FX “Super” Superior Heavy Slug Liner

It appears the new heavy liners are now stamped “slug”. Twist rate remains the same at 1:18 , but I wonder if anything else was changed?

So I just recently received a replacement liner from FX USA and it is indeed 1:16 TR. The dealers/vendors seem to be totally unaware of this change when asked. I hope to do some testing this weekend. My previous slug liner (1:18 TR) did not perform well above 34 grain, although I suspect it had factory defects. 2-3” groups at 25 yards. 6-8” groups at 100.

Below is a pic of my new liner - initial testing to be completed soon.

I forgot to mention my new 1:16 TR liner must have a slightly larger external diameter. While previous liners installed quite easily into my carbon fiber sleeve, this new liner is extremely tight, almost like a press fit. I’m not sure if FX intended it to be that way or not. At any rate there is no need to epoxy the liner and CF sleeve given the tight fit. They are essentially bonded with the press fit.

I did some testing this last weekend with the new 0.25 cal, STX Slug liner (1:16 twist). The results were discouraging and unpleasant to say the least.

My FX Impact M3 is setup as follows:

• 0.25 cal, 700mm barrel
• STX Superior Slug liner (1:16 twist) – latest and “greatest” version
• Carbon fiber liner sleeve
• FX carbon fiber tensioner kit
• Reg 1: 180 bar
• Reg 2: 145 bar
• Probe: Factory pellet probe
• Transfer Port: Slug side
• Moderator: DonnyFL Sumo (.25/.30)

I tried a variety of slugs including H&N, JSB, Patriot, NSA, and ZAN, however my main focus was on the H&N 38 grain heavies (0.249) and Patriot Javelin GEN2 36 grain (0.250). Test velocities ranged from 980 down to 880 fps.

Test groups were 5 shots each, utilizing 2 burners between each setting or projectile change. Velocity was very consistent from shot to shot as measured with my FX Pocket Chrono. Also, wind was very light…maybe 2-3 mph if any. Below are the 25-yard test groups. I didn’t see anything that really stood out as being tolerable except for the H&N slugs at 905 fps. Unfortunately, that group was not repeatable. Also, I started seeing a pattern where I would get 3-4 shots that “grouped” and then 1-2 fliers.





I took my best 25-yard groups from the H&N and Javelins and pushed things out to 100 yards. Results were quite awful and downright depressing. Below are some the targets from my 100-yard testing. You can see from the photo below I did have one exciting group in the lower right where 4 shots grouped well and then 1 flier hit 2” low. Again, I was unable to replicate this grouping.





After getting home from the range and feeling defeated I decided to the clean the liner with my Patchworm kit. The first 4 patches were extremely dirty with large amounts of lead shavings as shown below. It took another 50 patches to get the liner cleaned switching between Ballistol and Butch’s Bore Shine to get all remaining lead fouling out of the liner. Some lead particles were extremely difficult to get out and I ended up using a cooper bore brush to “scrub” the liner as the patches and chemicals would not pull them out. I suspect heavy liner fouling is what caused the fliers during testing.



So where do I go from here? Here are some ideas for next steps in approximate order.

• Polish liner with J-B Bore Cleaning Compound and Flitz metal polish
• Try heavier slugs such as 40, 42, 44, and 46 grain
• “Slug” the liner to determine actual groove diameter using a micrometer, then pick a slug that is within 0.0005” to 0.001” over groove diameter as a starting point
• Go back to the STX Standard liner
• Sort slugs by weight and diameter for better consistency
• Use a slug sizer
• Wash slugs with Dawn soap and then lube them with silicon spray or Ballistol
• Change from 0.25 caliber to 0.22 caliber and wave goodbye to the 0.25 caliber

Let me know if you have any other ideas or if I’m missing something. It’s frustrating to read comments from other AGN members about how they shoot MOA groups all day long. My experience has been just the opposite. And just for comparison, this same gun stacks 34 grain King Heavies when properly tuned with the standard liner 1:24 pellet liner.

DesertSilver said:

You really need to know your groove diameter to pick the right slug and make sure all of the slugs are the right size.

Click to expand...

One would think that after all the testing Matt Dubber and Hein Frommann did with the Javelin GEN2 slugs and new FX slug liners, that those Javelin slugs would perform exceptionally well without the need for the layperson to spend time, money and effort chasing their tail and measuring 10 thousands of an inch to make their gun shoot well. In my experience so far, the .25 GEN2 slugs are mediocre to poor performers.