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Concerns over Frame Wear - and the R9 Operation Cycle.

Some time ago, some owners noticed and were concerned about some wear marks showing on part of the R9 frame, which is Aluminum. I inspected my two guns and found much the same. Below is a picture of both frames.

Firstly and according to Rohrbaugh, this is not something to be worried about and I agree. Secondly, I have attempted to rationalize what occurs to explain as I understand it - see text below picture.

The front frame in the picture belongs to an early model, when frame was ''silver'' - self color. The frame to rear is an earlier version of the newer frame finish, in a darker anodizing. The areas within elipses is where the wear shows up - much harder to see in fact on the silver frame here. That gun was used for most of my testing and had about 370 rounds thru it.

The newer one which is used for carry - has only had perhaps 150 or so rounds thru but the wear is much easier to see - what might be called ''scuff'' marks and some slight burring.

R9 frames with some wear

Given time and some of that on CAD I could show some aspects graphically. But I will attempt (operative word) to do this thru description. Even better would be a Flash animation - not easy to produce but maybe one day!

The ''cup'' (depression - center right in elipses) in the frame is actually receiving the barrel lug base protrusion at fully unlocked - at which point it actually could prevent feed ramp from being any further back than level, with the mag' well. It is tho not designed to take that much of an impact!

Along with that at unlock is the actual and theoretically main limiting factor - the pin, in the barrel lug slot. That should prevent the barrel setting back any more on it's own so - the ''cup'' is actually a clearance device shall we say.

Now, also at unlock the barrel and lug is at its lowest point, having dropped, thus the contact with the wear areas we have seen by the exterior of chamber profile. I say contact - in fact from a design POV I expect with the incredibly tight tolerances in this gun, we have a theoretical ''barest kiss''.

However, if we consider the extreme violence of the event (firing) during a full cycle - it seems very likely to me that a two or three thou over travel downwards, and maybe a thou or so to rear (heck, this is a demanding gun to design!) - and we can see the slight attrition to the surfaces and thus a very small disturbance of the aluminum there.

I am still personally content that this is self limiting and I guess if tolerances were sloppy as heck, it might not even happen. Put this another way - it is a process that will occur during early useage of the gun, after which time it cannot happen any further.

Let me try and describe in words - the cycle of events -

At the instant of the slide beginning rearward travel, as round fires and pressures begin to back off from peak, we have the barrel moving rearward by approx 1/4", as recoil springs are being compressed by slide - (exerting as they do said rearward force against barrel lug) - at which point the lug slot allows it to drop on the pin, and there it stays while slide continues all the way to the rear.

The slide progresses then forward, stripping a new round - which is fed into the lowered barrel and chambered, assisted by the feed ramp. The completion of the auto load is aquisition of full battery with the slide having moved fully forward, the recoil assembly is now relatively relaxed, and we see the bolt face area impinged on the round's base to complete the action.

The last 1/4" or so as around goes into battery and the slide closes, is when the lug slot then rides over the pin to lift the chamber area (barrel rear if you like) once more and go into full lock-up. This incidentally is why that lug/pin area needs lubrication.


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