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Unread postAuthor: mark.f » Wed Mar 16, 2011 10:48 pm

Badabump.

Can't believe I didn't reply to this when you posted (didn't see it, probably). So first of all, sweet job! Beats my little 1377-base rifle any day of the week...

Can you give a comparison between the tube material and thickness of the tubing you used and the standard tubing for a 22xx? All I have been able to dig up is an OD of 7/8" for the 22xx tube. Of course, since you didn't start with a 2240, I'm guessing you don't know offhand. I even tried looking for the o-ring sizes on some custom parts which fit in a 22xx tube, but they don't list them, of course. :roll:

I'm looking at implementing something like this with a much lower shot per fill count, but with parts purchased from Mountain Air, and some reinforcing of the valve in the tube. I was planning on using Walter's method of securing the valve (if you don't browse the Crosman forums, it's simply using some countersunk screws with the heads in shear with the valve tube and body), although I believe I'll have to borrow a better drill press or outsource the work to a machine shop.

Again, great job!

EDIT: forgot to mention I would be using CO<sub>2</sub> pressures of 1200 PSI max.

EDIT II: Well, as luck would have it, I found the dimensions I was looking for right after bumping a nearly year old topic. 7/8" OD, 0.65" wall. By my rudimentary calculations it should be fine at 1200 PSI, although a simple hydrotest would be in order to test my valve security...
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Last edited by mark.f on Wed Mar 16, 2011 11:29 pm, edited 1 time in total.
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Unread postAuthor: Hotwired » Wed Mar 16, 2011 11:28 pm

Tbh, I've never actually understood how the air from the hammer valve is getting to the barrel in these.

Anyone feel like spelling it out, I'm clearly missing something.
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Unread postAuthor: mark.f » Wed Mar 16, 2011 11:34 pm

The hammer valve unseats and allows air out the side (top), and up behind the pellet. If you look at the below image, the outlet would be at the top. Just a note: this isn't a stock Crosman valve.

<div align="center">Image</div>

To further clarify, the bottom bit is a (delrin) valve stem. The metal extends out the back, and a spring sits on the "ridge", sealing the valve. When rapped forward, air passes past the reduced diameter portion and out the top port.

EDIT: Another decent link for a multipump.
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 16, 2011 11:40 pm

Hotwired wrote:Tbh, I've never actually understood how the air from the hammer valve is getting to the barrel in these.

Anyone feel like spelling it out, I'm clearly missing something.


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Unread postAuthor: Gippeto » Wed Mar 16, 2011 11:46 pm

Thanks Mark. :)

The tube I used is .065"wall 4130 in a normalized condition. The Crosman tube is mystery metal as far as I'm concerned, but the hydrotesting that Walter did on one specimen showed that the yield strength of the crosman 2240 tube is similar to that of normalized 4130. Similar does NOT mean "the same as".

The wall thickness is roughly similar, ( have a 2240 at work I'm "tinkering" with...I'll measure it in the morning) but keep in mind the crosman guns have a roll stamp...although this region WAS included in Walters hydrotest, there ARE folks who get nervous about pressurizing it.

When in doubt...play it safe.

Walters method of securing the valve is a darn good one. Used it on this build, and a revamped QB79 in an AR stock.... made a new tube and tank block with an HONEST 3000psi rating, extra screws countersunk into the (custom) valve too. Neat rig...running on 850psi regulated 13cuin...lots of HOT shots....did a "DYI" to my backstop .... @ 40yards. 8) :lol:

Make certain you use a good grade low profile socket head cap screw.

Aside...Funny you should mention Walter :) ...if all goes according to plan, I'll be meeting him (first time) on Saturday for the first "Alberta boys field target" outing. 8)

Bunch of rednecks laying a hurt on some gamo squirrels. :lol:

Later

Edit: Holy SHITE do I type slow. :roll: :lol:
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Unread postAuthor: mark.f » Wed Mar 16, 2011 11:52 pm

Thanks Gippeto. I definitely feel the need to play it safe, what with applying 530 pounds of force to a component normally seeing several* and aimed right at my face. Some sort of basic hydrotesting with a modified jack or grease gun is in the plans when I start working.

