I just got my ARMS 51 and mounted it to my Bushy A2.  Everything went well until I looked at the handguard cap.  The 9 o'clock edge was rubbing on the leading edge of teh SIR.  I then tried mounting the 51 on another bushy a2, and found that it rubs as well.  I had an arms 39 before and it was slightly misaligned.  I want to know if this is a problem with bushmaster A2's or ARMS.  I know that ARMS is really good stuff.  Thanks for any help.

I really dont know. I have only used a #51 on one rifle I've built. It was a Bushmaster... and it went right on with ease. Im sorry I dont have any more useful information for you.

I had the exact same problem with my #51.

I ended up relieving the left side, inner edge of the front tip of the SIR, the plastic 90 degree edge below it, then applying several taps of a brass punch to the edge of the handguard cap that it was in contact with.

I also did some work on the clamp that goes around the front of the carry handle.  What I had determined was when the screw securing the clamp was tightened, the SIR moved to the right, causing the left front edge contact.

When I get the chance I'll take pics of the front edge modification and post them.


Chris

I forgot to add that my AR is also a Bushmaster (HBAR).


Chris

I had a similar experience on a newer Bushy barrel, but with the RAS-II.  Both the 3 and 9 o'clock sides of the handguard cap were touching the front of the RAS.  

It was very minimal, but enough to bug me.  You couldn't fit a sheet of paper in between the pieces, but if you held the RAS in one hand, and held the barrel with the other, you could still flex it a little.  I took the RAS off and got a Dremel tool, making a few quick passes on the edge of the handguard cap.  Just enough so when installed, you could now see a little light shining through the space between the pieces.    

If you watch the end of the SIR when tightening the cross bar, you might see that it moves if you over tighten the front thumb nut. Suggest loosening it and help it back to where it wanted to be before the overtightening that most likely caused the mis algnment happened.
Just an educated guess, and a little experience. The inside of all the various carry handles vary greatly since none are machined to any mil spec.
Good shootin, Jack

Thanks for the help.  I just bent the HG cap so that the SIR would clear.  I can live with a bent cap so the barrel will free float.  Now I have to decide which forward grip to get.  

Deiter

Looking down from the top ....

[img]http://www.imagestation.com/picture/sraid85/p28d3afea161bef26743b6727a5d42b82/fabd1e1a.jpg[/img]

.... and from the bottom:

[img]http://www.imagestation.com/picture/sraid85/p0d5e090fdf5b68ec63969642fe131536/fabd1e17.jpg[/img]

You should be able to see the thinner leading edge on the one side, and the slight bend in the handguard cap facing that edge.  

I filed the SIR edge with a hand file, then sprayed the exposed metal with a flat enamel paint, as recommended by ARMS when I discussed this with them via e-mail.

As I mentioned earlier, I also noticed that the lower edge of the removable handguard was also touching the cap, so I filed it too.

I filed on the crossbar at the handle, so that I could tighten it fully.  I used an aluminum marker pen to cover the exposed metal on that.


Chris