Tuning Crosman Rat gun gets another mod.

This gun has been around for a few years so has gone through allot of mods, It started out in life as a 22xx with a Discovery tube and then a Blue Fork Design Gripframe was added some years later. Oh, and the buffer tube and stock off of my S&W MP15. It has just been sitting since I stole the FX liner off of it for my Blue Pistol a few months back. So, since I have another barrel liner that I recently straightened I thought I would put the Rat Gun back in service.

Decided to put one of Steve's 22xx SuperSears on it and it ended up being an all day job. It did not fit and removing the pins from the Blue Fork Design gripframe was a very difficult task. I gave up once and then just decided they were coming out so I really hammered on them hard. They did finally did break loose and I was able to punch them out so I could get the sear in place or so I thought anyway. Not even close to fitting it was. So, out came the Dremel, and 600 grit sandpaper, for some major remodeling of the sear. I did get it to fit and the trigger is pretty good now, definitely many steps above the stock Crosman unit, but not as good as a stock Supersear normally is. This is probly not something I would take on again. So just don't do it.

I was looking for new ways to get more out of a valve back then so managed to get quite a bit more volume out of this one. Installed with #10x32 screws so I can turn the pressure up as well. Did a gauge delete so I could get a couple more shots out of it.

Next came the 500mm STX barrel. I had already made an adapter and put an FX liner on the gun, in an earlier mod, so I just had to shorten up the shroud and add some baffles to make it werq. Made an adapter for the barrel liner out of Delrin with a couple of slots so air could go back into the shroud and a couple of setscrews to keep it from sliding around on the liner.

Had some baffles from the BNM days and used them and a spring to keep them tight inside. Then added a little actually allot of superglue to the end cap and pressed the parts together and held them for a few seconds. Almost glued my thumb to the shroud but I pulled it loose just in time. Nasty stuff that superglue is.

Then came the test to see if things were aligned correctly. So, I gassed the gun up or at least tried to as it leaked from the fill adapter so was a no go. I found the correct o-ring this time and replaced the wrong unit that was in the gun. Filled the gun to 2kpsi it held pressure and all was good. Slid a pellet in the barrel and fired off the first shot. Successful first test, no funny noises, and it didn't shoot the end cap across the room a big plus in my book. ;^)

So pulled out my retired Hawke 4x12x40 scope, retired cuz of a loose ocular eyepiece, put a set of rings on it and put it on the gun four shots later it was shooting just about right. 

I need to take it to the range for some chrony and accuracy testing and it will be done again. So long as I don't steal any more parts off of it that is.

Almost fergot did I say how light this thing is? It weighs in at 5lbs 11oz with the scope and rings and pellets in it. Gotta Love the Crosman Frankenstein guns for that.



The SuperSear that did not fit but I installed anyway.



The adapter I made to mate the FX liner to the BNM breech. Note the large threaded hole, center one up front, in the breech. I drilled all the way through the breech, then marked drilled and tapped the tube straight above the grip screw, so another 6x48 screw could be added in addition to replacing the stock Crosman 4x48 with a 6x48. Makes things a bit stronger it does.



Valve is a bit rough but used to put out some power when it had the long barrel on it. Put a gauge delete on it as well. 

Edit 4/3/22;

I put a less modified valve and a Huma regulator in as it now has a shorter barrel.

https://www.airgunnation.com/topic/still-another-mod-for-the-ratgun-and-once-again-the-true-cost-of-a-60-crosman/



Barrel installed with a Delrin adapter up front. Lines on the barrel are high spots I marked to straighten it as it was badly bent when I got it in trade.



Gun together with suppressor baffles and spring you see in the pic. Shoots the junk pellets I put through it through the same hole at ten meters which is no big surprise at that range.




 
You know, I was thinking just today about making one of those adapters for one of my crosman pistol/carbines. As I have a spare liner on my shelf. I've no means to make it, so will wait till I get a lathe eventually. Just funny I was contemplating the exact same thing basically, and there it is, lol. Nice work! That really came together nicely!
 
Well I took it out to the range and shot about 500 rounds through it trying to get it tuned with several pellet weights at speeds from 560 to 830fps. Accuracy was an on and off sort of thing. Last shot was a loud one as it blew the end cap off of the shroud and it and the baffles all flew downrange. 😳 Lucky that no one was around to witness the failure. Found them all in a straight line from 10 to 25 yards out. Probly clipping a bit when the velocity was up or down is my guess. Anyway made a new adapter that fits a bit tighter to the barrel, it lets more air back into the shroud also, and replaced the damaged baffles. 

Think I fixed the transfer port leak as well.

Now I just have to find those big o-rings I had on the scope eyepiece to keep it centered and I will be out for another test.

Edit;

I found them, now it's ready for some more testing.
 
Thought I should give this an update. Got the shroud end cap glued back on with hot glue this time as I know it werqs well and went out to the range again. Got it shooting 1/2 and 3/4 inch groups at fifty yards with a little tuning so everything is good now. I just wish the trigger was a little better but not going there again as it was a pain.
 
Well I finally got the Ratgun out to the range today and tuned it in to fire the 13.4 JSBs at near 700fps. There was a little wind and I kept getting four near the same hole and one flyer that opened the group up to .75 inch at 50 yards with unsorted pellets. So, for no good reason, I put a heavier hammer spring in and started tuning with slugs but one got jammed somehow and I could not get the empty mag out so that was the end of that. Looks like I will need to sacrifice the magazine to fix the problem. At least I know it shoots well enough to be a Ratgun anyway.

Edit;

Did not have to sacrifice the magazine after all I pounded it out with a hammer and a plastic rod and it sheared the slug. So I was able to get the mag out without any sort of damage to the gun.
 
Thanks

Looks like I am getting 25 or so at 650-700fps. I even counted them in case someone asked that question. Shot count is why I did the gauge delete. The gauge delete unit that comes with the Huma reg is much thinner than mine and has the o-rings at the front and rear instead of on the outside where they would get nicked when replacing the valve or servicing the reg. So I used it instead of mine.