AA/CZ T200 PCP Rifle - Chrony Results: Explanations Please?

[Aimstraight]

Mystery now solved - F1 Chrony string readouts are displayed in reverse order!

I ran the AA/CZ T200 rifle over the F1 Chrony (.177, 12 ft.lb rifle) using lubricated Superdome pellets and have some unexpected results. It has an AA Ten Shot Conversion fitted, so the shots were done fairly quickly in groups of ten shot strings. The cylinder was initially charged to 170 bar (that is the limit for the gauge fitted on the cylinder), the cylinder is non regulated, so I was expecting a power curve, what I did not expect was a power saw tooth? For the first 30 shots the velocity and power was fairly steady, then from shots 40 onward instead of a gradual reduction in velocity and power, there is a saw tooth effect? The velocity/power starts low then ramps up, repeating this cycle when the magazine is changed. Anyone have an idea of what is going on, maybe something to do with dynamics of the valve, hammer spring, cylinder temperature changes in between changes of the magazines? I appreciate a regulator could be the solution to even power/velocity, but I would first like to understand what is going on with the ten shot conversion/ten shot string situation.

Thanks in advance.

[Shed tuner]

A leak ?

[Aimstraight]

A leak ?

Hmm, what like a weak shot at the start of the string, then it improves seals towards the end of the string, then repeats after the interval when changing the mag?

Interesting thought. If the peaks are joined up, the trend is in the right correction (reducing velocity/power), but the saw tooth ramping velocity up while pressure in the cylinder reduces is counter intuitive.

[Shed tuner]

i'd shoot a mag. leave it an hour. shoot another mag. if a massive drop, you have a leak.

there may be other things going on, but try the simple stuff first..

PS it also look a lot like a dodgy regulator (leaking through), but you said you haven't got one ?

the real throught process here, is is the sawtooth drop time related ? If time related, something will be leaking - either out of the gun, or through a reg/prechamber, or somesuch.
I can't see how the mag change per se could affect it - unless the gun is blowback. Other option is single load, and chrono every 3rd / 4th/5th shots to save boredom - the other shots can be target practice, plinking whatever. is it a smooth decay ?

I like a challange - much better than .177 vs .22 or TX vs HW

[Aimstraight]

Will do next time I have the Chrony set up, also could try on single shot to see what goes on. I may well include in target practice rather than just wasting pellets.

Yes, it is an interesting one, it looks like I made that graph up! I did not really spot it from the raw numbers, but the graph really shows it up.

[air-tech]

How bizarre. I am not familiar with the 10 shot conversion, but is it the typical probe through the mag affair, with the probe finally sealing within the breech block/barrel itself? If so, it ought to make no difference to sealing which shot number in the magazine it happens to be, also the major drop between mag changes coupled with a gradual increase does not sit well with the possibility of poor sealing, I would expect more erratic behaviour.

[Aimstraight]

How bizarre. I am not familiar with the 10 shot conversion, but is it the typical probe through the mag affair, with the probe finally sealing within the breech block/barrel itself? If so, it ought to make no difference to sealing which shot number in the magazine it happens to be, also the major drop between mag changes coupled with a gradual increase does not sit well with the possibility of poor sealing, I would expect more erratic behaviour.

Yes, the probe/o-ring just pushes the pellet through the mag (all 10 pellets are held by a single large o-ring), which seats in the breach just like the single shot system. The results are certainly weird.

[Aimstraight]

Bollards! Operator error. The F1 Chrony readout of 'stored values' shows the last shot first, and the first shot last. So reverse all the reading and the graph makes a very nice curve!

[Rickenbacker]

Oh you silly bugger.

[TonyL]

Bollards! Operator error. The F1 Chrony readout of 'stored values' shows the last shot first, and the first shot last. So reverse all the reading and the graph makes a very nice curve!

Hee hee hee!

Never mind, sir, all sorted now. Nice little graphs there, although the earlier one looked far more entertaining.

And there I was getting ready for some nasty gremlin theories at work inside one of these pesky pffft guns from the dark side!

[Aimstraight]

Hee hee hee!

Never mind, sir, all sorted now. Nice little graphs there, although the earlier one looked far more entertaining.

And there I was getting ready for some nasty gremlin theories at work inside one of these pesky pffft guns from the dark side!

That's what had me going at first - a very mysterious thing! At least I know the gun and the Chrony are fine...it's just me that needs examining!

[Aimstraight]

Oh you silly bugger.

That is a polite way of saying it

[Rickenbacker]

That is a polite way of saying it

On a positive note, D: Very nice work with the coloured graphs.

When I use my Chrony, I need a pencil and paper to record the scores.

[Shed tuner]

haha, well that's easily sorted

I'd reduce the hammer spring a bit to get a better curve, or increase the fill pressure a bit (subject to safe limits as marked on the clyinder, obviously), as you have no initial "rise" and only ~30 shots in the sweet spot...

[Aimstraight]

On a positive note, D: Very nice work with the coloured graphs.

When I use my Chrony, I need a pencil and paper to record the scores.

The F1 has a 3.5mm jack socket on the side, a DIY lead with a pushbutton allows scrolling through stored data (low, high, spread, standard deviation, shots taken, fps); fps in reverse order. Still need a pencil to note them down afterwards; but must remember to note them in reverse order when collecting long strings - doh.