QB78 / XS78 / XS501 CO2 Caplet Spacer

I had issues with the front CO2 cap not puncturing very well and so not boiling off and pressurising the gas tube evenly. This meant I had to wait a minute before taking the 1st shot and around the 25th or so pellet I found I was losing velocity suddenly but would get it back if I waited a few seconds. This was likely because the time it took for the gas in the front cap to come out through the tiny pinprick meant the cap pressurised enough the remaining liquid CO2 wasn't boiling off. Waiting 10-15s between shots would get me another 5-6 good ones before all the liquid co2 was gone and the tube pressure dropped out.

I tried an alternative cap & piercer, but still had the same issue; just a pinprick made in the front caplets seal. I also had enough of the caps rattling against each other and the tube, so to solve both issues I made a little shaped spacer to both let the spike on the piercer block push in to the front cap more, and to hold the caps centred in the tube better. 4 small ports around the circumference to allow the pressure to remain even through the tube and the diameter small enough to drop out when unloading the caps. After adding the spacer, the front cap seal hole went from literally a pinhole size, to a good 1-1.2mm across. One thing I found was I had to be pretty lively backing the cap out the 1/3-1/2 turn needed to withdraw the piercer before it locked up, whereas before I had no problem. But there's no free lunches and that's a small cost vs the more consistent performance from shot 1 to shot 30.

I printed mine solid, from PLA - they never get hot enough in the tube to need anything else as even on a sunny day each firing drops the pressure and so temperature. However they could be made from almost anything that is stable in contact with air and CO2. I used a 0.40mm nozzle and 200um layers - there's no need for anything more detailed as it's a pretty basic part that rarely sees the light of day. Print 2 of the model, sand the backs completely flat then rough them slightly, and superglue them together back to back with the little pass-though cut-outs aligned.

Please note that this might also work in other CO2 rifles where the caplets are placed back to back and both pierced with at least the front one done with a spike on the inside of the tube cap. I don't know of any other rifles but the XS series that do this - the only other I know has 2 in the tube is the CR600 and that requires the front cap to be there just as a spacer, and it goes in neck-first. However if there are other rifles that could benefit from this little part please let me know and I will add it to the tags, so others can find it.