Greetings All,
I am wanting to convert a postban configured 20" Colt HBAR Match Target flat top rifle to a more useful M4 type carbine.
Would it be more cost effective to have the barrel and handguards replaced or to just buy a new Colt upper?
I would also like to change out the front receiver take down screw with a normal push pin. Is sucha conversion push pin made?
Thank you for your help.
xxxxx
If you have some basic tools, you can easily rebarrel your upper. You’ll need to do some research and reading, but it’s the next step in AR ownership.
BTW - I just rebarrelled a 20" Govt uppper with a CMMG 16" lightweight mid-length barrel and I’m very happy with it.
You’ll need a complete barrel assembly and handguards. If your receiver has M4 cuts, then you need a barrel that has them as well. If it does not, you can run a barrel with or without M4 cuts.
Good luck.
I also have a Post-Ban Colt H-Bar, I kept the the upper, it shot extremely well. Bought a CMT/Stag 16" upper to convert it to a carbine, now I have two guns in one.
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I agree with the previous response, if you have tools and could perform the barrel installation process it could be done.
Since your upper receiver have no M4 feedramp cuts, it’s better to get a M4 barrel assembly without any M4 feedramps, but if you don’t have any choice the M4 barrel with feedramps would work on the HBAR flat top upper.
As for the buttstock, it’s up to you if you want to convert it to a M4 collapsible buttstock, just get a M4 buttstock kit with carbine buffer tube, carbine action spring, carbine buffer, CAR receiver end plate and buffer tube castle nut.
You also don’t have to change the buttstock now, maybe just get a carbine lower half later on. 
To convert to a military push type pivot pin, your lower receiver have to have a small hole located at the front of the magwell fence, common to the area of the right side of the pivot pin.
If it does have this small hole, then you will need to get a military type push pivot pin, a detent pin and a detent pin spring.
If you don’t have this small hole, gunsmiths like AR15Barrels.com, ADCOfirearms.com, or any competent AR gunsmiths could install the hole in the lower receiver.
There is just a push type pivot pin that KNS Precision makes, and if you don’t want to rework your lower it would be a better choice.
Look at the third product from the top of the KNS webpage (KNS Push Button Pivot Pin .250" DIA):