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rjorge · New Member

Hello all,

I am new to the forum and I have been into airguns for about a year now. I started with a stock Crosman AS2250XT and turned it into a regulated HPA @ 1600 psi capable of slinging pellets @ 1030fps using 14.3 gr CP's.

My project now is to turn it into a .25 cal little monster!
So far I have the following:

-BNM breech & 24" shroud
-.22 & .25 cal bolts and blocks for the breech
-Marauder .25 cal barrel (19") turned to 7/16 with .169" port
- .169 metal transfer port
-2260 air tube sealed with stock cap + sealed disco gauge block
-Disco valve: .3" threads, inside bored out enough to not see the threads anymore, .172" exhaust port @ 22 degrees and rounded, slimmed stem valve to allow more flow when open, enlarged the valve seat to B (.242") & lighter spring.
-Disco valve front: bored the front to 1/2" just before the trigger frame screw clearance, and bored out past that to 11/32" or a little less.
-P-rod trigger group
-Stainless steel fittings and tube to transfer regulated HPA to inside the air tube.
-13ci 1600 psi output Expert HPA tank
-.43" x 1.75" hammer spring + guide total of 2"

I think I listed everything. Here are a couple of strings shot in .25 from 2000-1600psi:

JSB King 25.4gr
862.6
862.7
861.2
863.1
856.0 (below regulated pressure)
837.9

JSB King 25.4gr
859.9
858.6
Benjamin Dome 27.8gr
832.9
829.2
Beeman Kodiak 31.02gr
813.5 (maybe below reg?)
795.9 (below regulated pressure)

I have no idea why I am not able to squeeze more output out of this thing Mad

!Is my regulated output of 1600 psi not enough to push the JSB kings around 950 fps? Do you see anything wrong with my setup?

Any comments are welcome!

rsterne · Moderator

Most obvious thing is the 19" barrel.... I think it will be tough to break 900 fps at 1600 psi with that....

Bob

rjorge · New Member

rsterne · Moderator

Increasing the volume inside the valve is not necessary providing you make it easier for the air to get into the valve than out of it.... If I understand your build correctly, you are using a 2260 tube for a reservoir downstream of the regulator, which is plenty big enough.... Is the inlet into your valve still 1/4" or have you increased it a bit?....

Bob

rjorge · New Member

rsterne · Moderator

All the work in boring out the valve inlet won't buy much unless you increase the diameter of the valve spring seat.... that is where the restriction occurs.... You don't need much, even drilling to 17/64" is probably enough.... I worked over a valve spring to increase the ID at the front end (ie tapered the spring) and got the inlet to 9/32....

I don't think increasing the volume inside the valve will help (providing you have the flow into the valve as above).... However, a larger ID around the head of the poppet will help ease the flow in that area.... Again, you don't need to go crazy, as long as all the areas on the pressure side of the valve seat are 10-15% larger than the area of the throat minus the stem and all the ports on the outlet side....

Good Luck....

Bob

rjorge · New Member

I was only able to pick up another 6 fps from boring the valve a tad more. Since I have enlarged the inlet to the valve as much as I could, the next step was to increase the output of the regulator on my 13 ci tank. After shimming it with a larger washer I ended up blowing the 3k burst disk at only 2400psi. Crying or Very sad

I have some more on the way and hopefully I will be able to increase the output to between 1800-1900 psi.

I can't think of any other area to improve flow to increase the velocity higher than 870fps using 25.4 gr JSB Kings @ 1600psi. Is the disco valve able to handle a 1/4" throat without messing up the seat? Would that help any? going from .242 to .25

rsterne · Moderator

I personally would not recommend that you use more than 1600 psi on a 2260 tube.... The regulator, to protect the gun from overpressure in the event of a regulator failure, should have a 1.8K burst disc on the downstream side.... The Disco valve is too short to cover the roll-stamped area of the 2260 tube, so part of that area (which is weaker) will be pressurized unless you use an extended valve front end to move the O-rings forward.... While a Disco tube is rated at 2000 psi, I wouldn't subject the roll-stamped portion of a 2260 tube to that much pressure....

