I'm about to build a pump mag. What do I need to know?

Okay, I've been collecting pump mag parts for the last year or so, and I'm finally ready to put it together. But I want someone to check my math and make sure I'm doing this right.

I have all the right parts. I have a pump milled rail (done by Luke) and a Rainman pump kit. (At least I think it's a Rainman kit. It's whatever kit is on this mag.) I also have a pump milled body, of course, and a stock Level 7 classic valve with a CF frame.

So what comes next after I put everything together? I know I need to replace the bumper with a wave spring (which I have). I also know that if I fire the marker with the wave spring installed and the bolt resets by itself, I might have to trim down the bolt spring. I don't know how much I should trim at a time, though. I'm figuring I'll just cut off a 1/4 coil at a time or so and then retest until I hit the right length. (I've got a few spare bolts springs, so I don't care if I screw one up beyond use.)

I've also read conflicting things about the wave spring itself. Some people seem to think that if the spring is trimmed to the "correct" length, then there's no need to add the bumper behind the wave spring. Others say that I should cut down the bumper to go inside the wave spring.

So yeah....any help would be appreciated.

Use a worn bolt spring it should be just past the tip of the bolt or even with the bolt. Don’t cut a spring it will only cause you headaches. Don’t trim the wave spring. Cut the bumper down to fit inside the wave spring.

If it’s resetting itself. Make sure it’s chronoed. Use a weaker bolt spring or your wave spring is toast.

If you have questions ask. A lot of people don’t know what they are doing when it comes to pump mags.


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The trimmed bumper helps keep the wave spring centered (although the body itself does that to an extent). So that is recommended.

If you do end up cutting on a bolt spring, I'd recommend even going with 1/8 instead of 1/4 and make sure to put the cut end against the bolt. I also suggest using a dremel or hack saw to make the cuts and not trying to do it with wire cutters. If using a dremel, go slow to keep the heat down; you don't want to make the spring more brittle by heating it up repeatedly.

I don't know that this is more extensively true or just my experience, but I always found it much easier to make pump mags work using a powertube spring instead of spacers.

Good luck!

I might have just gotten lucky, but I chopped an old bolt spring about 1/8 rotation past where the curl leaves the flat terminal ring and it's worked for three years. Had to replace my wave spring last weekend because it wore out. I also had to make a new pump rod a few months ago, which was easier than I expected out of a wire hanger.

Oh, and if you're using a UL body, I'd highly recommend picking up one of KNM's snap on stock feeds. I've found that a lot of people don't really pay attention to movement if they're not cueing on a hopper, so you can dangle and sneak a lot more shots off with a stock class feed. Here's the link:
https://www.automags.org/forums/showt...90#post2916490

+1 for KNM's stock class feed.
If you want to go a bit further (and a bit more expensive), chop the feedneck off that body, drill and tap a 6x32 hole in front of it (like a phantom) and mount an Apocalypse springpheed to it.
I love my springpheeds!

Attachment 99843

This one is his model designed for ULE mags, but I used a phantom model on my riflemag.

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Originally Posted by zulubravo44

Had to replace my wave spring last weekend because it wore out. I also had to make a new pump rod a few months ago, which was easier than I expected out of a wire hanger.
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How did you know the wave spring was wearing out?

when it not longer stops the bolt from resetting

Quote:

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Originally Posted by captian pinky

when it not longer stops the bolt from resetting

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Gotcha. Thanks for all the help, guys. I'll start working on it.

This is what mine looks like so far, by the way.

Attachment 99844

Yeah....you guys were great. Luckily, one of my old springs was the perfect length, so I didn't need to trim it. All I had to do was shave down the bumper and add a little shim under the pump rod to help it pop up a little higher when it's pushed back. And now it's shooting great!

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Originally Posted by rawbutter

All I had to do was shave down the bumper and add a little shim under the pump rod to help it pop up a little higher when it's pushed back.

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Instead of a shim, why not just bend the tip of the rod?

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Originally Posted by luke

Instead of a shim, why not just bend the tip of the rod?

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Huh. Yeah, that might be easier. Why didn't I think of that?

Quote:

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Originally Posted by rawbutter

Huh. Yeah, that might be easier. Why didn't I think of that?

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Okay....I take it back. I'm not sure this was a good idea. Bending the rod might be easy for a paintball god with tons of experience with pump guns (i.e. Luke), but for a mere mortal like me, it was a huge headache.

First, I bent the rod a tiny, TINY little bit, but even that was too far. The bolt hit the rod when moving forward. Then I tried to bend the rod back, but if anyone has ever tried to straighten out a metal rod before, it's damn nigh impossible. It just spins in the vice. Still, I managed to get it bent back into shape somehow, only to find that again, I had bent it too far. The rod no longer hit the bolt at all. :mad: Fast forward an hour or so of bending the rod back and forth, I never got it perfect. I still had to use a plastic shim. But at least it's working again.

Part of this might be a problem with the pump kit itself. The rod seems to be bent too far back, so by the time it hits the "ramp" in the pump slot, it's too far back to catch the bolt in the right place. It just hits it on the side. By adding a little plastic shim in the slot, however, I'm changing where the pump rod starts to move up. So maybe bending the rod works for a standard AGD pump kit, but it didn't work for this.

Sounds like your bending it in the wrong spot.


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Quote:

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Originally Posted by rawbutter

Okay....I take it back. I'm not sure this was a good idea. Bending the rod might be easy for a paintball god with tons of experience with pump guns (i.e. Luke),

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I have designed exactly ZERO pump markers.
I have owned exactly ZERO pump markers.
I have built exactly ZERO pump markers.
I have however fixed several ill-bent pump rods that rendered the markers unusable.
In fact, I would argue that YOU have much more knowledge on the subject than me.
Dont blame the solution...
lol
:)

Quote:

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Originally Posted by luke

I have designed exactly ZERO pump markers.
I have owned exactly ZERO pump markers.
I have built exactly ZERO pump markers.
I have however fixed several ill-bent pump rods that rendered the markers unusable.
In fact, I would argue that YOU have much more knowledge on the subject than me.
Dont blame the solution...
lol
:)

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Oh, don't get me wrong. I'm not mad at you. I'm sure that bending the rod is a better solution than shims, which can fall out. But the tolerances are so tight that bending it into the exact right shape is very difficult. I might try again later, but for now I'm happy how it is.

The one thing to remember is that, when the pump breaks (99% pump breakages are in the wave spring), you end up with a semi. Albeit a Lvl7 mag, but a semi none-the-less.

Thanks TK! Even when you fail, you still give us a better than most gun.

Quote:

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Originally Posted by rawbutter

But the tolerances are so tight that bending it into the exact right shape is very difficult.

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Then you're doing it wrong, because it's actually very simple. :D

OP, maybe this will help you in getting the angle and length correct.

https://i.imgur.com/hYdaYrz.jpgh

Just assemble the marker without the body and you can see exactly how much to bend the rod. ;)