Aside from just shooting it to see what happens, I'd check the twist rate. It's not real precise, I know, but I've measured barrels that have been off to the slow end, and some to be tighter than spec. Aftermarket like what's on your buddy's NULA should be good, I'd think. It'd be an easy check and might give you some confidence to give it a go.
I've got a Mullerworks barrel that measures spot on to 1-8", Tikka and Wilson tighter than the spec'd 8", & Remington 6mm's (243's) that measure as stated 9.125" and as slow as 9.5".
He hit a coyote @ 841yds about 10 days ago w/22-250 and 75 A-max and all the dots finally connected. Now "The Race is On". He's already ordered a 240Wby NULA (1:7) and is wondering what "better bullets" he can get for his 1:8 NULA 22-250.