Non choked FX barrel liners

If your barrel is 600 mm you could buy a 700 mm liner and remove 100 mm from the muzzle end thus removing the choke. Carefully machine and re-crown end of liner. 

I don’t know if they have un-choked barrels or not, but I have had success with the NSA 23 grain .217 slugs. Clover leafing at 50 yds at 925 fps out of the .22 600mm STX Superior liner, not the heavy liner. Maybe your harmonics are not quite right. I actually got very lucky with my Impact MKII tune with the reg at 130bar, hammer adj screw maxed and power wheel at 5. With the MKII power plenum. I was looking for a tune that could share slugs and pellets via the power wheel. Same everything except power wheel on 2 for h&n Barracuda Match 21.14 grain. I don’t know what FX gun you have but that’s the setup that works for my Impact. I know it can be frustrating. I’ve had my Impact for about six months. Testing different projectiles and reg pressures. It’s taken me until just last week to find a good combination. Hope you have some luck. 

I wish I could help you this time as you have helped me a quite a few times.

I have not tried but I have heard several say the Brownells liners are a direct drop in with crowning and leade needed of course.

You say you have one fitted that works so I am a bit confused. Unless you specifically want to be able to get them from FX as such. 

Hobby, as you know, I had the same issue. Not only that, but the choke had no rifling. The rest of the bore did, but not the choke. It was 5 thou tighter than the bore/land dia. Terrible! Seems to me, FX owes me a barrel!

I removed the choke, polished the bore, re-crowned and it is now officially a laser. Woo-Hoo!!! Butttt+ it is now too short. GRRRRRR!!!

The cost is substantially less with the Brownell's liners as you know with mine being in .223. I have found the .223 gives better fps than the FX .218 barrel at the same reg settings. Not to mention less sizing down from the molds. Another Bonus! 

The CZ barreled Uragan in .25 I just received has a choke, but only slightly over 1 thou. It is a laser with my 38 gr cast at .2494 dia. First choked bbl. I have had that shot slugs worth a darned. Like you, I usually remove the choke early in testing. Every barrel so modded has improved greatly. 

Mike/Knife