So I would have to drill through the threads if I went through the back, which I have no intentions of doing.

It's approximately 6.5" depth from the front of the handguard to the necessary depth. Bit needs to be at very minimum 3/8" (size of bushing) in diameter, but can go up at much as 17/32" (width of the channel) in diameter.

I see some people have done the necessary modifications, but haven't gotten any replies to how they got it done or who they had it done by. Someone said they used a dremel in a picture thread.

The one machinist said they can go down to about 5.5" with a boring tip. The last 1" is the crucial part that is preventing the bushing to seat.

Any reccomendations on how to proceed (besides get a new rail set)?

Here are some quick MS paint drawings I did.