What Front Sight Post or FSB for a Colt 6520 to Flat Top Conversion?

[sundance435]

I bought a Colt M4 flat top upper to swap out for the A2 upper on my 6520. What size front sight post do I need, since the FSB on the 6520 is not "F" marked? Can I just swap out an entire "F" marked FSB, or will it not work because of the .625 profle?

Thanks in Advance!

[Surf]

I have done several of these Colt A2 to flat top conversions. In my experiences I have been able to stick on a Colt A3 carry handle and the rifles are usually right within a factory zero.

If you do have issues, you can first try a simple front sight post swap. Swapping out the entire base will generally require swapping out the entire FSB / barrel assembly. You could attempt other methods or go with a flip up or non pinned FSB but if you have zero issues, start at the front sight post. Again as mentioned on all of the Colt conversions that I have done, I have not even needed to change a front sight post, at least when using a Colt carry handle as irons.

[sundance435]

I have done several of these Colt A2 to flat top conversions. In my experiences I have been able to stick on a Colt A3 carry handle and the rifles are usually right within a factory zero.

If you do have issues, you can first try a simple front sight post swap. Swapping out the entire base will generally require swapping out the entire FSB / barrel assembly. You could attempt other methods or go with a flip up or non pinned FSB but if you have zero issues, start at the front sight post. Again as mentioned on all of the Colt conversions that I have done, I have not even needed to change a front sight post, at least when using a Colt carry handle as irons.

Thanks for the info. so far. I should have mentioned that I plan on using a TROY BUIS. What size front sight post will I need for that to work?