GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: sshewins on December 18, 2013, 04:30:14 AM
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Hey guys, I just got the 24" .22 barrel and steel breech kit today, so you know I had no option, but to install them both or face crosmaniac shame... Haha
Anyways, kit came with all the required hardware needed. BUT, when I tightened the rear breech screw, (yes it was shorter than the stock screw) the bolt wouldn't open fully. So, have any of you pried out the bolt o ring from the plastic breech and rolled it down the threads of the new, short screw? Well, I did, and it did lift the screw enough to not get hung up on the hammer spring. I think its fixed, but then again...
I suppose I'll trim the screw down later, but right now its workin!!
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Good job.
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If it works it works. As long as the breech feels solid and it cocks repeatedly I would call it good.
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It feels real tight. However, on a side note, I draped some tissue over the breech and fired it. Me thinks I have an air leak at the transfer port. Not big, but the tissue gave a slight cough when I fired it. Guess I'll have to get an o ring or two. Do I need one at both top and bottom, or just top?
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Scott,
The transfer port O-ring is a rectangular cross-section. If it has been damaged or lost, you'll probably have to order a replacement from Crosman. They are not commonly available.
Since yours is a .22 cal, you're better off with a short piece of poly tubing instead. No waiting for USPS and better airflow. What you want is the 0.25" OD, 0.170" ID kind typically used as a water line for built-in icemakers. Length and shape can be found the writeup linked in my signature.
But just in case you need to know, the O-ring goes against the valve. The short flange of the brass transfer port goes in to the O-ring, which leaves the long flange fitting against the barrel port.
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I like cheap and effective!
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I have a question before I start the poly tube thing. With all the talk of stripped breech screws, how much of a pain is getting the correct height the first time? Any guesses on what I should cut the length to?
And as always, thanks in advance. :D
After re-reading your response, it would appear I should visit you link. Oops
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I'm probably sounding like a broken record, but head to the hardware store and get a slotted #4-48 x 1/4". Chuck it up in a drill press (or handheld drill or Dremel) and spin the head against a file to reduce the diameter to fit the counterbore in the breech. Then when you tighten down to squish the transfer port, do so with complete confidence that the screw is not going to let you down.
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Broken record or not, that's some sound advise right there. Looking through your earlier write up, you had the poly tube on a stick or rod or something (for spinning the chamfer on). What was it, if you don't mind me asking? Save me the trouble of finding something .17 in diameter.
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his article says .....
" ....... Making new transfer port
This modification improves air flow from the reservoir into the barrel behind the pellet. The stock transfer port has an inside diameter of about 0.137”. Using common polyethylene tubing with an OD of 0.250” and ID of 0.170” (ex. often used to plumb refrigerator icemakers), you can fashion a new transfer port which has about 60% more crosssectional area. To form a good seal, it is important to obtain nice square cuts. To do this, I placed the tubing onto the shank of a snug-fitting drill bit. Doing so keeps the tubing from collapsing when cutting it with a sharp razor. Cut the
tubing to 0.20”L, then taper one end at approximately a 45° angle. I formed the taper on mine by rotating
it against a sanding drum spinning in the drill press.
The new transfer port is now ready to be installed. Place the blunt-cut end against the valve body and
the tapered end to the breech and barrel. ...... "
https://www.dropbox.com/sh/n3ro6yphs4ql2l4/orhYCuIPBw/Crosman%202289%20mods.pdf (https://www.dropbox.com/sh/n3ro6yphs4ql2l4/orhYCuIPBw/Crosman%202289%20mods.pdf)
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When I bought a hot valve from Mountainair it came with some of the 1/4"OD poly tubing to use as a transfer port.
In the directions it said to mill a short 1/4" recess in the barrel to accept the poly tubing. There had already been a recess drilled in the valve. The drilling/milling was done to accept the square ends of the poly tubing. I cut the tube by finding a drill bit end that would fit inside the tube then using a exacto knife. I used approx. 1/4" long tube and it had a little "squish" when the breech was tightened down.
I have not tried beveling the tube but it sounds like less trouble if the results are the same.
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Thanks Jeff. I clicked on the pic (on my alleged smart phone) and went by that. My apologies for looking stupid.
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Jason, I am curious if you also drilled the opening in the barrel 11/64 to closely match the new transfer port. I have the material to make said port, but its kinda tricky to make this stuff in the sleeper of a semi (I drive otr for a living) anyways, I started thinking if the TP is opened up, shouldn't the opening in the barrel and the valve be opened to match? Seems like the bottle neck effect would occur otherwise.
I went back through the PDF and saw nothing covering this, one way or another.
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I did not enlarge the barrel port on mine. There is not a lot of meat to the barrel so I would only attempt it if I had the proper equipment to mill a precise flat-bottomed seat for the poly tube.
Seems like when I looked at it, the hole in the .22cal barrel was not nearly as anemic as the brass transfer port. The fact it was tapered led me to shape the end of the poly tube to match to help form a good seal. My thinking was, a smallish but well-sealed transfer port beats out a large but leaky one.
Can you tell me the stock barrel port size? I want to say it was approx 0.155 but I don't know why I would recall. I wouldn't port larger than 0.162" which is 75% of the pellet diameter, otherwise you may damage pellets when chambering them.
Also, in case it wasn't mentioned previously in this thread, you don't want the poly tube in a .177 cal because based on Bob's testing, it will tend to lose velocity.
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I opened up the 1322's stock transfer port to about .160 also the 14.5" barrel, air passage in valve is opened 3/4 of way to exhaust poppet
seat, shimmed the pump cup with guitar pick (Daisy 853 foam wiper twist and doubled takes up the side space and provides a wiper) those
with enlarging valve volume got me about 650 fps...