FX Impact Mk II barrel questions?

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Stretch

Stretch

Member
Jan 27, 2019
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Virginia, United States
I just bought a "refurbished" FX Impact Mk II ( sniper / 700mm .25 cal) from UA last week and have been tuning it for 100+ yds and have a couple questions:

What barrel do FX Impacts normally ship with? I was told the barrel I got was designed for pellets, so is that the "standard STX" barrel?

Looking at the transfer port on the barrel, it appears that I have one dual ported side and then on the other side is a tiny port. Is that for 12 fpe?

fx transfer port 1.1630670736.jpg


fx transfer port 2.1630670748.jpg

 
The side with the P is for pellets and the side with the S is for slugs. The barrel liner is typically for pellets or hybrids and the heavy liner is for slugs. You have the updated transfer port which allows for switching the liner to get the maximum velocity for your given projectile.

You would have a liner for pellets on a newly purchased Impact but as you purchased used I couldn't tell you. The p is not for 12fpe but just backs down the amount of air allowed to push the pellet.
 
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If I remember correctly, the small hole is for low power in this setup. The normal transfer port for pellets is larger that the port shown.

The dual port allows more air to flow through for heavier projectiles such as slugs. the post down the middle is to prevent the pellet from falling through or hitting the front edge and deforming.

Which to use? That depends. What ammunition do you want to use? If the 34 grain JSB's are your choice, use the dual transfer port. It takes lots of air to move those things down the barrel efficiently. If you want to shoot the 25 grain the small port might be sufficient.

Is it for 12 fpe? I can't imagine anyone buying a .25 for sub 12fpe. That'd be something like 400fps, ridiculously slow. So, yes, the small port has me perplexed as well.

Personally (my opinion, my shooting, my method, maybe not yours), I'd use the dual transfer port for everything. Superior liner is designed for pellets and lighter slugs. Heavy liner for heavier slugs is my understanding.

I also have a very late production MKII in .22, I'll have to pull the barrel and see what it looks like. For that one, the small port might be enough to propel the 18 grain JSB's but not enough for the 25 grain JSB pellets. I have those on order.
 
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I had a daul port in my late model mk2 compact 22 small hole is for low power and other hole was for regular or normal power I switched out to huma V2 daul transfer port and probe gained over 30 fps just by swapping it shooting 18 gr jsb at 934 fps out 500 mm haven't gotten to much shooting done with it yet and am currently playing or tuning my raw for power and efficiency 
 
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my two cents here... the large double port in this case is for pushing slugs and heavy pellets. the small round hole is for pellets only. it isnt really a low power port per say. It almost looks like it may be an Ernest rowe dual port transfer port. the original liner were the stx pellet A liners. You would have to pull the line from the barrel and count the twist rate to be able to tell what liner it is.
 
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You may have to remove the liner and measure the twist from the outside to find out for sure what liner you have.

https://www.airgunnation.com/topic/official-fx-stx-barrel-liner-twist-rates/

Here's one cheat sheet on the Superiors and Heavy Superiors just incase you got lucky and got the Surperior. 

FX Twist Rate Quide.1630759315.PNG
 

Click to expand...

I would agree with others here in that you have a .25 cal. with a new duel transfer port and a Superior STX liner with a 1:24 twist rate. Measure your TR as jking suggests.



Patrick
 
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