It's in the title, dummy.

Stick mag masterrace.

1/1: magwell tolerance decreased to hopefully allow for drop-free function

Stinkfoot's UBAR Colt Mag Lower

This is a UBAR based lower that is Colt SMG mag compatible.  There is a printed LRBHO link that is based off of JP's link found in his 9mm conversion mag. If you have a 9mm bolt catch please try it and report back.  The lower is also modified to receive an ambidextrous safety.  

Parts List:

AR LPK

M3x25-30 (Feed Ramp)

M3x15 (Follower Link)

~4mmx~12mm Spring (Strength is not too important, but you want a decent tension downward on the follower link. I think the spring I ended up using was a cut down BIC spring but don't quote me on that.)

X2 M3x10 (Ejector)

PRINT SETTINGS:

Lower:  Print like any other lower you have printed before.  I will not advise you on specific print settings, but I personally use a .5 nozzle and .4 layer height for many of my 2a prints.  I like gyroid infill and generally do not go over 66% fill density.  

Feed Ramp: Print on front face.  Use your own judgement when it comes to walls/infill.  Initial test part printed with 4 walls, 66% infill.  Higher strength materials such as PC, GF-Nylon, etc. would be helpful for this part.  

Follower Link:  Print on flat side.  All walls

Ejector: Print on flat side. All walls.  I personally have not seen a printed ejector fail yet but it is also quite easy to template on some 1/8" aluminum available from your local bigbox hardware store.  If you insist on running a printed ejector I would suggest printing in a stronger material for longevity.  

Assembly:

Install LPK as normal and as per UBAR assembly (included in this package).  Install bolt catch before ejector.  You may opt to drill the bolt catch with 1/8" drill and install with M3 set screw.  Top ejector bolt may interfere with bolt catch installation.  

Follower Link spring will be dropped in cavity before installation into lower.  A small allen key will be used to depress the spring while driving in the follower link bolt.  This might be tricky to get right but you will know when the spring is not caught/bound by the bolt.  Ensure smooth function by lifting up on follower link.  It should snap down flush with the top deck of the lower.  

NOTES:  During my short testing phase of ~100 rounds I experienced one interia charge while loading a mag.  I did not investigate the reason for this happening.  The bolt appears to lock back reliably under regular fire. I will be testing this lower more and updating the release as needed.  Community feedback is much appreciated.  

DISCLAIMER:  If this was the closest functioning firearm within arms reach of me in a HD situation I would use it, but please understand that not many rounds have been fired using this lower.  I personally do not yet trust the follower link in a life-or-death situation but like I said low round count.  I may test and release a grub screw reinforced follower link in the near future if I find it necessary.  I will be using this lower more as my primary AR9 range lower for the time being.