I built a rifle using one of their standard long mag actions. I called them directly and have no complaints about their customer service. Their actions are as they describe... a hybrid Mauser 98-Win 70 retaining select features of both (as determined by the founder of the company). I believe (correct me if wrong) their actions are made by the same company/facility that makes the Ruger bolt actions (IIRC a company owned by Ruger). The rifle I built on the MRC CRF action is a good, reliable hunting rifle.
I have no idea about the 505 Gibbs issue but suspect possibly a common conflict between the length/size of the Gibbs cartridge and the basic design of the Win 70/Mauser 98 sporting CRF bolt action (also found in the Montana '99). In other words, that combination will never cycle like a short, straight walled, push feed carbine!!! At least that is what I suspect. I also suspect the bind issue in more common than most are willing to admit- that includes older Win M70s, CZ, Mauser 98s, Enfields and other similar actions. With any long length Mauser 98 type action mated to long, heavy cartridges, there will be some cycle speed issues- no way around it. By design, the bolt on a 98 type action is not fully aligned/supported in the full rear position- so it is not uncommon for the forward stroke to be a little "bindy" if not "manually" aligned (only perfected by much practice or luck of an individual's bolt cycling geometry) during the beginning of the forward bolt thrust. If the tolerances are too tight then field condition reliability would be sacrificed (this is especially true with military based designs). If too loose the alignment "binding" as described would be worse. Most reliable sporting rifle actions are defined by that compromise. Later, Winchester attempted to help resolve the rear position "bind" issue in their M70 by adding an anti bind bolt alignment groove in the right side lug. The Montana '99 does not incorporate that anti bind bolt alignment groove design feature as seen on the later Win 70- I don't know why MRC decided not to use it ??
The closest to an ideal CRF bolt action "big" rifle I've ever owned and used is a late New Haven Win M70 416 Rem. The one I have is a very exceptional hunting rifle!! Going one step further, if I were to design a best of the best (for me) CRF bolt action for a long and "extra long" mag including those based on the 375 HH length and those slightly longer and bigger, I would use most of the late New Haven Model 70 design features like the old style trigger, new design magazine follower, M70 3 position swing safety and the bolt alignment groove PLUS add some from the Mauser 98 like the larger gas escape ports in the bolt, a gas deflecting flange/shroud on the bolt and the left side toggle bolt release.