I modded my Glock 19 Gen 3, replacing the frame with an aftermarket Shadow Systems MR918 Gen 4 frame. I used the complete Gen 3 slide with factory internals. I was able to use most of the Gen 3 internals in the Gen 4 frame. The only Gen 4 specific parts I needed was the trigger housing and the slide lock spring. I also used a Heavy Armor Division slide adapter to get rid of the gap between the front of the slide and the frame. It isn't really required, but it looks a lot better.
The gun has chugged along without any problems for about 400-500 rounds. But cleaning it the other day, I noticed that the back of the recoil spring assembly (RSA for all the Glock-a-philes) was looking a little chewed up.
I also have a Shadow Systems MR918 build with their frame and slide that uses a Grey Ghost barrel (Shadow Systems has stopped making their MR918 Glock clones). It's basically a Gen 4 Glock 19 and uses all Gen 4 parts. The biggest noticeable parts difference is the Gen 4 dual spring RSA versus the Gen 3 single spring in my first build.
I was trying to figure out why the Gen 3 RSA was taking a beating. I Iooked closer and could see that the RSA channel in Gen 4 frame was slightly wider than the Gen 3. Guess the Gen 3 RSA was bouncing side to side whenever the gun was fired. Enough to cause some scrapes, but not enough to affect function so far.
Trying to figure out a fix, I noticed that a #10 flat washer is the same diameter as the back of the Gen 4 RSA. I also found a 6-32 3/4" button head screw fits easily into the hole in the back of the Gen 3 RSA. The screw head was a little bigger than the inner diameter of the flat washer. It was also a little thicker than the washer. Those two issues were easily solved by chucking it into my trusty drill to file down the diameter and take some metal off the top of the screw so it fit flush when the washer was placed on the end of the RSA. Spring tension - not the screw - holds the washer in place when the slide, barrel, and RSA are fully assembled. The screw head only keeps the washer centered on the back of the RSA. The flat washer might add a little extra tension to the recoil spring, but I don't think it's enough to matter. It also makes the RSA guide rod stick out of the front of slide about 1/16", but again doesn't seem to affect anything.
Everything assembles with no problems. But you have to hang onto the RSA when you remove the slide since it tries to launch itself across the room when you remove the slide. The Gen 3 RSA now stays centered in the frame. So far I've only fired 35 rounds through it with no problems, starting with some weak factory 115gr practice FMJs up through some reloads and 124gr NATO and then finished up with some 124gr JHP +P/+P+. I'll report back later if I have any problems further on down the road, but it looks like I'm off to a good start. Seemed to shoot close to original point of aim on an 8" plate out to 25 yards, but probably ought to double check it on paper next time I get a chance. Gen 3 RSA left and Gen 4 RSA right.
Mandatory pics. MR918 Gen 4 slide & frame top. Glock 19 Gen 3 slide and MR918 Gen 4 frame bottom. Both have factory parts in the frames except for the flat face triggers.
