Crosman 600

Vintage Crosman repeaters are very finicky about what pellets any given one feeds best. Having owned many 600s, in my experience they feed best with medium weight domes and/or wadcutters of the right length.

I've had best luck with 14.3 grain JSB Exacts and Crosman Premiers, RWS Hobbys and Meisterkugelns, and H&N wadcutters (model I don't recall). Even so, don't expect better than 90-95% reliable feeding and you won't be disappointed.

Also even so, the 600 is an awesome piece of vintage engineering; especially given it's a pellet gun that sold for way less than it's worth.

Mine-

Custom 600.jpg
 
Contact Henry Ford Airguns in Myrtle Beach South Carolina. He rebuilt mine several years ago and added a power valve. Mine was doing pretty much the same thing and now it functions perfectly. He even made me an extra 10" barrel. I don't shoot mine very much any more but it still shoots great when I do. As I recall he was very reasonable and pretty quick service. Hope this helps.
 
I understand that some C600s run with domed pellets, but neither one of my two C600s will. Mine run very well with RWS Meisters or H&N Sport wadcutters. Many pellets are too long for the feed arm and can lead to jamming.

A loose/worn cam ring may cause a jam, but I haven't been able to trace a jam to it. Recently, I replaced the -54/valve body o-ring on a C600 with over 12,000 pellets shot since the last rebuild. I mention this because the ring/cam was new 12K pellets ago and the ring was extremely loose on the cam, but still performed well. While I was I was in there I replaced the 12K cam ring with the original (that had less wear).

JG also has cam rings.

Another aspect of the cam ring/cam relationship can be how well fit or "worn" in the combination is. When my ring/cam was new, the ring did not traverse the cam smoothly until I stoned the edges with a diamond fishing hook file. This might be am issue if the re-builder installed new cam parts.

Jamming can also occur if the barrel/feedarm gap is too tight. My C600s run well with a .0025" gap.

Let us know how it works out.