Progress on two fronts.

Progress on two fronts.

Joined: August 20th, 2006, 5:36 am

December 13th, 2011, 2:46 am #1

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:

Hi 739.5
Lo 731.8
Av 734.9
ES 7.0
SD 2.0

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.

Dave
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Joined: March 28th, 2002, 6:54 pm

December 13th, 2011, 6:07 am #2

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.
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Joined: August 20th, 2006, 5:36 am

December 13th, 2011, 7:29 am #3

Since neither one of them would cock when I got them, I had nothing to compare it to, other than the other rifles I have on hand. The only other bull pup springer I've played with was an IZH MP 514, and that was mostly plastic. THAT was noisy, the hollow stock acted like an amplifier. I haven't done any accuracy shooting yet, but this thing could be the perfect little shop gun. And if I can squeeze a little more power out of it, it wouldn't make a bad short range truck gun, too.

For now, I'm running 1000 psi output on the ExpertHPA 13 in. bottle. I fully expect to do some striker work, most likely I'll make my own out of a variety of materials. I have some 7075 aluminum on hand that should work well, with the possible addition of a small steel insert. I'm also planning on a Delrin valve head. Do you modify the valve seat when you change out the valve head, and if so, how?

First up, I think I'll work on air flow, starting with opening up the valve. Then I'll look at porting, although I'm a little confused by some of what I've read in that regard. Not sure if I'm going to replace the flow through bolt with a probe, this is a .177 and I seem to recall someone writing that it didn't make much, if any, improvement on the smaller caliber.

BTW, the extra length on the air tube wasn't an accident, nor was it a random decision. Based on stuff you and Robert have posted, I knew I wanted more volume in the, well, lets call it a pre-chamber. Did some more research, and found a post on the Canadian forum by someone posting as rsterne. He did some research on his own rifles, and determined that roughly 1cc of volume was needed per foot pound of energy desired. I'm shooting for approx. 20 fpe, so my pre-chamber is actually closer to 25 cc's, and that doesn't include the valve volume, which will increase when I open it up. If you're interested in his post, here's the link: http://www.airgunforum.ca/forums/topic43657.html It's a good read, and the follow up info is also good. Anyway, I should be good even if I later change over to a .22 barrel and want 30 fpe . Later.

Dave
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Joined: March 26th, 2008, 2:38 am

December 13th, 2011, 12:57 pm #4

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:

Hi 739.5
Lo 731.8
Av 734.9
ES 7.0
SD 2.0

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.

Dave
seems like you are learning alot....

I dont mess with HPA/pcp much, I have one but it gets shot rarely.

Scot, Mike and Walter are the guys to listen to on this stuff, and Scot is right on with the lighter striker advice.....even works for Co2!!!

God bless,

Farmer
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Joined: December 5th, 2008, 8:43 pm

December 14th, 2011, 1:16 am #5

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:

Hi 739.5
Lo 731.8
Av 734.9
ES 7.0
SD 2.0

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.

Dave
you can remove weight from the hammer sides , this shortens the dwell time of the valve and can quieten it down and save air ,it worked on my 79 without power loss ,do it a bit at a time , if you over do it put a thin shim under the rear of the spring ,
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Joined: March 28th, 2002, 6:54 pm

December 14th, 2011, 5:07 am #6

Since neither one of them would cock when I got them, I had nothing to compare it to, other than the other rifles I have on hand. The only other bull pup springer I've played with was an IZH MP 514, and that was mostly plastic. THAT was noisy, the hollow stock acted like an amplifier. I haven't done any accuracy shooting yet, but this thing could be the perfect little shop gun. And if I can squeeze a little more power out of it, it wouldn't make a bad short range truck gun, too.

For now, I'm running 1000 psi output on the ExpertHPA 13 in. bottle. I fully expect to do some striker work, most likely I'll make my own out of a variety of materials. I have some 7075 aluminum on hand that should work well, with the possible addition of a small steel insert. I'm also planning on a Delrin valve head. Do you modify the valve seat when you change out the valve head, and if so, how?

First up, I think I'll work on air flow, starting with opening up the valve. Then I'll look at porting, although I'm a little confused by some of what I've read in that regard. Not sure if I'm going to replace the flow through bolt with a probe, this is a .177 and I seem to recall someone writing that it didn't make much, if any, improvement on the smaller caliber.

BTW, the extra length on the air tube wasn't an accident, nor was it a random decision. Based on stuff you and Robert have posted, I knew I wanted more volume in the, well, lets call it a pre-chamber. Did some more research, and found a post on the Canadian forum by someone posting as rsterne. He did some research on his own rifles, and determined that roughly 1cc of volume was needed per foot pound of energy desired. I'm shooting for approx. 20 fpe, so my pre-chamber is actually closer to 25 cc's, and that doesn't include the valve volume, which will increase when I open it up. If you're interested in his post, here's the link: http://www.airgunforum.ca/forums/topic43657.html It's a good read, and the follow up info is also good. Anyway, I should be good even if I later change over to a .22 barrel and want 30 fpe . Later.

Dave
I use a piloted spot face cutter to cut the seat flat and true to the stem bore.Then I undercut the head about 3 degrees..according to LD that makes the seal more reliable.I also make the head narrower at the seat,sort of an ice cream cone shape, and adjust the large end clearance to the valve wall in small increments to get the balance of power and shots I want. This is for a self reg valve, but it may help even with a constant pressure.

I also do something I've never seen mentioned...siamesed ports. I cut the barrel back (on a new one I'll turn it to a tight fit and lap it into the receiver..no o-rings and no play)partially drill the port,dremell a small plenum there and drill two tiny pilot holes into the bore, with a bridge between them. Then some work with diamond dental burs under magnification to smooth it all up. Final finish in the throat with a long tapered reamer. You can get a lot of flow with no pellet hang ups that way.

I'm a fan of wire probes, especially in .177
Last edited by classicalgas on December 14th, 2011, 5:16 am, edited 1 time in total.
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