Interesting Problem - 760 Pumpmaster
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Interesting Problem - 760 Pumpmaster
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Topic: Interesting Problem - 760 Pumpmaster (Read 3320 times))
Nail Gun
Blissfully Ignorant
Plinker
Posts: 226
yes
Real Name: Dave
Interesting Problem - 760 Pumpmaster
«
on:
January 02, 2013, 07:32:44 PM »
Please forgive me in advance for my poor terminology, I know what the parts are and what they do, that's about it though.
I got bored the other night and decided to do some work on the old Pumpmaster. I ended up making taller, gasket to better seal the breech and valve. I changed the spring inside the valve for a lighter one and added a stronger hammer spring. I also enlarged the transfer port, etc. Lastly, I made an o-ring out of neoprene and attached it to the end of the probe on the bolt to make a better seal in the breech.
After the mods she began sending CPHP's at 610fps (average) at 10 pumps. However, I noticed each time I shot it the back pressure would open the bolt 1/4". If I held it shut while shooting, my velocity would average in the ballpark of 630fps. Obviously with the bolt opening up it's allowing air to leak out of the breech while firing.
I tried bending the bolt handle out so it will lock in place better but that didn't help. Has anyone figured out a way to add a device to lock the bolt in the full closed position while shooting?
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plinker99
Shooter
Posts: 81
yes
Re: Interesting Problem - 760 Pumpmaster
«
Reply #1 on:
June 17, 2013, 09:44:17 PM »
hi nail gun,
i had the same problem on my 760 with the plastic receiver. the tab where the bolt locks into got slightly worn. i used a soldering iron & melted some plastic that i had to rebuild the area. i made it slightly higher & closer to securely lock the bolt in place.
here's a picture of the inside of the receiver. the silver colored area is where the bolt locks & needed repair.
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mav72
Expert
Posts: 1426
I’m here and gone like the Loch Ness Monster.
Re: Interesting Problem - 760 Pumpmaster
«
Reply #2 on:
June 18, 2013, 12:14:30 AM »
First of all do you have a later 760 with the plastic reciever? I just ask because I don't know much about the older ones with the brass bolts...
I have some ideas but I'm waiting on a 760 that I bought to move my "good" parts over to.... I doesn't get here till next week..
Anyways.....
1. I had a thought of using a thumb screw that they use for computers to hold the bolt in place but I haven't figured out a good way of doing it yet...
2. I don't know if it will do anything to hold the bolt or work at all, but I thought of slipping shrink tubing over the probe for added friction...
3. I haven't studied how it works yet, but I noticed that the trigger on my 760 will hold the bolt closed but there is a little slop... So I was going to look if there is some way to get rid of that slop...
4. You can add a little spring behind the trigger of the bolt but the problem is getting it to stay there.. There's also the issue of the spring tension cracking the plastic...
So yea after sealing up the guns, I'm having similar issues with my 760 and 2100...
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mav
BillK
Sharp Shooter
Posts: 877
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Real Name: Bill
Re: Interesting Problem - 760 Pumpmaster
«
Reply #3 on:
June 19, 2013, 12:25:16 AM »
Here are some pics of what I did so far. Just a test fit at this point.
I used a pocket clip from a Zebra all point pen. (Stainless) It rotates down and is held in place by a screw head.
The BB channel is plugged by the #4 screw & nut. So, no more BBs. Nothing else is effected.
Placement of the screws reflects the front of the bolt being ground down (dremeled) so that it allowes the probe to push the pellet further into the barrel support.
«
Last Edit: June 19, 2013, 10:00:28 AM by BillK
»
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mav72
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I’m here and gone like the Loch Ness Monster.
Re: Interesting Problem - 760 Pumpmaster
«
Reply #4 on:
June 19, 2013, 12:31:57 AM »
Quote from: BillK on June 19, 2013, 12:25:16 AM
Here are some pics of what I did so far. Just a test fit at this point.
That's some great ingenuity right there...!
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mav
cherokeesteve
The Cheap Airgunner/YouTube
Sharp Shooter
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Real Name: Stephen
Re: Interesting Problem - 760 Pumpmaster
«
Reply #5 on:
June 19, 2013, 05:46:34 AM »
Necessity is the mother of invention!
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Interesting Problem - 760 Pumpmaster