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PostPosted: Thu Mar 13, 2014 8:14 pm 
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Posts: 117
I had to have one of these rifles.

I have a block machined up to turn it into a reverse bottle gun.......Bob Sterne style :mrgreen:

I decided that the tube mike supplies is too long to hang a bottle off and i figured the gun would be too front heavy

I did manage to get hold of a short OEM tube from Mike M for $5. Using this I have the best of both worlds- either tune for an unregged gun using the long tube, or hang a regulated bottle from it.

Bob, reading through your post. I intend on carrying out the valve mods as you have. What set point would you set your reg at if you were to use a bottle? I was looking at your results I was thinking 1300psi? Would I be correct in thinking that I wouldnt have to shave 0.050" of the valve block?

Are they any other mods that you would omit, or recommend I include please?

I have stripped the gun and I must say they are great value for money from what i can see :P


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PostPosted: Thu Mar 13, 2014 9:51 pm 
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I would tend to go as high in pressure as you can while still running a 1.8K burst disc for safety.... so that means 1500 psi maximum.... You will get greater efficiency at the higher pressure because you can then operate on the "knee" of the curve, in effect tuning the gun to peak at 1300-1400 if it was unregulated.... I assume you are going for lots of power if you are going to hog out the valve?.... another reason to use as much pressure as sensibly safe.... If your goal is, for example, 30 FPE, you want a plenum at least 4" long (and 5" would be better) as the tube is 7 cc per inch of length.... and you want 1 cc per FPE....

Don't forget that the tube is threaded where it goes into the receiver, so I would recommend you make sure the bottle is supported somehow as it's a lot of weight on those threads (and prone to damage) if not supported by the barrel and/or stock.... better safe than sorry.... I don't think you have to shave anything off the steel backing block for the valve.... the 0.100" of available lift is likely enough....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon Mar 17, 2014 7:08 pm 
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I have done all the porting and the mods that you have done on your valve Bob.

The tank is on using my reverse block and the reg is set 1475 psi ( nearest I can get to 1500)

The OEM tube nearly 8 inches long, so that's almost 7 inches internal capacity. There should be more than enough volume for what I want.

The gun peaks out at 956 fps with JSB heavys, with the knee at 900 fps. Just where I want it.

One problem........ the gun is using 100 psi per shot due to lots of leakage and blow-back. Its really hard to tell where its coming from

I have changed the bolt o ring- still leaking

I have swopped the valve out for one of another gun- still blowing back.

I don't know what else to try to stop the leak and prevent the excess/ out of limits gas use??

Any ideas?


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PostPosted: Mon Mar 17, 2014 10:13 pm 
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Not sure what you mean by "blowing back".... but my guess on the excessive air consumption is hammer/valve bounce.... Usually if you are on the knee of the curve that isn't a problem....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Mar 18, 2014 4:26 am 
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I get a fair ole bit of air in my face.

At first It was the breach leaking at the bolt.

The valve stem seemed a little loose in the brass section where it slides through the valve. If the hole is oversize, then air would escape. That's why I swapped the valve out for an unmodded one..........still leaks.

Changed the barrel o'rings for new- still leakage :twisted:

There does appear to be any bounce, but I'll try winding adjuster out and bring the velocity down to see if that makes any difference


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PostPosted: Tue Mar 18, 2014 5:38 am 
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:shock: How am I just seeing this thread now......time to get my eyes checked.

Bob, great information, thanks for posting!!

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Jonathan

Im addicted to brake fluid..........but I can stop anytime....


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PostPosted: Tue Mar 18, 2014 5:45 pm 
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It helps if I put the 2 o'rings in behind the valve and striker block!!

:oops:


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PostPosted: Tue Mar 18, 2014 5:58 pm 
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Yeah, that would make a big difference.... *LOL*....

Time to look for the "knee" of the curve again maybe?....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Mar 18, 2014 6:06 pm 
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:mrgreen: :mrgreen:
After I run the shoebox for a few hours..............used all my air up try to sort that bugger out!!


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PostPosted: Sat Apr 19, 2014 12:28 pm 
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Bob.

When you machined the internal barrel groove for the o'ring, did you chamber the barrel first?

Nathan


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PostPosted: Sat Apr 19, 2014 6:14 pm 
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Location: Coalmont BC
The stock chamber is very long, so I shortened the barrel some and rechambered it before cutting the internal O-ring groove....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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