Pellet Weight for Steyr Velocity Adjustment?

[Gwhite]

I need to adjust the velocity of an LP10 that is using too much air. I've rummaged around on-line, and every source I've found agrees that the velocity should be set between 155 and 160 m/sec. HOWEVER, they never specify the pellet weight. I've checked several test targets, and all the ones I have specify the diameter, but never the weight.

I've found a couple mentions on-line that they have used R10 pellets, but R10's come in 8.2 grain & 7.0 grain weights. I know from repairing a bunch of Benelli Kites that the difference in velocity between those two weights is about 10 m/sec, or TWICE the width of the velocity window you are supposed to adjust for. The Steyr video on velocity adjustment never mentions the pellet weight, and the tin they are using is conveniently out of the frame.

I found one old posting that they tested a pistol with 8.2 grain pellets, but I've also found mention that they use 7.8 grain pellets. I'm not concerned about pinpoint accuracy, I just want to get the velocity in the right range. At least the difference between 8.2 and 7.8 would probably fit inside the velocity window.

The other part of the puzzle is what happens to accuracy and/or the stabilizer operation if you set the velocity with (for example) 8.2 grain pellets, and then shoot with 7.0 grain pellets. Is it better to adjust the velocity with the pellets you are going to shoot, or adjust the way the factory does, and accept the higher velocity with lighter pellets? I'm NOT going to waste my time doing accuracy tests, but if someone has any real data on this, I'd love to hear the results.

Thanks!

[thirdwheel]

Set the velocity using 7.0gr pellets this is the std pellet used, use a nice one R10 or better, and set the stabiliser with this pellet too and heavier pellets will not make the stabiliser change as it is spring catch and spring powered unlike the K12 where you have to take account of the pellet weight as the absorber is air powered but is very simple to do. Don't over think but I know I do too.

[brent375hh]

Steyr used to use R10 7.0 4.49mm.
I have tried everything from 480-540 fps. They all are quite accurate. I got my best groups at 523 fps average. That being said, it feels better, and I get more feedback at an average of 493, (150 m/s) which is where I have left mine.

[Gwhite]

Thanks! If Steyr sets their velocity with 7.0 grain pellets, that might explain what I'm seeing.

The pistol I'm working on is running just over 160 m/sec with 8.2 grain pellets. That means it's probably close to 170 m/sec with 7 grain pellets, which would cause at least some of the high air usage.

It holds air just fine if you let it sit with a cylinder installed. The means the firing valve seal & everything upstream from there is OK. It's possible there was some leakage around one of the breech seals & somebody cranked up the velocity to compensate. I replaced those two seals, but the batteries died in my chronograph, so I don't know what effect that had yet.

[Rover]

In my messing about with a couple of SSPs, i found the difference between light and heavy pellets to be about 45fps.

I like to set the gun at about 525fps for no good reason. I HAVE found, though, that an occasional pellet brand will
be grossly inaccurate until air pressure is played with.

[Gwhite]

I think I found my culprit... Once I got my chronograph working, I tested the pistol with the the new breech seals for 10 shots, using the same 8.2 grain R10's I had for the previous test. I got a slight increase in velocity, and it was chugging along very repeatably around 162 m/sec. Then I had three shots in a row that were over 178 m/sec, after which it went back down to ~ 162 again. I fired a total of 15 shots, and it consumed about 30 bar of cylinder pressure, which is about twice what it should be.

I think the regulator needs an overhaul. I don't see how anything else in the pistol could produce that sort of variation, especially upwards.

[brent375hh]

Probably just replacing the two piston o-rings and cleaning out the inside, especially around the inlet seal of the piston would put you back on track in 10 minutes of your time.

Putting velocity at 150 m/s gets about 160 shots per fill.

[Gwhite]

I have a dead regulator I swapped out from another pistol. I'm working on a drawing to fabricate a pressure tester, and I had hoped to finish making that before overhauling any regulators. I guess I will rebuild the first one and swap it onto this pistol and see how it goes...

[brent375hh]

I have a dead regulator I swapped out from another pistol. I'm working on a drawing to fabricate a pressure tester, and I had hoped to finish making that before overhauling any regulators. I guess I will rebuild the first one and swap it onto this pistol and see how it goes...

As long as you put the spring (belleville) washers back as they were, re-ringing the piston, and cleaning the inlet seat, you should have it functional as it was before. I clean it with ballistol and a Q-tip, then dry Q-tip. The above procedure is easy and fast to try before any of the below...

The hard part is taking out the inlet screw, and putting in a new o-ring there. I don't have any special tool, I just start at 3/4 turn out and through trial and error with 2 cylinders at 200 and 70 bar, I adjust the inlet screw until they both shoot the same velocity. Once I get that, I adjust the velocity to 150-155 m/s.

Adjusting for actual plenum pressure would require some flat shim washers to stack in with the belleville washers and some trial and error with a pressure gauge.

[Gwhite]

I'll have to study the diagram. The inlet screw is under the front cap, and I recall some mention of threadlocker & soaking in acetone... I have a two pin security bit that should fit, but the pins are square, and I may want to round them a bit before I chew up the holes in the cap.

It looks like I can replace the two piston O-rings without touching the inlet screw, so I may just start with that. I can also examine the end of the inlet screw to see if it looks gunked up.