RAW Rapid Strange Velocity Readings

[Zach]

I just had to rebuild the regulator on my .30 RAW. After I rebuilt it I set the regulator at 145 bar.

In a string of 36 shots the first 9-10 shots are pretty close in the low 900 FPS range. The next 10-12 shots will be in the upper 880 FPS range and the last shots will be back in the lower 900 FPS range again. I end with a standard deviation around 11-12 FPS.

Before the rebuild it would be in 5-8 standard deviation. Accuracy seems pretty good but the velocity swing seems strange to me. Can someone explain it? Do I need to adjust the regulator?

 

[Frank in Fairfield]

I am not qualified to answer your question but it sounds to me like your regulator is not working at all.

 

[nervoustrig]

A shallow inverted bell curve is a strange one. Is it repeatable? If it happened only once, it could be the nature of something settling...the belleville stack, the valve seat, etc.

Also, how did you set the hammer spring tension?

 

[Zach]

That's possible. It seems a littel to consistent to not be working at all but maybe not.

 

[Zach]

A shallow inverted bell curve is a strange one. Is it repeatable? If it happened only once, it could be the nature of something settling...the belleville stack, the valve seat, etc.

Also, how did you set the hammer spring tension?

It seems to happen pretty consistently. I left the hammer spring tension set where it was before I started. I tightened it slightly to up the speed when I started shooting is all.

 

[Ranchibi]

Zach, maybe try adjust the HS and tune it at the knee of 5% below max, maybe that will make it more consistent if you haven't already tried that. I think the reg rebuild may have changed your tune with the old HS setting.

 

[Zach]

Zach, maybe try adjust the HS and tune it at the knee of 5% below max, maybe that will make it more consistent if you haven't already tried that. I think the reg rebuild may have changed your tune with the old HS setting.

I haven't tried a lot of adjustment yet. I wanted to get some input before just making my best guess. I'll have to try that when I get some time again. Thanks

 

[HogKiller]

You did't happen to take any pictures of the reg did you? Does it involve any o-rings? As I'm not familiar with it, I'm guessing something got nicked during reassembly.

 

[Zach]

You did't happen to take any pictures of the reg did you? Does it involve any o-rings? As I'm not familiar with with it, I'm guessing something got nicked during reassembly.

There are a couple o rings on the regulator piston and one under the pin disk. I replaced them all. When you say something nicked are talking an o ring or a brass or steel part? I don’t have any pictures.

 

[HogKiller]

There are a couple o rings on the regulator piston and one under the pin disk. I replaced them all. When you say something nicked are talking an o ring or a brass or steel part? I don’t have any pictures.

A o-ring and I'm just making a wild ass guess. Also lubricating them with a good synthetic oil helps, NOT Y^%$# silicon. I'm basing it off of my Mavericks and what it appears to be doing.

 

[Zach]

I will have to take it apart and check and check everything out again when I get a chance. Thanks

 

[Cloud9AG]

IMO, 11-12fps SD variation won't show up in POI changes. I deliberately test speed changes when I setup a new rifle or select new pelelts, and with all the variables related to my steadiness, the wind, the pellets, etc...I never see a measurable change in POI until I get to about 30fps ES and over 15fps SD. That fps variation can be down to pellets, although you said it was repeatable, which makes me think it isn't pellets.
The insides of regulators require everything to be just right to function properly. Using the proper grease is a rather crucial item, because excessive stiction on the o-rings can affect how quickly the regulator returns to it's setpoint and if it does so reliably. RAW uses just a little bit of Krytox GP205 (or 206) on their regulator o-rings. Also, I've seen regulators "settle in" after a few hundred shots, so you might shoot it a bit more and see if it improves.
Happy shooting

 

[Zach]

IMO, 11-12fps SD variation won't show up in POI changes. I deliberately test speed changes when I setup a new rifle or select new pelelts, and with all the variables related to my steadiness, the wind, the pellets, etc...I never see a measurable change in POI until I get to about 30fps ES and over 15fps SD. That fps variation can be down to pellets, although you said it was repeatable, which makes me think it isn't pellets.
The insides of regulators require everything to be just right to function properly. Using the proper grease is a rather crucial item, because excessive stiction on the o-rings can affect how quickly the regulator returns to it's setpoint and if it does so reliably. RAW uses just a little bit of Krytox GP205 (or 206) on their regulator o-rings. Also, I've seen regulators "settle in" after a few hundred shots, so you might shoot it a bit more and see if it improves.
Happy shooting

Thanks for the info. So far the accuracy seems good the strange velocity just bugs me. But I will keep shooting and see what happens.