Can someone provide the spec on the magwell dimension and magazine dimension for the M16 series of weapons? I’ve got some magazines that wont drop free at best, a couple that wont insert at all and I’d like to know if its the magwell (doubtful) or the magazines (again) before I raise a stink.
Thanks-
BB
Let me guess, non Rev M Pmags? If so, file down these nubs.
Negative. I don’t want to get into manufacturer info yet, suffice it to say they are the only game in town for this particular purpose and they don’t have a stellar track record. All my pmags and USGI mags are A-OK.
It is perfectly acceptable to aske the question and state what the products in question are. What would not be acceptable would be to bash the products in an open forum w/o having tried to resolve the issue.
Ah; then the magazines in question are C-Products 5.45x39 magazines.
Mag wells and mags have a + and - dimension. So a variance is allowed per the TDP.
What happens often times is that one is at the bottom of the spec and the other is at the top and you get an issue. Both are still in spec though, but just won’t work together.
C4
It seems odd that there would be overlap in the dimensions. Then you have parts that don’t work together and no one to blame.
Not really odd as about 95% of the parts in the AR/M16 have a + or - allowance.
Remember that it is a mass produced fighting weapon.
C4
What you are saying is that there is a possible interference fit designed into the system (TDP) for parts that are supposed to fit together without force. That’s what I thought was odd. I would expect every in-spec mag to fit in every in-spec lower. That’s what tolerances are for in mass production.
It is this way in every manufactured part.
They all fit. Dropping free might be a different animal. 
Remember that the parts being discussed (magwell and mag) are assumed to be “in spec.” We have no way of knowing this though.
C4
for reference, my DPMS and CMMG lowers all drop free for USGI, RevM pmags, and older pmags with no modifications
It is possible those lowers are beyond the upper limit of the spec, or as Grant said, you have lowers that are on the bottom limit and mags on the top limit. While not acceptable to most, the magazines could be perfect per the TDP, and the lower as well.
What? No it’s not. Not for parts that are supposed to fit together by hand. I’m going to guess that the mag/magwell is supposed to be a clearance fit. The other options for fit are transition and interference, and those don’t make sense for this application.
BBB mentioned that some of the mags won’t fit at all.
Let us all go the fantasy land where we’re all at Grant’s shop, we have the lower/mags BBB is asking about, and we have the gages Colt (or Colt’s subcontractors) uses in production. I bet the mags fail gaging.
Then I buy a BCM lightweight middy and I go home happy.
I was too vague, but you are correct. I was referring to “drop-in” type parts, again, for most anything out there.
I’ve got at least 50 mags, Pmags and USGI, thermolds (MILSURP), all drop free from the lower (Mega). I dont think its the well. Also the CPI mag that came with the upper drops free.
Since the magazines are 5.45 mags and not 5.56 and they are an afterthought I think it’s highly possible that they are out of spec.
I also have two Mega lowers and they drop all of my magazines free (USGI and PMAG).
I would contact C-products and see about exchanging them.
The vendor (44mag) is going to exchange them no cost; great customer service there. FWIW CPI exchanged a bunch of 7.62x51 mags that were also out of spec for me last year, so they will stand behind their product (although I had to pay shipping).
I believe that the 5.45 mags are mad by Cproducts. They are not known for producing a quality mag.
C4
Wow, thanks a million. I just built a MEGA lower and was pissed to find my Pmags didn’t drop free. Never had this problem on my DPMS or Bushy lowers (made by the same company).
Removing those little tabs did the trick!!