QB78D Carbine Project

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I have had 3 safepacs now but on crosman 2240 platforms. The 177s performed the best for shot count, the 22 obviously netted higher power.

I recently ordered one of his direct to valve drop blocks for a 2240 bottle gun since I couldn't get this safepac to give me any consistency over more than 3-5 shots. Unless I restrict the t port down to under .125, it won't produce a good curve with anything worthy of hunting power. I will eventually have it on a back up pistol for those not DRT critters when I get to them and they try to bite!
 
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Boostcreep said:
I have had 3 safepacs now but on crosman 2240 platforms. The 177s performed the best for shot count, the 22 obviously netted higher power.

I recently ordered one of his direct to valve drop blocks for a 2240 bottle gun since I couldn't get this safepac to give me any consistency over more than 3-5 shots. Unless I restrict the t port down to under .125, it won't produce a good curve with anything worthy of hunting power. I will eventually have it on a back up pistol for those not DRT critters when I get to them and they try to bite!
Click to expand...

Thanks for the info! I've pulled both washers from the HS guide so I'm back to the beginning. I'll have the tap tomorrow so I can tap the TP and see how that affects things. Though, fair warning, I have a custom tuned QB coming in tomorrow, so it's likely this will be put on the back burner for a day or two.
 
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UCChris said:
Thanks for the info! I've pulled both washers from the HS guide so I'm back to the beginning. I'll have the tap tomorrow so I can tap the TP and see how that affects things. Though, fair warning, I have a custom tuned QB coming in tomorrow, so it's likely this will be put on the back burner for a day or two.
Click to expand...
Slacker! Lol

You should do a thread on that one too
 
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Hi Chris,

Regarding the return spring on the Foster check valve, to the best of my knowledge you’re correct, those are the only two things it affects. Inability to drain the reservoir by gently cracking the bleed screw, and inability to hear a familiar click when it opens.

As for the 79 headed your way, it’s yours so you’re welcome to share as much or as little detail as you want. (y)
 
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nervoustrig said:
Hi Chris,

Regarding the return spring on the Foster check valve, to the best of my knowledge you’re correct, those are the only two things it affects. Inability to drain the reservoir by gently cracking the bleed screw, and inability to hear a familiar click when it opens.

As for the 79 headed your way, it’s yours so you’re welcome to share as much or as little detail as you want. (y)
Click to expand...

Thank you for the clarification on both points!
 
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Minor update, the transfer port has been tapped. I've only tapped aluminum previously and boy howdy, brass taps sooo easily. I'm going to drill the set screw TP tonight, then it's just a waiting game for my barrel orings. Supposedly, they'll be here Tuesday.

PXL_20221215_235616486.jpg
 
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The orings showed up last night way ahead of schedule, but I had already committed my evening to quality time with the wife, so I didn't get to installing everything until this morning.

Went from a .18" TP to .05" TP. I figured this would be way too small, but better to start low and work up. Again, this was with the hammer spring back to factory config and still the full length barrel. I started with a fill to 1500 psi, cause I wanted to make sure my tapping job would hold before increasing pressure.

Screenshot_20221217-104603.png


Screenshot_20221217-104616.png


Clearly on the back end of the bell curve, so gonna test starting at 1700 psi next. First impressions are that this is the first time this gun hasn't felt like a mule I'm wrestling with. It's also clear that this gun would greatly improve with a lightweight hammer. With the smaller TP, the gun is very good natured other than that super heavy hammer just slamming around . Also, I was surprised that I'm getting the speed I'm getting on the back end of the bell curve. I thought .05" would be wildly too small and I'd be at like 300 fps.

The aforementioned wife has a list for me today, so I'm off to do chores and then I'll update with the 1700 psi test.
 
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Couldn't resist and decided to run a quick string between a couple chores. Filled to 1700 psi and took a shot which read in the low 600's, so I decided to fill to 1900 psi and run a test. Here's the 1900 psi string.

Screenshot_20221217-113422.png


Screenshot_20221217-113408.png


Still on the back of the bell curve at 1900 psi. Looking at my initial testing, I was getting a bit of valve lock at 2000 psi and a bit more at 2200 psi, so I'm a little confused. I guess I'm gonna run a 2000 psi test and just keep upping the psi by 100 until I find the start of the curve. Off to do more chores!
 
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Here's a string starting at just a smidge over 2100 psi. Not sure what is up with the fast first shot followed by a slow shot, so I'm gonna test 2200 psi next. As it stands, we've got a curve of 13 shots in a 31 fps spread from 611-639-608. That's 4.8% from max, which should be tight enough for 30 yard accuracy.

