Dear all,

I would like to build a SBR and need some practical advice, I'd also like to understand how this whole large hole, Colt thing works.

I want to build a SBR. I may have access to a circa 2001 Colt lower.  I'd like to mate it to a DPMS upper.  

1) will this work??
2) Do new colts have standard sized "small" hole.  if so, when did they change?

3)  I've heard of bushings and stepped screws.

4) can you mate a large hold upper to a small hole lower?  if so what do you need?

5)  can you mate a small hole upper to a large hole upper?  if so what do you need.  

Thanks for all your assistance.

Best regards,

Don

You can mate large hole uppers to small hole lowers (works the other way too) by using one of the several types of adapter pins available. However, Colt lowers also have different sized hammer and trigger pins so you have to buy the correct parts for the larger Colt pins (if available).

Still, it's only a slight inconvenience.

1)  Yes

2)  Yes.  They switched in the early 90's IIRC.

Ya learn something new every day! I thought Colt's civi models were all still large pivot, large hammer and trigger pins.

Heck, I saw the topic header,
and was thinking "Small holes feel better ... large holes work better"
But I don't think it applies here.

The easiest way to mate a small pin upper to a large pin Colt lower is to buy this:

[url=http://store.yahoo.com/cdnn/arunfronconp.html]Conversion pin[/url]

I frequently run my small pin Colt M4 upper on a large pin preban Colt lower and this pin works very well.

Thank you all very much.  Bottom line is its a no brainer.  

If a big hole upper and a small hole lower, use smaller pin with bushing through big hole upper.

If a small hole upper and big hole lower, use stepped pin.  

Now just out of curiosity, about what year did Colt change??  Did it correspond with pre-ban to post-ban change and elimination of AR-15 designation.

Thanks again,

Don

Read this:

[url]http://www.biggerhammer.net/ar15/coltcolors.html[/url]