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Jaxom · Senior Member

Got off on a bit of a tangent in my other thread about converting a discovery to .25 cal. Sorry about that. I got a ton great news in the last few days, so things are really looking up for me now. Things keep going this way, I could possibly have my kt project done and my discovery at least started before the end of the year.

I've done even more research on discovery's. Haven't found any step by step guides on converting them. Although there is alot on tuning and doing some mods on them.

Although I've been given advice on an ag gunsmith that could do some of the work, I'd like to do as much of it on my own. I still apperciate the advice though...thanks.

Let's say I've bought a stock discovery in .22 cal. Then I've ordered a lother .25 cal barrel. My first concern would be how to get the barrel and breech to work and play well together. Ideally, I'd love to ask if RJ machine could make me a long riser breech. But I'm not sure if he'd be willing to do that as a one off. Of course I'd also need a matching extended bolt as well.

The next issue to resovle is the gas tube and valve. Pellets in .25 cal range in weight of 21.6gr all the way up to 61gr! Most range in the mid 20's to mid 30's though as seen on pyramyd's website. In order to push these heavier pellets I'll need more pressure. To achieve higher pressures, I assume I'll want better gas tube that can handle the pressures in the first place. Then a better or tuned valve so air flows better.

As notied in many threads on here, you can only push the pressures so far and then you end up with diminishing returns. What I'm understanding is happening, is the hammer spring isn't strong enough to hold valve open long enough to allow the higher pressures to flow through.

I think I may have a solution to this. First would be to contact a gun supply and accessory site such as say Midway USA. and see if they might be able to assiste with a stronger spring they could recommend. May even have to send them one of the 5 I've recieved from Crosman to give them an idea what I'm using and what I need to replace.

A second option, is to contact a company that makes spring directly. Explain to them what you are looking for, and that you need something for a prototype you are working on. Most companies are more then willing to send out samples of their product in order to potentially get future orders. I don't want to go of on that buisness tangent again, but if this does work out, I may just end up making a large order from them anyways, so I'm not scaming a spring company in anyway.

I would really like to do this. Anyone have any other suggstions or comments? My only real alternative that I can think of is to get a 2240 or 2260 and convertiing that, and that would mean turning one of those into a discovery and modifiy it at the same time, that'd be a major headache!

Thanks,

Jax

yourdaddyjoe · Supporting Member

As per your last paragraph.... But that is half the fun.... I love my wana be disco 2260 carbine.... 955 fps and 10 shots per fill, ain't that bad...

rsterne · Moderator

More valve volume will be important.... the Boss Max-Flow valve should work.... Wink

I have a stronger hammer spring coming.... I'll let you know how it works on 2000 psi.... which with a bigger valve should be enough for .25 cal.... Shocked

My understanding is that the Disco tube is OK up to ~2500 psi.... I read somewhere that the tubing Crosman used had a burst pressure of 10,000 psi, which with a 4:1 safety margin (standard) would mean that the "yellow" range on the Disco guage (2000-2400 psi) should be safe.... I mean wouldn't Crosman have made the colour red if it wasn't?.... Rolling Eyes

I found a spring company (Trakar in Ontario, Canada) that has an incredible variety of compression springs.... They list a spring with the same specs (diam, wire) as a Disco spring as 7.2 lbs/in.... and have others at 11.4, 14, and 18.5 lbs.... all the same OD and length.... Their minimum order is only $30.00.... Cool

What I'm saying is that it shouldn't be that tough a project.... Mr. Green

Bob

Jaxom · Senior Member

Bob, Joe...you're both highly respected in doing these things, which would be more effcient project?

No matter which I would choose to use as a platform, I would need an after market breech made. Besides RJ Machine, who else makes breeches for either the disco or 22xx's?

OR could I order a metal breech from crossman and modify it enough to accept a .25 barrel?

Same goes for the extended bolt. I would need one of those made as well in as much I don't have a lathe right now.

