Paintball

[Cap'n Newb]

Hey, gang,

Got a question. I performed a stock bolt mod exactly as described on the VM Empire site (chamfered face, overbored internals, etc.). Beautiful job, if I do say so. Got her all back together and she works perfectly. Except that the velocity is markedly lower than before. The bolt adjustment is right where I left it, by the way. My first guess was that, because the entire bolt/barrel assembly is essentially an expansion chamber, the increased volume of the bolt is effectively shortening the barrel. But in terms of overall volume, the increased volume of the bolt would only amount to a negligible change in barrel length. So now I'm thinking that the initial burst of high pressure/low volume air that normally gets the ball scooting along has been changed to less-high pressure/low volume air, so that even though the overall amount of air in the barrel is the same, the lack of that initial boost is the culprit.

The valve is set on the smallest hole, so I can always go higher. I'm just interested in the physics of it, because I wasn't expecting this kind of change.

Anyone out there actually perform this mod and notice any such difference?


Thanks,

Cap'n

[russc]

I'd definitely go to a bigger hole. I always run on the biggest, in fact I usually open the valves up.

[EvilEd]

I must say in all the years I have had that mod up there you are the 1st to say you lost fps.

[Cap'n Newb]

Okay, update.

I took everything apart and started thinking about the problem. As I was fiddling about, I noticed that the top bolt was rather loose in the body. I noticed this when I first reassembled the marker. Normally it is quite tight. And then it occurred to me that I replaced the o-rings on the bolt when I put it back together. Sure enough, there is visible light all around the bolt. And I mean, lots of light. The bolt, with o-rings, will literally free-fall through the body, even past the magic fingers. I even flicked it through the body (and past the fingers) with my own finger, and it sailed right out.

So now the matter is clear: air is getting past the o-rings. Or rather, some air is managing NOT to get past the o-rings, and is going out the barrel.

I tried dropping the bolt through the stock barrel, and it fell right through that as well, something it never would have done before. Basically the rings are almost flush with the profile of the bolt. In fact, a single sheet of regular copier paper, folded crisply in half, generates the same profile, under 16x magnification, as the rings do. I think this is about .006," if memory serves.

Anyone ever heard of new o-rings being too snug or small? If so, any way to swell or stretch them a little?

Perhaps remove them and lay down a thin layer of material in the grooves to "lift" them? That's a bit extreme, but I bought several sets, and don't want to waste them, and don't know where to get any others.

Anyone have a micrometer who can measure the profile of the rings versus the bolt? Or simply, their diameter on the bolt? Or even a good close-up picture of the stock bolt? I just want to be sure that my memory is not playing tricks on me. I definitely remember the rings being fatter and higher profile than these.

I think.

This is a weird twilight zone experience, to be sure. Never heard of anything like it.

Thanks again,

Cap'n

[Cap'n Newb]

Well, all's well.

I put a single wrap of teflon tape down in each groove, popped the rings back in, and she's perfect.

Like buttah!

[EvilEd]

glad to hear it's all fixed