I don't think the issue is with the PMags, even with the short follower, or with the bolt catch. I think the issue is with the TDP itself.
Looking at the drawings, I see that that bolt catch body can be +/- .003" thick but I don't see a tolerance spec for the length of the foot or tooth of the catch.
The bolt catch slot has a tolerance of +/- .003" in terms of front to back location from the front pivot and +/- .003" in terms of thickness/width.
If the slot is at max, the width is at max, and the bolt catch is at min, you can have an off set of .009".
Not much, but this weekend I added a bolt catch that was .011" longer than the one originally in my carbine. This is what .011" can look like:
Short length
.011" longer
Now take in account that before you even add up the bolt catch length tolerances, a polymer mag is any where from 0.013~.016" thicker that a GI mag in terms of the actual mag body. By default, that is going to mean the follower is 0.013~0.016" further forward before you look at anything else.
GI mags will work. Even at the worst case scenario, the bolt catch's .009" potential offset is good enough to grab a GI mag. That link to the AR15.com thread shows it too.
But when you add another 0.013~0.016", things can get sideways.
I would contend that a polymer mag, even if made perfectly, can fail in an "in spec" lower.
My understand is that the most recent TDP update for this area is 2006, before Gen1 PMags came out. My belief is that the that TDP spec has not been adjusted to account for the polymer mags and even if manufactures strictly adhere to TDP, this issue will continue.
Judging by the posts on this and other forums, it's fairly common. It's also mostly blamed on out of spec parts and/or poor magazines which are easy things to point too and for the most part are correctible if you get enough parts to sample with.
I wouldn't expect Colt or FN to change the TDP to adjust for polymer mags unless the military/government starts using them as a basis of design and functionality. But I think aftermarket bolt catch manufactures might want to take a look at this. The mags can't change. Polymer mags are simply thicker by the nature of the material.
All the above being said, I'm just a hack with a laptop.
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