Big Bore MSP From the 1980s....

[Duane38]

Hello!  Been a while for me to post.  Things have settled down a bit in my world, hope everyone else is doing well!

I am looking for the article on an American gentleman who built a big bore MSP, one which I can't seem to find via Google searching; had the info once upon a time....

With this rifle, the gent utilized a ram-rod type of air delivery/pump tube system (much like some Philippine guns). In the article, IIRC, he was hunting deer with it, too. 

I'm certain the pump tube must've used a rather small piston in order to achieve usable pressure, for obvious design and functionality reasons.

Can anyone share/find this gun?  I am just a curious sort to learn more. 

[K.O.]

only one I can remember is the foot pumper... do not know about a big bore... think theyalso made a shotgun iirc...

Eskopeta

found a ytube...

[rsterne]

Not quite in line with your post, and I don't know what caliber you are looking at.... but I can give you a rough idea of how big a valve you might need.... MSPs generally have a valve volume of about 1/3 the barrel volume, assuming you intend to dump all the air with one shot.... Going more than 50% wastes a lot of pumping as more of the air goes out the muzzle after Elvis has left the building.... and less than 1/4 the barrel volume produces less power than most guys seem to want.... So, if you were looking at a .357 cal, which has a bore volume of 0.10 CI per inch of length, and a 24" barrel, you would have 2.4 CI of bore volume, so a valve volume of 0.8 CI = 13 cc would be a good place to start.... up to a maximum of about 20 cc....

I built a .25 cal MSP that I called the Millenium Pumper, based on a Disco tube and the pump lever from a 392 (actually the Mac1 Billet version)…. It had a valve volume of 28.5 cc and took about 80 pumps to get to 1800 psi.... That gun was set up as a retained air pumper with 2-3 shots per fill, but if you chose to dump all the air produced 54 FPE with a 25.4 gr. pellet.... I did not have any 34 gr. JSBs at the time, but I would expect about 60 FPE with that pellet weight (SD)…. With the same pump, it would take about 55 pumps to fill a 20 cc valve volume to 1800 psi.... At that pressure, you should be able to drive a .357 cal. 81 gr. pellet at about 800 fps....

Bob

[Duane38]

Not quite in line with your post, and I don't know what caliber you are looking at.... but I can give you a rough idea of how big a valve you might need.... MSPs generally have a valve volume of about 1/3 the barrel volume, assuming you intend to dump all the air with one shot.... Going more than 50% wastes a lot of pumping as more of the air goes out the muzzle after Elvis has left the building.... and less than 1/4 the barrel volume produces less power than most guys seem to want.... So, if you were looking at a .357 cal, which has a bore volume of 0.10 CI per inch of length, and a 24" barrel, you would have 2.4 CI of bore volume, so a valve volume of 0.8 CI = 13 cc would be a good place to start.... up to a maximum of about 20 cc....

I built a .25 cal MSP that I called the Millenium Pumper, based on a Disco tube and the pump lever from a 392 (actually the Mac1 Billet version)…. It had a valve volume of 28.5 cc and took about 80 pumps to get to 1800 psi.... That gun was set up as a retained air pumper with 2-3 shots per fill, but if you chose to dump all the air produced 54 FPE with a 25.4 gr. pellet.... I did not have any 34 gr. JSBs at the time, but I would expect about 60 FPE with that pellet weight (SD)…. With the same pump, it would take about 55 pumps to fill a 20 cc valve volume to 1800 psi.... At that pressure, you should be able to drive a .357 cal. 81 gr. pellet at about 800 fps....

Bob

Yes, sir.  Remember that build well from the Green.  I've been on the forums over ten years now and have to privilege to see many creations come to fruition.

This particular rifle, IIRC, was once featured in an air gun magazine in the 1980s. Additionally, I think someone may have either sent it to me in an email or shared via forum.  Can't remember exactly.  Been a few years now.  More interested out of curiosity than anything else.

Though, do plan on building a big bore MSP at some point.  May use an air displacer piston design to establish efficiency, where an initial charge of air (3.5kpsi) is used (pump and/or probe for initial charge).  In practical theory, where one shot drops the pressure off to be topped back off for the next shot sort of affair. This should diminish the exuberant amount of pumps needed for a refill.  Now that not only have I drawn up lever designs, but actually built many to see if reality matches that of paper mathematics and theory, there is a high volume and high ratio lever/pump design I'd like to try on this build.

You may recall the .22 caliber SSP I started on a few years back.  That has long been finished and turned out to be an exceptional rifle; 13.5 ft/lbs with CPs and drives tacks.  Has a 10ci of air, or 163cc of sweep volume with the piston design, operating at 144 bar.  Later on I will post pics and maybe a video.  Life has been slowing down a bit since the political world has been.  I'm back for a bit now...