I hit the range with my new pistol build this weekend.  This is my first AR project chambered in 9mm.



Parts consist of:

- RRA 10.5" Upper
- RRA Bolt (unramped)
- RRA Magazine Block
- Spike's Tactical Pistol Lower
- Various buffers: RRA 9mm; Spike's ST-T2 heavy buffer (a little bit heavier than an H2) w/ and w/o ST-9BS buffer spacer
- 5x ProMag polymer magazines
- 2x C Products steel magazines
- Aimpoint CompML2 (not shown)

After reading through the "Rimfire and Pistol Calibers" forum several times, I was expecting a lot of tweaking to be required for this build to work.  When I assembled the pistol, I put the top of the magazine block flush with the top edge of the lower, so if I needed to make adjustments I would have a good reference point to where I started from.  

When dry-cycling the gun, I could not find a mag block position that would cause the C Products magazines to activate the last round bolt hold-open feature (ProMags worked fine).  I initially considered sending them back, but decided to wait until I could function test them with live ammo.  Much to my surprise, when firing live ammo, both the C Products and ProMags locked the bolt back after the last round every single time (I tested this at least 3x with each mag)!

I initially tested the gun with the RRA 9mm buffer, then with the ST-T2, and finally with the ST-T2 & ST-9BS combo.  I did not notice any difference in function or change in recoil impulse between them.

The gun is actually fairly shootable with an Aimpoint if you put your cheek on the tube and hold it far enough off your shoulder that it doesn't recoil into you.  I was able to easily keep 4" groups at 25 yards shooting offhand.  I think with iron sights it would whack you in the nose if your eye was close enough to use them properly (nose to charging handle).  

Out of about 100 rounds (all hand loads) I had 3 mis-feeds, 2 of which were on the first round out of the magazine.  These may have been user-induced by inadvertently slowing the bolt when pulling the charging handle.  The first round out of each magazine fed properly when using the bolt release.

The main purpose of the upper will eventually be for use on a registered receiver M-16, so I am considering having the bolt ramped and attaching a 3-lug suppressor mount to replace the A1 flash hider.  Other than that, I am very satisfied with how well everything works so far.