Umarex Zelos/m60b mods worth it?

[kgun88]

I have an m60b in .25 cal that has been internally modified for more power via porting. I'm currently pushing 25-29 grain pellets at around 950 with room to go up if desired.

My question relates to further modifications and if they are worth it from a gain perspective. I'm considering adding the c88 plenum, fx 700mm barrel kit, and the stx superior liner so that I can push pellets and light slugs under 34gr.

The reason I'm considering these mods is because I want to squeeze as much power as possible for hunting while still having the tack driving precision for bench work. In 25 cal there are limited options for hunting type pellets, and the factory barrel doesn't like slugs. Another reason I'm considering the mods are because it will actually reduce the weight of the gun and shorten it a little with the new shroud while gaining 100mm of barrel. I'll also gain the ability to swap to a slug liner if I want to go heavier on the slugs. Is my logic wrong here?
Has anyone done the barrel conversion and plenum, if so what type of gains did you see in accuracy and available power?

 

[Vetmx]

I can’t give you advice on your long gun. But I can tell you what I dealt with when modding my Zelos compact. First, my hats off to C88 for offering what they do. Save me from machining it myself. With their valve, it’s good. But I had to play with springs and shims to get it right for my personal standards. Their barrel kits. Great bang for the buck. But a liner with a sleeve is a sloppy fit. Had to address that. Their shroud kit is machined to perfection. But they skimped on the air stripper and the gun is very loud. I machined a new air stripper and it’s wonderfully quiet. The gun is very sleek. No way I want an apparatus hanging off the side of it while hunting. So no external plenum for me.

 

[kgun88]

I can’t give you advice on your long gun. But I can tell you what I dealt with when modding my Zelos compact. First, my hats off to C88 for offering what they do. Save me from machining it myself. With their valve, it’s good. But I had to play with springs and shims to get it right for my personal standards. Their barrel kits. Great bang for the buck. But a liner with a sleeve is a sloppy fit. Had to address that. Their shroud kit is machined to perfection. But they skimped on the air stripper and the gun is very loud. I machined a new air stripper and it’s wonderfully quiet. The gun is very sleek. No way I want an apparatus hanging off the side of it while hunting. So no external plenum for me.

I was going to also purchase the carbon fiber sleeve that goes between the liner and shroud which should help with the sloppy fit? As for the noise, I'm not really concerned because the moderator should eliminate enough of the bark for my needs. Did you gain any accuracy or velocity with the barrel swap?

 

[Ratzy]

Plenum are a good thing.
Properly sized you get the same power with less air
Or more power with the same air

Poppet valve guns don't get as much benefit from plenum as tophat (AirForce) style guns. The dwell on the poppet needs to keep the poppet open long enough to deplete the plenum below regulator pressure setting. If not it is possible to get inconsistent chrony numbers. The next shot that takes the plenum below regulator pressure may have less air than the shot before.

So poppet valve guns usually have smaller plenum than tophat style guns to prevent this (hysteresis).

 

[Vetmx]

I was going to also purchase the carbon fiber sleeve that goes between the liner and shroud which should help with the sloppy fit? As for the noise, I'm not really concerned because the moderator should eliminate enough of the bark for my needs. Did you gain any accuracy or velocity with the barrel swap?

I’m talking with the CF sleeve, it’s a sloppy fit. I didn’t gain any speed because 500mm is 500mm. But my gun has the stock barrel cut down to 500mm. The person who did it chose to cut off the choke and the gun shot like sh#t past 30 yards. So in my case I did get back to having a gun that shoots as it should. It may be a smidge lighter without the solid barrel on it. But that doesn’t hurt me with a low power .22 shooting 16gr pellets. With a .25, and especially if you’re pushing it, the added weight of a solid barrel will be advantageous. But you gotta do what you gotta do then just deal with it. Hammer bounce is also an issue with this gun. Had to deal with that and now mine has a pretty clean report when shot.

 

[xsarfc9x]

My stock barrel was inconsistent and required a lot of cleaning so I've got the C88 liner on mine and a 500 superior and 700mm heavy liner. It lightens the gun up a lot, which for me is a bonus.

It was a process getting the liners sorted with testing pellets/slugs and making adjustments but I've .22 I've settled on .217 JSB KOs at 950fps with the Heavy liner. Getting MOA +/- at 100m.

Check tension of the barrel shroud and uses some weak loctite on the barrel kit and shroud grub screws. DaveG and Paul that sells on eBay have drilled a small hole in the end cap so you can insert the drill bit to really tighten it down.

Adjust the pellet probe dept by removing the top rail and turning the cocking rod in. My accuracy improved a lot after adjusting it in 1.5 turns.
I didn't measure the liner lead in vs the stock barrel lead in but I'm assuming the FX liner lead in is longer. Even with larger sized slugs I had little to no resistance chambering them when I initially installed the liner, vs the stock barrel I had some.

Try a few moderators. I have about 6 and some improved accuracy while others made it worse. I settled on a 3d printer Subscriber mod my friend printed as it got me the best accuracy.