I assume you are using Disco valve retaining screws to locate the valve.... We don't know how strong those are, but assuming mild steel, they only have slightly more than a 2:1 safety margin at 2000 psi.... If you had a regulator failure and a 3K burst disc, and the tank was full.... you end up with 3000 psi in the tube.... That's really pushing it on the stock screws.... Therefore, unless you upgrade the screws, that is another reason to stick to a 1.8K burst disc.... and a 1600 psi maximum regulator output....

Don't despair.... check out this thread, it's similar to what you are doing.... http://airgunhome.com/agforum/viewtopic.php?t=8104

I achieved well over 900 fps on 1600 psi with 25.3 gr. JSB Kings.... All the details are there.... Throat size was 0.234" BTW....

PS, I ran the numbers through my spreadsheet.... With no other changes, dropping my gun from a 24" barrel to a 19" barrel should lose about 45 fps.... As I suspected, you're pretty much there with the barrel you have.... Mr. Green

Bob

Yellowdman · New Member

I've got a custom I built based off one of my AS2250XT's using a Don Cothran stainless HPA 2260 tube cut down 1 inch, B&A MaxFlow Valve that I tweaked to flow air, I don't run a valve stem spring and the back part of the max flow valve is drill out and polished, reshaped delrin valve stem that has a o-ring groove ground into the tip to keep it falling through the valve into the airtube. Drilled the exhaust port and barrel port to just a tad over 11/32 and I use a 1/4" poly tube. I put a crosmods AS adapter on and made a new air transfer tube out of stainless tubing and extended it to the brass end cap I made, I used the crosman transfer tube blocks. It's got a heavy hammer spring in it I stole from my newphews paintball gun. I made hammer cocker handle cause it was hard to cock with the bolt probe. It's a stainless Don Cothran breech with a 19in .25cal LW barrel and a custom bolt probe I made. It will sling jsb 24.39 exacts and 26gr polys at 950fps on 1600psi and 990-1000fps with 2100psi of air. It launches 43gr Eunjins at 860fps or 70.6 fpe! It's an airhog plus it's loud and proud! Laughing

It will shoot through 2x4's at 40ft with no problem well except when you shoot a knot. With the 13ci tank I get 5 full power shots before I hit the regulator cut off and the power starts to drop but it still gets great numbers down to 1600psi and with the 22ci tank I get more like 7-8 full power shots. It's accurate too! I might try upping the pressure to 24-2600 psi and see what she'll do. I've got plans to build another one based of this design and it will be a .25cal repeater. It will be down the road though cause I just got a .25 Mrod and I'm gonna have fun with it.

end plug

pic of the rifle with the 22ci tank installed sitting next to my Mrod

Also got a tricked out AS2250XT that spits out .22 14.3gr @ 950fps on 1600psi running through a tricked out B&A 2250XT valve. It was my first go at modding. The scope you see on it is on the Mrod right now. Laughing

Sorry didn't mean to thread jack but I had to show what I got.
My name is Dave and I'm new to this forum so Hi everybody! Cool

rsterne · Moderator

Yellowdman · New Member

Thanks Bob! It gets about 20 shot's total on the 13ci tank regulated at 2100psi output. It gets 5 maybe 6 full power shots from 3000 to 2100 psi then I just refill it. I remember the last shot clocked at 860fps with a 25.39gr pellet at about 1000psi and then there wasn't enough pressure in the tank to keep my valve stem closed. It does get a lot better shot count when I put the 1600psi regulator on but that reg is on my 2250 though 99 percent if the time or I would just put it on and use it.

rjorge · New Member

That is a very nice build there Bob!!!! I can't believe how efficient that thing is! Shocked

I want one just like it! :D
I have taken some precautions pressurizing the 2260 tube like you have mentioned. New screws and I only pressurize the tube when I am shooting. I also have an extended valve end on order from Joe, and I am waiting on Don Cothran to answer my emails! I placed an order for a 2260 SS tube a week and a half ago, but I havent heard back from him...

What a nice collection Dave! While I was in college I had access to the Engineering machine shop and I made several custom pieces on a lathe. Here is the link to my first build. http://www.crosman-air-pistol-owners-forum.com/board/index.php?topic=3649.0 You got me looking even harder at a mini lathe now! The little machine shop 7x12 are on sale right now for $699.95 Very Happy

I just need to go ahead and get one. It is good to know that I can achieve my goal @ 1600 psi. I just have to figure out how! What is the size of your barrel port and what kind of bolt tip do you have??

