Carbine pistols - 2 types?

[gun'sRgood]

Pics of which?

BSW

Sorry, I thought you had both the AUG9mmP? But i guess your comparing it to the Tavor? But if you do have one of these, Sure would love to see it! Thank you.

 

[gun'sRgood]

I've got both types of 9mm lowers - one PSA dedicated AR-9 lower that takes Glock magazines - and a "standard" AR lower with an adapter setup to take the 9mm Colt style magazines.

The Colt-mag adapted one has never jammed once. The dedicated one had some teething issues but not related to the lower - at first I tried a Rise Armament trigger group in it but got light strikes. Went back to milspec and no more light strikes (and I've since switched to A CMC trigger with no issues). I also had some feeding issues on that one but only with aftermarket KCI magazines. With OEM Glock magazines it has never jammed.

You typically have to setup the buffer a little differently for 9mm (heavier buffer and a spacer) so I wouldn't consider it particularly practical to switch a regular lower back and forth for PCC use, but if it'll be a permanent fixture the adapter block works just as well. As to types - be aware that almost none of the 9mm AR's setup for Glock magazines will lock back on the last round (this is due to the magazines being single-feed so the follower is rather far from the bolt catch). The ones that take Colt style mags often do.

Also, if you're planning on using one for Glock magazines you need to make sure that your 9mm BCG is compatible with Glock magazines. Typically if they'll work with Glock mags they'll work with Colt mags too, but not always the reverse (strictly Colt style BCG's will get caught on the feed lips of a Glock magazine).

The adapter block that I personally use is the AR-stoner model here:

https://www.midwayusa.com/product/1019567735?pid=900392

I also tend to use AR-stoner brand magazines with it.

My upper is a standard upper with no dust cover or forward assist. Tried a strictly 9mm PCC upper and I didn't like it as my handguard's anti-rotation tabs wouldn't mate up to it.

Almost all the rest of my 9mm specific parts (barrel, BCG, buffer) are by FM products.

Here's a pic of my upper on both the lowers.
View attachment 981587

The top pic is with the Glock? It looks like it's stamped "multi" I know for AR15's this stands for both or either .223 or 5.56. What does it stand for here? I'm also told that there's no real "ballistic advantage" with a 9mm barrel after around 5". Seeing the length of your barrels I'm guessing your choose these for accuracy? Or for more of something to hang onto? Does the longer barrel slow your rounds? Sorry for stupid questions.

 

[mgmorden]

The top pic is with the Glock? It looks like it's stamped "multi" I know for AR15's this stands for both or either .223 or 5.56.

On regular AR's "Multi" is just there because people can build a whole host of difference calibers so it doesn't really make sense to stamp it on the receiver. It leads to crazy situations like an AR in .300 Blackout that has a lower marked .223 or 5.56 - better to just not list any cartridge and list "Multi" so that people can just build what they want. The marking only needs to be on the barrel.

I'm also told that there's no real "ballistic advantage" with a 9mm barrel after around 5". Seeing the length of your barrels I'm guessing your choose these for accuracy? Or for more of something to hang onto? Does the longer barrel slow your rounds? Sorry for stupid questions.

"No real ballistic advantage" isn't the same as as no advantage at all - it's just that there's a point of diminishing returns where adding extra barrel doesn't result in as much of an increase. You're still going to get SOME extra velocity (and certainly not loose any) by adding more barrel (up to a point, but at 16" you're still generally gaining).

Here's a good table: http://www.ballisticsbytheinch.com/9luger.html

If you'll notice at the bottom end every inch of barrel you're making very large gains in FPS. Towards the end of the scale the gains are either very small or occasionally dropping (but then going up again later and trending upwards, meaning that the variance in speed from round to round is greater than the potential velocity gains).

As to why I chose that barrel length - it's the stock. These are PCC's not pistols so I have to have at least a 16" barrel or register as an SBR. You can also go shorter and use a "brace" rather than a stock but just my personal opinion they look goofy and feel like "half assing" it - no shade to anyone who wants to use one they're just not for me.

 

[briansmithwins]

Bolt carrier details. 9mmP carrier on the left. It's simple blowback and has no locking features. The right op rod on the 556 carrier is longer as thats where the gas piston impacts. The 9mmP has no gas piston and both op rods are the same length.


Bolt faces. The 9mmP bolt has a post above the bolt face. This is a safety that interlocks with the firing pin and prevents out of battery firing.


Barrels. The 9mmP barrel doesn't have the gas piston area of the gas block.


Stocks. 9mmP stock on the bottom. It has a ejection port with a built in shell deflector and can't be swapped over for LH operation. There a Corvus aftermarket shell deflector on the 556 stock.


Ejection port details.



Mag adapter details. Besides holding the 9mmP mag in the correct location it includes the ejector and bolt hold open.




Position of the ejector within the ejection port


Mag adaptor in the stock. It's a clever design that prevents inadvertent operation of the normal mag catch used when the rifle is configured for 556.


BSW