Send the lower in and will have it shipped out in about 2-3 days. We use controlled milling machines to get an even deep and perfect cut from front to rear.
The gun is just a tactical model with carbon tube added. They did try to weld up lifter but it is to short and still bites on load 2. You can get by with it but it is like raceing indy with a stock car. If you are SERIOUS about 3-gun, it still needs a lot more.
By just looking, it still needs the loading port opened up right, safety easier, and bolt lightened or maybe not. A lot better but still no cigar. At least Remington is trying new things.
I started shooting uspsa open in 1992-3 and made grand master in 95. I was shooting 50-65 thousand rds a year and 2-3 times a week practice and 2 matches a month. Depends on how much you want something.
Your problem is the bolt lugs are not going into battery. Clean barrel lug recesses and bolt lugs. Put marks-a-lot on bolt lugs, assemble and rack a few times. Look where lugs were dragging and remove a little from them and polish lugs until no drag marks..
It is recoil orperated and the x-tra weight of tube & shells won't let it cycle unless heavier shells are used. Mine would orp. with 3 drm. but not 2 3/4 drm.