Crosman 2240 mods

Mods done so far:

  • RJMachine steel breech
  • 14.5" barrel from Crosman 2289
  • 2289 hammer spring
  • lighter valve spring
  • valve volume increased
  • valve face threads shortened
  • exhaust port expanded to 11/64" interior diameter
  • transfer port expanded to 11/64" interior diameter
  • matching 11/64" interior diameter seal
  • exhaust port interior angled/ported
  • barrel recrowned
  • Crosman 4x32 scope will do for now

Before I get started I want to say a little about that RJMachine breech. This thing is a great piece of steel. Great machining, tight tolerances, Robert Jones really did a wonderful job on his breech. If you never do anything else to your 22xx airgun, it deserves to have one of these on it. Besides, if you *do* do anything else to it you'll need to get rid of that awful plastic breech that Crosman puts on them. And you won't be disappointed with Robert's work in the least. I know of two other after-market breeches for these guns, but I am most impressed with his. Definitely money well-spent, as far as I'm concerned.

So I've gone through three different transfer port seals now. The first two didn't seal very well, I believe. And I think this third one might be ok, but I'm going to try one that's just a hair taller and see if it makes any difference. I still need to polish the exhaust port's interior, but I got lazy. I followed these two guides for doing my exhaust and transfer ports, and valve mods:

I angled the exhaust port quite a bit.

You can see here that the angle is such that it almost reaches the seal face.

I cut a bunch of the threads off, leaving just over half like the mod article suggested.

The article said to take about 1/4" out of the valve face's interior using a 25/64ths drill bit to match the existing inside diameter. Instead, I used the next size up, 13/32nds, and drilled out a bit more than 1/4" into it.

The factory valve spring is too short to use after taking all that material out, so I used the 2240's factory hammer spring and cut some off the end. I switched to the 2289's stronger hammer spring, so the 2240's original hammer spring was just a spare at that point. And it was long enough, and weaker than the factory valve spring and it did the trick nicely.

I drilled out the exhaust port and the barrel's transfer port to 11/64ths, and made a seal out of 1/4" polyethylene tubing, which also has an 11/64ths interior diameter to match the two ports it is sealing together. And the transfer port got a slight chamfer, using a 1/4" bit. You can see the transfer port here through the RJMachine steel breech.

I made an HDD (hammer debounce device) out of the polyethylene tubing, and it worked ok, but the material is too soft to last. I'm going to make one out of some harder plastic at some point. It gave a lot more shots, since less CO2 gets wasted when the hammer isn't bouncing into the valve multiple times per trigger pull. This allows the hammer to fly forward without any drag, but as soon as it starts snapping backards the HDD expands against the walls of the bolt bore and brakes it. This stops the hammer from opening the valve multiple times as it bounces back and forth between the hammer spring and valve spring tension, which obviously just wastes gas. It fits over the hammer's cocking pin, with the slot/opening facing backards. The opening/slot is what makes the device expand, the hammer snapping backwards makes the pin attempt to back out of that opening/slot and makes the body expand in that bolt bore, creating friction to slow the hammer. Forward motion isn't restricted though, so your shot velocity remains unaffected. You just get way more shots per fill since it isn't re-opening the valve after the pellet's already gone.

The crown on my barrel was almost non-existent. And what was there, was slightly off-center. So I knew I should take care of that. For the barrel recrowning I kind of followed this:

But I approached it a little differently. I didn't bother cutting the end of the barrel off to start fresh, as I didn't see much point. Reworking the existing crown got rid of enough material to make it the same as a completely new crown from scratch. And it got rid of the off-center problem, too, so I don't see why anyone would bother chopping off a hunk of their barrel, unless maybe they don't want that flat spot that Crosman puts on the end to position their front sight. I used a rotary tool's spherical grinding stone in my cordless drill, which had a diameter of about 3/8" to make my crown. After putting a pellet in the barrel I pushed the grinding stone into the end and let it do its thing. It didn't take very long to grind a new crown into it. It did leave it pretty rough, though, as the particles of the grinding stone were relatively big. Polishing the crown with 600- or 1200-grit sandpaper definitely wasn't going to be very easy, it is such a small area to reach with stiff sandpaper. So rather than attempt that, I just took the sandpaper to the grinding stone and smoothed it as much as I could with the 600-grit. This made the stone a lot smoother, and I used it on the crown again, and it did indeed smooth out the rough finish. I repeated this again with the 1200-grit, and it turned out to be quite satisfactory.



Shot counts have dropped dramatically, going from around 30 usable shots to barely breaking a dozen. Although part of the reason for that is the thing is still running on powerlets, and the fact that I was taking a shot every 10 seconds here. The tube got very cold during the process, despite my hand never leaving it in an attempt to keep as much heat in there as possible. Once I switch to bulk CO2 the temperature issues should no longer be a concern, and I should be seeing much more consistency between shots.

Data set #1 is with no changes except the 2289 barrel swapped on, with Crosman's metal transfer port seal still being used. Sets #2 and #3 are with all mods done except the angle on the exhaust port. And those sets are also with a bad transfer port seal, I believe. Set #4 is with the exhaust port angled, and a different transfer port seal again. I think I need to put a good polish on the exhaust port's surfaces. I have just left it how the Dremel cutting bit left it. It's pretty shiny, but I'm sure some 600-grit and 1200-grit sandpaper would help out some anyway. I will eventually be bulking it with the B&A Boss Max-flow valve system and a 3.5oz bottle in the stock, so I'm not *too* concerned about making this valve perfect anyway.

Update 06-09-13:

So I yanked the valve apart again and polished the interior of the face with a rotary tool and a bullet-shaped felt polishing pad bit, and polishing compound. Walls are very shiny now. I didn't get the back end of the face as shiny as I would have liked, but the felt bit sheared off about halfway down, rendering it useless. I took off about half the cotton from a cotton swab so the swab would fit into the port, and used it with the polishing compound in the rotary tool to polish the interior of the exhaust port. It's all nice and shiny now, too, so hopefully everything will be flowing a little better now. I'll have to do some testing tomorrow, no time left at the moment. I'll throw up those results when I get the chance. I've got a good transfer port seal now, I believe, so that's another item off the list of things to do. Phew. The biggest concern I have now is I may be rubbing up against the limit for the 14.5" barrel, and any other work I do will be wasted until I get a 24" barrel on there. So that's really high on my shopping list now, hehe. So at the moment this chart below doesn't have numbers with seal #4 yet, should have time to do that tomorrow.

Future plans:

I've got to get that 24" barrel first, but after that I am thinking about making more valve alterations. I don't think it'll be worthwhile until I've got the longer barrel to take advantage of more gas. I think the 14.5" is already close to the limit, where it is still expelling gas but the pellet's already left the muzzle. I'd like to attempt what Lowell did with his valve. This involves removing a lot of the parts inside the valve body to gain even more valve volume, and moving them outside the valve body. His inspiration came from the overhead valve design in car engines. Instead of pushing the valve closed from inside, he's got his valve being pulled closed from the outside, just like a car engine closes its intake and exhaust valves. Put a tophat on the end of the valve stem with a spring between the valve body and the tophat, voila! At the very least, you gain the volume of the spring's steel. If you've converted to bulk-fill and no longer need the powerlet piercing pin, either, and can cut it off to gain even more volume. And I suppose you could also shorten the valve stem even more by cutting off the rest of it, and just leave the little button that seals, cutting off the portion of the brass that serves as the valve spring guide. Very good idea! I don't know yet if this was Lowell's own idea or if he'd seen someone else do it, but he's being tight-lipped, so perhaps he's being modest.