vertical stringing in the colder temps?

[SPAK]

Hey guys,

Before I get too far, my first bet is shooter error. I took my .30-06 load of 59.0gr RL 22 208 AMax 22"barrel out yesterday and shot a string of 15 shots. Barrel was thorougly cleaned, no copper (that I could tell without a scope)

CCB shot 1st shot was low about 4". No biggie. Next 4 were right where they should be, but group size was about 1MOA at 100 yards.

The next succession of 5 shots strung vertically, almost in a straight line. At most there was 1/2 MOA of horizontal.

Next 5 shots did the same, vertical stringing.

Through the shot string Concentrated on breath control and trying to use the same amount of stock weld and shoulder pressure (pulling stock into shoulder pocket).

So here's the question: Loads were developed at around 60deg temps. Yesterday temps were about 30 degrees on the kestrel.
My velocities were almost 100fps slower than when loads were developed initially. Group size normally is around .25-.5MOA pretty consistently.

Could the 100fps slower induce vertical stringing? I guess I've seen some temp sensitivity reported with RL 22 but this is my first time actually seeing it first hand.

Any thoughts? Like I said, it was colder, and the first time I've been out since it's been really cold...sure felt like it was in the mid teens for temp but the meter said right around 30 deg... I'm leaning towards shooter error.

 

[Greg Langelius *]

Re: vertical stringing in the colder temps?

Yes, to velocity deficit/vertical. The velocity difference could be placing the load outside the accuracy node.

Tweaking the load very slightly upward might reposition the load more squarely centered within the node's accuracy window. With a 100fps difference making an issue, I'd suspect the load is slightly slower than the ideal centering within the 'good' velocity band.

Shooter error rather less so, since you clearly anticipated and hedged against it.

I would also check the barrel channel for marginal contact that occurs at some temps and not at others, and bedding/action screw tension for potential looseness. Optics mounting, too.

Greg

 

[SPAK]

Re: vertical stringing in the colder temps?

Thanks Greg,

I checked all bolts prior to the outing to make sure they're within spec. At this load I get a slight shine on the case head but they ejector mark itself doesn't look shiny. 1x brass. I have some suspect that my sizing die is not set up correct and I'm getting a crush fit. Most of the cases when I close the bolt down I can feel the bolt closing down on the case with slight resistance.

I'll work on the headspace and tweaking the load. FWIW my velocity ranged from 2615fps to 2722fps at these temps.

at 60deg my velocities ranged from 2728-2736fps.

 

[jrob300]

Re: vertical stringing in the colder temps?

I shot a lot of RL22 in my 300WM's. I've since switched to H1000 because, among other things, it is less temperature sensitive than RL22. They both drive 208's fine in the WM. I'm not sure if that would carry over to your '06 or not.

FWIW

John

 

[Greg Langelius *]

Re: vertical stringing in the colder temps?

More info always helps.

Looking at the way the ES opened up, I'd be thinking the ignition is becoming less consistent at lower temps. This could also most certainly be at the core of the increased vertical dispersion. In fact, discounting the lower ends of your reported velocities as ignition issues, I only really see a much smaller velocity drop-off. My suggestion now would be to go with a 'hotter' primer. When faced with this choice, I often substitute with Winchester primers as a test. If they work, maybe a magnum or magnum match primer could resolve the issue. Or simply go with Winchester, if they help the accuracy.

If the hotter primers confirm my suspicion, then my next question would be whether the questionable ignition reliability that occurs at lower temps is also occurring to a lesser degree at warmer temps. The one thing about hotter primers that you can count on is that there's pretty much a whole lot less question about ignition reliability. Winchester primers definitely have a place in accuracy reloading, and that place is the one where ignition is questionable, like with long powder columns, slower powders, and compressed loads. One of more of these conditions could be present with your load, and I apologize for not thinking of this sooner.

I've never been a big fan of Chronos as an accuracy tool. I neither trust the numbers, nor count on them as infallibly and directly related to accuracy. When the manufacturer's stated error rate is +/-1% of reported velocity, ES and SD numbers that are less than 1% of reported velocity tend to become somewhat debatable, IMHO. My most reliable accuracy tool is the target.

Slight bolt drag on closing is actually an ideal situation, don't mess with the dies.

Greg

 

[SPAK]

Re: vertical stringing in the colder temps?

Thanks Greg, I'll try switching out the primers and report back.

I did an experiment last night with empty fired cases Mil surplus. After 3 dry fires and opening the bolt, I got what looks like an ejector swipe very similar to what I am getting on my fired winchester brass. I know that Mil surplus brass tends to be harder, but what could be causing the ejector swipe?

 

[Greg Langelius *]

Re: vertical stringing in the colder temps?

Maybe the ejector is a tad rough. I really wouldn't get too concerned about it as long as the ejector works, and the rounds chamber without difficulty.

If the ejector is really flinging the brass a good ways, maybe the ejector spring is stronger than it needs to be, and could be figuring in that bolt drag upon closure. All the ejector really needs to do is get the brass to clear the action, any more is just extra.

Again, as long as things are working, I wouldn't let it bother me that much. Ejector swipes are simply a cosmetic issue.

In fact my match gun has a single feed follower and a disabled ejector. I prefer to seat the cartridge and pick out the brass by hand. It keeps it cleaner and eliminates a good bit of the damage one sees when brass gets fed and chucked about afterward; and besides, it makes it easier to keep track of any relationship between flyers and pressure signs on the suspect cartridge.

Greg