Question: Colt Match Target M4.....

[xXxplosive]

Have a Colt Match Target in .223 and was wondering if I can get a different caliber upper to switch out for this same rifle ?
If this is possible, please steer me in the right direction.
Suggestions please......

[Eric D.]

Depending on the caliber you're wanting to use you will probably need a different hammer in your lower. You would also benefit from using buffers meant for other calibers.

[xXxplosive]

What calibers would be acceptable to the .223 Colt lower ?

[Eric D.]

I know for a fact 9mm needs an unnotched hammer which is also usable with .223 and that there are buffers made for use with 9mm. I can't speak for 6.8 or 6.5 though, you might check the "beyond 5.56/.223" section.