Big Bore Pumper

I've been toying with the idea of building a pumper air rifle in 9mm. I am currently building a .22 cal pumper that will kick out a 24.5 gr JSB Monster at 580 fps. I dont really have a goal in mind and dont really know what is realistic for a pumper in 9mm. I would hope for over 500 fps with a 75 gr. round ball.

My first thought is to scale up the size of the pump tube and valve to match the increase in size of the pellet. My main concern is if I increase the diameter of the pump tube and piston I will not be able to acheive enough PSI. If I keep the pump diameter at 5/8" like a Crosman pumper and increase the volume of the valve it will take to many pumps to fill the valve.

Anyone have any idea what the volume of the valve should be or what psi I should be shooting for to launch a 9mm projectile out of the end of a barrel at a reasonable rate? I'm looking for input, pointers and ideas.....

Joatmon wrote:I've been toying with the idea of building a pumper air rifle in 9mm. I am currently building a .22 cal pumper that will kick out a 24.5 gr JSB Monster at 580 fps. I dint really have a goal in mind and don't really know what is realistic for a pumper in 9mm. I would hope for over 500 fps with a 75 gr. round ball.

My first thought is to scale up the size of the pump tube and valve to match the increase in size of the pellet. My main concern is if I increase the diameter of the pump tube and piston I will not be able to achieve enough PSI. If I keep the pump diameter at 5/8" like a Crosman pumper and increase the volume of the valve it will take to many pumps to fill the valve.

Anyone have any idea what the volume of the valve should be or what psi I should be shooting for to launch a 9mm projectile out of the end of a barrel at a reasonable rate? I'm looking for input, pointers and ideas.....

I would think you could compare what's already on the market for a reasonable goal.

i.e. and although PCPs: I've got a Career Infinity that will put out 933 FPS with 32.4 Eun Jin pellet. That's a heap more than 500 .

Too, there is the Career Ultra that, after tuning, can put out a substantial FPS with much higher grains . . .even 92 grain pistol like bullets.

Then there is my Evanix Rainstorm (RS) that can produce 933 FPS with 21.5 gr Kodiak pellets.

To me, these are ideal velocities because they remain sub sonic and don't attempt to recreate the powder burners, don't tip the projectile and, well, the faster you can get up to a point is optimum for a flatter trajectory.

Of course, I'm no where near expert but I think I have my understanding in this arena correct.

Hopefully someone else with chime in with more information.

But the thing is that you want to do a "pumper". So to compare a pumper to a pumper, as it were, you could check out the FX Independence (click for link) that is a pump among other things. Perhaps if you could study one of these then you could stumble on something that would be competitive in the market?

I've often thought about what it would be like to have one of those as I'm a big fan of independence and self sufficiency. You know, the more you can do on your own, the better and all that (says the guy in the wheelchair most of the time )

But, then again, you are also asking for a "reasonable FPS" to push such weights as you describe. I think you are on the right track in finding out what you have to meet to make it a worthy "Pumper" producing enough FPS to push a desired weight hard enough to make an impression (pardon the pun but I just couldn't resist!)

Let's talk about it a little more. I'm not bad in the idea department. I'd like to hear more.

I may not have the answers but, odds are, I may know someone that does!

X2 on studying the XP Independence pump, I'm sure it must be a multi-stage or it wouldn't pump up so fast. If you doubled the diameter of a pump piston for instance, it would be about 3.5 times harder to pump due to the area increase. I think a two stage where the large piston pumps up to 800-1000lbs and the smaller piston takes it up to 1500-2000lbs would be the way to go.

Thanks for the link to the Independence, I didn't know there was such an air gun available. It looks like it uses a longer pump arm with a shorter pump stroke for more mechanical advantage. That is one of the options I was thinking about. I was thinking about a larger valve/ resivoir I hadn't thought of making it large enough for multiple shots though..... It might be a bear to pump the initial charge but maintaining that charge with 3 pumps per shot would make it worth while. I have some new ideas now.....

