Tippmann 68 Carbine Velocity Issues

[Myrkul]

I recently acquired a Tippmann 68 Carbine off of craigslist, and this thing refuses to chrono above 260. When I first got it I pulled it completely apart, replaced all the "o" rings, and dropped a lighter valve spring in the CVX valve. It cycled great, but over the chrono it was maybe shooting 240s. I added the strongest tippmann drive spring I could (red mad man), polished the hammer, and drilled out the cross section in the powertube, backed out the IVG to maximum flow, swapped the screw with a shorter one, and added an RVA (set to all the way in). Also switched to Co2.....this got me to 255 or so. I have confirmed that the linkage arm is straight, it is not bent and glides smoothly. Additionally I have confirmed that the front bolt is fully intact and the hole for the linkage arm in the front bolt is still plugged at the bottom.


At this point what other things can I do to get this thing shooting correctly? Paint was D3fy, shooting out of an .687 8" Lapco Bigshot Barrel. I like to run my guns @ 285 fps and I'm pretty anal about not shooting anything below 275 in an actual game. Ideally I'd like some more home brew mods to get this shooting velocity, but at this point the only other thing I can think of is just picking up a Ninja SHP reg and running 1100 PSI straight into the valve. Are these CVX valves like cockers in the sense that they have a "bell curve" of ideal input pressures? Or is there an easier solution to this?

Pic of the sexy offender

[glaman5266]

Just a shot in the dark here- maybe try running the bottomline straight to the valve w/no x-chamber? If that doesn't work, maybe a siphon bottle? Not sure how durable the valves are in the 68 Carbines are though... And I thought the CVX valve didn't come out 'til the Pro Carbine. Hmm.

[Myrkul]

Just a shot in the dark here- maybe try running the bottomline straight to the valve w/no x-chamber? If that doesn't work, maybe a siphon bottle? Not sure how durable the valves are in the 68 Carbines are though... And I thought the CVX valve didn't come out 'til the Pro Carbine. Hmm.

The CVX valve came out early into the production of the 68 Carbine, eventually they came stock and for a time older ones could be sent to Tippmann and converted to CVX. I called Tippmann and they confirmed that this one had the CVX valve because of the specialty brass fitting (pictured below) that screws into the body and has a crazy tiny "o" ring on the top that is pinched against the CVX valve body to create a seal. I suspect this fitting is a choke point for the valve, since the air passage is TINY, but Tippmann also made it pretty clear to me that the specific fitting was the reason they would no longer be able to do any "more" conversions, because they were out of the fitting and would never be able to get more, so I'm reluctant to drill it out and see if the extra volume helps (I am sure it would). I'm not overly concerned with the durability of the valve at higher pressures, it takes all standard CVX parts except the valve body itself and the external "o" ring.

I've built and used siphon tanks before for a Sheridan P-68 that was doing the exact same thing, it did "work" but co2 fills at my local field are hit or miss and the continual pain in the ass of finding someone who could correctly fill a siphon tank made sure the gun and tank didn't stay in my collection for more then a few months. So the SHP is definitely a more attractive solution to me then a siphon tank.

I'll try pulling the expansion chamber later today and report back.

Specialty CVX adapter fitting:

[glaman5266]

Didn’t know any of that. Good info. Thank you.

On that thought- how different are these CVX valves from the newer ones? Would a valve swap work?

[Cunha]

Dang now I can't decide if I should just use a tippmann 98 as my tippy of choice. Sorry I can't be of help. the only thing I can think of is to swap everything from a different gun that confirmed works, or part by part swap till you find what works (like a real science guy)

[Myrkul]

I sadly only have the one carbine.

If anyone wants to send me a second one so I can do this strategy I'm game though!

[BrickHaus]

You look for a brass filter in every fitting? Could still have one hidden thats clogged up.

[Myrkul]

Everything was torn apart to remove 20 year old nasty ass Teflon tape, and resealed with blue locktite. When I pull the expansion chamber tonight I'll double check for clogged filters, but I don't think anything is there.

[Myrkul]

Didn’t know any of that. Good info. Thank you.

