Shortening a CZ455 varmint barrel - how short to go?

Running into problems with 22LR subs pretty much all going supersonic in the 20" barrel. Previously there was the odd one which would do it, but as the barrel has now had just over 1000 rounds through it, it's obviously just broken in, and the normal condition is supersonic "subs".

This is quite a problem, as most of my shooting is around orchards with a spotlight. The neighbors are more than happy for the shooting, but just don't want to hear it. A supersonic crack is hard to ignore.

So my question is....how much to chop off? I was thinking a 14" barrel would do the job.
Has anyone else done this, and how does it shoot? Is there a noticeable drop in muzzle velocity?

Have you tried several different kinds of subs?

Yes thats a strange problem to have, subs are regulated to be below speed of sound.

Ive only used winchester, cci, and kilwell subs which i think are winchester. The winnies are most accurate in my unique (25 inch barrel) 10 22 but the sportco prefers cci. Cant remember any going bang through the silencer.
I believe as a general rule of thumb 22 ammo peaks in velocity wwith a barrel length of around 12-14 inches, after that it slowly drops.
Might be time to check your ammunition, as from first principles chopping it wont make it better and could bugger any resale value.

I chopped the barrel on a 22 to 12" making the gun 'minimum legal length' which plenty of people have done. It probably improves accuracy because the barrel is relatively thicker and stiffer for its length than before the chop. The downside is that suddenly the muzzle is sitting at ear height when the gun is slung on your shoulder - producing a very uneasy feeling and having me check all the time that the rifle wasn't on half open bolt with one up the spout.
So I wouldn't chop it any shorter than a length that keeps the muzzle just above the top of your head. But this will only improve 'handiness' and probably not fix your trans / supersonic sonic problem as Marty Henry has said. Maybe you should stop storing your ammo on top of the heater ??

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Originally Posted by quentin

Running into problems with 22LR subs pretty much all going supersonic in the 20" barrel. Previously there was the odd one which would do it, but as the barrel has now had just over 1000 rounds through it, it's obviously just broken in, and the normal condition is supersonic "subs".

This is quite a problem, as most of my shooting is around orchards with a spotlight. The neighbors are more than happy for the shooting, but just don't want to hear it. A supersonic crack is hard to ignore.

So my question is....how much to chop off? I was thinking a 14" barrel would do the job.
Has anyone else done this, and how does it shoot? Is there a noticeable drop in muzzle velocity?

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Have you cleaned the barrel?
My CZ went though a stage of starting subs starting to go super sonic, I cleaned the barrel (had well over 1000 rounds through it) and it stopped doing it.
Certain makes of ammo were more likely to do it than others so perhaps try a few different flavours.

You shouldn't notice much if any drop in muzzle velocity, lots of research shows 22lr reaches max velocity in the first 16" or so.
I'd chop it to what ever was the most practical/looks the best.
16" is a safe bet, but plenty of folk have gone 12" or less.

Try CCI Quiet

From what I understand longer than 16 inch starts slowing 22lr subs down
There was a website that chronie then chopped barrels from 20 inch right down to 4 inches, inch by inch
Maybe try a barrel solvent first and it may well fix the problem

Cheers all. I'll start with a thorough clean. Normally I just pass a boresnake through. My 10/22 went about 30,000 rounds without a clean, and didn't have any similar issues....guess the CZ is a totally different beast.
I'm using CCI segmented subs, as having ricochets when a bullet passes right through a rabbit is not ideal.

it will go FASTER if you cut it shorter...try some winchester 42grn...but be aware if your rifle likes it you wont be going back to anything else.
from my understanding having read of this quite a few different times and places the .22lr can only use a certain length of barrel (12-14" from memory) after that the resistance of barrel slows projectile down...guys cut barrel down 1" at a time and chronied results proove this out...I BELIEVE this is why guys trying to go subsonic with centre fire have many different powder amounts for same cartridge.... if you really concerned about projectile passing through..open out the hollow point more,a 2" nail works fine as does crossing the tip with a stanley knife.....they mightnt feed through mag but will work for first round anyway and if you hit you wont need a 2nd one.

BBTI - Ballistics by the Inch :: .22 Results

interesting reading Bill......just looking at the first three on 2nd graph point out reduction once over 18" .

Most subsonic ammo seems to be pitched around 1050 fps, a good 75 or so fps below the average speed of sound 1125 -1150 fps. So its at the bottom of the transonic range. Low pressure weather systems can lower the speed of sound a few fps as can hot weather but these are just academic.
You shoot with a silencer I guess after cleaning Id start again, see if you can get some cci quiet or winchester z to use as a benchmark then go back to your preferred round. Also if you have the opportunity try them in another suppressed rifle. Your 1022 may not cycle properly but would be a good test bed if its threaded, and you could always use it as a straight pull.

Have a look around for either Highland super quiet (around the 900fps so really subsonic) or Aquila SSS (60gr subs) or some of the other brands may do a super quiet. As mentioned, going shorter will more likely increase the speed rather than slow it down.

https://www.guncity.com/22aguila-sss...gr-x500-220313 (950fps apparently)

https://www.guncity.com/cci-quiet-22...fps-x50-338874 (710fps)

Giving it a really thorough clean seems to have sorted the supersonic subs issue - at least back to how it used to be.
Now I just need to get enough rounds through it to close the grouping up again.

I think I will grab a box of the CCI 40gr Quiet Segmented rounds to try. No chance of a supersonic round, and probably ok for rabbits at less than 100M. Time will tell.

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Originally Posted by timattalon

Have a look around for either Highland super quiet (around the 900fps so really subsonic) or Aquila SSS (60gr subs) or some of the other brands may do a super quiet. As mentioned, going shorter will more likely increase the speed rather than slow it down.

https://www.guncity.com/22aguila-sss...gr-x500-220313 (950fps apparently)

https://www.guncity.com/cci-quiet-22...fps-x50-338874 (710fps)

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Ouch 20 bucks a box for the aguila's. They would have to be awesome for that coin

The aquilas tumble in my 22s all have the std 1:16 twist. 1:10 might be right but who does fast twist 22s?