Can someone please advise what wrench(es) works well with the SR-762, as well as ones which are best avoided? I don't anticipate removing the barrel, so am hoping one of the combination tools for AR-15/M4 might work. I'd prefer American made...the Magpul wrench looks good but pricey;, I queried Magpul but have yet to hear back. My immediate need is only to remove/replace the castle nut to install a sling mount, but I'd like a general purpose utility wrench. Suggestions, please? Many thanks.