I have a 10.5", 5.56 classic pistol w/HAR-15 pistol brace, that i want to swap the 5.56 brarrel for a .300BO one. I purchased the BO barrel already. Can I remove the front sight base, pistol gas tube, barel nut, etc. and reuse then on the new barrel? I’ve never built an AR before so this is all new to me. TIA for any help.
Yes, but you will need to drill the barrel for the FSB if it is the right size gas block for your new barrel.
My recommendation is simply to build that 300 barrel into a new upper. Use a free float rail and lo pro gas block.
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GG has it right. its a lot less headache, to simply build that barrel into a new lower receiver and then swap uppers when you wish to use it. All you need for the build since you’ve got the barrel is the following:
Stripped lower receiver
forward assist kit
dust cover door kit
low profile gas block
gas tube depending on the gas length of the new barrel, be it carbine, mid-length or rifle
a muzzle device of your choosing
a free float hand guard of your choosing as well.
you can always swap opticss from each upper you have, so you dont have to buy more optics unless you want to.
best of luck.
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Thanks to you both but that defeats the purpose of the build. I want a retro look barreled in .300 blackout hence me buying the barrel and converting a pistol i already have. Btw, I already have a 8.5" blackout pistol.
Then your best bet is to find a gunsmith that already has the fsb jig and drill press to do it.
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This is is one i have in 5.56. I have an odg on order that i will use for this project.
You need to make sure the gas block journals are the same size. You also have to check the gas system length or you will need a new gas tube. You also will have to add a new buffer and maybe spring as 5.56 and 300blk will shoot differently.
I have built so many ar’s i can do it in my sleep. Drilling an FSB is not something i would do, even though i have access to tools. You get 1 shot to make it right or you mess it up to the point it cant be fixed.
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i agree again, with gg. i’ve built well over 100 im sure and i wouldnt ever drill a fsb myself… specially since i dont have the jigs to do it.
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Im so bright my mama called me son, so i don’t want to dissapoint her and fail, so there’s that.
PSA .300 Blackout AR-15 Barrel 10.5" Pistol-Length 1:8 4150V Nitride
This is the description of the barrel I bought. I don’t have a picture handy but search the description if you want to see it.
you’ll need a pistol length gas tube.
Yeah, figured I would need that one. The other parts I have to look around for.
If you are going from carbine gas to pistol gas you will also need handguards as the other ones wont fit. I dont know that i have ever seen pistol length a2 clamshell handguards…
well the rifle length will work, depending on where he puts his FSB. if he runs a low profile FSB for the pistol carbine gas block, and then buys say the armalite clamp on F stamped Front sight block, itll make it look like its a normal old school setup almost, with the exception of noticing the clampon at the bottom of the F stamped FSB… thats a work around, if your desperate… it also would help you cause you wouldnt have to worry about drilling the barrel for the roll pins of the traditional FSB/gasblock. just an idea…
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I’m not a gun expert but if I had a 300 BO barrel I would build a new upper. That way you’ll have two guns.
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yeah but then you’d be caught building yourself another lower, and then… well these things multiply like catholic rabbits if you’re not careful . 
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I have a couple of lowers and uppers but they are going to be built up later. This is somthing I think PSA should do but I will have to have a go at it myself. Life is short and I am not getting younger so there is that. I am a “idea” guy, whether it works or not I gave it a shot. Mind you, not all my ideas are good but they are mine.
i just saw this thread and am i right that you want to “do it your way” and that just means you have to drill the pin slots for the F post sight?
if thats it i have a suggestion, if i may.
there is a you tuber named Toney, and i bet thats not all his name but he wanted to do that with a rifle he was putting an after market wooden furniture set on. it turned into an ordeal.
could be nobody makes a barrel with the demintions you want cut for an F post sight so its up to you to drill it.
and here is more unasked for info that i hope you can ignore instead of being offended by cause ill be 70 in a couple of weeks, maybe.
the pins that are used for that are tapered. i dont know if that means the drilled holes need to be.
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TDav, thanks for the advice. Btw, I am just a few years behind you, lol.