Looking for direction on an AR pistol build

[TangoDown]

So for the longest time I've wanted to build an AR pistol. Yea I know I can buy one for the same price or cheaper with a warranty. However for me it's about the build itself, not just the gun. I also want a pdw for home defense that I can throw into my car as needed. So I'm torn on the caliber. Im waiting for the lower to arrive but I'm debating between 300 blackout or a pistol caliber. 300 blackout would be good for exterior defense but can over penetrate.

I was thinking 9mm or 45acp and use hollow points which should reduce the risk of over penetration a little.

Also, I decided agaisnt a shotgun for home defense already, it's not for me. So what does the board think? Also I'm no against .223/5.56 per se, I kind of wanted a different caliber in part for the novelty.

[mds587]

I love my 300 BLK, and with a 10.5” barrel it’s surprisingly quiet, especially with subsonics. It’s super versatile. If you’re worried about over penetration, you can keep some 200+ grain subsonics in it for HD and have the capability of generating a lot more downrange energy with lighter supersonic loads if needed. 9mm and .45 are both great, but are much more limited as far as what you can do with them.

[mds587]

9mm is hard to beat for ammo cost though, if you plan on training with it frequently.

[mds587]

And regarding 5.56, every short-barreled 5.56 I’ve had is extremely loud and has a super bright muzzle flash. Very fun outside, but not super fun at an indoor range, even with ear protection. I can’t imagine how concussive they would be in a hallway with no ear pro.

[Elk34]

Ounce a 9mm hollow point fills up with dry wall it acts like a fmj

[mds587]

Yep...

[Tim McBride]

5.56 has the lowest penetration(of the cartridges listed) in drywall, mostly due to its habit of yawning early.
However, it's mostly academic, I'd be more concerned with what weapon system do I have the most training with, what is the most effective cartridge for that system, and what is cost effective for me to continue training with. Then consider the effects of shooting indoors versus outside, suppressor or not, dot/lvpo/iron sights, etc, etc.

[Tim McBride]

Ounce a 9mm hollow point fills up with dry wall it acts like a fmj

Some of the latest "barrier blind" duty ammo is actually still effective on tissue after passing through drywall.

[Elk34]

The point I was making was ,don't miss..

[TangoDown]

Thanks all for the info. You guys are right that staying on target should be the first priority via training but let's be honest; even seasoned operators can miss and I won't be nearly as trained or experienced as them. So I'd like to start with a round that, if I do miss, will reduce the chance of over penetration. I'll still train with it often, including taking classes. I'm just trying to cover as many bases as I can.

@mds587 that's good info about the 200 grain round. For home defense I'd definitely prefer to use a suppressor which is why I was looking at 300 blackout to start with. I started backing off though after watching that video.

EDIT: So I just got a new concern. I was watching a video about 300 blackout rounds for self-defense in the home and the author noted that there's rounds that might be considered AP which aren't legal for pistols. Since my intent is to build an AR pistol, I'm now concerned running afoul of the law, moronic as I feel the law is. I was specifically looking at Lehigh 300 Blackout 78gr High Velocity Close Quarters round but after watching that vid I'm questioning myself. BTW, here's the ATF analysis: https://www.atf.gov/file/11266/download