Decided to make the tool I needed to tear down one of the two QB 89 bull pups I got from Randy Mitchell. Ground down a socket to get what I needed, once I got the barrel nut off, the rest of it was pretty straight forward.
I was surprised at the build quality of this little beast, for the power, it's really overbuilt. Big compression tube, a main spring that would be right at home in a Gamo springer, and a 19" barrel, all in a package just over 2' long. It's mostly wood and steel, and the metal work is far better than I'm used to seeing on Chinese guns, especially older ones. Almost no rough tooling marks, bluing is decent if a bit thin, and the inside of the compression tube was already nicely polished.
The piston seal was synthetic, another surprise, although it's installed with a shoulder screw like a leather seal would have used. A first gen synthetic seal, maybe? This was rough, tight, and bone dry, but like the rest of the rifle, it cleaned up fine. It's still tight, but since I don't have a spare, and don't know where I'd get one, I decided to be conservative. The spring was a bit canted, so I decided to change it, I had a couple of JM's old Merlin square section springs on hand, and it looked like a perfect match. The Merlin is a little shorter than the stock spring, but it's stiffer and has fewer coils, so I think the spring rate is about the same. I added a top hat and cut a thicker base on the spring guide, so the preload ended up about the same. Velocity is only 440 fps with JSB Expresses, but I made the guide pretty tight, between that and the seal, I'm not surprised the velocity is low. It may speed up a bit as it wears in, but if it doesn't, I may open it up and do some tweaking. Or I may just leave this one as it, and work on the other one . I think part of the power loss is the transfer port, it's incredibly long and has two right angle turns. Something else I may have to play with.
Shot cycle ended up nice, and it's a lot quieter than I expected. I read several posts that mentioned how noisy it was because of the action right next to your face, but I don't think this one is any worse than any of my other springers. And it's much quieter than my HPA QB!
Speaking of which, it continues to hold air, and I got the chance to do a chrony string. I did a 25 shot string with AA Heavies, here's the results:
This thing is still brand new, I don't have 50 pellets through it yet! Just about 12 fpe, and other than the tube swap and the HPA tank, I've made no other mods. The 25 shots only took the tank pressure down to 2000 psi, and it wasn't at 3000 when I started. It's pretty noisy, so I know I'm wasting air. Not sure where I should start, I'm thinking valve mods first, but I'd welcome suggestions from those of you that have already been there.
All in all, a good day in the shop, and I'm really looking forward to continuing the HPA conversion. Considering the results so far, this is going to be good. Can't wait to start on #2 ! Later.
they are twangy things from the factory ..having all that commotion against your cheekbone doesn't help.If it seems quiet, you did a nice job inside.
What pressure on the HPA QB? I'm a fan of light strikers to quiet and reduce gas use. I've run QB pcp's at 2000 psi on a striker 70% of stock weight with a delrin valve head. Factory spring, no shim. That's where I'd start.
The QB HDD should work well with your setup too.