AP velocities

[rk]

I chronographed (CED Millenium) my APs with the following results (all with 10 shots average (feet per second), std dev, low-high):

CM162EI (cylinder with 100 bar pressure, but not "locked out"): 430, 7.2, 415-437
CM162EI (150bar): 442, 5.2, 433-451
Steyr LP1P: 435, 6.2, 422-443
FWB P34 477, 2.2, 474-482
IZH 46 (not "M"): 408, 2.2, 404-411

The reasons I did this were: 1. I shot a match with my Morini, got two low 8s which I didn't call, saw that my pressure was down to about 100bar, switched cylinders (150 bar), and "problem" was "resolved". I do realize that the 8s may have just been 8s, but this did spark the velocity question. I thought that the regulator was supposed to provide the same pressure for each shot; in the Morini, the lockout mechanism is supposed to prevent allowing a shot with inadequate pressure from occurring. The data above seem to suggest (I am not a statistician and thus the data above, though suggestive is probably not adequate...) cylinder pressure may have some effect on pellet velocity. 2. It "felt" like the Steyr had low velocity because its discharge noise is so quiet compared to the Morini and especially the very loud FWB (I suspect the discharge noise is a function of compensator design and barrel porting...). I wanted to check to see if I need to "up" the velocity adjustment on the Steyr...

Questions:
1. Does anyone know if the cylinder pressure has any bearing on pellet velocity?
2. Morini factory velocity is supposed to be 492-508 feet per sec. I've never tinkered with any velocity adjustments (on this or any of my APs) - why do they all seem low (except the IZH46 which seems to chrono as expected).
3. Should I be concerned about accuracy, barrel dwell time (probably insignificant), or anything else with these lower velocities?

One comment - I'm hoping I don't need to be concerned as I seem to be shooting well these days: Last 3 practice matches with the Morini: 582, 580, 576...

Thanks,
Rich K.

[TargetTerror]

What pellet are you using? All these guns will be outputting a set amount of air, so heavier pellets will yield slower velocities than lighter pellets. Also, it seems to me that pellets that fit tighter in my bore tend to tear the paper more than looser fitting pellets. I suspect the tight fit might be robbing the pellet of some energy as there is more friction to overcome in the barrel, but I haven't chronoed this so it is hard to say (and it also could just be the weight of the pellet).

[rk]

H&N Finale Match (rifle=heavy) 4.49mm.

Rich K.

[Steve Swartz]

1) As long as the pressure lockout mechanism does not engage, the amount of pressure in the charging chamber is the same (regardless of tank pressure); that's how a regulator works.

2) Even when the lockout mechanism engages, pressures will still be uniform for quitge a few shots. I just shot 30 shots beyond the lockout on my 162EI and didn't notice any dropoff (measured) until the 24th shot.

3) The relationship between charging chamber pressure, velocity, and hole on paper is somewhat errr "indirect" at that. Even with a significant drop of pressure (say 20%) the change in velocity will not be of the same oom initially (more like 5%) which affects the position of the hole on paper not much- certainly not 10 ring to 8 ring.

Something else must have been going on. While not ruling our a mechanical problem (you velocity measurements are interesting- but with only ten shot series, not much can be inferred), the "Hoofbeats = horses" cause is probably the "software."


Steve

[Steve Swartz]

. . . to satisfy your curiosity, lock your pistol into a vice and run a string down from "almost locked out" beyond "locked out" and record what happens to velocity and POI . . . maybe do this at least a couple of times . . .

that's the only way to tell.

Steve Swartz

(my prediction- as has been discussed by others in this forum before- is that you will find the "bottom" [where POI is actually affected] is pretty far below where you think it would be)

[Mark Briggs]

Just to add some real-world numbers to Steve's comments, I have done testing on my CM162EI-Short and have found that from lockout I can count on 17 shots before the point of impact drops by more than half a pellet width. So, If I'm past the 40th shot in a match and hit the lockout I can finish the match, but will have to watch the last few shots because lower velocity may turn a 10 into a high 9.

