I currently own a 10.5" Pistol AR15 in .223.  I would like to convert this pistol into a rifle with a 16" 9MM Barrel.  Will the same barrel parts such as the delta pack and front hand guard cap work with my 9MM build?  If so, would it hurt to use the current parts I pull off of the 10.5" .223 Barrel for the new 9MM Barrel?  Also, can I use the same buffer spring and buffer for the 9MM build?  I am looking around for parts and realized that I could convert my current AR pistol to a rifle by changing a few things.  I do not intend to convert this back into a pistol once I attach the 16" barrel to the upper receiver, and replace the pistol buffer tube with a carbine buffer tube.  Just to be safe, I will do the upper conversion first.

first the buffer... my NFA lower came with what appears to be a standard AR buffer, with a spacer... not sure of the spring but it appears to be a standard spring...biggest difference is the weight of the bolt itself as it is direct blow back...you may need to tune the entire buffer, spring and bolt, but probably not...

upper... you can use the standard upper with the delta ring... there are sources for 9mm barrels with front sight posts installed... I knew mine was going to have an optic mounted, so got a plain barrel... if you use a plain barrel you will need to supply a gas block or something to act as the end cap of the hand guard if you use the delta ring... it is IMHO a lot cheaper to just use a threaded hand guard to secure the barrel

I use a NFA Glock lower, so do not have a last round bolt hold open as I use a standard Aero Precision upper...if you choose to use a Colt/Uzi stick mag and a conversion block for the mag well, I believe the standard bolt hold open works...

Here is a basic list of parts needed.

LOWER PARTS
stripped 9mm lower (or AR15 lower w/ magwell adapter)
Lower Parts Kit (9mm hammer required if using non-ramped bolt
Standard buffer tube/spring/buffer (I prefer a 9mm dedicated buffer or 5oz buffer or an A2 buffer if using the A2 tube)
New Frontier buffer bumper (I consider this a mandatory peice for proper stroke
buttstock
Bullet button or build featureless if in states that require it.



UPPER PARTS
Barrel (any 9mm AR type barrel with 9mm extension)

Upper receiver (any upper receiver should work)
I like slick side or side charger uppers.

Bolt (ramped bolt for standard AR hammer---9mm hammer for non-ramped bolt)
AND...bolts used for Glock mags will need to be shaved for the magazine lips.
Lone wolf , NFA and others offer this service. Most bolts are using this design now.

Handguard w/ barrel nut
muzzle device (most 9mm barrel threads are 1/2 x 36)

NO GAS BLOCK/GAS TUBE ARE NEEDED.
It is a blow-back type of operation.

But if you want to run a gas block for whatever reason, it will need to match barrel diameter.

Thanks for the info.  I'm very versed in rifle applications but had questions before I build this 9mm gun. You reccomended the buffer bumper even with a 9mm buffer weight?

9mm buffer will be a little longer and a bumper is not needed.  I use the Spikes ST-9X buffer.

will i need a dedicated 9mm upper receiver to achieve last round bolt open on a qc10 lower?

No.........If you are referring to glock qc 10 lower........I used a aero precision upper without the forward assist............but I do rec using wolff extra power magazine springs to give the last bolt hold open lever more lift............

I second the wolffe xtra power mag spring suggestion. My qc10 gsf  wouldn't lock the bolt back without the xp springs.

same here.........anyone tried using a factory glock 17 magazine spring in a factory glock 19 magazine?

9mm newbie here.

So from what I'm gathering, a 9mm build can use all regular .223 AR parts with the exception of bolt, barrel, and something with the lower (either a dedicated one or mag block)?

Also, i read that the glock mags are too wide to fit in a .223 mag well, so if you go the mag block route, youve gotta go with the colt setup?