Now I am not looking for an argument here, but if a friend is shooting the same cartridge as myself, same bullet, same powder or equivalent, same speeds, same seat depth because the same reamer was used. I would fire his ammo in my rifle long before I'd fire a box of Hornady ammo in my rifles. If I would have to apply pressure to close the bolt, because his sizing technique differs from mine, all bets are off now.
Why, because I trust him, plus he is off to one side of me running his bolt like it was stolen firing his ammo. Plus I probably had some influence in his load.
Granted, I know people I don't even care to be beside when shooting, after listening to them talk about loads.
I lost count of the times at the range I have watched guys-gals fire factory 6.5 creed ammo, first 6 shots go off without a hitch, the blow the primers out of numbers 7,8, and 9.
I by no means am telling you that it is ok to fire anyone else's loads, heck, stick to your convictions. But some common sense can be applied here. I guess I just may be different, but I most likely would shoot a friends ammo long before I sampled his wife's cooking that looked like a stool sample.