i have a Colt M4 upper that was hacked and made into a large hole upper to fit on a Colt SP-1 lower.

recently i found a SP-1 upper to put on the large hole lower so now i have an upper i cant put anything on.


i bought a bushing that slips into the large hole upper to fit on the  small hole  lower but there is still a woblble.

the upper is marked M4.

if i were to get an upper from bushmaster and replaced it, would i comprimise any quality if i swapped uppers?

My freind has bushys and  colt, I have a colt, I've switched tops with them and they fit fine, I like bushy