Why colt cm091 can accept 7.62x51 and 5.56 uppers?

[DefiantDad]

For the Colt Modular Carbine (CMC) CM901 Multi-Caliber Rifle:

Can someone explain how the lower is different from the AR15 lower that I have, which I was told can only accept .223/5.56 uppers and not the x39 or x51 uppers?

Thanks.

 

[rcmodel]

The Multi-caliber lower is long enough to accept 7.62/.308 length magazines, and uppers, bolts, etc..

Your 5.56/.223 length lower isn't.

rc

 

[Robert]

Like rc said, it is special built to do that. A normal AR15 is not.

 

[rcmodel]

and not the x39

Forgot to mention your .223 lower can accept 7.62x39 uppers.

Just not 7.62x51 NATO uppers.

They are too long.

rc

 

[Bartholomew Roberts]

The CM901 is basically an AR10 lower that uses a special magwell conversion kit to accept .223 mags and is also able to take .223 uppers or CM901 7.62x51 uppers.

 

[Auto426]

Colt uses a special magwell insert that pins onto a mil-spec 5.56 upper using the front takedown pin. That block fits into the Colt 901's larger magwell and is secured using the front takedown pin on the 901 lower. The insert allows for the use of M16 STANAG mags and spaces them properly to work with the 5.56 upper.

 

[DefiantDad]

Thanks guys