Originally Posted by
TinyCrumb
I'm super familiar with 10.3" barrels and Crane spec (.070) but I wasn't aware they had a spec for 11" barrels. Surprised it's that close.
For 10.3" barrels, Crane spec will definitely give you issues with .223 powered ammo. You'll short stroke a bit unless you're using full 5.56 nato pressured. The shorties do get gas port erosion more quickly over time so it'll "work itself" in to reliability with .223 but you won't have it from the start. Most people who want reliability seem to start with something around .073/.074. But again, this is for 10.3", not 11".
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To the OP, where are you having this done? If you have it done at a reliable shop you shouldn't need to worry about any of this. Shops like ADCO maintain lists of standard port sizes they use for each size they chop/thread for with proven testing and reliability. And you also wouldn't need to worry about FSB issues as they deal with them all the time. I'd highly recommend sending it off to them, for $70 to get something you know will be reliable and something they do thousands of times a year in their sleep it's a pretty great price. I certainly wouldn't be playing with a smith who's requiring you to spec the port size and explain how to disassemble the FSB - especially with a work gun.