I corrently have a Colt lower and Upper. (i'm a Colt guy) My question is, my lower is from a Sporter I bought Pre-Pan. I have since turned it into an M-4 type with new stock, A-3 upper, and other asourted goodies. I digress, back to my question, Is there a diference between the Sporter / Tactical / LE lowers?

I'm no expert but I'm just a Colt owner since 1971 and still have two current Colt models now.

Since the early to mid '90s up to until now Sporter, Match Target, and LE series are mostly similar in features which are the A2 type lowers with fences at the right magwell, the front pivot pin are the small mil-spec size of .250" diameter but the trigger and hammer pins are the larger than mil-spec size of .170" diameter (mil-spec size are .154" dia.), the hammer, disconnector,  and triggers will also have the larger holes for the .170" pins.

Some differences also are some lowers in the early '90s have pinned sear blocks then later around mid '90s until currently they went to a non-machined web which connects the left and right side of the lower to prevent the use of full auto sears.

Also some lowers have drilled holes for the detent and spring of the military type push-pull pivot takedown pins, some are not drilled.

Older Colt Sporter models from 1964 up to about 1989 to early '90s, most lowers have a large and offset pivot pin .315" diameter, small mil-spec size hammer and trigger pins of .154" dia. and have an A1 type lower without fences on the right magwell.

There are a small number of lowers that are different like large pivot hole with large hammer and trigger pins, there are also some very rare ones with small pivot pin and small hammer and trigger pins.

Starting this year with the new 6940 and 6920 LE models, Colt are changing the trigger and hammer pins to the smaller mil-spec size of .154" diameter, they will be changing all their lowers this way.

A good book about the AR-15 is the Black Rifle II: The M16 Into the 21st Century by Christopher R. Bartocci.

Here's a link for more info on older Colt models, most info there are good but there are only a few that are not accurate.


http://www.biggerhammer.net/ar15/


ETA: If you have more questions about pre-ban models take a look at the AR-15/ M-16 Retro forum.


AR-15/ M-16 Retro Forum - link

Thanks, now I have another dilllema... The BCG that came with the original wepon had the rear lower, portion shaved off (i'm assuming so it couldn't be converted to full auto) and now I have a colt BCG that is full auto capable. I have not had a chance to shoot the wepon since I've installed the new upper. Given what you have said I am affraid I may damage something if I do. The rifle will complete a functions check the way I learned in Basic Traning... Any Ideas?

Bolt Carrier: The M16 bolt carrier will have about a 2" closed section at the rear that actually trips the auto sear in full-auto fire. Semi-auto versions have either a reduced closed bottom section (about 1/2"), or a completely open bottom (made so that an adapter to M-16 configuration cannot be installed).



Colt pinned sear block on the lower receiver, it protrudes upward so that M16 full auto bolt carriers won't work, but both types of AR-15 semi auto carriers should work fine.




If you have a Colt lower receiver with the sear block in my picture above, your Colt full auto BCG won't work, the sear block would interfere with the bottom rear of the carrier.

You could switch to the open shaved bolt carrier if you have a sear block, it would work.

Check your lower if the pivot pin hole is .250" diameter, also check to see if your upper pivot pin have the same size hole diameter, also check the upper to lower gap, they should be small and even gaps.

Function check it, make sure you are safe and unloaded first, if it passed then you should be fine.

Thank You!!! I checked it out and I do not have the BLOCK, I do have the M16 BCG, and it performed the functions with no issues. I think I am good....
Thanks again.....

That's great, the M16 BCG are more reliable than the other semi auto BCGs.

My two Colts a LE 6721 Tactical Carbine and my M16A2 USGI upper (on Match Target lower), plus my LMT carbine all have M16 BCG and they had been running fine for about four years now, no problems at all.

Take your AR out to the shooting range and shoot it, and shoot it often.

Thanks again, I plan on taking it out soon, and often, as soon as life gives me the time.