On that thought- how different are these CVX valves from the newer ones? Would a valve swap work?

Unfortunately a valve swap with a newer CVX won't work. I'd have to keep the body the same. It's the valve internals that are interchangeable.

I actually have a spare (albeit beat to death and dirty as sin) 68-Carbine valve I&I recently sent me by mistake. Took me a while to figure out what it was till I matched them, but I luckily didn't even have to tear anything apart for these pictures. You can see how much smaller the Carbine valve is, I think this decreased volume is what is primarily responsible for the low velocity, and since I can't think of an easy way to add valve chamber volume because of that adapter fitting, I'm thinking the SHP Reg is looking like a better and better option.

Right: Tippmann 98 CVX valve (1/8" NPT version)
Left: 68-Carbine CVX valve

[Cunha]

What about a pro carbine CVX valve since all pro carbs have em?

[Myrkul]

What about a pro carbine CVX valve since all pro carbs have em?

That sounds like it would work to me, does anyone who has both care to chime in?

Another interesting thought, Jordan here is running modified Prolite powertubes in his 68- Carbines, and he said he had trouble getting them to shoot low enough to be field legal. Following his advice is what caused me to drill out the cross section in the powertube for mine, sadly for marginal to no improvement. I wonder if deliberately switching to a Prolite powertube would yield better results? Anyone know where to find one of those? Alternatively, maybe I could wrap the 68 carbine power tube in Teflon tape at the base to create a better seal against the body? Do we think that would help or just have the same impact everything else I've done has?

[Chappy]

How is the front bolt oring? Any drag? If it’s swollen it will cause low FPS, though usually bolt stick as well. I generally take them off as they make no difference.

ps when I drilled out my power tube I got about a 30fps jump so I’m feeling like there is something else going on here

[Myrkul]

How is the front bolt oring? Any drag? If it’s swollen it will cause low FPS, though usually bolt stick as well. I generally take them off as they make no difference.

ps when I drilled out my power tube I got about a 30fps jump so I’m feeling like there is something else going on here

Front bolt "o" ring was replaced with the others, I tried pulling it as per your recommendation, and noticed it liked to catch on the front detent on the return causing some inconsistent recocking. I threw it back on since there was no noticeable velocity improvement with it off and it moved freely and easily anyway and won't chew through my detents this way.


During the disassembly I finally shredded the seal at the top of the adapter fitting, it was fishing line thin and probably original, so I'm not terribly surprised. Figuring I had nothing else to loose at this point I grabbed a spare clippard rubber grommet that looked around the right size, slapped it in the valve, and then drilled out the adapter fitting to increase valve volume. I had to screw it in extra tight to get the rubber grommet and now drilled out adapter fitting to seal, but its the first thing that worked! I "think" I have the velocity issue fixed, at least it looked that way when test firing in the back yard. I'll have to make it to a chrono to tell for sure, (hopefully in the next few days) but it was noticeably hotter and much louder so I'm very optimistic.

[Cunha]

Hey, Cool!

I still can't decide what tippmann to go for. I like the cleaner look of the old 68 carbines vs the pro carbine, but I do like that all pro carbines have cvx valve, and if you chop the shroud off the pro carb can look pretty clean.

Anyone with more experience have their thoughts on the pro carbine feed design vs a metal (or even plastic) 68 carbine feed design? Which one is more solid or functional?

[Myrkul]

I have not yet had a problem with the feed neck on the 68-Carbine, (I also haven't used it) but in my initial digging while waiting for this one to arrive I heard nothing but complaints about the feed neck. Apparently people were super good at knocking them off. I'm honestly not sure how, it seems sturdy and robust and sometimes I need to pry the latch on mine with a screwdriver to get it open, but the stock feed neck was apparently the big complaint back in the day.

[glaman5266]

I personally like the foregrips. I think the ones with the cut off foregrips look janky with all the squared off metal. Simpler & smaller? Yes. Aesthetically pleasing? Nope.

