Re: Magpul PRS vs UBR stock
Short version: I've had both on a JP LRP 07. I prefer the UBR. I suggest that you run your scope in low rings and don't worry about adjustable cheek-piece.
Here's what I found:
The PRS is bulky and cumbersome. I guess the length of pull feature is fine. My main problem with the PRS is that the shelf/cheek-piece that goes up and down is just way too short for my big fat face. I can't get a good cheek-weld on it because half my face is hanging off of it. I can't be the only one with this problem. It is purposefully too short because it needs to be-the cheek-piece is designed so that it will not interfere with the charging handle on AR type rifles, while it is in a raised position.
Now, here is how to make a useable cheek rest on an AR:
I once had a dedicated SPR setup (20" upper with collapsible stock) that had a scope in a quick detachable mount. It was higher than it needed to be, in order to clear the back up iron sights. The setup couldn't be changed because it was an issued rifle. So, all that could be done was to use layers of duct tape, exercise mat, and pieces of clip-board, to build up the cheek-piece to the correct height, and length. The clip-board stiffener was so that the cheek-piece could extend forward enough to be useful, but sit high enough to allow the charging handle to be operated, with the help of a Badger Tactical extended latch. The setup was ghetto as hell and looked terrible, but it was set up in a perfect position-you could lay in your good prone shooting position, face on the cheek rest, close your eyes, relax completely, then open your eyes and the scope would be perfectly clear and visible-perfect relief, perfect height. Length of pull was adjusted by running the stock back and forth. This means no stress on your neck, no restricting blood flow to your noggin and fuzzing up your sight picture. The goal was to allow the shooter to stay on that scope for a long time, while observing a target, and to be in the most natural position possible to engage a target, if need be.
Fast forward to the JP LRP 07. I found that the PRS stock stank, and I switched it out for a UBR. The UBR felt solid as hell. The cheek rest on the UBR is a little wider on top (or so I perceived it) than the PRS and it just felt ten times better. Length of pull can be preset so that when you extend the stock, it is the correct length for you. I cured the height issue by running my scope (Leupold LRT M2 3.5-10) in the lowest possible Badger rings I could find. I also mounted the rings to a Badger +20 moa riser that put the scope just little farther forward, which helped the position. The scope was in a perfect spot for a good neutral, stress free shooting position.
If you insist on backup irons, now you can rock sights by Dueck, Ashley?, and Knights Armament that are offset to the side and won't interfere with your optic. Or, you can run a short range optic like Trijicon RMR, Aimpoint H-1, Leupold Delta Point, etc. If you do that, run a 1'Oclock mount, I've tried a scope ring mounted Fast Fire setup and it sucked ass. Daniel Defense offset optic mount was FAR better, much easier and more natural to use.
This setup worked great for the side-charging JP rifle, but the same setup will work on the top-charging LMT MWS that I have coming, as a replacement for the JP rifle. I will configure this gun for 3-Gun Heavy Metal competition and run a Leupold Mark VI scope (hopefully, it will actually ship this year.) in as low a mount as I can get it, with KAC offset sights for backup/close range.
SO, there's a couple years of money and experimentation for ya. Hope it helps.
