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VM Empire Where the VM-68's and PMI-3 Come out to play

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Old 11-26-2015, 01:13 AM   #1 (permalink)
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Join Date: May 2006

Need to Start Sourcing Out Hammer O Rings for the VM 68

Well, its official. I think I was one of the last to have a lot of parts for the VM 68s. I kind of have to if I run a 250+ rental fleet and do custom VM-68s. If you are all wondering, I'm the guy who made up the "orange" VM ball detents and also had new springs made up, along with bolt rings. I've also made up other things for the VMs like venturi bolts, Thompson stocks, Vertical ASAs, custom brass barrels and so on. Most of this stuff was not openly sold and was used within the private fleet of VMs the MBoB uses. I'm not a business or a hacker, or a "store", or an Ebay seller. I'm just someone trying to keep one of the best and meanest markers ever made functional.

And so... I have been using the last of the factory original manufactured parts for the past 10 years. I started out with just over 600+ VM-68 Hammer O rings. Over the past two years, it had began to show that the VMs we had were burping more and more. I would change out the o ring on the hammer and that would solve the issue for 500 rds or so and then back to burping. What I wasn't noticing was that the hard texture of the hammer o ring was turning to soft "taffy". In fact, the entire batch of rings that I had was doing this. We stored the parts and o rings in climate control - steady 60 F - in airtight bags in the dark. But urethane, as Drum has painfully pointed out, has a shelf life of 10-15 yrs tops. My original O rings from Sheridan/Crosman are from the mid to late 90s. It's now late 2015. Do the math

Titus and I played around with the idea of making more hammer o rings. But since these hammer o rings aren't officially "o rings", but rather injection molded urethane "washers", we, or actually I had to pony up almost a $1000 to have a mold made. The reason I cringed about this, was that if the mold was "off", I wouldn't know until I was about a 1000 O rings made into the project. I just couldn't afford the financial risk at that time. And then there was needless drama between Titus and I, and I lost my good friend and this ultimately became a dead end.

Anyhu, others have tried valiantly to make more of these VM 68 hammer o rings. Mader was the first. They worked and they were very affordable, BUT, they had horrendous issues. Mader's hammer o rings were made from stamped out of sheet urethane... I assume 70 durometer - Two problems in one. They were TOO SOFT and that made them elastic like rubber bands. The blowback exhaust would unseat this type of hammer o ring from Mader and push it against the body of the hammer, thus causing the o ring to act as a "bumper" that would prevent the hammer from striking the valve stem deep enough to create enough exhaust for blowback. The result was triple tapping burps and then decock.

The other issue with Mader's hammer o rings was that they were stamped out. Stamping Urethane is much like stamping rubber. It "mushes" when pressed and the outer cut edges are not smooth. On Mader's hammer O rings, they were concave. This was bad because there was less contact service for the O ring to the internal diameter of the VM 68. If you have ever seen a stock factory made hammer o ring, you can see that the outer edges are rounded and perfect. That, and the fact that the factory hammer rings are at least a 90 durometer.

Craig Palmer recently made a small batch of what looks like delrin made hammer o rings. I was able to get 3 of them to test. From what I understand, these a made by hand individually and the outer edge is rounded by hand also. This can lead to imperfections. Its simple human error and is in no way meant to be a dig on Craig and the Palmers. I personally commend his innovation and effort to help out us vm-68 knuckleheads. But sadly, only one out of three I obtained worked flawlessly. With the effort and cost put into making these, its not a feasible option for someone with more than the casual number of VM-68s to maintain.

Injection molding as it has been pointed out to me through various avenues is the "only option" to achieve a perfect replica of the factory hammer ring. But this includes fabricating a mold, and doing the dance of test and hope that the first batch is the correctly made batch.

So, is there anyone that can help me with this process without me paying an arm and a leg? I'm not trying to create a monopoly here. I just want to make an easily assessable part for folks that still use this marker and to also keep the ton of VMs I have working and taking names. And I'd like to do it right on the first try.

Just like the Ball Detents I made a few years back... I think I gave away the first 500 of them to folks that needed them. I want to do the same with the vm hammer rings if I can get help with making the injection mold and sourcing out a place that can make them and is reliable enough to produce them in a timely manner.

Help?


Warmly,

Smiley
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Old 11-26-2015, 01:13 AM   #2 (permalink)
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Second half of my research:
Quote:
The hammer seal is a slight problem. You have a few choices to look at.


1. Machine the seal groove to fit a standard -113 O-Ring so the seal is inexpensive and easy to get in several different materials. This may take some experimenting to get the groove diameter correct.

2. Use a -015 O-Ring and a cap seal. The cap seal can be machined from several different materials depending on what material works the best. This will also take some experimenting to get the cap seal wall thickness correct. This will be middle of the road cost wise. We may be able to make a few cap seals from Hytrel.

3. Machine or mold a special seal ring. This will be the most expensive to do and will require testing to make sure it works correctly. If the first mold is not correct a second one would have to be made. We are not set up to mold urethane only 80D Nitrile at this time.


With any seal the lubricant you choose can affect how the seal material will age and work. Most material shrink when molded, many swell from the contact materials, some shrink from the contact materials, all change size with temperature and all will take a compression set with some being worse than others. Working pressure will have some effect on the compression set also.


