I have got myself confused and don't know what to get. I was looking at getting an 11.5 AeroPresion upper but then saw the 10.5 PSA completed uppers on sale today. My limited understanding is that the 11.5 barrel is better, but not sure it is going to make that large of a difference. Any help would be greatly appreciated.

Are you thinking that another inch equals better or more to it than that?  There is not going to be much of any real performance difference between the two; not enough to worry about anyways.  It would be easier to give you some direction if you linked to both that you are looking at.  PSA sometimes offers uppers with the CHF barrels, so knowing which two that you are looking at would help.

I don't remember where I heard I just remember hearing that 10.5 vs 11.5 was about 100 fps slower and to try not to go below 11.5 if possible.

PSA Upper
Aero Upper

Military's done just fine launching 77grn OTM's out of the 10.3" barrels on the Mk18. For most uses though, it's generally considered that the 11.5-12.5" range is a great balance of ballistics and size.

If you want to go for the smaller side of things, get the 10.5in. If you want to get slightly better ballistics or reach out a bit further, get the 11.5".

Bravo write up

I read this when putting my pistol together and definitely helped me out.

Thanks, that was some covered some of the questions that I had.

I doubt I would be pushing it past 100 yards. Just trying to get something that will be reliable. I think the PSA got my attention due to the longer rail and thinking that might be more comfortable.

Reliability does and does not care about your barrel length.

It does, because dwell time, or the time the bullet spends after passing the gas port and before leaving the barrel.

It doesn't, because you can (to a point) compensate for a short dwell time by just making the gas port bigger.

Either way, the shorter you go the more your gas port size matters. If you go too small you'll be under-gassed, but as always, you can go too big and over-gas your rifle, especially if you're running something like the 5.56 IMI Razor Core 69gr instead of lower pressure .223 Tula 55grn. Personally, I wouldn't expect much trouble with either barrel setup. The 10.5/3 range is generally considered to be as short as you can go without having to deal with with much if any issues. You start getting below the 10.3in range, your gas system and gun gets more finicky.

I'm a big fan of running an adjustable gas system, but another way you can go about it if you do need to make adjustments is by tuning your buffer spring and reciprocating weight. If you're under-gassed, lighter spring or less reciprocating mass can help with that. If you're over-gassed, heavier reciprocating mass and/or heavier spring pressure will do it.

For under-gassing, that's how it be. But for overgassing, this is just a bandaid, as you're still dumping well more gas than necessary into the BCG/Receiver. So while your longevity may be marginally down compared to an adjustable gas block, it'll fix your function issues.

TL;DR - Either should be fine. Pick the one that makes you happiest.

Buy the PSA upper that you like. Anything 10.3 or longer
has a proven carbine length gas system, up to the 20's,
of course. I wait for the Magpul kits to go on sale.

I only shoot paper to dial in my new optics, but after that
usually just steel. I hit steel with no issues, at 375 yards, as
good as with my 16" or 20" rifles. And my pistols all have red
dot optics.

Buy it with no worries.

Thanks, the usually only buy chrome lined so it being nitried was throwing me off and this is my first pistol build.

Do the PSA if that's what you want. I have parts coming in to do an 11.5"; just because that's what I want to do. I have a 10.3" and 10.5". I don't see getting any better than those two. Both are great functionally and have good accuracy. Hell, for that matter, though I keep it at it's intended (by me) 30 meters or less, my little 8.5" is damn good (mostly PSA). Sometimes we just over-analyze stuff imo.

Yeah, Paralysis through analysis is easy when you start looking at all of the different variables.

I did the 10.5" PSA kak kit they offer
its phosphate and 1:7 chrome lined barrel
...went with a noreen billet lower

https://www.flickr.com/photos/165766533@N04/32158241658/

https://www.flickr.com/photos/165766533@N04/32158241658/