You're not really torquing the barrel down like you would a mauser barrel so a super strong "O" framed wrench isn't needed. I have a wrench similar to this one for the past 15 years or so AR-15/M16/AR-STYLE .308 ARMORERS WRENCH - Brownells Mine isn't a smith ent... but it's the same wrench and you can find them for about $25 new at a gun show. Look around and you'll find a similar one with the M4 spanner wrench in the handle for somewhere in the $20s also. It's how the head is formed thats important. This style of wrench grabs about 2/3rds of the points on the barrel nut. You aren't going to strip the nut points or break the wrench unless you try really hard. The back side of mine also has three nubs formed into it in case you want to use it on a free float tube.