Paintball

[HurtCow]

It's ok, I'm the king of trying everything except for the obvious fix. I love tinkering and messing with stuff so I'll just dive in.

[HurtCow]

Ok I drilled out the largest valve hole, and added a weaker valve spring. Sometime this weekend I'll re-assemble it and see what it's doing now.

[HP_Lovecraft]

The reference to drilling the transfer port refer to the early gen VMs. They had a smaller port, minimizing any benefit gained by drilling the valve. With most Vms, you should be fine with just drilling the valve.

That said, about a hundred things can cause the low fps. the orings might just be bloated from age. The bolt screw might not be at a "stop". it might have a cocker cupseal. the transport port and/or valve screws might be the wrong size. The spring might be warn, or missing its guide.

When you go to air it up for a test, keep some washers handy. If the fps is still low, drop them behind the spring until you get a good fps.

[HurtCow]

Thanks HP. I wanted to try everything else before shimming the mainspring. The gun's actually in great condition besides the velocity issues. I have a 2nd I picked up from the same guy, also backbottle, which I haven't tried out yet.

[Sgt Hollywood]

Just curious, but why did you want to try everything that was more complicated than shimming the main spring first?

[Prepaid Lenin]

Huh, my brother managed to chrono nicely with a tank forward ASA and CO2 this afternoon by just turning the valve a click. And before that it was shooing HOT.

Hopefully HPA is not gonna be any more difficult.

[HurtCow]

Originally Posted by Sgt Hollywood

Just curious, but why did you want to try everything that was more complicated than shimming the main spring first?

Cause that's how I roll.

Actually shimming the spring is the obvious choice. Opening up the valve is more scientific, which allows me to rationalize to myself that I actually improved it, as opposed to applying a band-aid.

[HP_Lovecraft]

I do agree with that logic. The vm was designed to go over 300fps stock, so only getting 170 is a sign of a problem somewhere. Sure shims and/or a liquid tank would get you to 300psi, but still doesnt fix the problem, and effeciency would crap out as well.

but...... if nothing else works...

[Sgt Hollywood]

Except drilling and lighter springing is not getting the VM back to a stock setting. It's kinda like swapping out an engine ECM and exhaust for something that could have been a $5 sensor failing.

The shimming was just to test to see if it was a weakened hammer spring causing to short (opening and duration) valve strikes, and if so replace the spring.

However, the things he's doing are commonly done anyway so no harm, he just might end up replacing the "$5 sensor" in the end anyway.

[HP_Lovecraft]

Originally Posted by Sgt Hollywood

However, the things he's doing are commonly done anyway so no harm, he just might end up replacing the "$5 sensor" in the end anyway.

The difference in paintball, especially for those of us that use old guns, is that the "$5 sensor" may be no longer made.

Sure, it might just be a weak spring, but if nobody has them anymore (ie Skanline, IIsports), its not something you can replace at the hardware store.
Likewise, if the internal passages are worn, new orings alone will not resolve the issue, and honing might end up taking parts out-of-spec.

Drilling, however, was done with even brand new VMs back in the day, to offset effeciency issues, and cold weather performance. So much that sheridan paid attention, and modified later models with a larger transfer port, and internal EC from the factory.