Help!   I just swapped the guts out of a oly lower into a stag lower (was having mag latching issues with it that I attributed to oly maybe out of spec).  Now I seem to have a different mag latch issue that seems limited to HK mags (when empty) where it seems that the finger portion of the bolt catch gets under the rear tab of the HK mag.  This sometimes seems to be causing HK mag not to seat unless I put pressure on the bolt catch button no matter how many times I reinsert the mag.  Now when it seizes like this a HK mag won't latch but a GI mag will.  So I am wondering if any one can tell me the correct lengh that bolt latch finger should be?   I haven't fired the new rebuild but in charging handle cycling a mag of dummy rounds (no primer/powder) rounds. Rounds seem to hang on the feed ramps at times and I wonder if a bum bolt catch could be causing this as I previouiy had no problems with the upper cycling when on the oly.  Sorry to be rambling / thanks for any input!

Thanks for taking the time to reply. I changed lowers because it had issues with many different magazines.  I believe the old lower (1986 vintage SGW/Oly)  was out of spec as I had a number of compatability issues with various uppers.   After the swap, I got the HKs and I figured (from the hype on this board) that they of all magazines would be issue free.  The bolt latch finger on this build is visibly shorter then that on my other ARs and seems to slide under the top of the rear of the HK mag follower. The HKs work well with my other guns.   Now am I reading you right in your given measurement is taken from inside the mag wells wall?

Another way to describe this paticular issue could be explained as follows:  If I hold the bolt release in when I seat the empty HK mag the mag will not seat and latch.  Now if I do the same on my factory Colt the mag will latch.  Also with the upper removed and an empty HK inserted and captured by the mag catch the bolt release stays flat on the top of the upper (no mag spring upper pressure).   If the HKs are put on the upperless Colt the bolt release latch is up/engaged.  I know I am nickle and diming this issue but having particular quirks on a weapon is annoying to me

Thanks again, On further examination I think the mag well is a little on the loose side and allows the mag to be tilted a little bit not catching the bolt release. (beats being tight with the upper though).  An unrelated question if you don't mind.  I know your company will cut a barrel down, but do you also do reprofiling.  I'm contemplating getting a 16" m4 cut to 14.7" and am wondering if you can cut that 0.700"diamter x 5/8" long step behind where the flash hider would be perm re-attached?