CZ 631 velocity ...what numbers are you getting from your cz

[airbuddy3]

cz631 /cz630...? and with what pellets /pellet wieght..?
           
           
                                                         Frank

[Unregistered(d)]

Don't have a chrono. Penetration tests using ballistic putty (the home depot stuff) have it equal to my Beeman P1 pistol using 7.9 crossman Premiers. Probably about 530 - 550fps.

[RCvan]

I haven't shot the 631 for quite awhile. My son had it and it came home needing work. As I remember "alanpo's" 530 to 550 fps. is right on the mark. These are very nice guns and benefit greatly from a lube tune. Sometime this week I will try and get a few shots across the Chrony. and will report back. Lets hope that the new 634 hits these shores before long.
            Chris

[RCvan]

I had the time today to shoot the 631 and these are the results that I saw. Shooting Daisy max speed pellets through the 631 with factory barrel 605fps to 612fps. With my carbine barrel (17") I was getting around 545fps to 552fps. I hope this helps
               Chris

[airbuddy3]

Thanks guys ,  these are similar #'s to what I am getting
           
                                             Frank

[wchilton]

My 631 with a tight-fitting bronze guide is shooting 650fps with 8.44 grain ft pellets and shoots with absolutely no twang.  A 630 I tuned with a looser delrin guide (slight twang) is putting out about 640fps with the same 8.44 grain pellets.  On both of these I floated the piston...used delrin rings for the 630 and teflon rings for the 631.  Have maybe 0.1 inch of spacing on the 631 and no extra spacing on the 630...McCarri spring is supposed to allow up to 0.85 inches of spacing and I may add some, along with some weight in the piston just to see what the gun can do.

[SteveU452]

I'm confused as to what you mean by "floated" the piston. Where exactly do the rings go, and what do they do?
           
            Also, if I were to make a new spring guide, where do I want to take up the excess space that causes the twang? Is it between the guide and the inside diameter of the spring? How much space is necessary?
           
            Thanks for your help. I am enjoying my 631 more all the time.
           
            --- SteveU

[wchilton]

To "float" the piston, I machined 1/8-inch wide grooves around the circumference near the front and back to hold the rings in place and then machined plastic rings to fit and just slightly extend above the surface of the piston so that there is no play between the piston and the compression chamber.  It accomplishes the same thing as buttoning a piston... eliminates all metal-to-metal contact between the piston and the compression chamber.  My understanding is that this helps with smoothness but not so much with velocity.  The McCarri spring had a lot more preload than the factory spring so I suspect that's what improved velocity.  I made the spring guide pretty tight.  Tight enough you can't just push it straight into the spring but have to twist it on.  The last 1/2-inch at the base of the guide I made even tighter (couple thousandths of an inch) to really control that end of the spring.  I also put a very thin top-hat in the piston to control that end of the spring.  I was hoping the tight guide would "wear in" a bit and velocity would improve and that is the case!  After about 300 rounds my 631 is shooting 670fps with the 8.44 grain pellets and 680fps with 7.9-grain CPL's.  Accuracy is as good as any other gun I've shot with open sights...haven't scoped it yet.

[KCJRC]

Being new to air rifles and starting to develop a growing interest, can someone explain how they calculate their velocities.
           
            Thanks
            Keith

[airbuddy3]

Is measured using a chronograph , which as its name implies ..measures time , the time your pellet travels between its two sensors ..and gives you a reading in feet per second.You can then use this reading allong with the wieght of pellet used to give the energy at the muzzle .Some chronos will give a readout in energy ..like the combro ..a small chrono the size of a pack of cigarettes attaches to the end of your rifles barrel , choose the pellet wieght , and it will give you fps and foot pounds energy .
            using the chrono you can tell if your rifle /gun has benefited from a spring change , or needs a seal , or likes certain types of pellets over others ..weither its shooting at manufacturers specs or within legal guidelines.
           
            cheers , Frank.

[KCJRC]

Thanks once again Frank.
            Sounds like a sophisticated little gadget.  
            When you state "within legal guidelines", can I assume one can actually get "muzzle" velocities high enough to enter the realm of "gun" legislation? (or am I just way off the mark here?)
           
            Keith

[Harry-Holland]

Hi,
           
            After a decent lube tune and fitting custom made steel spring guides, my 631 gives an average speed of 620 fps over 10 shots, with RWS superdomes of 8.33 grains. The extreme spread is only 3.5 fps, amazing.
           
            Greets, Harry

[wchilton]

Any legal guidelines would depend on laws where you live.  I'm aware that Canada has a FPS criteria for determining whether an airgun needs licensing and in some European countries there is an energy limit (12 fpe) above which an airgun is considered a firearm.  In the US, federal law does not consider airguns to be firearms but some state and local laws have their own criteria.  The chronograph itself is just used to measure velocity (or compute fpe, etc.).  It's a handy little gadget and can be bought for under $100 depending on what features you think you need.  For the price, it's the easiest way to measure performance.