Wish I had the facilities to custom make everything, but the Mountain Air components ought to work well. :)
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Unread postAuthor: Hotwired » Thu Mar 17, 2011 6:50 am

Cheers mark/jack, was mostly bothered by the way barrels seemed to be sitting on top of the reservoir without apparent means of connection.

Anything in particular keeping the port between reservoir and barrel sealed?
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Unread postAuthor: inonickname » Thu Mar 17, 2011 7:05 am

Hotwired wrote:Cheers mark/jack, was mostly bothered by the way barrels seemed to be sitting on top of the reservoir without apparent means of connection.

Anything in particular keeping the port between reservoir and barrel sealed?


Pressure forcing the seal on the valve against the seal face?
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 17, 2011 7:14 am

Hotwired wrote:Anything in particular keeping the port between reservoir and barrel sealed?


Image

btw here's an enhanced view of the internals originally posted by Gippeto:

Image
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Unread postAuthor: Hotwired » Thu Mar 17, 2011 5:51 pm

inonickname wrote:
Hotwired wrote:Cheers mark/jack, was mostly bothered by the way barrels seemed to be sitting on top of the reservoir without apparent means of connection.

Anything in particular keeping the port between reservoir and barrel sealed?


Pressure forcing the seal on the valve against the seal face?


No, I'm meaning the short upright section joining the barrel to the valve assembly, how it attaches to both parts and to what extent it is sealed.

I mean it looks like its a nipple screwed into the barrel section and being merely held down on the valve port (possibly on an o-ring) by force from the screw at one end and the barrel/reservoir clamp at the other.
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Unread postAuthor: mark.f » Thu Mar 17, 2011 6:09 pm

It's neither. It's shaped exactly like the part you see in the drawing Jack posted and is made of some type of plastic (had to get a replacement after loosing mine :oops: ). Its reduced diameter ends sit through the transfer port and breech port and are held in place by the connection between the breech and gas tube themselves.
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Unread postAuthor: Gippeto » Thu Mar 17, 2011 10:22 pm

Hotwired wrote:No, I'm meaning the short upright section joining the barrel to the valve assembly, how it attaches to both parts and to what extent it is sealed.

I mean it looks like its a nipple screwed into the barrel section and being merely held down on the valve port (possibly on an o-ring) by force from the screw at one end and the barrel/reservoir clamp at the other.


Close enough to accurate. The "o-ring" in the stock setup is square in cross section...more like a quad ring. The seal on the barrel end is metal to metal..no threads. Some folks give a wrap or two of teflon tape to the small metal piece (transfer port) to facilitate an improved seal.

Common practice is to replace these two pieces with a single piece of 1/4" od plastic tubing such as ice maker tubing or 1/4" plastic air line.

Occasionally referred to as the "poly tube mod". :wink:

http://www.network54.com/Realm/CFTech/Bioportupdate.htm
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Unread postAuthor: Gippeto » Tue Jun 07, 2011 11:11 pm

Actually found a little bit of time to play with this of late. Was firing the 15.9gr exact jumbos at a peak of 712fps using a 2240 striker spring. Changed to a Discovery striker spring, and they are now blasting out with a peak velocity of 920fps. :D

But the shot count (12 shots with a 90% cut off) sucks. :roll: Will be doing some more work I'm thinking...would like 20 shots with a 95% cut off. (lowest velocity on either end of the string is 95% of the peak velocity)

Will be reducing the diameter of the transfer port, increasing fill pressure and striker spring preload. Likely still need a heavier valve spring.

Getting there. :)

Later.

Newer pic...

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Unread postAuthor: LovableAirGuns » Wed Jun 08, 2011 4:45 am

that is so nice im currently building one but mine probably more on the ghetto side but just a question did you build the striker and valve?
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Unread postAuthor: Gippeto » Wed Jun 08, 2011 9:12 am

The striker is a copy of the one in my 2240, could have just bought one, but then I would have had to wait on shipping. Didn't take long to make.

Made the valve too. Should be a pic of things at the beginning of the thread.

:)
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