Combro and CO2 pistols

[lensman57]

Hi,

Has anyone used the Combro Chronometer with CO2 pistols? I have tried to use mine but seem to get unrealistically high ft/s readings. Could this be due to the cold CO2 gas or is my Chrono is on its way out? I get the expected results with my PCPs and Springers when using this Chrono so I know that it is giving the true MV.

Regards,

A.G

[blooregard]

I'll bet it is not reading the projectile but is reading the gas as well.

I sometimes get the same effect on my F1 if I am too close. Unfortunately with the Combro, unless you make some kind of intricate device you don't have many options for moving back.

That said, is there much point chronoing a CO2 pistol ? Generally their power is well within the limit and the power source is too vulnerable to external influence to check consistency reported is anywhere near where it will be on the next session or indeed the next magazine.

[Aimstraight]

I used a Combro on an FWB CO2 pistol that seemed to be shooting a bit fast. It substantiated my suspicion and I was able to adjust the velocity downwards, so the Combro proved useful. I also compared the results with an F1 Chrony which also showed high.

[lensman57]

I'll bet it is not reading the projectile but is reading the gas as well.

I sometimes get the same effect on my F1 if I am too close. Unfortunately with the Combro, unless you make some kind of intricate device you don't have many options for moving back.

That said, is there much point chronoing a CO2 pistol ? Generally their power is well within the limit and the power source is too vulnerable to external influence to check consistency reported is anywhere near where it will be on the next session or indeed the next magazine.

Thank you for your reply. I also think that it is reading the gas rather than the pellet. I am trying to stop the leaks on my cp88 and find ways of getting the co2 to go through the barrel rather than the sides of the gun, no success as yet, so it is beneficial to see if these make the MV higher. At times I can see the pellets leave the barrel and follow the trajectory.

Regards,

A.G

[Aimstraight]

How come you are getting leaks from the sides of the CP88; the slide closes over the rotary mag? There is a spring loaded brass nozzle that mates with the rotary mag intended to give a good gas seal.

[Robet]

I tried the Combro on my CP88 and was surprised to see the readings much higher than expected!

So yes, I guess we can be certain that the Combro doesn't work properly on CO2 pistols or at least the Umarex replica types.

Would have thought it would be low with all that gas around, maybe Mr Combro can confirm it's not suitable for CO2 pistols.

Tried the old method with yellow pages for the CP88 against my HW75 & HW 45 on full power.
The CP88 penetrated slightly more than the HW75 and the HW45 penetrated twice as far as the other 2 which is what I expected.

So I might try it with a silencer fitted or just not bother as per blooregard's comment.

Cheers, Rob

[Aimstraight]

When made safe/no gas, maybe check the spring loaded action of the brass nozzle? Also check that the indexing is working correctly. If the pellet is not exactly aligned with the barrel, the pellet might clip the edge of the barrel, resulting in low MV and also preventing all the gas entering the barrel (blow out of the slide).

[Retracted_Yeti]

Put a piece of paper in front of the muzzle...job done, stops the co2 affecting the sensors.

HTH.

Roy.

[Aimstraight]

Must admit I never contemplated using the Combro on the CP88....fitting it to the rectangular muzzle would be tricky.

[Aimstraight]

Put a piece of paper in front of the muzzle...job done, stops the co2 affecting the sensors.

HTH.

Roy.

Yes, think I've heard that before from Robin (wrt to oil mist from springers).

[lensman57]

How come you are getting leaks from the sides of the CP88; the slide closes over the rotary mag? There is a spring loaded brass nozzle that mates with the rotary mag intended to give a good gas seal.

Hi,

I can assure you that I can at times see the CO2 coming out of the sides of the gun. Perhaps that spring loaded brass thingy is not making enough contact with the magazine. I also don't think that the spring loaded slide action is correctly designed as it pulls the slide/ barrel assembly away from the mag when closed. If you tighten the securing screw for the slide spring in front of the gun it actually pulls the slide back by quite a margin making the barrel's O ring that is supposed to seal the mag loose contact and leak. There is also a lot of high pressure CO2 in the mag chamber during the discharge as I am convinced that it pushes the pellets back and makes the pellets jam the indexing mechanism. TBH I am not impressed with the design of this gun, German or not. The slide/ barrel is also not a tight sliding fit on the guides, it can be easily rocked side to side as well as up and down enough to make sure that even at 5 metres one is not going to get a 2" grouping. If anyone knows of a good stripping guide to CP88 I'd be grateful for a pointer. On the positive side I have managed to make a silencer for it out of Aluminium that works nicely if there are no leaks from the side of the gun.

Regards,

A.G

[harvey_s]

Put a piece of paper in front of the muzzle...job done, stops the co2 affecting the sensors.

HTH.

Roy.

Roy's right - it works a treat

[lensman57]

Put a piece of paper in front of the muzzle...job done, stops the co2 affecting the sensors.

HTH.

Roy.

Hi Roy,

Thanks for the trick but I just tried it, three times and it gave a reading of 1068 ft/s. Such a powerful gun. Maybe they sold me the real stuff.

Regards,

A.G

[harvey_s]

If you're using round heads it could be cos' they're tearing a hole and the gas is blowing by...flatheads give a nice clean hole.

[lensman57]

If you're using round heads it could be cos' they're tearing a hole and the gas is blowing by...flatheads give a nice clean hole.

Hi Harvey,

I was using RWS Target CO2, they are flat heads I believe.

Regards,

A.G