Can I convert my FX Wildcat MKI from 22 to 25?

I think they come in .177 - .22 and .25 - .30 configurations. I myself am shopping for a .30 cal, and I believe there are two iterations. My opinion.

You should be able to, It's not very common to hear about. After you pay $350 for a barrel,probe,magazine's. Then spend the $50 in pellets and 2 days of tuning and fussing with your regulator in your gun. Maybe you'll want to buy a $100 regulator tester to. FYI the regulators in the Wildcats are all the same. Or, you could sell your .22 and replace it with a more common .25 for same price as the one you sold. added $60 in shipping and you have a FX tuned .25.

If you have your heart set on changing it call Newman at Fx USA he'll give you the low down. 

If life doesn't force your hand to sell it. Might I suggest you keep for a while. Giving you time to decide if you prefer the .30 over the .22. My experience has been the .30 are assume gun's but the ,22 are a staple gun. Meaning you love the .30 but you'll probably shoot the .22 pellet for pellet more. Also if I might suggest trying a Fx Bobcat,Vulcan 2 or Taipan. There all great shooting bullpup's. 

If you just change out the barrel, probe, and up the reg and not change the plenum, your gun won't be very efficient with air and might not get the power you want. I dont know how different the transfer block is between a .22 and .25 but I'm sure its different. Maybe someone else can chime in. Chuck, where you at?

You’ll have to change out the hammer weight, and don’t forget the shroud depending on which length barrel you get. Yes, the reg’s are the same, but settings are different. 

I like Mr Hosted’s advice. I, too wanted a Wildcat in a 30, and picked one up barely used last March. I’ve got it finally set to where I want it, but due to a lack of pellet availability that leaves me done with testing any other styles or weights of pellets. I found myself wanting another wildcat due to the lightweight platform and everything good about the gun that you all know about, so I decided to pick up another used but well maintained one in 25 caliber. I can already tell this will be my go to gun, and basically leave my 30 cal, 87 ft pounder thumper for long range target shooting. My 25 cal is set up for around 56 foot lbs but gives me 36 shots at that power, and due to it being an earlier model of the MK2, it has the 600mm barrel which is way more compact and even more lighter than the 30 cal. I plan on using the 28 grain Barracuda Hunter extremes on this 25. 

Lastly, this gun is not user friendly as far as doing the work on it yourself, and if you do this swap it will involve taking apart the gun to about 85% disassembly. If you don’t know what you’re doing, you’re either gonna end up with a gun that won’t shoot, shoots like chit, broken parts, and have a table full of hairs pulled off of your scalp. Don’t even think for one moment that you can just youtube it, cause I’ve looked at every YouTube video out there on the wildcat, and only enough info is given to get you in trouble. I can almost guarantee it.

Dont mean to be discouraging on your ideas of swapping caliber sizes, just putting hard facts out on the table. It’s a great gun, love it, but I am it’s master as I know everything about it. And yes, I’ve left my share of hairs on the table to get to where I am with it, it and pretty much made chuck lose his voice over the phone with his guidance. I think he’s disowned me as a friend since then, ha, ha!!

Good luck, man, and merry Christmas.