QB79 HPA build for GTA member

[UCChris]

Glad you are understanding what I'm talking about. Sometimes I tend to get long winded and redundant.

I'm headed to the local hardware store at 6 am to get parts for my adjustable comb and buttpad extension kits. There are adjustable comb kits available on the internet, but they range from $35 on up. I may have found a ingenious way to make an adjustable comb kit for a mere $10 of parts.

[Buldawg76]

Chris
That sounds good on the adjustable comb and if it works out we need pics so it can be duplicated by those who want/need it.

Got some more done on the 79 last night and going to test and setup the reg today but got to contact Jason to see if he can tell me now much pressure increase one .005 shim provides so I can only have to adjust once or twice since I don't have a manifold made up to keep from having to fill the entire bottle to test pressure instead of just the reg itself.

Mike.

[UCChris]

I have the extended buttpad setup and I've been working on the adjustable comb. Problem is, I only have a coping saw (yay for living in college dorms) and I've been sawing for an hour and a half and only gotten 1/3 of the way through the comb. I'm going to give a guy in my parent's neighborhood a ring. He does custom canoes for a living and I'm hoping he'll have a bandsaw. I will take pictures of the process.

[Buldawg76]

Yea I have a woodworking buddy with a full shop of tools so that's where I will head for my wood work projects. If its mechanical I have a garage full of tools from days as a master mechanic but a body man or wood worker I am not so that's best left to those who have done that for a living.

I believe a coping saw will work if you have enough elbow grease but its not how I would want to do it as a band saw is the way to go for sure.

Mike

[nervoustrigger]

Mike, generally you can expect about a 100psi increase from the thin shims (0.005" if memory serves).  I want to say the thick (red) shims measure 0.015" so that would be about 300psi.  Just treat these as guidelines though, actual results may vary depending on the particular spring rate of the stack.

[Buldawg76]

Mike, generally you can expect about a 100psi increase from the thin shims (0.005" if memory serves).  I want to say the thick (red) shims measure 0.015" so that would be about 300psi.  Just treat these as guidelines though, actual results may vary depending on the particular spring rate of the stack.

Jason
I just got one regulator set and I ended up with approximately 50 psi per .005" shim which is what Ninja Ray thought it would be but then my dead head gauge may not be that accurate either as it is a small 1 1/2" non liquid filled gauge.

The first test of the reg as factory stock showed it to be 1100 psi as stated by Ninja website with 3 .005" shims installed so I added a red shim which are .020" ( not .015" ) for a total stack of .035" and it now reads 1300 psi on my gauge so I have it where I think I need to be and getting ready to shoot it over the chrony in a bit to see if it has picked up from the 775 fps range it was shooting at to the 890/900 fps I am after.

It has the cock on open mod as well and had two shims on the end of the spring guide that were 1/8" in thickness so I added another 1/16" shim and it is at the point it will just cock so spring is at max preload as well. If I am not at my desired fps I will tear farther into it to see if any valve mods have been done or porting done to improve the flow and if not then look into some work there.

Mike

[UCChris]

Well, I sawed away with the coping saw for a good hour and only got 1/3 of the way through the comb. I'm headed to a friend's dad's house to use his band saw. Got all the other parts cut and finished, so I'm just going to have to cut the comb, drill the necessary holes, and epoxy some stuff together.

[GD Giles]

Chris I know you're glad to have her back! Looking forward to pics of the comb mod.

[Buldawg76]

Got my reg set at 1300 psi output and hammer spring maxed out and filled to 3000 psi and shot a 20 shot string for some numbers and pretty happy with the results as is now.

3000 psi down to 2600 psi for 20 shots at 71 degrees F
Lo = 844.6
Hi = 857.1
Avg = 853.4
ES = 12.50
SD = 3.31

So while not at the 890/900 fps desired it is much better than the 775 it was at with JSB 10.34s and if the shot count is consistent with the air used I should get 80 shots shooting from 3000 psi down to 1400 psi just before it comes off the reg. I am going to mount a scope and see how it groups next and shoot it at this weekends FT match if it groups good at sight in and see if I need to really tune for the extra 40/50 fps or leave it alone and enjoy it.

Mike 

[UCChris]

Got most of the work done on the adjustable comb. Just have to drill a couple more holes in the comb piece and do some epoxying. I also turned the power down to 12.84 fpe. It is crazy quiet now and still super accurate. I just need to get the shroud in the mail and finish the comb and this project will be done!

[Buldawg76]

Looking good Chris especially for cutting by hand with a coping saw and should help with the cheek weld when shooting for sure. I want to see the finished project as well.

Mike

[Gertrude]

looking good so far Chris.

[UCChris]

Well, I am a doofus. I left the aluminum rod that I'm using for the vertical adjustment bar at my apartment when I went to my parents house. I still got some stuff done on it (the pictures posted above) and when I left my parent's house, I left my epoxy there. Gah!

I couldn't sleep so I decided to drive up there again, this time with the aluminum rod, to pick up my epoxy and cut the rod to size. Got all the parts epoxied and they are setting right now. Should have pics by morning.

[Buldawg76]

Sounds like me and my mind as I forget it most days and end up going around without it just making like I know what I  am doing. But I have an excuse I am old and feeble minded and retired so I don't have to think unless I want to. HaHa.

I hate when stuff like that happens.

