I have a buddy who has a Remington 783 in 308 who's mag consistently presents rounds to the feed lips with the rim too far down to be pushed out by the bolt causing a bolt-over-rim failure to feed. We took the mag apart to verify it was assembled correctly and it was but still the issue persists. Is this a common problem with this rifle or just a factory f*ck'ed mag spring?

My Remington 783 in .308 does the same thing.  I chalk it up to just a cheap gun even though it shouldn't do that.  I use my left hand to apply a little pressure on the front of the magazine when I cycling the bolt and that seems to help.

Wow that's terrible. I expected better from Remington. I guess they couldn't do a cheap rifle and have it all work right. The 770 had a super shitty bolt and now the 783 has a shitty mag.

I only paid $289 for it at Walmart.  Other than the mag issue it seems to shoot fine and I have no problems plinking steel plates at 500 yards with it.

The rifle seems to shoot and for the money seems excellent except the magazine issue. I'm surprised Remington didn't catch this in R&D. Hopefully they or someone else will come out with an improved mag

My 783 was doing the same thing, where it would push down on the back of the rounds as the bolt was slid back on the full magazine (4 rounds) and the back of the round would stay pushed down, preventing the bolt from catching the rim when coming forward. The fix is relatively easy. Take the plastic floor of the magazine apart from the metal box. There's two small plastic tabs, one on each side, which need to be carefully pried/released from the metal box. Inside is the follower with accordion spring attached. Lift the back of the spring, the end which lays against the back of the plastic follower, below where the back end of the rounds rest. Insert a clean penny squarely betwixt the spring and the plastic follower. Use a suitable adhesive, which is both strong and a little flexible, to hold the penny in place. Don't use enough glue that it gets beyond the outside perimeter of the follower. Just need to hold the penny in place. When the glue cures, reassemble. Done.
Before this I tried tweaking the feed lips and had only the slightest bit of success with that. It took it from missing and sliding over the top round maybe 70% of the time to around 50% of the time. The penny fix has been 100%, always catches all rounds.

I also gave this synthetic stock my standard stiffening treatment. I've done the same with my Mossberg ATR and 4x4, and Savage Axis. I remove the stock and rough up all the channels in the fore end with a die grinder and burr. A dremel with sandpaper would also work. I also drill small holes through any internal ribbing. The idea is to get a good bonding surface for epoxy. From wally world I buy 3 packs of JB Weld and a small bag of hard plastic small beads. I mix up the JB weld and use a popsicle stick to put a thin layer in the stock. It doesn't need to be perfect at all. Then I pour in some plastic beads, slowly, and evenly distribute them in the fore end. Then another layer of JB. I use a sturdy toothpick to mix the JB in with the beads and get everything coated well. More beads and JB. The idea is to pretty much make a concrete of sorts with the beads and JB Weld. I fill it to just a little below the barrel channel groove and use stacks of books to level the whole stock as needed and hold it upright. After the JB cures, I put the stock back on. The fore end is much stiffer. I like good stocks, but I also like this cheap option... because I'm cheap.