XM15 pump kit project

[OPBN]

So I have had an old SL68II sitting around in my basement for awhile that I modified, and have yet to use. Regardless, I have seen some pumpmag projects around and had an urge to build one, but always put it off due to the investment in $150+ for a kit. When XM-15, mentioned, he was coming out with a kit and it was going to be sub $70, I posted my interest and ended up being first on the list. Long story, short, I got the kit and ended up building a pump. I wanted a front grip, but wanted it shorter so I optioned to have XM-15 mill the block to accept an RTPro vert ASA that I had laying around. In order to cut some weight, I figured to have the front grip act as a reg as well, so I removed the reg from the valve and picked up a cap from Duece Machina from MCB. (BTW XM-15 offered to make one as well if needed). I am now using a Bob Long HP reg to regulate the input to the valve.To keep the rail from hanging out, I cut it down and sent it to Lukes to get pump milled, something XM also now does. For a body, I used a minimag body that Lukes had previously done a vert conversion on, and a Redz Cam-Loc feedneck is keeping the Winchester hopper in place. I removed the stop lid and epoxied a spring lid from an old pod I had laying around. I also ended up with a good deal on a Micro CAII that I picked up on Ebay. Winning this was one of the dedciding factors in making this marker, as well as selling the Micromag body which left me with a single frame and valve with a Phase II back that no one wanted to buy.

What actually impressed me the most was the fact that this thing actually worked ON THE FIRST TRY! Sort of. I did realize after a few shots that it was still firing semi auto, but clipping the main spring solved that. It has been awhile since I used CO2, and so far, I have found my FPS to be somewhat erratic. I was testing in my 60 degree or so basement, and will have to do some more fiddling to see if I can get it better. I am thinking about sending the valve out to get devolumized, wondering if this will help, or if it is the Bob Long reg that is inconsistent. I know CO2 by nature is not very consistent, but was defintiely hoping for better than this.

Here's a pic of the semi finished project. Additional plans are hooking up some sort of "hitman mod" and than sending it out to get reanodized in gloss black.

http://i307.photobucket.com/albums/nn308/oldpbnoob/pumpmag006.jpg

[Smoothice]

Looks good. You could try putting your valve reg back on and seeing if that makes the consistency better. Then you will know it is your vert reg. Then you could look for a better one.

[OPBN]

Looks good. You could try putting your valve reg back on and seeing if that makes the consistency better. Then you will know it is your vert reg. Then you could look for a better one.
Thanks, I know it doesnt have a lot of "wow factor", but I intended it to be all business. I hadnt considered putting the reg back on. I really figured that a Bob Long reg would be a good quality regulator. Maybe it's not used to co2? . I need to get more testing time. Weather is too cold to do it outside and my wife gets pissed when I shoot paint in the basement as it seems to get everywhere. I wouuld also like to get it on a real chrono. The one I have is a handheld and you have to reset it after every shot. Doesn't give a very good idea of what real world play would be like if I was shooting 1-2 shots per second rather than, 5-10 seconds between shots.

[Smoothice]

When I saw it I said "wow".

I think it looks really good. I like that the valve ends with the rail. Very clean. Not sure if dovolumizing it will help with consistency. But if should give you more shots on a 12gram. I did a bunch of testing when I had my valve done. It seemed to make a big difference.

http://www.automags.org/forums/showthread.php?t=249841

[OPBN]

You and I spoke about the devolumizing briefly in another thread. Results were interesting, barrel length had quite an effect on efficiency. Wondering though, you mentioned having a MM valve that you modded as well. Ever have a chance to test this one and write down results? Do you ever use the modded valves with full size tanks? I can't see why there would be any difference in the results, but want to make sureas I would like to have the flexibility.

[Rudz]

Idk if that BL reg is the best for co2

Id try a Palmers fatty, they're made for CO2 and HPA

Devolumizing would help with efficiency

Looks good, nice and clean, I like it

[OPBN]

I really wasnt looking to invest $90 into a reg for this though. I picked up the BL for $15. It'll have to do for time being. I also see that the max output on the Palmers is only 400psi. Wasnt 100% sure that it would work. I have the BL turned out pretty far and it's supposed to be an HP reg.

[hill160881]

i have a palmer reg that would work i think. It is chrome to.

EDIT: the net is moving fast so pic already up. Is this what you need.
http://i971.photobucket.com/albums/ae195/hill160881/Temp/100_0826.jpg

[MAGpie]

Busy putting a tac-pump together with the XM kit. I too was supper hyped when I saw the cost! Just need XM to still mill the body and rail for me, and that will happens soon as I send them off to him!

Can't wait!

[OPBN]

i have a palmer reg that would work i think. It is chrome to. I will get some pics and pm them to you at lunch.

I have a direct mount that I bought a few years back for another project that would work, but wouldnt give me the look I am after.

[hill160881]

0-800psi output.
http://www.palmer-pursuit.com/cart/index.php?main_page=product_info&cPath=28&products_id=172

Here it is on there website.

