I am now offering solid brass (and aluminum) barrel spacers for Crosman 22xx and 13xx.

These will typically fit the normal 7/16" OD barrels against either 3/4" OD or 7/8" OD gas tubes (that's pumper vs CO2 ODs).

These ship at approximately 12" overall length and YOU cut to fit. A band saw, dremel, etc can cleanly cut them and they can be dressed on a sander or with steel wool.

There are too many variants between gens and breech styles to offer cut-to-fit lengths.

The photos below show typical lengths on a new-gen 2240 with both plastic and steel breeches.

Two cut-to-size lengths.

As installed on plastic breech 2240.

As installed on 2240 with normal-length steel breech.
 

For your consideration, the below data is off the PLASTIC spacer listing. These are genuine Crosman barrel spacers. They fit between the bottom of your barrel and the top of your main tube. These are specifically for a Crosman 2260, but can be cut to fit any 22xx gun. They also fit the 13xx. As it will ship, it is 12.5" long and 3/8" wide. The two photos of the random guns show where the spacer is MISSING. That's where the spacer goes! They may or may not actually fit those guns, they're just posted because they're showing the gap. For your non-22xx project gun, here are some caliper-measured dimensions: A 22xx main tube diameter is .875". A 22xx barrel diameter is .435". These spacers are .400" wide at their widest point. These spacer are .139" tall at the outer edges. The spacer's thinnest point is .020", in the middle. The spacer can be cut with a pair of scissors, hack saw, etc and cleaned up with sandpaper or a file.