Interesting incident with my chronograph

[Guest]

Just wanted to take a minute and discuss something that really freaked me out (sort of) after a range trip today. I spent some time in the 80deg and up temps with a southerly wind of about 6-8mph sorting through somewhere between 150-200rds of ammo (not sure how much, as I took about 200rds, but didn't make it through it all because I had to wait a while for barrels to cool down between strings, even with four rifles). I had my 270Wby, 8x57, and two rifles I've been loading for that belong to friends - a 7mmRemMag and a 300Wby. Overall, the loading and shooting has been quite satisfactory, with the notable exception of the 300Wby, where accuracy has been less than stellar. I believe it may be a combination of shooter and insufficient load work, but don't quote me on that.

Anyway, the point of this prose is more about a little mishap that wierded me out. I was shooting, having a good morning, and noticed that I got some high velocities for my 270Wby 130gr loads. Max loads of 7828ssc, so I expect them to run around 3500, which they have been. But today, I got the following three shots: 3582, 3606, 3586. Accuracy was about 3" at 100yds, and I expected ejector marks and sticky bolt lift. I got neither. Lifted the bolt with one finger, casehead looks smooth. So I keep shooting. I get around to the 300Wby, and am shooting 180gr Hornady SST's over H4831sc, and get three readings: 4182, 4144, 4115. I'm really freaking out, because I don't have any pressure signs, again. I shoot the next three, at the max charge, and get just under 3200fps average, so I know something is screwy. I figure it's the bright sunlight, and I keep shooting, switching out to a different rifle. I get some pretty strange velocities, including a couple of 4400+ readings, and decide to walk down to the chrony when the range is cold. I can't really see anything wrong, but then I notice a very fine little thread of spider silk waving about in the wind between the rods holding the diffuser. Stretches from front to back, and keeps waving in the breeze over the two sensors! So I clean the darn thing off and go back to shooting, no more problems whatsoever.

I just thought it was funny. Oh, and it freaked out the guy next to me when he read 4489fps on the display after I shot the 270Wby 130gr E-Tip load for the first time. It was pretty cool to think I'd found holy grail there, by the way!

I'll get some pics on the groups and results overall here in a little while, or maybe over the weekend.

 

[bullet]

THANKS FOR THE STORY!!! That was fun to read and that certainly was a weird event to say the least. I like it when you said, "It was pretty cool to think I'd found holy grail there,...!"
Thanks again for sharing it with us, I could just see you trying to figure what in the world was happening. :lol: 8) :shock:

 

[FOTIS]

Man you got a couple of fast barrels! :lol: :lol: :lol: :lol: :lol: :lol:

 

[Guest]

I've been trying to figure out how to set up my scope to take advantage of the 180gr at 4100, but so far, I don't think I can adjust it properly with the existing adjustment range! I calculated it, and I now have a 375yd point blank range, and only 11.8" of drop at 500yds! This is going to be great! I just hope it has enough power for the jackalopes I'm going after in September!

 

[Greg Nolan]

I've run into this same problem. I discovered (in my case) that my chrony was not fully opened. It's hinged in the middle and opens up to full size where it gives a normal reading. In this case it was not opened up fully so the angle of the sensors (slightley closed so closer) cause it to read super high velocities. It doesn't take much of an angle to really skew the velocities. My 7mm RUM was giving me 4100 fps instead of the 3400 I was expecting. Another wierd thing I found was that if I was set up under high voltage power lines (My favorite long range site) I got false or bizarre readings.

Good Hunting
Elkhunt :grin:

 

[Guest]

Yeah, Greg, the hinge was the first thing I checked, but it was down and tight, just like it's supposed to be. It took a little figuring, but it was definitely the spider silk, as I was getting expected velocities from everything up to a point, then I got freaky stuff, off and on, and then I fixed it and all was well.