Some more 1377 to .22 conversion velocity numbers

Some more 1377 to .22 conversion velocity numbers

Joined: March 21st, 2009, 1:34 am

June 16th, 2011, 10:43 am #1

Found this old thread while searching for some velocity numbers on various barrel lengths for a 1377 converted to a .22.

http://www.network54.com/Forum/275684/t ... Velocities

I have a current gen 1377 with crosman steel breech and shoulder stock. One year ago I added an 18" .177 barrel and a homemade hammer spring guide (no preload) and achieved 650 fps on 12 pumps with CP 7.9's. I found the tree rat stopping efficiency of this combo to be less than ideal (compared to my .22 Disco), so I ordered a 2260 barrel, and disco .22 bolt probe. With the stock 24" barrel and disco probe installed, it pushed CP 14.3's to 560 at 15 pumps, and retained just a light puff of air. Not exactly what I was after, so I found some more info on "stuffing" the stock plastic piston to reinforce it, and also some info on changing the valve spring out for a lighter one. I also decided to cut the barrel to 20". I did the stuffed piston and the lighter valve spring in two separate stages in order to see what each did on its own. Stuffing the piston was worth about 25 fps average increase at all pump #'s. The lighter valve spring was worth another 30 fps average at all pump #'s.
Now the gun does 520 @ 10 pumps, 585 @ 15 pumps, 625 @ 20 pumps, and 660 @ 25 pumps, and dumps absolutely all of the air. I tested 30 pumps, but found it only increased to 665, so I assume I am now being limited by the stock transfer port and the fact that I did not remove any material from the valve stem or port angle.
Nevertheless, it is a potent little thumper now, and I like the option to vary pumps over a wide range for low or high power.

Thanks to all who post on this forum, I enjoy reading about the modifications, and it is a wealth of information for all of us do-it-yourself'ers out here.
Last edited by 2fastsnake on June 16th, 2011, 12:08 pm, edited 1 time in total.
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Joined: March 21st, 2009, 1:34 am

June 23rd, 2011, 10:16 am #2

Well, I have to say I am pleased with the new-found critter stopping power of my converted .22 cal rig here. Nabbed 3 tree rats over the past weekend, farthest out to about 22 yards with a head shot, and found the stopping power to be immediate. No more runaways like I was experiencing with the .177 gun. I have to say, I have always been a big subscriber to the "placement, not power" school of thought, but in a sub-800fps gun, .177 just doesn't seem to cut the mustard on tough tree rats.
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