Shot count: 15
Low: 601
Hi: 649
Avg: 627
STD Dev: 12.6
Spread: 48.0

12/17/22 12:23:23 PM,649
12/17/22 12:23:33 PM,611
12/17/22 12:23:42 PM,623
12/17/22 12:23:53 PM,630
12/17/22 12:24:02 PM,627
12/17/22 12:24:11 PM,637
12/17/22 12:24:21 PM,636
12/17/22 12:24:31 PM,633
12/17/22 12:24:40 PM,632
12/17/22 12:24:48 PM,639
12/17/22 12:24:56 PM,634
12/17/22 12:25:04 PM,620
12/17/22 12:25:11 PM,618
12/17/22 12:25:18 PM,608
12/17/22 12:25:27 PM,601

Screenshot_20221217-123330.png


Screenshot_20221217-123354.png
 
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Boostcreep said:
@UUChris, what weight pellet are you using for testing? Didnt know if you stated that yet or not.

i know when i had the rifle on co2, it performed the bedt with the 10.5 crosmans. That'll change im sure with the shortened barrel.
Click to expand...

10.34 JSB, so we're right around 9fpe average.

2200 psi fill showed that the bell curve is definitely starting just at/barely under 2100 psi.

Shot count: 19
Low: 520
Hi: 644
Avg: 602
STD Dev: 39.8
Spread: 124.0

12/17/22 12:48:39 PM,542
12/17/22 12:48:50 PM,527
12/17/22 12:48:59 PM,520
12/17/22 12:49:08 PM,537
12/17/22 12:49:16 PM,581
12/17/22 12:50:20 PM,618
12/17/22 12:50:29 PM,609
12/17/22 12:50:37 PM,615
12/17/22 12:50:47 PM,627
12/17/22 12:50:55 PM,636
12/17/22 12:51:06 PM,639
12/17/22 12:51:14 PM,644
12/17/22 12:51:22 PM,641
12/17/22 12:51:29 PM,630
12/17/22 12:51:38 PM,634
12/17/22 12:51:46 PM,625
12/17/22 12:51:55 PM,616
12/17/22 12:52:01 PM,605
12/17/22 12:52:09 PM,595

Screenshot_20221217-125439.png


So now I'm at a crossroads. This gun was supposed to be a 12 fpe carbine woodswalker for going after squirrels. However, I've unexpectedly come into possession of parts to revive my bottled Prod that I gutted for my wife's Prod bullpup. That bottled Prod will be tuned to 12 fpe and get a ton of shots off the 9ci bottle. So there's no use having this gun tuned to 12 fpe, while having it weigh more and less shots than the Prod build. I just took delivery of a custom 16 fpe QB79 carbine from nervoustrig, so I don't see much use in tuning this gun to shoot like 3 shots at 18 fpe, since I've never shot at anything with 16 fpe and wished I had 18. So I might just keep these here at 9 fpe. It fits nicely between the 12 fpe Prod and my 6 fpe Bandit pistol. It will be a fun little gun for popping sparrows and mice, or doing some undercover backyard paintball sniping.

I'm hoping that Jason's backlog of projects frees up sometimes next year so I can still get a lightweight hammer built for this gun. I'm going to keep the barrel full length, cause there's a pretty decent chance that I'll swap the full length barrel into the 16 fpe rifle after it goes to Jason for his magic and that'll give this gun a 15" barrel.

So I'm gonna slap a red dot on this guy and do some accuracy testing, but it's seems this project is quickly coming to a sort of standby, pending closure status.
 
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It was doing about 675 with the 10.5s on co2 @ 85° so you're hitting the same power levels with a super restricted port.

Man I'm itching to see what it would do on a 3000 psi fill and a spring to open it. That small port should give you a ton of shots then.

The other option to conserve the air would be to stiffen the valve spring but that's obviously more involved tuning. Taking the whole rifle apart each test gets old lol.
 
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Boostcreep said:
It was doing about 675 with the 10.5s on co2 @ 85° so you're hitting the same power levels with a super restricted port.

Man I'm itching to see what it would do on a 3000 psi fill and a spring to open it. That small port should give you a ton of shots then.

The other option to conserve the air would be to stiffen the valve spring but that's obviously more involved tuning. Taking the whole rifle apart each test gets old lol.
Click to expand...

I will indulge you and test with the 3k fill and the two shims!
 
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Boostcreep said:
For science!
Click to expand...

Slight problem, the valve starts locking at 2200 psi with the two washer I have. Since it's still cock in close, I can't use a rear RVA like Jason uses on his builds. So I gotta dig through my springs and see if I have anything heavy enough to run this test for ya.
 
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UCChris said:
Slight problem, the valve starts locking at 2200 psi with the two washer I have. Since it's still cock in close, I can't use a rear RVA like Jason uses on his builds. So I gotta dig through my springs and see if I have anything heavy enough to run this test for ya.
Click to expand...
I cant remember the size of the spring for the QBs, but maybe a gauntlet hammer spring could work? They're very similar in design.
 
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