[koleah]

Also think about getting a 3.5oz co2 tank instead of the MicroCA. More shots, less fumbling around, smaller overall package.

If you're sticking with 12grams, think about going to microline instead of macroline for more devolumizing effect.

[reckid1986]

^^^^ive heard of people using weed-wacker string inside of the macroline to devolumize as well^^^^

[kobeastly]

bob long regs can be hit or miss with co2. My first one (bought in 01 or 02) worked great with co2. The two that I have now hate it. I had one guaged and was using it on a sniper II and the pressure would bounce between 240 and 350.

reg at 350
shoot
reg at 240
shoot
reg at 350
shoot
reg at 240
shoot
reg at 350
and so on.

[OPBN]

I have some of the really thick walled Macroline that I am using, should devolumize more so than the thinner walled stuff. Out of curiosity, should I mainly use this after the reg or before? Seems like before the reg would diminish the expansion of the CO2, but maybe I am missing something.

Is there a link to a discussion about devolumizing? I might need a better grasp of the theory behind this to better understand it.

[SSP REAPER]

I have some of the really thick walled Macroline that I am using, should devolumize more so than the thinner walled stuff. Out of curiosity, should I mainly use this after the reg or before? Seems like before the reg would diminish the expansion of the CO2, but maybe I am missing something.

Is there a link to a discussion about devolumizing? I might need a better grasp of the theory behind this to better understand it.
Contact Loguzzzzzz for more information. He has done it successfully on many, many classic valves. :D

[OPBN]

I meant the theory behind the benefits of devolumizing in general, not just the valve. I don't truly understand why it helps. I'm used to just the opposite with Tippmanns where you add expansion chambers etc to increase the volume it seems, not to decrease it.

[Ando]

I don't know who came up with the idea of shoving stuff like pipe cleaners, Q-Tip sticks...etc... into the macro-line to devolumise it. All that does is increases the time it takes for air in the tank to recharge the valve due to the BS in the line which I admit, is a moot point when it comes to a pump mag (can't shoot it fast enough) but why do it?

As for the devolumizing of a valve which is where the magic happens. By adding shims to the front chamber, your taking away the amount of air (volume) it uses. One thing to remember, the greater the volume, the greater the velocity and vice versa. One marker operating at 500 psi will fire a paintball at the same velocity as a marker that operates on 250 psi. The 250 psi marker uses a greater volume of gas to achieve the same velocity though.

Now with that being said, by reducing the volume of the chamber, you now need to increase the pressure to attain the same velocity before the shrinking of said chamber.

Note: Volume is constant so no mater how much pressure you input, volume is not going to change. (I think I got that right) :tard:

http://www.grc.nasa.gov/WWW/K-12/airplane/Animation/gaslab/Images/chprmt.gif

Lets use this animation as an example of the front chamber. Temp has nothing to do with this so just blank it out.

Theoretically speaking. Lets say the to reach 300FPS, the volume of the front chamber needs to be 4 cubic inches (which is where the animation starts at the top) and we need 100psi to attain that speed. Now by reducing the volume by half, the amount of pressure will double to 200psi to attain that same FPS.

But there's a few things you have to take into consideration when doing this with a mag. The achilles tendon for devolumizing a mag is the Reg Piston. We know the piston is only going to take so much pressure before it starts venting out the back so there's a balance you need to figure out. Each reg piston is going to be different (as we've seen on some lvl 10 installations) so trial and error with whatever your using to fill the chamber is something you'll need to figure out.

If I'm correct on what I said before about volume being constant when pressure is applied (it's been a while for me) :p No mater how high the pressure is increased, the volume of air in a chamber stays the same. I know there was a discussion at one time that increasing the pressure to the marker increases the amount of air the marker uses which is false (if I'm correct that is).

Just look at an air tank for example.

You have a 68 cubic inch tank rated at 4500psi. If you fill it to 3000 psi, is the volume any smaller? No, it's still a 68 cubic in tank.

Again. You have two 68 cubic inch tanks. One rated at 3k the other at 4500 psi. Will you get the same amount of shot's out of both? No you won't and why is that? Because of the difference in volume or pressure?

[OPBN]

Well, I have capped off the reg and using the Bob Long, so I shouldn't have to worry about venting.

[Ando]

Ya...I'm not sure how the cap works but good luck with your setup :cheers:

In a nut shell. The smaller the cavity the less air your going to use. Someone posted before that they were getting like 30 or so shots off a 12 gram after devolumizing the valve. I've done like 3 of them but never tested it on 12g, I use a 22ci tank on one and 2 3oz bottles on the others.

One thing I did forget to mention. It was a while since I did the mods to my valves so this issue might have been from something else I was working on but I did have an issue of shoot down when I filled the chamber up to much. Again...This issue might have been from something else I was working on so take it for a grain of salt.

I know it had something to do with one of my pump mags and I had set it so i could get at least 5 shots off before experiencing any shoot down.