Can't speak for the .68 Carbine, but I like the feed on my Pro Carb. Doesn't rock around much & if it ever does I can pad it with a little felt like people do with their 98 elbows.

[Gradyfest]

The metal 68 Carbine feed is really heavy and you will feel it on the gun. It also wears its mark on the receiver with use as the steel moves against the aluminum. The plastic one is just way soft and falls off literally by slightly angling the gun to one side with a full hopper.

The Pro Carbine solves all this and also you gain the ability to slide the front grip including feed forward. You now have fast access to the breech to run a pull thru squeegee without taking the barrel off. Slide the handle back again aligning the feed and your back in the game.

68 if you’re running a exp chamber or vertical and don’t need the front grip though. Pro Carbines with the front grip and a exp chamber grip look funny to me.

[Gradyfest]

Nice Carbine! I have almost a couple dozen 68 and Pro Carbines now, love them! The 68 Carbine CVX is the Pro Carbine CVX, one in the same. It’s pretty rare to find a 68 Carbine with the old floating rope valve, and only on early serial numbers, fun FYI. Anyways, there are only two parts in the Carbine CVX valves that are the same and interchangeable with the 98s CVXs. Those parts being the valve stem and the front valve seat.

One thing that can happen and they fixed the design with the 98s is that the front bolt can get a hole worn in it from the linkage arm causing drag on the power tube and velocity issues. I’ve seen a couple rental power tubes with a actual notch in them from the linkage arm passing thru the bolt. You shouldn’t have to crazy modify these or open up the valve like you did to get velocity. Did you try other barrels, don’t know if that short barrel is helping?

[Myrkul]

I checked the front bolt, it certainly looks used but not really more so then expected. I did check the linkage arm hole and it has not yet worn though. Power tube was round and smooth. I borrowed a buddies 16" A-5 barrel and the velocity was no different. So I really don't suspect that the barrel is causing any issues. (That and I love these 8" lapcos on my tippmanns)

[Gradyfest]

Oh and my vote is Carbines over 98s all day. They are the last real quality gun Tippmann made. You get the same CVX in the 98s and A5s but in a quality machined aluminum alloy receiver over cheap pot metal cast receivers.

[Rolling Thunder 67]

Quick ?, is the hole in the CVX valve tapered,if i remember correctly it is, along with the adapter fitting. At one point someone may have over tightened the fitting in the valve to stop a leak and pinched the spring with point of the adapter fitting in the valve body. I mention this as you mentioned when you enlarged the hole in the adapter fitting and replace the seal you had a noticeable increase in velocity. You may have inadvertently corrected the velocity issue with replacement of the seal . i mention this as i had a 98 that i was asked to tech and found that someone had drove the airline so far into the valve that it pinched the spring and wouldn't allow it to move freely in the valve body. i know the hole for a 98 is straight which allows you to over tighten the airline very easily, causing the binding of the spring. Might be worth keeping in mind if you continue to have velocity issues.

[Myrkul]

This....is most likely what happened. The adapter was only slightly tapered, but directly on the "top" there was a significant lip that was designed to pinch an "o" ring between the top of the adapter and the bottom of the valve. I don't think it is possible to screw it on tightly enough to pinch the valve spring without destroying the valve, but I think it was definitely screwed on tight enough to malign the lip on the adapter piece and restrict airflow. Once I drilled that lip off is when the velocity improved.

Either way, I should hopefully get a chance to chrono it this weekend and will report back!

[Meleager7]

Oh and my vote is Carbines over 98s all day. They are the last real quality gun Tippmann made. You get the same CVX in the 98s and A5s but in a quality machined aluminum alloy receiver over cheap pot metal cast receivers.

Agreed (although i have a soft spot for the shark gill Model 98) ! ......and the 68-Carbine/Pro-Carbine detent change is so much easier, as is replacing hammer seals, main springs, rear bumpers, etc.

Imagine if Tippmann decided not to switch to castings and stuck with machining parts, and then improved upon the Pro-Am /Carbine design? Would we have seen Vert Feed carbines? Electro Sear Tripper carbines? Low pressure, high volume carbines? It could have been pretty cool !