Who owns a CZ MTR,or an RAP?

[Rosecrans1]

Grayfox........time really helps with the feeding of shells in the RAP-Grendel. That said you still need to be able to feed bullets, period. The heavier the mag spring, the worse the RAP Grendel feeds out of the box. I had great success with the ASC 5 round mags. When I took my RAP apart and cleaned all the oil off everything and put it back together, I only torqued the action to 50"-lbs as I think 60 to 80 that Ruger calls for on their plastic stock has a huge effect on feeding. I ran shells through the gun when I took it out of the box and it sucked. After I had it apart and back together at the lower torque settings, it fed much better. Not perfect but substantially better. I used a drop of blue Loctite on the action and rail screws as well.
I bought a stock someone had on Gunbroker for the RAP Grendel complete with the factory Cprod mag for 60 bucks last Summer and when I put my bottom metal, (OK, it's not really metal), in this new factory stock with the action, it fed perfect! There is a lot of open tolerances in these RAPs and your aftermarket stock would be no different.
So, long story short for feeding issues: No heavy mag spring! (ASC 5 round worked best for me). Check the torque of the action. (Mine liked less than Ruger calls for). Experiment and make sure you thread lock the action. Shoot it. The more it's shot, the better the action smooths out and feed issues disappear! Hope this helps a little.