What is the difference between a regular barrel and a “slug” barrel

Different twist rates

Aren't they "unchoked" generally?

Twist rats of an FX pellet liner is around 1:30, FX Slug liner is around 1:15, or so. (Just to give you a reference.)

Some airguns just use a regular unchoked barrel with a different twist rate as a slug barrel. Twist rates are a little different for sure but from what I have read and seen on vids the FX barrel ID and choke ID are slightly larger as well. This larger ID helps as the slug is not so easily compressed as the pellets. The choke is also made in a specific way that is different from regular FX liners/barrels an FX secret way that would not be disclosed on the vid. ;^)

Keyman62421 Many slug liners and some barrels made by big name companies are not choked but the FX barrels needed to be to shoot well.

Twist rats of an FX pellet liner is around 1:30, FX Slug liner is around 1:15, or so. (Just to give you a reference.)

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This isn't in line with my thinking and experience, shooting the H&N Rabbit Magnum II (24gn) in my FX Impact mk2 resulted in a substantial leading at 950fps. The pellet was skipping over the rifling too much twist, by shot 5 the pellet was stuck in the liner due to lead buildup. Dropping the velocity to 834fps to reduce leading and it sprayed pellets like a shotgun with BBs. The strength of the pellet material also plays a part, softer skips the rifling, etc.

In my opinion a smooth area in front of the chamber to standardises (resize) the projectile (pellet) is useful. It can then enter the rifling at known OD. Someone needs to air guage the liners to determine the correct ID.

Powder rifle manufacturers usually specify the twist rate of a barrel, along with its calibre inside the packaging or advert.

In my youth we referred to springer air rifles as slug guns! Funny how things change.

Slower twist rate. They vary by caliber (what works best) so giving one twist rate and saying it's a slug rate is true, but it's not universal at all. They also have varying degrees of choke (or maybe none in some cases) 

Also twist rate varies on the slugs OAL...

https://youtu.be/TLK5j2urOJ0

Diabolo shaped pellets require little to no spin to stabilize in flight because air drag does the job much like an arrow or shuttlecock. This is why they lose velocity way faster than regular bullets which are referred to as slugs in the airgun industry to distance themselves from firearms. Many people mistakenly call firearms cartridges "bullets".

Slug liners as in the case of FX were designed specifically to shoot the 2S bullet shape and have about double the twist rate of pellet liners but also shoot diabolo shaped pellets well. I believe the FX liners have a little more choke than the pellet liners.

So how does one know the specs of their liner?

I bought an FX Impact X before these discussions came about.



The Australian version seems to have a different finish at the muzzle. When I unscrew the shroud there is no end piece to unscrew, it just the liner. Which seems to mean once the shroud is removed the liner could just slide out...

I'm shooting JSB 18.13gn .22 pellets and would have liked to shoot .22 slugs, like the Rabbit Mag II from H&N but swapping liners is too much mucking around.

When in doubt, measure it yourself. There's a jam nut that holds the liner. Mine is as you described as well 

I bought a new Crown in Belgium in June of 2018.in .25 with a standard 600mm barrel. It is 1 in 19 inches. It was not stated as anything but pellet.

Pulled out the liner, marked one of the lands at the muzzle. Followed it to 500mm rotating it to the mark. Not scientific, so its approx 1:20" twist. I'm guessing too long to stabilise pellets heavier than 18.13gns and possibly to shallow too.

Can anyone tell me…i bought fx barrel kit .22 700mm from one of online shop, but the seller can not inform me what kind of pellet liner inside the barrel kit…A or B ??

Regards

Can anyone tell me…i bought fx barrel kit .22 700mm from one of online shop, but the seller can not inform me what kind of pellet liner inside the barrel kit…A or B ??

Regards

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You will have to measure the rifling twist on the liner. Follow one rifling around with a pencil until you make exactly one revolution. Then measure the length between the complete revolution to get the twist rate in inches. There is two rates for those liners. A 1:19". B 1:16"