<< Previous Topic | Next Topic >>  

CZ200 velocity problem

December 3 2017 at 9:22 PM
Brazos  (Login Brazos2)
YF12

I have a friend with a .22 caliber CZ (AA)200S. He bought it used and has had an issue with it and brought it to me to check out. I put it on my chronograph and it did the same thing for me. First I took the air cylinder off my CZ200 and put it on his rifle. I figure using my chrono and my air cylinder took two possible problems out of the equation. When we shot it the first 5 shots were very tight, around 835fps, take or give a couple fps. Then instantly it started shooting in the 750fps range and again for 4-5 shots that were very tight fps wise. Then it shot up to the 815fps range for 4-5 shoots that were very tight fps wise. I stopped there as it was doing exactly as he described. The velocity is very tight for 4-5 shots and then instantly jumps up or down 50fps and shoots tight 4-5 times and jumps 50 fps again. No classic curve. What would cause this on a CZ200? One thought I had since shooting the rifle is he had it turned up pretty hot to be shooting a .22 caliber pellet in the 830fps range. This is a CZ200 and I am not sure what velocity a .22 cal CZ200S should be shooting but that seems too fast. Maybe the main spring is over tightened?

 
 Respond to this message   
AuthorReply
gubb33ps
(Login gubb33ps)
YF

Likely wound up too tight.

December 3 2017, 10:41 PM 

Yep...do think he has it wound up too tight. Back off the main spring tension by a full turn and see how it does. May not be real happy to be under 20 foot pounds, but mine starts acting up once I get past 18-19 foot pounds (and seems at it's happiest at about 16).

It's a surprizingly short spring travel. Bolt works a pivoting lever (left side)that works the mainspring compression, so the spring travel is NOT as long as the bolt travel..so one full turn out is a larger change than it seems.

This next one is NOT YOUR PROBLEM (probably). You tried two air tubes...the chances of the o-ring on both of them beeing bad is pretty slim.

But it's worth noting.

The other thing that can creep up on you is the o-ring that seals the rear end of the air tube. If the o-ring leaks, you won't feel it as the stock channels any leak forward along the air tube (where you are not likely to notice it).

This was a rading I got..figured I needed to stop and figure out what was wrong.
photo f2f7489a-ac86-47c4-8e81-a68e22af60f1.jpg

Was the o-ring on the end of the air tube. Age/hardness/crack...new o-ring put it back shooting like it was suppose to.

photo f289f725-18a9-41ca-a168-cfbed4c0efd8.jpg


    
This message has been edited by gubb33ps on Dec 3, 2017 10:43 PM


 
 Respond to this message   

steve
(Login skipperckwpeg)
YC

tuning the CZ.

December 4 2017, 11:24 AM 

BobD may respond here, he put up some of the best tuning info for the AA/CZ platform. Only way I could get a 177 near 20 ft lbs was to take the air cylinder apart (very hard if it is factory and never been apart) and remove what is called the 'pot' inside. It is kind of like a simple regulator. Other than that, tuning the CZ involves both the hammer spring tension AND the air strangle screw. You need to adjust both. And yes, I agree... just heavy hammer spring tension alone is as for trouble. HTH.

 
 Respond to this message   
Brazos
(Login Brazos2)
YF12

Re: tuning the CZ.

December 4 2017, 4:54 PM 

I think this person just wants an accurate rifle and is not hung up on power. It would appear the rifle is a straight shooter but with the velocity jumping all around it won't be.

 
 Respond to this message   

steve
(Login skipperckwpeg)
YC

On tuning the CZ BobDs write up is on the Archive page....

December 4 2017, 6:39 PM 

I was able to tune my CZ to 15 ft. lbs. just using the stock hammer spring and air strangle screw. Have not had time to do a full shot string on the chrono yet.

 
 Respond to this message   
gubb33ps
(Login gubb33ps)
YF

Simple view of it

December 4 2017, 7:31 PM 

Can make it simple...but labor intensive (you have to test.cronograph a lot).

1. Open the transfer port restriction screw up.
2. Fill to 2800psi and shoot 25-30 shots.

3. For now, IGNORE the energy per shot.
4. If the shots start slow and increase in speed by quite a bit over those 15-20 shots, then you need to increase the striker spring tension....adjust the spring tension in 1 turn IN and try again with a new 2800fpsi fill.

5. If the shots start fast and decline over those first shots, then you need to LESSEN striker spring tension a bit ...adjust the strker spring tension OUT 1 turn and try again.

6. Ideal is for the velocity at 2800psi to start off about 3% slower than whatever the max speed turns out to be...and decline to about 3% uder that max speed.

7. Fill to 2800 psi and now look to the transfer port restriction screw. If you want max-reasonable power for the best shot count, then just screw the transfer port screw in a little bit at a time until you notice an unexpected deacline in speed/energy. Then back it out 1/4 turn...that's about as much energy for the fill pressure as you can have with a decent shot count.

8. If you have an eye on even less energy (lets say you fixed on 12 foot pounds), then just keep tuning the transfer port restriction screw in until you get there (starting a little low at 2800...peaking at somthing like 2400...and falling down under 3% of max at about 210-19000psi).


Havbe two of the critters....the abocve pretty well works for botu with good efficiency/log shot counts....just nto the mega energy some folks crave.

 
 Respond to this message   
 
  << Previous Topic | Next Topic >>  

Airgun Calculators    Num of fills calc    Capacity Calc

******** Kalibrgun High quality, superb Accuracy, outstanding Value. ********





D I S C L A I M E R
JK's Airgun Forums, moderators, and administrators are not responsible for any problems that may occur from reading or using content posted on this forum, as they are the exclusive responsibility of two parties: the person who posted it and the person who acted on said posted information.Use of our forums by people under 18 years old is allowed only with legal guardian(s) present.