Group size shrinks when cylinder pressure falls

[martynB]

This may be complete madness but I am experiencing a strange situation where by my group size dramatically reduces when the cylinder pressure in my EVO10 drops towards the lower end of the green zone. Sorry I don't have the pistol in front of me so I can't see what the gauge markings are at the bottom end.

This has happened enough times for me to suspect that either there is a problem with the pistol (less likely as its new out of the box less than a month old) or more likely there is something wrong with me.

The difference is striking, my normal mean radius on a 10 shot card is 13mm to 15mm, on the occasions when this has happened my mean radius drops to ~8mm, but significantly the group is typically tight in the 6 ring at 6 o'clock.

My question(s) is could the higher pressure be resulting in greater recoil which I am failing to control as I do tend to see a much more stable follow through; is the velocity of the EVO 10 too high, I looked at a Styer video on changing the velocity and it seemed to say that 160 ms was an appropriate velocity, I have measured the velocity as 170 ms, should I dial this down a bit and see if things improve?

I am new to 10M AP so I am wading through a whole heap of bad habits from other disciplines so would appreciate and thoughts and suggestions.

Thanks

Martyn

[northpaw]

Adjust velocity down to 160 - 155 m/s.
My LP10 does its best at 153 m/s , with RWS R10 pellets.

[django]

if you new on 10 m shooting , don't mess with pressure etc. New gun need +/- 5000 ammunition to settle on good condition.
if you can shoot 560-570 than you can make adjustment on your gun, because you know what you're doing. I can tell you this because i can shoot 560+ with my brand new out of box steyr without wasting 5000 ammo, make tuning, mambo jumbo thing, only make click on rear sight.

Why your grouping smaller when pressure getting low. Its easy..you shoot, shoot..many shoot and you don't realize that your muscle memory start to develop and your group smaller after so many shooting. That's why you should adding more dry fire than live fire. Steyr has recoil dumper you will never realize its recoil. I shoot morini 162Ei right now. Its hasn't recoil dumper, it has recoil kick harder than your steyr evo but i able shoot 50/50 , 49/50 sometime. And it still on factory setting. I am just recreational shooter, not a pro.

My other shooter some said, my pistol shoot so loud different than other. maybe it has too much velocity. But i said " I don't care" i'am good with this. I am just shooter not a gunsmith shooter who always tuning his gun when he shoot bad Lol

[Rover]

Unless you have the gun in a vise, you don't know how well it's shooting. Do that until the gun is empty and give us the result. Otherwise go with the post above.

[martynB]

Thank you all for you comments and advice, sorry for the delay in responding, work dominates.

Martyn

[KH250]

A theory is just that until you prove it. Crono it and see If there is a velocity variation between 200 bar at the start of the tank and down near 60 bar at the end of the tank. If there is a significance variation, do what Rover suggested and mount it in a vice as Steyr suggests with a quality pellet like a RWS R10. My Steyr only starts to slow down around 50bar.
It would surprise me if the group size changed this much with a velocity variation. Usually the human factor is the biggest one in group size with an air pistol. Leave the velocity alone until the pistol has done a few thousand shots. Give the springs time to settle down. My Steyr is sensitive to small movements of the velocity adjustment screw.

[KH250]

Crono? Think I missed a H.
LP10 chrono results attached, did not start at 200 bar so shot count not correct for a full cylinder.

[KH250]

Put my LP10e and LP50hp in vice on the weekend. JSB med 8.02gr 4.49mm and JSB S100 4.50mm used in both. LP10e does 155 m/s with the JSB med pellets and the LP50hp does 220 m/s with the JSB mediums. The S100's have nearly the same five shot group size, they do not seem to care how fast they go. The JSB mediums do not work quite as well, hardly call it a terrible group. My mount for the pistol could be improved. I do not expect to get the test target sized group when I test pellets. I also do not expect the LP50 to have quite as good group as the LP10e, as it is shooting from a magazine into the barrel. One for Rover, RWS basic LP50hp.

[mctrucky]

Hi Martyn,

Got to say if your average mean radius is 13mm, I would not be complaing.... If that is the external radius you are holding a 10.3 size group. The Olympics and World Records await....

But if we assume I am misunderstanding your measurements...

As the cylinder pressure drops there should be no change to velocity, or recoil, due to your gun having a regulator to allow for this presssure change. Your velocity charts back this up.

There will be a very minor weight change as the cylinder emptiest, but enough to notice any effect on point of inertia and recoil, no, just no.

So it is in your head. Most things with pistol shooting are. And theroies about what work and don't work can be self fullfilling as that is the way the brain works.

If you are like me, it can be hard to accept things without proof.... So get the gun in a vice and test away. Dont go tweaking or adjusting unless you are fixing something. Recommended velocities are nominal. Different pellet batches weigh differently, so will produce different velocities. But from a vice if the group of 20 shots is 9mm or less then you have no excuses for not hitting the X with every shot. If the group is wider than that, tweak away...