9mm and .308 cal Disco Build



Author Topic: 9mm and .308 cal Disco Build  (Read 16658 times)

Offline rsterne

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9mm and .308 cal Disco Build
« on: December 24, 2011, 05:12:46 PM »
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline Butcher45

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Re: 9mm and .308 cal Disco Build
« Reply #1 on: December 24, 2011, 05:30:17 PM »
I've always liked the idea of a .308/.32 Disco with a twist rate suited for lightweight slugs.  Shrouded.  What a fun walk-around sqwerl gun that would be!

I'll be watching this build with enthusiasm.

Offline Gary

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Re: 9mm and .308 cal Disco Build
« Reply #2 on: December 24, 2011, 06:27:06 PM »
This interests me. Have you done any mods to the valve? I wouldn't think a stock valve would have enough power to push a bullet out the barrel but what do I know.
Gary

Offline airpuffhunter

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Re: 9mm and .308 cal Disco Build
« Reply #3 on: December 24, 2011, 06:43:54 PM »
come on Bob, those disco conversion are always interesting.
I hope it goes well, and perform better than spected
« Last Edit: March 21, 2012, 05:01:23 PM by airpuffhunter »

Offline Rescue35

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Re: 9mm and .308 cal Disco Build
« Reply #4 on: December 24, 2011, 07:12:45 PM »
  • Trenton, TN
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Offline rsterne

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Re: 9mm and .308 cal Disco Build
« Reply #5 on: December 24, 2011, 07:54:38 PM »
Just a quick report.... The Disco valve does leak out the back around the stem when fired, so I replaced it with another which does have the O-ring.... I also have some blow-by past the O-ring that seals the bolt, I'm going to have to chase that down.... As I figured, the small hole in the gauge block is starving the valve for air and the velocities are down quite a bit compared to the Carbine I did.... I don't think the lack of velocity is due to the enlarged exhaust ports in the valve in the Carbine because I got 498 fps with a stock diameter (0.140") transfer port.... In any case, here are the preliminary results, with two different hammer springs and on CO2.... 77.8 gr. EunJin pellets....

Stock Disco valve and ports, stock gauge block (1/8" hole)

Pressure .... Disco Spr.... 0.040" Spr.

2000 psi ...... 290 fps ...... 355 fps
1500 psi ...... 350 fps ...... 390 fps
1000 psi ...... 350 fps ...... 380 fps
800 psi ....... 340 fps ...... 340 fps

CO2 (70*F) ... 315 fps ...... N/T

The next step will be to drill out the through hole in the gauge block to at least 1/4" so that the average pressure at the inlet of the valve during the shot cycle will be higher.... With the tiny 1/8" hole (which is stock for a Disco) I'm effectively trying to get 40+ FPE of output from only about 5cc of HPA.... and as you can see, it's just not working.... I know the potential is there because I saw over 70 FPE from the Carbine during testing.... Now to pull it apart yet again....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline rsterne

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Re: 9mm and .308 cal Disco Build
« Reply #6 on: December 26, 2011, 10:28:11 PM »
I drilled out the gauge block today to a 1/4" through hole, and as expected the velocity increased.... However, it was still under 500 fps....

Stock Disco valve, gauge block drilled to 1/4", 0.040" wire spring @ stock preload

2000 psi .... 390 fps
1500 psi .... 450 fps
1000 psi .... 390 fps

The gun is getting a lot of shots, I'm guessing well over 20 between those pressure points.... It would appear that the ports in the stock valve are simply not big enough and/or smooth enough to flow enough air to get over 35 FPE.... Since my Carbine, with a shorter barrel, did that at similar pressures (the valve was ported out) it was time to pull the gun apart again and hog out the valve.... I milled out the exhaust port to 3/16" on a 20 degree angle, drilled the valve throat to 1/4", and streamlined it with my Dremel.... Then I bored out the valve to 0.62" ID (mostly to allow more flow around the head of the poppet), leaving only 2 threads, and shortened the front end to match.... I then tapered the inlet portion and countersunk both ends of the gauge port to streamline the flow.... There is still more that can be done by making a new valve front end with larger passages to eliminate the gauge block, and thinning the valve stem, but I'm trying to learn as much as possible by doing things in a progressive manner.... I also fixed the air leak around the nose of the bolt by simply lubricating the O-ring so that it could move a bit.... Sometimes the fix is almost too simple.... This time I saw quite a large jump in velocity.... Still using the 77.8 gr. EunJins....

