Lab radar "warm up" ?

[X Count]

So I've been doing some fairly standard testing but with a rifle which is giving quite good ES of around 10.

One thing I'm noticing is if I shoot a 5 or 10 shot group and allow a few minutes (approx 5min) for the barrel to cool my first two shots of the next group will be 10-15fps slower. This is a 1.25" parallel 30" barrel so it's still warm between each group and I'm just trying to keep it at a consistently warm temperature throughout testing.

Yes I've seen big speed ups with dead cold and clean barrels but in this situation I'm wondering if the variation could be coming from the lab radar rather than the barrel?

 

[RegionRat]

I'm wondering if the variation could be coming from the lab radar rather than the barrel?

Doubt it.
Odds are in favor of it being the rig rather than the chrono.

The Doppler works on timing more than some type of amplifier gain or anything all that sensitive to temperature. Tends to be one of those situations that is very different than say the type of circuit in your load cell scale that is sensitive to warming and gain.

 

[Chris Edmondson]

The cheapest way I can imagine to determine if it's velocity metrology is using both a doppler and a magnetospeed, you already have the doppler.

 

[PatMiles]

So next time you're going to shoot, fire up the LabRadar 20 - 30 minutes before you start setting up your shooting gear.

 

[SeabeeKen]

Run a garmin next to the labradar. You may find it instersting

 

[divingin]

Yes I've seen big speed ups with dead cold and clean barrels but in this situation I'm wondering if the variation could be coming from the lab radar rather than the barrel?

Clock (and delete) a couple of shots from another rifle (yours or a fellow shooter's), and that eliminates that problem (unless you shoot alone with a single rifle, I guess.)

I personally don't see how that would occur, but a quick test would rule it in or out.

 

[X Count]

Clock (and delete) a couple of shots from another rifle (yours or a fellow shooter's), and that eliminates that problem (unless you shoot alone with a single rifle, I guess.)

I personally don't see how that would occur, but a quick test would rule it in or out.

Yep this is the next step.

My thoughts were the same as others that it shouldn't need warm up shots but for a barrel that is still fairly warm and giving good ES otherwise I was expecting more consistent fps for the first couple of shots.

 

[Fuj]

I was expecting more consistent fps for the first couple of shots.

Shoot any foulers first ?? I usually won't arm the unit until after
a minimum of two fouler/sighters.

 

[JPB4BAMA]

I seem to remember Laurie Holland noted something similar to this in his writeup on primer testing several years ago. That being that I think he noted a depressed velocity on the first shot of a "restart" from barrel cooling between strings of the test. Unfortunately I can't seem to find that article. Maybe someone else has a copy of Laurie could repost it. I don't remember if he ever ascribed a root cause or not, its just that this scenario rung a dormant bell in my brain.