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Old 12-08-2019, 01:02 PM
Guesty

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Cz457 22LR choked barrel?



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I have just slugged my 22LR and found an obvious choke in the bore, about 0.5” from the muzzle, under the muzzle threading.
The rifle doesn’t shoot that well, the best ammo is SK RM which only does a consistent 0.75” at 50 yards. It doesn’t like Eley, RWS or the other usuals either.
I have done the usual upgrades, such as trigger spring, firing pin reprofile and glass bed, with not much improvement. I’m beginning to suspect the choke, so just wondering if everyone else’s is choked, and if anyone has had success with cutting it off?
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Old 12-08-2019, 01:20 PM
wkd
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Oh boy, here we go!
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Old 12-08-2019, 01:33 PM
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Uh oh, I’m guessing this has been done to death before?
I did quick search, but will have another proper look...
BTW, it’s a 457 Varmint.

Last edited by Guesty; 12-08-2019 at 01:38 PM.
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Old 12-08-2019, 03:06 PM
Mike_AK
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That is not unusual and is expected. CZ barrels are hammer forged. When you turn down a hammer forged barrel, it causes the bore to constrict slightly in the area where the metal was removed, in this case where the barrel was turned down and threaded. A button rifled barrel will do the exact opposite. That is why manufacturers of button rifled barrels choose the tightest end of the blank after it is drilled for the muzzle.
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Old 12-08-2019, 03:33 PM
Guesty

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Thanks for the info Mike.
The barrels on my centre fires are also hammer forged, where I haven’t noticed the choking effect but they do all have much larger diameter muzzle threads meaning less metal has been removed so I assume reducing the effect.
I must admit to being a but disappointed with the accuracy so far as it’s no better then the fancy 10/22 I had before.
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Old 12-08-2019, 03:45 PM
R4B1DM4U53
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If anything, the bore tightening up at the muzzle would be considered a good thing. Much talk on the Anschütz forums about "choked" muzzled. Others with CZs have reported increased accuracy after having their muzzled threaded. I would next look at your chamber with a borescope. My 455 Fullstock shot over 1" until I lapped the burrs out of the chamber.
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Old 12-08-2019, 03:52 PM
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Yup, I do believe that choking is regarded as generally a good thing, but I’m beginning to wonder if the very obvious ‘step’ feeling on pushing a slug through my choke might be too much?
Interestingly my last Anschutz a 1517 HMR was factory muzzle threaded, but counter bored under the muzzle threads I guess to avoid this very issue.
I have had a look with a bore scope and seen nothing untoward, and the rifling and crown seems good too.

Last edited by Guesty; 12-08-2019 at 04:52 PM.
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Old 12-08-2019, 04:10 PM
Mike_AK
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Try taking a patch saturated with JB Bore Paste on a spear tip jag and running it the full length of the barrel 20 times, 3/4 the length 20 times, half the length 20 times and 1/4 the length 20 times all from the breech end right in front of the chamber to the muzzle end but not letting the patch exit the bore. This worked magic on my 452 Varmint. Clean up with Kroil when you are done.
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Old 12-08-2019, 04:24 PM
fourbore
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Guesty, I think you maybe on the right track. A precise deliberate choke is a wonderful thing, assuming it is done right. An accidental constriction is not a good thing.

This whole line of thought is exactly why I dont want a threaded barrel unless I intend to screw something very important on the barrel end.

shooting 0.75 at 50 is not at all unusual for CZ. I dont expect CZ to offer a replacement for that. Going on that assumption and also replacing with another threaded barrel may have the same issue, I would be tempted to have and inch cut off the end and recrowned. That could be a low as $50 job. Or DIY?
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Old 12-08-2019, 04:46 PM
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Sounds like a good plan. I do have some JB and was already wondering about smoothing the step out a bit. If it doesn’t work I could try counter boring the muzzle threads. If that doesn’t work then chop an inch off and try again. If I do wreck the barrel as least it is fairly easily replaced.
I guess 1.5MOA isn’t the end of the world, but I have a feeling it can be better and it might be fun finding out.
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Old 12-08-2019, 09:14 PM
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Quote:
Originally Posted by Guesty View Post
Sounds like a good plan. I do have some JB and was already wondering about smoothing the step out a bit. If it doesn’t work I could try counter boring the muzzle threads. If that doesn’t work then chop an inch off and try again. If I do wreck the barrel as least it is fairly easily replaced.
I guess 1.5MOA isn’t the end of the world, but I have a feeling it can be better and it might be fun finding out.
Or, instead of going to all that trouble, you could buy a cut rifled barrel from, say, Lilja and forget about it.
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Old 12-08-2019, 10:06 PM
Mike_AK
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Quote:
Originally Posted by FALPhil View Post
Or, instead of going to all that trouble, you could buy a cut rifled barrel from, say, Lilja and forget about it.
Lilja barrels are button rifled.
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Old 12-09-2019, 12:11 AM
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You might try shooting it with the thread protecter off. I have a few threaded barrels where accuracy changed when i did this, or when i untorqued the thing.
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Old 12-09-2019, 09:00 AM
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My understanding of machining is that removing material from the OD of a bored cylinder increases the diameter of the internal bore. This is consistent with what you are finding.

Also, as a highly trained Internet gunsmith chokes should be at the very end of the bore, NOT set back from the muzzle.
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Old 12-09-2019, 09:21 AM
Mike_AK
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Originally Posted by Bigbore View Post
My understanding of machining is that removing material from the OD of a bored cylinder increases the diameter of the internal bore. This is consistent with what you are finding.

Also, as a highly trained Internet gunsmith chokes should be at the very end of the bore, NOT set back from the muzzle.
Your understanding relative to a hammer forged barrel is incorrect.
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