I'm building on an OOW receiver, and on their website it says they're 1.24mm.  Do you grind your trunions at all to fit in there?  it seems like that would give it a better fit, but not sure if it's neccesary.

1.24 mm? Wtf. Hmm must have left ya some extra "mistake room."

the rails are too thick where they go into the front trunion and rear trunion. I have a belt sander that I use to make the rails thinner here. also a grinder is usefull inside the front trunion rail area.

basicaly, just grind on the rails, untill the trunions slide in there nice and easy.

it is easy to take off a LITTLE metal on the rear trunions. sometimes it helps it fit better.

some kits use thicker receivers, so it just depends on what you have.

check it and see, only grind if it needs it.

use a cutoff wheel on a dremel
run it down the slots of your trunnion
takes all of 30 secs  

yes, that is a good trick too.

Thanks for reminding me.

better to have a little extra meat on the reciever than not enough !!

the receivers are 1.24" too long in the front
as in if u rivet front trunnion to receiver without filing to fit
the dust cover will have a gap where it sits in its groove in rear sight block
trigger guard first.....mag to front trunnion....FILE!!!.... dust cover to rear trunnion
i learned that shit the hard way