My father in law had a couple of extra 3k burst disks, so I put the reg back at 1600psi and tried a couple more things that could be restricting the flow. The first one was the bolt. I currently use a flow through bolt and I changed it to just a regular tip that pushes the pellet a little past the barrel port. I shot a couple of strings from 2000psi down to 1600psi.

JSB Kings
876.5
Benj Domes
856.0
852.5
Beeman Kodiaks
832.9
830.9

JSB Kings
876.6
876.2
876.2
872.9
874.3
863.9 Below Reg.

So I was able to gain a little more fps. Still far from what I want! I went ahead and bought some shims for my reg to up the pressure to 1800 psi. Hopefully it will pump it up to the low 900's + better efficiency! I probably need to change the spring too.

rsterne · Moderator

rjorge.... Don't forget, the cocking knob on Dave's gun will add quite a bit of mass to the hammer.... I'm guessing the hammer isn't stock either, unless he annealed it to drill it and then re-hardened it.... Not sure what spring he is using.... but certainly you can push the power on a .25 cal 22XX/Disco by using a valve with larger ports and increasing the hammer strike....

As you can see by my thread on my 2560, I usually push the hammer strike until I find the plateau in velocity and then back it off until the efficiency increases.... It makes a huge difference in the number of shots....

Bob

Yellowdman · New Member

Hi rjorge I checked out your first build and I like what you did. I've seen a couple different people make a extension for the valve and had impressive results.

Yeah Don C. can be a hard guy to get a hold of. Even though he says he's retired he's really not. He makes custom parts for a lot of different companies and his pellet gun hobby takes a hit from it. If you email him a couple times he tends to get back to you.

My transfer port tube size is 1/4x.17 poly. I take a sharp .18 drill bit and work very slowly by hand to shave of some of the interior wall and bore it out a little. My barrel breech port is 11/64" or just a tad over like the valve exhaust port. I touched up the port holes with my dremel so it made them a little bigger than 11/64". I've made 6 different bolt probes and I've narrowed down a couple shapes that seems to work well with different pellets. I like through bolts a lot and I made one but it was really difficult to get the pellets to push in and I bent a few bolt handles while trying. Since it pushes on the pellet skirts it didn't allow the skirts to compress into the barrel smoothly and it ended up cutting off part of the pellet skirt. Here's a couple pics of the two designs that are working for me right now. I'm tempted to make one shaped like the marauders bolt which is like a flow through bolt but it's half open. There are so many different pellet skirt shapes that it's hard to make a good probe. You'll notice that on the tip of my valve stems I made a bulb shape. It's perfect for the short pellets with shallow skirts and pellets like the benji's and eunjins with deep skirts, it pushes them all just past the breech port for a perfect fit in the barrel. The pic of the bolt in the rifle is a little bit fatter towards the o-ring, my thinking is that it helps direct the air flow better but it's pretty close between the two with only a couple of fps difference. It does seem to work better with heavy 31-46gr pellets though.

My hammer is stock. To be able to drill the hole for the handle I marked the spot and used a grinding disc in my dremel and ground the hardend material away so I could drill a hole. I honestly don't know the spring size but it's big and I had to drill out the hammer and the AS adapter to allow it to fit without any binding. It's pretty stiff and I think it would be good up to 2800psi maybe even 3000psi. I have to run a lighter spring for 1600psi.

I bought a mini lathe last summer just so I could make my pellet gun parts and I've been having a blast with it. It's a pretty small one so it's hard to make the big parts but I'm making by. I recently lost my job and I'm trying to get a government grant to go back to school for CNC training so I can play with the big machines Laughing

We'll see what happens, I don't want to go back to retail.

I've got this extra bolt that you can have if you want it. Email me your address and I'll ship it to you. The tip isn't as bulbed as the other two but it still worked pretty good. I can't promise that you'll see an increase in power but it can't hurt to try it. Here's a pic of it.

robert w · Senior Member

power dont come easynice job