Jump to content
Brian Enos's Forums... Maku mozo!

Funky Chrono readings...


cypher

Recommended Posts

I need help figuring this out.  Any and all input would be greatly appreciated.

I took my new PACT Chrono to the range today to Chrono some rounds  I had some old stuff  (200 L-SWC over 5.7 of 231) and some stuff I just loaded (same bullet over 4.2 of Clays) brass on both was mixed.

All firing was done in 5 shot strings.  I started out with the 231 loads.

Nothing surprising here, in fact, the performance was very consistent. Most of the groups averaged around 810 fps for about a 160 pf.  This was around 10:00am in Pinellas Park, FL. My largest extreme spread for all the groups (10 groups) was 52.8 fps.

I was pretty cool with that.

Next I fired the rounds I had loaded with Clays.  Again the results were not surprising.  This time my loads averaged about 840 fps for about a 168pf.  Largest ES was 73.6 but most were around the 25 to 35 range.

I was fairly happy with the results up until this point.  I took a  break fired some other rounds over the chrono (38's, 357's & 40's) just to see.

The guy I was shooting next to told me he had just attended the Area 6 Nationals and the load he had been shooting (172-3 pf) when chrono'ed at the Nationals only got 165.9 pf.  He said I should chrono my loads again (because now the light had changed) to see if they were different.

Well I thought "Why not?"  By this time a couple of hours had passed since I had first started and the light was indeed different.  So I was curious to see what effect if any it would have on the readings.

This is where it gets weird... I shot my new loads first (4.2gr Clays) the avg. velocity was in the 1200's!!!  This equated to a pf of 240 or thereabouts... The rounds didn't feel any hotter than those I shot before.  I checked each round for signs of pressure everything seemed OK though.  My ES for this string (I only shot one at this point just in case something was horribly wrong) was only 23.7 fps!

I quickly loaded a magazine with 5rds of the 231 loads and shot that... they averaged 1137 fps... and again with a very low extreme spread.  (something like 36 or so).

I shot some commercially reloaded 230 FMJ just to see what that did;  1089 fps and very consistent from shot to shot.  

I had brought my 11 year old son to the range with me so asked I asked to borrow his .22 rifle  (Ruger 10/22 18" bbl).  I was curious to see  how fast these would chrono...  He was shooting WW Wildcats... Guess what?  1129 fps, also with no wild variations. Now up until shooting his .22 I was sure that it was the lighting that had thrown some a monkey wrench into the Chrono's accuracy.   After this I wasn't so sure.  Those readings seemed about right.  I had some Stingers in my bag so I decided to shoot a few of those over the Chrono as well.  They measured in the mid 1600's in fps.  That seemed about right too.

I shot some more of everything including some .40s it was all in the 1100's  (the .40 loads had chrono'd high 800's before).

I should mention that the light had changed sginifcantly during this time.  The sun was almost directly overhead now.  I had the diffusers up the entire time I was Chrono'ing.  The temperature had risen a bit too.  But I and my ammo supply were both in good shade (no direct sunlight)  I would guess the ambient temp.  when I started shooting was about 77 or so and about 91 when I finished...

Could someone offer a logical explanation for what happened here.  I mean I could see if the light was playing havoc with the Chrono's sky skyscreens and I was getting all these crazy readings, but why didn't it affect the .22's.

I've had light play games with my chrono readings before but usually the readings were all over the place or they were something totally unbelievable like 6576 fps or something like that.

This is a new one on me.

Thoughts, comments?

Thanks.

Homero

Link to comment
Share on other sites

I had the same thing happen to me just last week.  I have a PACT I.  I got some crazy readings of 265 fps for loads that should have been around 700+ and then I got those mysterious 1100fps readings too.  I was in bright sunlight with it nearly overhead.  I moved the chrono about 45° to the right and that solved the problem.  I'm not sure why it happened but I'd guess the shadow was beating the bullet over one of the screens and vice versa.  The next time I get the first couple of funny readings I'm just going to try and move the chrono.

Joe

Link to comment
Share on other sites

cypher,

Think about putting a translucent umbrella/shield/sheet over your skyscreen setup. The sensors are going to be most accurate when they have an evenly lit backrop to work against. The skyscreens help, but aren't a total solution.

E

Link to comment
Share on other sites

Another trick, when using Pact's diffusers is to somehow get a shadow over the actual window in the skyscreens. (Where the light enters.) Depending on where the sun is, often the diffusers won't shadow the window.

But the best trick of all, for pesky sun conditions, is to place the skyscreens on a table under a white colored metal roof/awning, so the entire skyscreen setup is in the shade, and the screens are aimed at a pure white surface. (Like we have here at the practical ranges at Rio.) I've never had any problems whatsoever when setting up like this.

be

Link to comment
Share on other sites

OK... So the general consensus seems to be that it was the lighting that was making the Chrono go buggy.  I accept that and I will take the necessary steps to avoid that situation in the future...

But just for my own edification can someone offer an explanation why the buggy readings only happened with centerfire ammo and not with the .22 LR.  I'm just curious why it would happen with one and not the other.

Homero

Link to comment
Share on other sites

A while ago, back when the IPSC e-mail list actually had useful info on it :), there was a discussion of the "Glint Doppler Effect" of sun reflections from shiny bullets fooling the skyscreens.  Half the people never believed it, and the other half thought of black magic-markering a bullet or two to see if it helped or not.  Maybe something to try next time just for the sake of science. With .22's being smaller, maybe they shine differently.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...