Mike

[UCChris]

Mike,

Did you say that you were going to modify a Crosman endcap to fit the QB so you could more easily use a power adjuster? Do you know what modifications that requires? My adjustable comb idea totally failed, but I have an even cooler idea if I can make a Crosman endcap fit.

I'm talking about part 17 in this here diagram.

http://www.crosman.com/pdf/manuals/BP1K77xx%20&%20BP9M22xx%20EVP.pdf

[UCChris]

Here you can see how my comb was setup. The rod was simply epoxied into the comb, then a hole was drilled in the buttstock with a tee nut used as a threaded collar for a set screw.



Simple, nice design, but when the set screw was tightened, the epoxy failed and the tee nut detached itself from the stock.

So, in a fit of rage, I did this.



Not actually in a fit of range. I've decided to try something else. Hopefully this next idea works, lest I waste a $95 stock...

[UCChris]

I hope your project is going well Mike. Inquiring minds would like an update!

[Buldawg76]

Chris
Got under the weather for a couple days and then had a FT match Saturday that is an all day affair and was just worn out so rested most of the day today.

But on your adjustable comb its a shame you hacked the end of the stock off as I could have told you what to do to remedy the set screw and threaded insert from coming loose. They make threaded inserts like a heli coil for repairing stripped thread in metal for use in wood. It is as simple as drilling the proper size hole in the stock and threading the insert into the stock to sit flush with the surface and the insert has the inside of it is threaded for a machine screw or set screw to go into so that it would have tightened down on the rod to hold the comb at whatever height you needed. If you can drill the stock and piece you cut with holes that can have wooden dowels inserted into the halves and glued in place to effectively make it one piece again it a simple modification to install the inserts for the set screws to hold the comb in place. See the link for the inserts from McMaster Carr below

 http://www.mcmaster.com/#standard-threaded-inserts/=11txmqn

For the power adjuster yes the disco end cap is one of the end caps that can be used to place the adjuster screw in the center of the end cap for a RVA in a QB and the other is for a 2240 but it requires drilling and threading the cap for the RVA screw so the disco part is a simple bolt in and buy a threaded screw to fit the threads already in the end cap of the length required which I have figured to be 50 to 60mm long. To install the end cap you just need to drill a hole thru the top of the breech 180 degrees opposite the hole that the trigger screw that hold the breech plug in place with now. Then measure the length of 8-32 thread screw you need to put in the top of the breech that will thread into the hole in the disco end cap and another one for the trigger side as well so the end cap will be held in with two screws from the top and bottom instead of the one screw it uses now. The disco end cap is threaded 8-32 in the two holes that the screw for the QB end cap passes thru now so the center is open with no screw blocking it. You can drill the top hole in the breech big enough so that using an allen head screw would allow the screw head to sit against the breech plug and not the breech itself and leave it sunken in the breech somewhat so it would not interfere with scope ring mounting. The threads in the QB breech plug do not need to be drilled out as the 8-32 screw will pass thru the plugs threads easily without issues so you can always go back to the stock end cap it you decided to. Or just buy the screws that hold the disco end cap on the disco and they should be the right lengths but the trigger side is a flat blade screwdriver head with a square middle driver head that tends to get buggered up easy with repeated removal so I prefer allen head screws plus you can get grade 8 screws instead of the cheap unknown grade crosman screws. The crosman screws are numbers 26 and 27 in the attached schematic. If you use the lengths given in the schematic to get allen screws from your local hardware store you should be good for a nice fit in the QB but may require some custom fitting of the lengths so they don't protrude into the RVA screw cavity of the end cap.

Hope this helps and sorry for the late reply as I wish I had caught you before you cut that stock UUGH.

http://www.crosman.com/pdf/manuals/BP1K77xx%20&%20BP9M22xx%20EVP.pdf

Mike     

[Buldawg76]

Chris
Forgot the update on my 79. you saw the chrony numbers I posted with max hammer spring tension with just using the cock on open mod the gun came with from you know who with the spacer and shims inside behind the spring guide so have not installed a crosamn end cap RVA as of yet but did play with reg pressure some and found that upping the pressure from 1300 psi that the numbers were shot with to 1350 psi and it only gained me 10 fps and was using much more air. So now going down to 1250 psi to see if I loose fps or stay the same at 850 fps average it was at 1300 and if so will gain some efficiency with less used air but if fps drops will go back to 1300 for the time being  until I can get my RVA made and installed so I can add some more spring tension as I tried adding a spacer that fit inside the hammer cavity but it bound up the bolt on closing and caused a loss of fps due it creating hammer drag.

So as it is now have to fill and shoot a string at 1250 psi to see if I have lost fps or stayed the same and then do some grouping sight in to see if it even likes that velocity before I try to increase it because if it groups well out to 55 yards at 850 fps with JSB 10.34s then I don't see a need to up the fps at this time until I shoot some matches to see if it is an accurate FT gun. I am basing my goal of 900 fps on my Mrods velocity with those same pellets and its accuracy in FT matches but it does not mean the QB will like shooting them that fast so just still in the testing stages.

But at 1300 psi and with a 20 shot string I am happy with a predicted 80 shots per fill and still not be coming off the reg since matches are 60 shot max per session.

Mike

[UCChris]

Thanks for the updates Mike! Don't stress about the stock. I found a different way that is going to be every bit as awesome. I'm on my phone which makes typing out replies a royal pain, so I will write up a better reply tomorrow when I get back to my computer.