Joatmon wrote:Thanks for the link to the Independence, I didn't know there was such an air gun available. It looks like it uses a longer pump arm with a shorter pump stroke for more mechanical advantage. That is one of the options I was thinking about. I was thinking about a larger valve/ reservoir I hadn't thought of making it large enough for multiple shots though..... It might be a bear to pump the initial charge but maintaining that charge with 3 pumps per shot would make it worth while. I have some new ideas now.....

I don't know, really: If you check out the Walther Falcon, that one, I do believe, is like 50 lbs to cock it. I can do it fairly well but I've gotten practiced at it, know where to grab the AG to get the best leverage, etc.

However, I've handed it over to some big he man types that got a surprise when they tried to cock it so nonchalantly like I was doing! I do it on purpose, don't cha know! I like to see 'em get that look on their faces: Precious to no end.

But the point of the matter is that with the right fulcrum placement even a short rod can get you some high torque. Just MHO.

Couldn't be cheap metal that's for sure.

No problem on the link. I haven't been swimming in the AG sites here of late but you'd be surprised what you'll find with a little bit of looking on the net.

Keep us posted on it even if it turns out to be just an idea. Never know about those. Powerful things when entire countries can be founded on just one of them!

I'm busy the next couple of weeks, after that I'm going to start building a pump. I'll have to get some materials ordered and a gauge so I can start experimenting with some of the ideas I have.

Joatmon wrote:I'm busy the next couple of weeks, after that I'm going to start building a pump. I'll have to get some materials ordered and a gauge so I can start experimenting with some of the ideas I have.

I was doing some admin stuff to the site and saw your post. Wanted to say that I'm impressed with your enthusiasm.

Highly interested in your work as well. Maybe you could post an on going thing about your work and the problems you run into.

A lot of people only post the end product and the good stuff. Personally, I like to see the mistakes so I can learn from them as you do.

I've got a shelved project of running two Shoeboxes, for instance, that when life stops throwing me curves I want to do something like that on. You know, all the bad mistakes I made, etc, along with the better stuff that I could be right proud to say I did.

The heroin in the story has to have some ups and downs to be the hero!

Too, I just opened up all the forums so that all can see links and pictures in the forum without becoming a member so I'd like your opinion about that: See, you'd of had to sign up to see something like what I'm suggesting you post as a series and only our members could have seen that sort before I made the change.

Now that I've opened up all the forums that the public sees to pictures and links, do you think this would be a hindrance or not matter at all to what you post about such a thing as an on-going series showing all the bad as good progress and why you chose to go this or that route?

Your input is valued.

I'm not really into the admin side of forums, so I dont know what the down side of nonmembers being able to see pic's and links would be I can't think of any. Being able to see pic's before becoming a member might help people decide if they want to be a member of this forum.....

I will start a new thread when I begin my build and show my progress from start to finish.

Well, there is a lot of truth to your words but there is a certain, if not misplaced, sense of "group" thinking that occurs with members in that if they know that others have to give up some personal information would be the only that saw what they posted in links and pictures, as in a picture of a mistake or a goof up, etc, they'd be more comfortable sharing.

I've had this debate with a few of my close friends and it's a wash. Both sides of the coin have valid points. Your stance, it would seem, is like mine as it doesn't seem to phase you because you'd still be willing to post a series of sorts. That's a good thing, I think.

And truthfully, it was a new product offer that finally tipped the scales for my way of thinking: A foster fitting from Will Piatt that I think all would benefit from having access. Too, I think opening up the forum better supports and promotes this sport; a goal to which I think is a worthy cause and one of the reasons this very forum came to be.

I'll look for your posts on your project. Maybe I'll gain enough inspiration to renew my efforts on some of my own projects that I'd like to share likewise.

Thanks for your input. It *is* appreciated.