Bored out valve and ports, streamlined gauge block and valve inlet, 0.040" wire spring @ stock preload

2000 psi .... 460 fps
1600 psi .... 525 fps
1400 psi .... 545 fps
1200 psi .... 540 fps
1000 psi .... 490 fps

I decided to try a heavier hammer spring, just shy of coil bind and got a few of shots right around 2000 psi of 660 to 680 fps (80 FPE).... so the potential is definitely shaping up.... I plan on doing the remaining valve mods next and eliminating the restriction of the gauge block....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline rsterne

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Re: 9mm and .308 cal Disco Build
« Reply #7 on: December 28, 2011, 10:23:53 PM »
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline Rescue35

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Re: 9mm and .308 cal Disco Build
« Reply #8 on: December 29, 2011, 12:09:48 AM »
Not only do you do great machine work and understand the fluid mechanics that take place inside an air gun but you do a great job of documenting and explaining all of it. Thanks Bob and I'm looking forward to your next installment on this project.
  • Trenton, TN
"Research is what I'm doing when I don't know what I'm doing." -Wernher von Braun

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Offline rsterne

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Re: 9mm and .308 cal Disco Build
« Reply #9 on: December 29, 2011, 01:18:49 AM »
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

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Re: 9mm and .308 cal Disco Build
« Reply #10 on: December 29, 2011, 01:35:59 AM »
You've got my attention!  Great reading!  The workmanship looks very clean.  Thanks for sharing your experience!

Offline rsterne

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Over 90 FPE Today !
« Reply #11 on: December 29, 2011, 10:50:18 PM »
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline Rescue35

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Re: 9mm and .308 cal Disco Build
« Reply #12 on: December 30, 2011, 10:34:45 AM »
Wow Bob,

When you mentioned shortening the valve stem I thought about the hammer also. Have you thought about turning a longer hammer (proportional to the length of stem removed) and returning to the 1.75" long spring. That would add a fair amount of mass. Although it really is mainly academic at this point. You are getting some great numbers there. This thread will be getting printed out and added to the notebook.
  • Trenton, TN
"Research is what I'm doing when I don't know what I'm doing." -Wernher von Braun

2260 PCP converted
1322 supercharged

Offline rsterne

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Re: 9mm and .308 cal Disco Build
« Reply #13 on: December 30, 2011, 01:18:15 PM »
« Last Edit: December 30, 2011, 01:20:20 PM by rsterne »
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline Rescue35

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Re: 9mm and .308 cal Disco Build
« Reply #14 on: December 30, 2011, 02:13:28 PM »
I didn't think about the sear engagement. Duh.

Since f=m X A my line of thinking, since you had more room meant you could add mass up front. I like your idea on the external cocking, I think you had done this with one of your other guns. That will gain you the benefits of both. More mass and acceleration.
  • Trenton, TN
"Research is what I'm doing when I don't know what I'm doing." -Wernher von Braun

2260 PCP converted
1322 supercharged

Offline lloyd-ss

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Re: 9mm and .308 cal Disco Build
« Reply #15 on: December 30, 2011, 05:30:35 PM »
Bob,
Nice project and very nice of you to share such great documentation with everyone.
Lloyd
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Offline echochap

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Re: 9mm and .308 cal Disco Build
« Reply #16 on: January 03, 2012, 09:39:27 AM »
Nice gun and the best write up I've seen on a big bore build. That's a good shot string in the 700s, seems like a compact little mid range gun for medium size quarry. Again, excellent job building and communicating!
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Offline rsterne

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Re: 9mm and .308 cal Disco Build
« Reply #17 on: January 19, 2012, 05:17:13 PM »
I spent a bit of time in the shop today.... it sure felt good to be back out there.... I tried a 1.75" long 0.045" wire hammer spring, and also the same length from 0.051" wire.... The lighter one wasn't as good as the 2.00" long one I tried previously, and the heavier one was only marginally better, peaking at 736 fps.... but it was VERY difficult to cock.... So far (with the stock hammer) the best spring is the 2.00" long x 0.045" wire one....

I had a few 132 gr. cast bullets that had been sized to 0.357", and tried them out.... They were VERY hard to load, I actually had to tap the bolt closed.... They only hit 540 fps (85.5 FPE), probably because of the tight fit.... I will have to get a smaller sizing die to use with this barrel if I want to try anything other than the EunJins....

The next project is to make a new hammer with rear cocking knob and the ability to accept longer/stiffer springs....

Bob
  • Coalmont, BC, Canada
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal:
.177 Diana 34, 1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), .22 BAM B-26, .22 BAM B-51 (50 FPE), .25 Hatsan AT-4410 Long (70 FPE), .22 QB79 HPA (26 FPE), Disco Double .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, .308 & .357; Mk.III is .410 shotgun and .458 cal)

Offline ronbeaux

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Re: 9mm and .308 cal Disco Build
« Reply #18 on: January 19, 2012, 09:00:43 PM »
I soo look forward to your posts and knowledge. I am committed to advancing in the machine techniques. Thank you!!
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Offline lloyd-ss

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Re: 9mm and .308 cal Disco Build
« Reply #19 on: January 20, 2012, 02:44:10 AM »
  • Central Virginia

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