Aluminum13-XX FTP Kit from S&A

While waiting for my latest parts order for the 78's to get here, I decided to do a little work up with one of the kits I had ordered in from Eric a while ago. Figured I'd go with .177 as I'll soon be doing one of the 78's in that caliber.

I wanted to achieve a couple of things:

Get close to 500 fps, with minimal pumps.

Get close to the 560-600 fps that most of the European competition guns are tuned for.

Platform is a 22-89 back-packer, with 24" .177 bbl, and SBK steel breech kit aboard.

I went with the stock 13-XX hammer spring and valve-stem return spring, just to try and get this into a neophyte type of experience for those considering it for the first time. I didn't port the exhaust hole in the valve, or manipulate the the stock transfer port in any way. It is a 22-89 transfer port. I did not modify the piston, or valve in any way.

For you guys that have been around for a while, there are modest volume gains to be made over what's already in the package. The valve face could lose up to .008" or so, and still be fine. The piston face could with-stand about .006". I'd reduce the diameter of the rear piston half of the piston assembly, by a couple of thou, just to smooth out the pumping a little.

I tested with the 8.2 gr RWS Meister.

5 pumps averaged 513.2 fps over ten shots. Just a hair over. Going to a heavier pellet like the Cr. Ultra Mag would probably give numbers in the upper 480's.

7 pumps averaged 584.8 with the Meister- very close to what the big names are tuning for in their upper end competition guns.

I think the package is a good one. The lock-nut system is robust and strong, with no slipping of the final adjustments. The new parts should be dis-assembled, and cleaned before installation- there is a bit of aluminum powder in the parts from the machining process...

Regards,

Doc Sharptail

Nice review.... In .177 it's a good idea NOT to start fiddling with the ports in any way, the stock ports are plenty big enough for up to 800 fps, and in fact if you start hogging them out you are more likely to lose velocity than gain.... That doesn't apply in .22 cal, where going to 5/32" ports (including the barrel) will show gains.... You should NEVER drill out the barrel port in a .177 Crosman barrel, the 0.134" port is as big as you can go without causing loading problems anyway....

Bob

Here's a quick group with the meisters, 580'ish...

http://i174.photobucket.com/albums/w...ps3dd2aaa8.jpg

This was shot with the little 4X, almost antique, Weaver 3/4" steel tube, alluded to elsewhere on this forum...

Regards,

Doc Sharptail

Great review Doc

I only have one piece of input here and that's only because I've spent a lot of time fiddling with this.

Reducing the diameter of the rear piston wont help it get smoother it actually just increases the point loading on the sharp edges of the slot as seen in the diagram. The most ideal would be to increase the diameter to within a few thou of the ID of the tube. That would give the greatest bearing area and the lowest point load.

The trouble is the slots are stamped and that bends the edges of the slot inward. which precludes using a perfectly sized body.

Attachment 952

How about the largest possible piston with a 5/16" flat milled along the bottom where the slot is so that it doesn't touch the sharp edges?.... not where the O-ring is, of course....

Bob

I wasn't aware that aluminum could with-stand the stamping process... It is extrudable in some forms, so I guess anything's possible.

My experience with the pivot arm end section of the FTP assembly comes from hand fabricating them in brass- with some pretty crude methods for cutting the slot. Reducing the rear section diameter helped smooth the the pumping action out a lot. I had it suggested to me to mill an O-ring groove into the rear section- smaller than the piston head- to smooth the pumping out even more. It never had to come to that, though...

Regards,

Doc Sharptail

I think Sean is talking about the slot in the tube, Doc, not the slot in the piston.... The tube is often not round and has sharp edges on the inside of the slot.... My suggestion of a flat on the piston a bit wider than the slot was to eliminate contact there....

Bob

Quote:

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Originally Posted by rsterne

How about the largest possible piston with a 5/16" flat milled along the bottom where the slot is so that it doesn't touch the sharp edges?.... not where the O-ring is, of course....

Bob

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Ya...I like it. That would completely eliminate the possibility of point loading on the sharp edges of the tube slot.

I thought Sean was discussing the slot on the rear piston section :icon_redface:

To be honest, I haven't had much trouble with the tube slots on any of my 13-XX's.
They are done much better on the phase 1 13-22, but there seems to be little concern for me in that inch or so of travel on current production...

Regards,

Doc Sharptail