Questionable chronograph readings?

[pibulloncrack]

Thanks for all the input everyone.

zeke - I listed the OAL incorrectly in my initial post. I intended to type 1.13, thank for catching that.

My biggest concern was the shots reading into the 1300's. I have been using these loads for some time. I have even ran them through other chronographs, one being the same make I used. I have never gotten readings over 1250 and averages of around 1190. These rounds were from a fairly recent batch so I was trying to rule out a change in my setup that I may not have caught or this new chronograph be that far off. From what I am learning here, I am begining to lean toward a change in my setup.

 

[fredj338]

These were hand weighted 357 loads of 4227, trimmed cases and using a Lee FCD. So I was a little suprised at this variations in volocity.
But these were loads using very well used mixed brass, so there may be something in the neck tension
However, I noticed on this outing that I was shooting closer to the chrono than I usually do

Sorry OP, didnt mean to hijack you. I'm done.

Generally a muzzle blast issue affects every shot, not one or two, & generally you will get an error message or really weird reading, outside the possible realm of the load.

 

[fredj338]

My Speer #9 has a chart where they Chronied shots through pistols of the same make, model and barrel length and the variations were pretty drastic.

Yep, all guns & barrels are diff, even those of the same make, made on the same equip. I have 5 diff 4" 357mags, S&W, Colt & a Smolt. They all give diff vel readings with identical loads. Some as much as 150fps diff. So I have learned just about anything is possible, within reason, in a given bbl. I even had a 2 3/4" Ruger ss that was faster than most 4" guns. I never took measurements & stupidly sold it, but I suspect tighter bore & smaller cyl gap.

 

[Alk8944]

pibulloncrack,

Just a few clarifications. For the individual who suggested muzzle blast may be having an effect, and the one who said it would affect every round. First, muzzle blast can be an explanation for low velocities as it can trigger the start screen before the bullet gets there so the transit time is falsely increased. Second it can be random, and usually is. One of the advantages of the Oehler 35P and its' three screens which provide two separate velocity readings that serve as a cross-check.

If you are using a different chronograph than in the past I would not be particularly concerned about "set-up". Most modern chronographs have a set screen spacing that cannot be changed, and you would only see the difference you mention (1200-1300) if the screen spacing was ca. 8% shorter. That difference would be easily detected.

It sounds like the crystal frequency in the clock is a bit off. I would suggest contacting the manufacturer. If it is a reputable company they would have no issue with replacing the unit for you.