As for absolute velocity measurements, your standard deviation numbers are pretty high. I'd suspect any number of things including reliability of your measurements as a factor of available lighting (some chrony's give misleading numbers in low light conditions) as well as reliability of your pressure regulator. SD on my CM162, LP-10, LP-1 (Co2) have all been below 5.

[rk]

I really appreciate the responses. It is reassuring to know that I've got enough to keep shooting the 162EI after lockout. I suspect (as implied and I agree) that shooter error started me off on this short "diversion".

All the guns were tested at the same time under similar if not the same conditions. I agree that the extreme spread and high standard deviations of the Morini and Steyr were a bit alarming especially because those of the FWB and IZH were low. Though a higher "n" will result in better stats, it won't decrease the spread... Chrono technique/light conditions or regulator problems (per Mark)??? - I may retest (but I have a feeling that more testing will result in the need for more testing (for something else), and I hate testing (I'd rather shoot...)).

I shouldn't ask, but I will. Are regulators commonly or uncommonly known to have problems or to go bad? Do they need any maintenence?I've never heard of the problem...

Thanks again.

Rich

[Fred Mannis]

I shouldn't ask, but I will. Are regulators commonly or uncommonly known to have problems or to go bad? Do they need any maintenence?I've never heard of the problem...

Hi Rich.

Here's a good reference to an earlier discussion of this subject
http://www.targettalk.org/viewtopic.php ... =regulator

Fred

[Richard H]

I shouldn't ask, but I will. Are regulators commonly or uncommonly known to have problems or to go bad? Do they need any maintenence?I've never heard of the problem...

Thanks again.

Rich

There aren't really alot of parts that can go bad really just seals and the regulator (aside from trigger issues). So they don't go bad often but when something does go bad it is usually the seals or regulator.

It's not really a big deal for the LP10 if your in the States you call Scott and he ships you a rebuilt one you ship the old one back and you pay a rebuild fee, not that expensive either. Buying a new regulator is a little more expensive (I have a spare for all my air guns) but from then on in it is just a rebuild charge and I'm never without one.

[rk]

Thanks Fred and Richard H. for the regulator info - much appreciated!
Rich K.

[Steve Swartz]

Rich:

Will we be seeing you at 3X/Top Gun?

Steve

[James]

The standard deviation seems fine. My pistol does about 8-9 fps. It would take quite abit, maybe 40-50 fps to see a change in poi.

My kite shoots in the low 500s 500-515 with diabolo basics 7gr

[JulianY]

. . . to satisfy your curiosity, lock your pistol into a vice and run a string down from "almost locked out" beyond "locked out" and record what happens to velocity and POI . . . maybe do this at least a couple of times . . .

that's the only way to tell.

Steve Swartz

(my prediction- as has been discussed by others in this forum before- is that you will find the "bottom" [where POI is actually affected] is pretty far below where you think it would be)

I think steve is right , this is the only way to know for sure.

However you are talking about an olymipc gold class pistol. You should be able to shoot a full 70+ shots with a morini in a vice and never drift off the ten. if you do you need it servicing.

J

[Steve Swartz]

My point exactly- if your air pistol will not hold a cloverleaf inside the deep ten ring from full cylinder all the way down to lockout, something is wrong.

If it will, then the velocity variation is pretty much interesting but irrelevant.

Steve Swartz

(as a reformed rifle guy, a 10% coefficient of variation* is a Big Deal at 600+ yards . . . for an air pistol at 10 meters, a 20% coefficient of variation is probably No Big Whup.)

* CV = (standard deviation)/(mean) so a 50 fps sd out of 500 fps velocity might look frightening but is only a 10% change in velocity. At short distances, velocity differences do not represent a large change in projectile drop- certainly not a linear, proportional relationship