Bob, since you're handy with the numbers, you wouldn't happen to know what the pressure ratings are for 2260 tubes are would ya?

rsterne · Moderator

The 2260 tube, as far a Crosman is concerned, was never designed to have ANY pressure in it.... only the valve and powerlet were pressurized.... Shocked

Having said that, the QBXXs use the same size tube, and they DO have a factory bulk-fill setup.... It would make sense, then, to assume that in the case of the QBs, they are designed to be safe with CO2 up to 120*F.... so check out this chart:

http://www.warpig.com/paintball/technical/gasses/co2pv.gif

Note that at 120*F, the pressure in a properly filled (ie not overfilled) CO2 setup can reach 1900 psi.... however CO2 bottles are rated at 1800 psi, so that would SEEM to be a safe maximum using a QB tube.... Is the Crosman 22XX tube the same material?.... who knows.... but typical DOM tubing of the same size is rated at 2000 psi with the typical 4:1 safety factor.... Joe and I both feel that you should NOT push a 22XX tube past 1800 psi, and in fact I recommend that you have a 1.8K burst disc to make SURE the pressure won't go above that.... 1.8K burst discs, BTW have a 200 psi tolerance, so that means that it might let go at 1600 psi.... or at 2000.... Rolling Eyes

Understand, I'm not recommending that you put ANY pressure inside a 22XX tube.... but for myself, I feel confortable running a 1400-1500 psi regulator with a 1.8K burst disc on the downstream side.... Please note that the Disco tube is good for a bit more.... judging by the guage, 2400 psi should be OK (it's yellow up to there, red beyond).... and I read somewhere that the burst pressure on the Disco tube is 10,000 - 11,000 psi.... which means it is NOT good for 3000 psi with the recommended 4:1 safety factor.... From what I understand, anything not engineered with a 4:1 safety factor must be hydrostated to be proved safe.... Shocked

To answer your question.... I haven't a clue what a 2260 tube can withstand.... but I personally wouldn't push it past CO2 design pressures.... ie 1800 psi.... Wink

Bob

yourdaddyjoe · Supporting Member

According to my source at Crosman... The gas tube all start from the same tube stock.

The real info I need is proprietary and they won't share....

I was lucky to get that much info. from the source.

From dealing with "Drill Pipe" and touring the manufacturing plant in OK...

The only difference I can fathom between the Discovery/Marauder tubes and the other 22xx tubes is the hardening processes...

So whether the Disco/Marad tubes are heat treated or Induction hardened to meet the pressure requirements... I don't know...

Did I babble or do you understand my ramble....

yourdaddyjoe · Supporting Member

Here is some interesting reading on Induction Hardening.

http://en.wikipedia.org/wiki/Induction_hardening

During the week I spent at the factory of Charles Machine Works (Ditch Witch) for training... I was soooo cool to watch the process.... The coils would be Ice cold while the metal in the middle was red hot....

yourdaddyjoe · Supporting Member

Hey Bob.... Your link is "Forbidden".

yourdaddyjoe · Supporting Member

This is trippy

http://www.youtube.com/watch?v=y_-Iv9FddOU

Even Better! How bout "Red Hot Ice"
http://www.youtube.com/watch?v=aLwaPP9cxT4

Jaxom · Senior Member

I'm sorry guys. I do read what you've posted, I just had a blonde moment there. Of course a 2260 tube wouldn't be able to hold the same pressures as a disco tube. Just the nature of the beast Co2 pressures vs HPA/PCP pressures duh!

That being said, it looks like, should I want to go this route, using a disco tube would be the best solution. After all, it has the higher ratings to start with and should I want to push the pressures higher using a heavier spring, I could do so and know it would be safe to do so.

I think before I go further, what I really need to do is read up on your 2260-disco converstion project Joe.

Jaxom · Senior Member

Okay, did that reading. I think, since I'd be starting from scratch because I don't happen to have 2240 "just laying around". My best bet w ould be to save my pennies and just buy a discovery and modify from there.

