I recnetly picked up a few FIRSH rail systems and wanted to install one on a bull barreled varmint rifle. The barrel nut that came with the FIRSH is only for HBARs and is too small to fit the bull barrel. Does anyone know if Olympic Arms sells another barrel nut for larger diameter barrels? I just need the inner hole diameter to be slightly larger, not the outer diameter.
Any other solutions for fixing this problem? The rifle has a free float tube on it, and the barrel nut for that will thread onto the FIRSH, but it is a little loose and not indexed properly for the FIRSH (the torque screws at the back of the FIRSH are on top when it is threaded all the way on - not on the bottom - and the existing barrel nut already on the rifle has a ring on the back that doesn't allow for another half-turn that I need.
Let me guess, you're using an RRA varmint barrel? Most bull barrels are about 1" diameter but the RRA varmint barrels are 1 1/16". You're also going to find that most barrel wrenches are 1" diameter and won't fit over the barrel. I contacted Oly about the barrel nut issue and the guy I talked to basically said I was on my own.
Here's what I had to do when building this rifle with a 24" RRA varmint barrel and a "Long Carbine" FIRSH:
- Spend a couple hours using a half-round bastard file to enlarge the opening in the barrel nut until it would fit over the barrel. A drum sander in a hand drill would probably be faster but I wanted to be very careful not to remove too much metal.
- Use a 1" drum sander chucked up in a hand drill to enlarge the opening in a GI barrel wrench so that it would fit over the barrel. A 1" drum sander is about the perfect size, just work it down into the slot until it fits.
- Since I was using a longer tueb that covers the gas block I had to shave the railed portion off the top until it would fit. I used a belt sander to take the rails off, which gave about the same thickness on top that it has on the sides. Then put a 45 degree bevel on each sideto make sure it would clear correctly.
- The gas block fits very tight, I had to use a torch to heat the gas block, then use a block of wood and a mallet to get it on all the then align it right side up.
I've only taken it out to the range once but I was very happy with the results.
I had a similar problem with my Hogue free float tube and a rock river arms (Wilson) bull barrel. I used a sanding wheel that has flaps of sand paper all around its shaft. This is an item you put into a hand drill to reem out tubes. It worked great. I sanded a little at a time and checked for fit until it slid on. HTH