Thanks for the reply. Mine is also a midlength, while the AA 12" is a carbine length. All of the tables I look at mentioned 10-18" barrels for carbine and 14-20" for midlength, and the closer to the middle of that range you are the better. So, a ~13.5"/midlength combo doesn't look like a good idea.
(I was used to dealing with my last chop on a 6.8, where the company uses same length gas system in both their 11.5" and 16" barrels). So, thanks for pointing that out.
Just to wrap this up a bit...I did hear back from AA:
Hello,
Thank you for contacting us. We are sorry, but we will not provide the gas port size of the .50 Beowulf weapon system. This is proprietary information. Please also be aware that we will not support customers in the disassembly or modification of our factory-assembled weapons.
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So...so much for going that route.
ADCO said they do have some data on the round. They also said if I sent a 20rd box of ammo, they'd make sure it was dialed in correctly before they sent it back. So, if I do decide to cut it down a bit, I'm confident they'll take care if me as they've always done in the past.