Mind you I still have my 2300kt project to finish. Just gotta get a few more dollars for some bits I want from Mountain air, then the bulk bits from joe. Should have the parts ordered from mountain air within the week.

My major concern of course since I want to change to a larger, heavier caliber, that I have enough engergy to push those heavier pellets down range.

Choice #1 is to go with the stock discovery valve, then modifying per what joe has suggested.

Choice #2 is using a boss valve that I will have to drill and tap it so as I can mount it in the disco tube.

Bob, you wouldn't happen to have a chart comparing a disco valve vs a boss valve do ya?

Of course this whole project would come to a fast end, if I cannot find somewhere to get a breech and bolt that will accomadate my .25 barrel. Suggestions?

rsterne · Moderator

Just got a B&A Max-Flow Valve today and I've drilled and tapped it so that it can mount in my Disco.... As soon as I can get the time, it will be installed and tested.... Cool

Patience, Grasshopper.... Mr. Green

I did some measurements of the B&A.... I don't want to publish their dimensions, but I can say that it's slightly larger inside than the Disco one I modified.... plus the tapered front end is larger.... The angled transfer port is about the same size as a stock Disco port, however (and therefore slightly smaller than the valve I'm currently using).... I have no idea how the 22XX valve poppet will work with HPA.... It may need a Disco exhaust valve, time will tell.... Wink

Bob

PS - Joe.... that link worked when I posted (and still works for me).... looks like they have blocked access.... Evil or Very Mad

yourdaddyjoe · Supporting Member

Bob... you will want to use your Disco valve stem if you dont want a leak down the road. I just replaced mine after blowing out 3 2250xt stem seals. The over molded ones work much better.

rsterne · Moderator

hmmmmmmmmm.... so much for the idea of using a Max-Flow valve without mods (other than mounting it properly).... Rolling Eyes

I also notice that the opening pressure is less (spring looks the same although I haven't tested it yet).... and then of course it doesn't have the valve stem sealing O-ring like a Disco valve either.... Rolling Eyes

Anything else I need to change, Joe?.... Faq-U

Bob

yourdaddyjoe · Supporting Member

Not that I can think of yet Bob.... But then again... I have only had one cup of coffee so far today.

Yea.... that soft seal of the 2250xt stem is fine for Co2... It just can not handle the pressures of HPA. The over molded Disco stem works much better. Or... our good friends at Mountain Air have Delrin valve stems...

http://www.mountainaircustomairguns.com/New_accessories_page.htm

I put the same set up in Guys 2250/QB79 tank conversion after he wore out the B&A.... God knows how many rounds he put through it.... Lets face it.... we shoot a lot...

The stem guide area wore down enough that even after replacing the valve stem... the best we could get out of the original B&A was about 450 fps... turned out that it was leaking around the stem. This is the first time I have heard of someone wearing out a B&A valve. Way to go Guy....

I moded up a stock crosman valve to close to the same specs, minus increasing the internal volume and instantly went to 955 fps. I should have used earplugs... my ears were ringing the rest of the day...

Yea I was lazy... but I wanted to get out and shoot...

With the extra volume in the connecting tube between the block and valve... I did not see the benefit of increasing the ID of the stock crosman valve... BTW... Guy is happy with 955 fps in .22

See... halfway through my second cup and my train of thought got back on track...

One more thing on the B&A.... Polish the stem seat area into the exhaust port. The one I did use was a little rough an contributed to the 2250xt stem seal failure.

I suggest using the appropriate lube on the stem to reduce the wear on the brass... Diver's grease maybe? I am sure you don't want a petroleum based grease in there...

Metal is metal and it will wear out...

Please do not take the above statements as knocking B&A. Straight out of the box "it is the best aftermarket valve" you can get you hands on.

Even with the stuff I make... there is always room for improvement. After all, I know there are smarter and more talented people out there... Like you, Bob.