James Perotti's bul...
 

James Perotti's bullpup PCP build ( so far )  

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robnewyork
(@robnewyork)
Joined: 2 years ago
Posts: 31
2018-02-25 11:13:51  

002
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003 (1)
002
001 (1)

 

 

I'm uploading for james ,thx


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-02-25 15:18:42  

Thanks Rob. This bullpup was inspired by Rob's, based on the CP1M pistol, I decided to convert this one to pcp. The reservior is 80 cc's, the gun is 15" long, without the butt stock. The butt stock will screw on to the main tube for easy take down.  


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dan_house
(@dan_house)
Joined: 2 years ago
Posts: 78
2018-02-28 10:11:49  

sweet

 

James,what trigger gripe frame is that?

On the Lunatic Fringe of American Airgunning
Proud sponsor of team_subsonic
Charter member of the Western Heretic Alliance


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-02-28 15:11:38  

Thanks Dan, The grip frame was machined from a 1"x 4" x4" block of aluminum. I modled the gun on ROBNY's bullpup, which can still be seen on page 5  on the old yellow forum.


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-03-25 08:27:54  

I'm still working on my cp1m to bullpup project, the firing valve still needs some work.  The pistol is .22 cal. and it's shooting  in the 15fpe. range, with the stock barrel. Here's a recent string, fill pressure is 2500psi. 704 699 699 699 702 703 709 716 712 711 714 719 726 720 727 719 729 729 726 722 722 718 722 714 715 706. end pressure  1275 psi. I'm hoping I can flatten the string with a bit more work.   the pellet was cp's


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-05-01 11:28:18  

I'm still working on the tune. I've been able to get 30 shots over 700fps. I wanted 21 fairly close shots, this is the flatest string so far. 720 715 721 723 730 737 730 743 729 745 743 748 733 748 747 746 744 746 735 714 738 738.


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Steve in NC
(@steve-in-nc)
Dealer
Joined: 2 years ago
Posts: 335
2018-05-02 09:20:42  
Posted by: James Perotti

I'm still working on the tune. I've been able to get 30 shots over 700fps. I wanted 21 fairly close shots, this is the flatest string so far. 720 715 721 723 730 737 730 743 729 745 743 748 733 748 747 746 744 746 735 714 738 738.

Very nice, James!

temp

Assuming the 2500-1275psi = 6760bar-cc pressure consumption figure applies to both strings, air utilization works out to about 16bar-cc/fpe for the longer string, 18 for the shorter.  Not too bad for this relatively short barrel.

But could it be you're still looking at some hammer bounce?


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-05-02 13:41:36  

Hi Steve, Yes, there could still be some hammer bounce, and I think the valve spring might be to heavy, and preventing the gun from regulating better?


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Steve in NC
(@steve-in-nc)
Dealer
Joined: 2 years ago
Posts: 335
2018-05-02 19:42:10  
Posted by: James Perotti

Hi Steve, Yes, there could still be some hammer bounce, and I think the valve spring might be to heavy, and preventing the gun from regulating better?

Well, a softer valve spring should move the MV peak toward lower pressure, which would probably necessitate less hammer energy and a lower fill pressure, which in turn might equate to fewer useful shots per fill.

How about going the opposite way: Stiffer or more preloaded springs for both valve and hammer which should accommodate higher fill pressures and therefore more energy to propel more shots per fill?

Is there some other reason you're filling to only 2500psi instead of 3000?  Is there a safety MWP issue in play?


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robnewyork
(@robnewyork)
Joined: 2 years ago
Posts: 31
2018-05-02 21:55:14  

james, please email the latest pics , I cannot find the ones from a week ago..


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robnewyork
(@robnewyork)
Joined: 2 years ago
Posts: 31
2018-05-03 16:31:52  

006
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001
004


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-05-03 17:36:28  

The overall length of the gun is 21 1/4", the length of pull is 14" The gun weights about 3.5 lbs. scoped.


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-05-04 05:35:11  

Hi Steve, I chose 2500 psi. for the fill pressure, because I didn't want cocking the gun to be a physical exercise, it's a little stiffer than I would have prefered. I have tried heavier valve return springs and lighter, the same with the hammer spring. I've tried stuffing the valve, I've tried maybe 75 different combinations. Oddly, over dozens of strings, (with the debouncer installed), the gun seems to use less air and get more shots, on the faster strings, and any attempt to lower the velocity, results in more air usage and less shots.


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-06-01 09:22:58  

Here's  my latest 21 shot string, fill 2500psi. reservior is 80cc's  742 740 746 744 746 744 751 750 743 750 750 747 746 749 740 741 732 746 742 746 742 ending pressure 1470psi. I'm lossing air to hammer bounce still, I might try increasing the area of the valve seal so it's a little harder to open, it only overlaps the valve throat by .007" right now


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Steve in NC
(@steve-in-nc)
Dealer
Joined: 2 years ago
Posts: 335
2018-06-01 17:50:33  

Hell's Bell(curve)s, James!  Is that li'l sucker regulated?  That string certainly looks like it is. 

JPSAXpup

That's amazingly flat, considering the pressure range, with first and last shot clocking in with exactly the same MVs.  Why did you stop at 21 shots?

 


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Steve in NC
(@steve-in-nc)
Dealer
Joined: 2 years ago
Posts: 335
2018-06-01 20:39:24  

PS:  Assuming 14.3gr pellets, the average energy for that string is ~17.4fpe for an air utilization of 15.5 bar-cc/fpe.  Not too bad for such a short barrel.


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-06-02 08:05:16  

Hi Steve, Yes the pellets are 14.3, I swapped the 8" barrel for an 11" barrel, But I'm not sure it's gaining much velocity wise. I'll swap them back at some point just to see. I wanted at least 21 shots, because the gun came with three 7 shot mags, and the pressure drops off a cliff at 24 shots Yes, it looks like I'm finally getting a handle on the shot string, I had to go with a heavier hammer spring, to get the shot string under control. Now to try to cure the hammer bounce, ands pick up a few more shots.


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James Perotti
(@jpsaxnc)
Joined: 2 years ago
Posts: 75
2018-06-09 08:14:01  

 I'm going to stay with the 11" barrel. This is probably the best tune I can get on the gun. Even though the air usage isn't the best, this is where the gun preforms the best. Here's a 26 shot string. 747 749 746 750 754 750 752 757 755 750 753 753 757 756 759 754 755 753 756 759 754 755 752 759 750 751.  av. 753 fps.  av. FPE 18.0 


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