1720T + CO2 Question

[d_ray50]

I would like to ask some of you engineer type people a question . What would i have to do to shoot bulk fill CO2 in my Crosman 1720T ? Can I alter the spring in the valve and make it work . Even better what I would really like is to alter my valve so the front part will accept a 12 gram cartridge and pierce it and add the proper screw in front cap with proper length rod to hold the cartridge . I wish someone would come up with a kit for this .

[screwwork]

Edit...
Degass 1720T removing all air from tube, fill with Bulk Co2 to less then 2k PSI. Tune gun to shot at lower PSI. You shouldn't have to make any adjustments to the valve spring. You may need to increase hammer spring if you're unable to get FPS you desire. 

I got off topic.
I don't know about converting a 1720T to Co2, but the 2400KT CO2 Air Rifle from the custom shop with carbine stock, .177 or 22. - 10.1" or 14.6" L/W barrel for less than $140.00 Both the 1720T & 2400KT are single shot breech's, you can get a longer barrel, do a little trigger work and it should shoot like a dream.. Just my 2¢ worth

[fivestar45]

You will have enough striker spring pre-load to play with. Getting the power up might be a problem with the small cap valve. You will also need a larger I D T/P also for best results. I think you will like the l longer co2 shot count over the air fill.

[WyoMan]

I’ll second all of that and recommend porting of at least .140” (9/64) for the valve, sleeve and barrel.

Additionally, you may need a heavier valve return spring. I don’t know what spring is in there but the Delrin exhaust valve can be finicky to seal with a fill from empty. Especially with co2 as the smallest of leaks will freeze the valve and tube… this kills the incoming pressure and it just gets colder and leaks even more.

You may also experience hammer bounce (short, second opening of the valve) because the valve is easier to open (850 psi vs. 2000-3000 psi). A short, stiff, spring used with a modified oem hammer assembly is an easy fix:



Shown above is a 13xx hammer spring with some coils removed and a hammer with the striker flange removed. The flange was removed so the striker could be recessed inside the hammer. Both are designed to create a “slingshot gap” between the valve stem and the hammer. This works well at arresting the hammer bounce because the drop sear in your gun is dragging on the hammer when fired.

This is probably tmi for now, but like fivestar45 noted, you’ll probably like the increased shot count. Using carts with this setup would require a lot more work…

Wyo

[d_ray50]

Thanks for the information.

[d_ray50]

I have read that .110/.109 is the max useful size you can go on the TP . Is that because the valve is drilled out to .110/.109 ?

[fivestar45]

I have read that .110/.109 is the max useful size you can go on the TP . Is that because the valve is drilled out to .110/.109 ?

 The co2 is lower pressure and moves slower. So bigger is better HOWEVER...your 1720 is a .177 so a restriction to that rule would limit the T/P diameter to what won't let the pellet get hang up. In your situation I'd go with .110"-/115". Do not forget to open up the barrel port to match your new T/P dia.