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d4rksabre 09-02-2006 10:52 PM

VM-68 velocity woes
ALright, I have a VM-68 Magnum that I picked up a year ago from a kid who had no idea what it was. I've never had good luck with it shooting high enough, even with the valve at 12 oclock and the bolt screw all the way in. So all you VM owners out there, tell me what I need to do to get this beast back in shape! :confused: (and yes, i've read over the tech tips on VMempire, I'd just appreciate some more one on one help :D)

HP_Lovecraft 09-02-2006 11:31 PM

Its a common problem. Sometimes just because parts have worn out.

Simple solutions are to add shims behind the spring (I think dimes fit well). After that, drilling out the 3'clock to be larger then the 12'clock is a common solution. Though, older VMs have a narrower transfer port, so that might have to be drilled out.

Bad orings also cause that. As they get old, they get bloated, and add a great deal of friction.


MadCat 09-02-2006 11:39 PM

I agree with HP, drill out 3 o'clock to be larger -- bigger hole, more gas passes through.

If you can get your hands on a valve from a pro-shot kit, you won't have to do any drilling.

If your main spring is worn down (or worse...cut down) you won't be hitting the valve hard enough to get that beast kicking. Check that too. I haven't used dimes, but I have used thick washers to compress the spring a little.

Make sure that you lubricate the hammer and bolt well (and make sure that it's nice and clean in there)

d4rksabre 09-03-2006 12:09 AM

I just put a new main spring in it yesterday and it didnt change the velocity any. I also shimmed it with washers. I may try drilling the 3 oclock, but i dont want to ruin the gun, so id rather stay away from drilling it...kind of a last resort issue. I've kept it well oiled too, but maybe i need to rip the whole thing apart and check all of it. I'll do it tomorrow.

Chaos 09-03-2006 12:28 AM

I had some issues with mine,turned out to be the cupseal causing the problem.It was an aftermarket one though.You could try a weaker valve spring,it'd make the valve stay open a bit longer allowing more air to come through,it'll make it a bit more of a gas hog but,then it's a VM and they all are

HP_Lovecraft 09-03-2006 06:54 AM

Thats true about the cupseals.
The aftermarket ones tend to be shorter so that the manafacturer can make the exact same cupseal to fit both the VM and Autococker/Sniper.

WOrks in both, but tends to cause FPS issues with the VM.

Anyway, there is no risk in drilling out the 3'clock hole, since that hole is NEVER USED. Just make sure you remove the brass core, and you should be all set.


d4rksabre 09-03-2006 02:27 PM

alright, so it turns out im a dumbass and my valve is at 6 oclock, not 12 (i thought it was twelve from like a year ago) i checked it, its at 6. I dont have an adjustment tool though. any ideas on how to do it without the tool?

Edit: I took the VMempire's suggestion about the 3/8ths bolt and it worked. its definitely shooting hotter and LOUDER lol. I'll chrono it at somepoint, but it seems to be better now. yay!

MadCat 09-05-2006 12:43 PM

Ah VMs....I think I'm going to cuddle with my horde this evening

d4rksabre 09-05-2006 12:53 PM

id imagine that being quite uncomfortable

sniperfan 09-06-2006 08:57 PM

Heres what always worked for me: Run it as a siphon tank. Lots more energy available from the liquid CO2. Its a little harder on cup seals, and sometimes you'll look like youre shooting a muzzle-loader on a cold, humid day, but it works great for reliability and velocity.

As far as the other stuff, springs get weaker as the gun is used. When I used to go thru a VM/PMI3, I would replace the hammer o-ring, the bolt o-rings, cup seal, and recoil spring.

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