PDA

View Full Version : Help! Old Colt Lower has a different front take-down pin.


Rangem4
01-15-2013, 7:34 AM
What do you do when you build a new ar using a new upper with an old colt lower?
Please see photo. My new Colt has the detent spring and grooved pin. This old Colt lower just has a hole and the holes in the upper are a bit smaller than the lower.
Thanks for your help.

kendog4570
01-15-2013, 8:20 AM
Early Colt AR-15's and Sporters had a 5/16"(?) diameter front pivot screw, instead of the original design .250" captive pin. There used to be an off set takedown screw/pin so one could use a USGI A1 upper on a commercial lower. Not sure where you would find one these days, but I bet they are out there somewhere.
The rear pins are all the same.

kendog4570
01-15-2013, 8:30 AM
DPMS has them.

http://www.midwayusa.com/product/316328/dpms-offset-screw-and-nut-ar-15-matte

pdq_wizzard
01-15-2013, 8:33 AM
I thought all of the old Colt's were listed by name?

ar15barrels
01-15-2013, 5:16 PM
I thought all of the old Colt's were listed by name?

Believe it or not, lots of people own listed-by-name guns.
You just needed to register them back in 1989 or in 1999 during one of the open AW registration periods.

stevie
01-15-2013, 6:10 PM
Your picture is showing the rear pivot pin which is standard size.

Your front pivot pin will be large as may be your trigger pin. As noted, there is a adaptor to use a small pin upper to your large pin lower.

Mack sure you check your trigger pin..

Seesm
01-16-2013, 12:57 AM
I just built a sweet look alike large pin but in reality it's a small pin to make my 80% look like a large pin so my old SP1 upper and parts look killer. I could find anything that looked 40 years old and original so we made it.

Rangem4
01-16-2013, 6:26 PM
Your picture is showing the rear pivot pin which is standard size.

Your front pivot pin will be large as may be your trigger pin. As noted, there is a adaptor to use a small pin upper to your large pin lower.

Mack sure you check your trigger pin..

I am confused by your comment. The pin I am talking about (the pic represents the forward pin) is the front pivot pin forward of the trigger. I am not concerned about the rear lock-up pin it is the same size.
I did order the kit from Midwayusa. Believe it or not it is on backorder.

ar15barrels
01-16-2013, 6:35 PM
I am confused by your comment. The pin I am talking about (the pic represents the forward pin) is the front pivot pin forward of the trigger. I am not concerned about the rear lock-up pin it is the same size.
I did order the kit from Midwayusa. Believe it or not it is on backorder.

You posted a picture of the takedown pin which is at the rear of the receiver, close to where the stock attaches.
The pivot pin is the front pin which is forward of the magazine well.
On some colt receivers, the pivot pin is larger than standard.
On those guns, the takedown pin is still the standard 1/4" size as your picture shows.

If you are talking about the fire control pins, those are the selector hole (3/8"), then the trigger pin (5/32" is standard, some colt are oversized) and then the hammer pin which will be the same size as the trigger pin hole.
The magazine well is just forward of the hammer pin hole.

Perhaps these descriptions will get you using the correct terminology so that people can better understand what you are asking.

Grumpyoldretiredcop
01-16-2013, 9:52 PM
Another option that would work if the OP can find one is the Daniel Defense "Big Hole" upper (https://danieldefense.com/big-hole-upper-receiver-assembly-b.html). That upper was made with the larger SP1 pivot pin hole and came with a push pin that has a ball detent. I have one on my RAW SP1.

Pretty hard to find these days, though.

jameshenry
01-21-2013, 12:06 PM
I have been using the midway dpms offset pivot pin in my sp1 with new uppers with good results. Be sure to check for loosning ocasionaly. I used blue loctite to keep mine tight

ar15barrels
01-21-2013, 12:43 PM
I have been using the midway dpms offset pivot pin in my sp1 with new uppers with good results. Be sure to check for loosning ocasionaly. I used blue loctite to keep mine tight

The proper loctite to install a sleeve with is going to be green loctite.
It is specifically made for retaining cylindrical parts on shafts instead of threaded parts.

patriot_man
01-21-2013, 9:21 PM
You can get it sent off to be permanently converted to the small pin.

http://m60joe.com/ does great work.

redcliff
01-22-2013, 2:35 AM
It's a pain to send the large pin Colt lowers anywhere since they're a named receiver that needs to have been registerred and you legally have to send them through a licensed AW dealer in California for it to go anywhere.

I have no problem using the adapter screw to mate a small pin upper to a large pin lower. The p.i.t.a. is when you try to go with a large pin upper to small pin lower utilizing the little off-set bushings. The green loctite ar15barrels recommends would probably be the hot ticket for that.