H006587R51, Black, made in Huntsville, picked up today, 1-15-19.  Oiled it up,  then fired 85 rounds of mixed brands off my back porch just to check function with minimal problems:

Twice a Mag fell out after the first round was fired...haven't figured it out as none of my fingers or hand  touch the release when firing!  Forgot to check which mags they were.  This was early on.  Maybe I did somehow press on the release without knowing.  This doesn't seem a mechanical issue,  more like human error.

Then,  on two occasions,  the second round in each mag failed to chamber.  Turns out these factory loads from Slovakia were a thousandth longer than the longest of the others and the second round hung up by touching the front lip of the mag, and the slide failed to close.  The other 5 rounds in each of the mags fired after that.  I put those aside for use in a different 9mm.

Ammo:

Freedom XTP HP      115 OAL 1.075  (7 rounds shot)
Remington +P HP      124 OAL 1.120  (7 rounds shot)
Magtech    FMC RN   115 OAL  1.155  (14 rounds shot)
Hotshot     FMJ  RN    124  OAL  1.160 (14 rounds; couple hangups on mag lip)
My Reloads  FMC RN 115  OAL  1.120 ( 4.5gr 231)  (43 rounds shot)

Some primers showed light strikes mainly on the Slovakian ammo,  but non failed to ignite.  Maybe they use a harder primer.  I use Federal or Winchester.

MAG Feeder Lip Measurements:

#1.   Rear 0.352  Front 0.338
#2.   Rear 0.351  Front 0.338

I have a bunch of light 100 grain bullets that I used to load 380's;  going to load up a few to try in the R51 just for grins since it seems to do well with 115's.  I'm out of 231/HP38 powder but have plenty of Clays and Bullseye on hand. 

Overall,  couldn't be happier with the initial showing.  FWIW,  after shooting enough to see it was functioning ok,   I leaned a piece of tin,  about 6" wide by 12" high up against the stump about 25-30 feet away,  and It seemed to group well and shot POA.  When WX warms up I can put up some targets to see how I do.

Only CON for me is that the grip seems too thin with front grip too aggressive.   Might try making some fatter grips one day just for fun or perhaps a rubber cover..

Forgot to add:  Take down was easy;  putting it back was a ball breaker.  Might start hosing it down with hot water!   

visited two local gun shops today to get pricing;  one said his distributor had 100 guns available,  and the other said his distributor had "red lined" them, meaning they were no longer available.  He didn't know if that simply meant they were not being stocked by that distributor, or if Remington had stopped making them.  I doubt it was the latter,  but who knows as there seems to be a lot of unsold ones on dealer shelves.

Doing a little shopping and want to find the newest possible.  One dealer has the above but said he thought it was fairly early.  Forgot to ask if it was Charlotte or Huntsville.  Serial nr is 0035612R51.  Does this indicate approx date of mfg?

Been into guns for many years and do a bit of reloading for common calibers,  mostly now just for 9mm and 45acp.  I use Dillon 550's.  My other pastime is driving my 3 wheel Slingshot.  A couple years ago while in KY I stopped at gunstore and looked at the R51.  Was really tempted then but felt that perhaps the bugs had not been worked out enough.  Am now about ready to take the plunge.  I live in the Triad area of N.C.,  having retired from the Govt some years ago.