70 D Nitrile (NBR) is about the best for compression set with HNBR next, then urethane and Teflon is the poorest choice.

Last edited by infamoussmiley; 12-14-2015 at 09:27 AM. Reason: update
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Old 11-26-2015, 04:40 AM   #3 (permalink)
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This place make square rings by extruding the I.D. and O.D. then cutting them to width:

Backup Ring, Back-up, O-Ring, Square, Quad, PTFE, Polyurethane

"The tube is then machined into various cross-sectional configurations by using a precision grinder or lathe-type cutting machine. By using the process of extruding material, expensive molds are not required giving designers flexibility in sizing to their exact requirements."

What about machining the groove in the bolt to take an "off the shelf" round urethane O-ring ?
Other CO2 blowbacks function with round O-rings

Have you tried backup rings with round O-rings ?
The Purpose of the Back-up Ring is to stop O-Ring extrusion. Normally used in applications where pressure is 2500 PSI or higher.


Last edited by Smiley; 11-26-2015 at 04:54 AM.
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Old 11-27-2015, 10:51 AM   #4 (permalink)
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Smiley,
I've moved on past that in a positive way. I hold no grudges and time heals all wounds. I'm A-OK to forgive and forget if you are
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Dealer for APP, CCI, Nelson, Leland, Valken, Tippmann, & Procaps.
Please donate to make a difference in my fathers life
Willing to be a 3rd party for shipments to Canada anywhere in the world just PM me.
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Old 11-29-2015, 12:44 PM   #5 (permalink)
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i just purchased 2 vm rebuild kits from palmers... so you saying the hammer oring is not correct?

https://co2reg.com/index.php/paintbal...-seal-kit.html

and bacci has one as well though bacci states they may have issues...(note just reread your statement and the ones bacci has is mader's... nevermind)

https://www.baccipaintball.com/vmp159.html
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Last edited by Lextreme; 11-29-2015 at 12:52 PM.
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Old 12-01-2015, 11:50 AM   #6 (permalink)
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It's funny, I was thinking about this exact subject last night. I'd spent some time talking with coworkers about paintball and how my main gun (an EXC-68) was old enough to drink; and easily older than almost everyone I shoot with it! It got me wondering about the lifespan of the few hammer rings I've got left on-hand. I've also got a CAR 68 that I'm putting back into service, but it needs a whole new set of seals, too.

Anyway, Smiley, you're definitely not the only one interested in solving this problem. I don't have any technical expertise in the area, but I'd be willing to put money towards an initial run of rings, if the VM Empire brain trust can come up with a workable solution...
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Old 12-06-2015, 05:48 PM   #7 (permalink)
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Quote:
Originally Posted by Titus View Post
Smiley,
I've moved on past that in a positive way. I hold no grudges and time heals all wounds. I'm A-OK to forgive and forget if you are
thank you, Titus. Maybe we can continue on with this endeavor in front of us. PM inbound to you.
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Old 12-06-2015, 05:58 PM   #8 (permalink)
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Quote:
Originally Posted by Smiley View Post
This place make square rings by extruding the I.D. and O.D. then cutting them to width:

Backup Ring, Back-up, O-Ring, Square, Quad, PTFE, Polyurethane

"The tube is then machined into various cross-sectional configurations by using a precision grinder or lathe-type cutting machine. By using the process of extruding material, expensive molds are not required giving designers flexibility in sizing to their exact requirements."

What about machining the groove in the bolt to take an "off the shelf" round urethane O-ring ?
Other CO2 blowbacks function with round O-rings

Have you tried backup rings with round O-rings ?
The Purpose of the Back-up Ring is to stop O-Ring extrusion. Normally used in applications where pressure is 2500 PSI or higher.

https://www.sealanddesign.com/images/content/backup.jpg

Hi Smiley,

I'm not sure what you are referring to here in the email. Can you explain what you mean??

Smiley
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Old 12-06-2015, 06:00 PM   #9 (permalink)
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Quote:
Originally Posted by Lextreme View Post
i just purchased 2 vm rebuild kits from palmers... so you saying the hammer oring is not correct?

VM68 / PMI 3 Seal Kit - Parts & Accessories - Sheridan / Crossman - Guns and Parts - Paintball

and bacci has one as well though bacci states they may have issues...(note just reread your statement and the ones bacci has is mader's... nevermind)

New VM-68 Hammer Oring
I'm not saying that. If you have burping, it is because of what I said in the initial post.

Smiley
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Old 12-06-2015, 06:04 PM   #10 (permalink)
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Quote:
Originally Posted by Giuseppe View Post
It's funny, I was thinking about this exact subject last night. I'd spent some time talking with coworkers about paintball and how my main gun (an EXC-68) was old enough to drink; and easily older than almost everyone I shoot with it! It got me wondering about the lifespan of the few hammer rings I've got left on-hand. I've also got a CAR 68 that I'm putting back into service, but it needs a whole new set of seals, too.

Anyway, Smiley, you're definitely not the only one interested in solving this problem. I don't have any technical expertise in the area, but I'd be willing to put money towards an initial run of rings, if the VM Empire brain trust can come up with a workable solution...
Thank you for the offer. But for right now, we need a way to source out a venue that can make this "washer" for the hammer o ring.

- Smiley
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