Just recently procured the knowledge on how to put one of these bad mamma jammas together. Now I would like to build my own lower and replace some parts in an old lower. Want to know which LPK are a go, no-go. Obviously if I could find LMT or Colt, I’d be happy as a pig in shit. Need to be pointed in the right direction please.
I’ve used CMT and DPMS with no problems. Either one will do the trick…
I just used a CMT/Stag in mine with no problems except the hammer had a broken j-spring so they are sending me a new hammer no questions asked. Great customer service.
Brownells has Colt lower parts. You can probably piece together the whole LPK for about the price of a complete gun! 
I use the Armalite LPK with no problems.
I’ve used the following, with my thoughts on each.
RRA - great kit, installed fine, decent finish on parts
DPMS - I had no problems. I see more ppl have problems with these than others, but they’re also a little cheaper. Mine installed and works great, some pins a little tighter than other brands
Stag / CMT - very nice, good finish, I like their triggers (very smooth)
White Oak kit with no trigger/hammer from Adco - this kit was excellent, the finish was outstanding, everything is exceptionally smooth functioning and fits perfectly
These are just my impressions with the particular kits I received. A few had a missing spring here and there, but I don’t remember which ones. While I don’t think there’s a huge difference in most kits out there, buy based on what you can afford and what your end goal is. For example, if you’re going to install a 2 stage trigger, the White Oak kit from adco saves you about $20 that you can put towards the trigger… just something to think about. Good luck!
I have used a RRA kit and it have no problems.
DO major manufactures of AR 15 like Colt and LMT make there own small parts or do they buy them from different part makers?
I think you’ll find that they source a handful of parts from CMT/Stag. In fact, CMT/Stag is probably (assuming) the largest supplier of miscellaneous AR parts around.
I believe that Colt make a total of 7 parts in house. LMT makes at least two items in the LPK’s (to my knowledge).
We sell LMT LPK’s and also have our own (FYI).
C4
Grant did a good job here of not tooting his own horn so I’ll do it for him, or better yet do a search on it. Anyways Grant put together his own LPK with quality parts from different sources. I’m happy with mine and I know that many others are happy too. Plus the price is good and the customer service aint that bad either.
When in doubt search, learn, apply 
About $200
160-311-100 SPK94773 COLT AR15 FIRE CONTROL KIT $92.48
160-311-101 SPK94772 AR15 RIFLE ACCESSORIES KIT $89.80
160-308-150 SP64576 PISTOL GRIP $15.00
and you may still end up with a screw type pivot pin.
Grant, can you tell me what seven parts Colt makes in house? And do you know who makes the rest of Colt’s parts
Thank you for your feedback and am glad you like our LPK.
C4
I could, but half the 7 would be a guess. Sorry that I do not know more.
C4
I know there is a difference in diameter for the pins in a FCG in auto and semi. Other than that, should any ar-15 trigger, hammer and their respective pins be universal for all ar-15’s? I guess the point is can i use a colt ar-15 FCG in my RRA lower? It should be noted that as of now I have the 2-stage match trigger. Not a fan. I want to change it out for something a little heavier like what i have in my 6920. I believe the diameter for the pins is .154". Is that standard or abnormal? Help please!
Grant’s LPKs are getting rave reviews. I have two comming. If Grant will not toot his own horn then I will. His customer service is great. I would give him and his LPK set a chance.
Let me know how you like them.
C4
Grant,
Where is your LPK on the site? All I could find was the CMT set.
If you click on “gear by manufacturer” and then select G&R Gear, you will find them.
http://www.gandrtactical.com/cgi-bin/commerce.cgi?search=action&category=GRTA
C4