hi , i bought a 5.56 11.5" psa pistol last week. to make it a 300 black out can i just change the upper with bcg and ch or do i need to change the buffer too?
The short answers is yes. The longer answer is more complicated and we need to know more what barrel length and if you plan on shooting super or subsonic 300 blackout. The BCG and charging handle and magazine could be used for both 5.56 and 300 blackout, but I would recommend having BCG and CH for each upper. The buffer for 300 blackout is complicated as well. Many gas systems are set up for heavy buffers when shooting supersonic and regular buffer use when shooting subsonic. Hope this help and welcome fellow gun enthusiast.
I bought a PSA multi caliber pistol lower, and a complete 300 Blackout upper from PSA as well.
The more i shoot it, I feel that it cycles supers harshly, and it short strokes on subs.
I bought a heavier buffer, and I’m headed to the range tomorrow. I’ll report back, but from my research, advice here, and my own personal experience, I think I heavier buffer is needed for 300 Black.
Mine came with a carbine buffer, FYI.
If that doesn’t work I would highly recommend a NIB full auto bolt carrier. I would really highly recommend it for every AR that you have. All my AR runs NIB full auto bolt carriers. It makes cleaning the bolt very simple. You should have a more reliable AR since you don’t have to run your AR with any lube or if it makes you feel better I wouldn’t put much lube at all on the bolt carrier.
Hoping to win one 
It is best to do a whole new upper, and make it and your Magazines color coordinated.
An 11.5" 5.56 probably uses an h2 buffer already. That will work with a shorter .300blk. However, if it were me, I would put an adjustable gas block on the 300 upper. That way I wouldn’t have to mess with the lower.
As for the bcg and charging handle: both will work for both calibers. But a general rule for bcg’s is this:
New barrel and new bcg = ok
Old barrel and new bcg = ok
Used barrel and used bcg is not ok.
BCG’s are cheaper than a whole new upper, and it’s no reason to risk a major malfunction over $100 cost. Plus with a separate bcg and charging handle the switch is that much easier.
And I cannot emphasize this enough: color coordinate. A 300blk will chamber in a 5.56 barrel and will cause catastrophic damage when fired.
I screwed up though. I went in to buy an H2, and a flat would spring.
I got irritated when they didn’t have a flat buffer spring, then got excited at 300 Black for less that $1 per round.
I walked out with an H buffer, no flat spring, but 100 rounds of 300 Blackout. Didn’t notice I had the wrong buffer till I was home.
We’ll see how it goes tomorrow…
Mind if I ask here?..
Looking at putting together a pistola, and hear 300 is a better option vs 5.56.
This one seems to check most of the boxes…thoughts?
https://palmettostatearmory.com/psa-10-5-pistol-length-300aac-1-8-nitride-10-5-m-lok-upper-with-bcg-ch-5165449628.html
I’d mate it with something like this…
https://palmettostatearmory.com/labor-day-sale/lowers/blem-psa-ar15-complete-moe-ept-sba4-lower-black.html
Of course there are some cooler lower options for a few more bucks.
I pretty much did the same thing, but 8.5” and a pistol lower with just the tube.
I added an SBM4. Personally I didn’t see the need for an adjustable brace on a pistol.
No regrets so far.
IMO, the only issue with .300 is ammo. its so much fun to shoot, ammo gets expensive quick. I have more .300 blackout AR’s than every other caliber combined. But I fell in love with it early on. Might also help explain my dislike for the AK’s, who knows.
As for “better”, its a matter of perspective. If you aren’t planning on reaching out more than a couple of hundred yards, and you need knockdown power, yes. It will be better than a 5.56. If you’re just looking for fun poking holes in paper or ringing a metal target, 5.56 will probably be the better option. Ammo is cheaper, it has better velocity, overall range, and less drop to account for.
On the other hand, running a mag of sub-sonic 300, even without a suppressor, is some of the most fun I’ve had with pants on.
Just change the upper don’t forget a 5.56 will load and fire in a 300 blackout blowing up the rifle and possibly causing injuries