It sounds like you may have a magazine box problem. The front of the box should line up either perfectly with, or a thousandth or two behind the feed ramp.
I've found that most Remington internal "boxes" have issues with fitting. If it shifts ahead of the feed ramp, try removing the box and bending a small amount of the lower front edge so it's pushed farther back in in the bottom metal. On my rifle there was more than .100" of slop in the fit when I took it out of the box. If the magazine box is pushed all the way back in the bottom metal, and the bolt still catches the case head to feed the round your good-to-go. If not, remove the bolt stop and file/grind a small amount off of the rear part that stops the bolt. This will allow the bolt to travel back far enough to catch the case head. IF you need to do this it won't be much.
As for max OAL, it's generally considered to be around 2.830". I load up to 2.825" in my BDL. You can purchase a new magazine box from Midway (about $30) but it requires modification to the bolt stop, the removal of that 'stub' at the back of the feed ramps, and possibly the ejection port, but you can then load cartridges well over 2.900" OAL (.110" more than stock).
To find the max OAL for your rifle just create 3-4 dummy rounds that are 2.850" and keep shortening by .005" until they feed reliably.