Trust but Verify, a Chrono Story.

[CrashDodson]

Good stuff here.  Thank you.

[motosapiens]

one of my shooting buddies went to the 7th round at his first A1 (2013) to make minor. He was sweating. I was standing there smirking at him for not chrono-ing at home, so that's probably why I know the rule.

[motosapiens]

1 hour ago, Hi-Power Jack said:

Oh, come on now, Moto - the reason we have this Forum is that

 

Everyone does NOT know all this stuff.   

 

 

Yeah, I'm just busting on Rowdy because he's a better shooter than me and he was already home and comfy after the early A1 match while i was still on my feet RO-ing last weekend.

[jwhittin]

See this posting which will give you a simple way to know you will always meet PF using your first 3 rounds.  It doesn't matter what you measure at home, comparing it to the official chrono results is like comparing apples and oranges. The link between the two is the confidence level.

Bottom line is you should always use your measured STD to calculate the min average velocity needed to make PF.  I recommend adding 2 to 3 times your measured STD to the average velocity required to meet PF for your bullet weight.  There are three reasons why you DON'T want to just add a few power factor points.  First is using just the average velocity of your chronograph can introduce significant error as you don't know how accurate your chrono is (see this article http://www.appliedballisticsllc.com/Articles/ChronographChapter.pdf ).  Second, for consistency (and PF) the STD is the most important parameter.  The difference in STD between chronographs is very small (typically <5 fps) because it is a variance.  Lastly, if your reloading process changes, it can cause you to fail PF. If you don't monitor and use your STD, you would never know.

Edited April 7, 2017 by jwhittin

[hermans]

jwhitten is now touching on the real issue here! The way I have been doing it for the last 30 years is a little different that his method, but it boils down to almost the same thing.

A day or two before the match I always shoot 5 rounds over my chrono. I then delete the lowest and the highest velocities and use the remaining 3 to calculate my power factor. The power factor should then be at least 5 points higher than the minimum required, but does not have to be higher that 8-10 points using this method, and using this method I have NEVER failed the chrono at a match.

So yes, your standard deviation is very important, my method just needs a little less calculations!

 

[PaladinPrecision]

On 4/1/2017 at 4:40 AM, rowdyb said:

 

Lessons:

• Do not run close to the edge. This ammo batch had recently been chronoed at 128pf the weekend before at Optics Nats. That's too close.

That is exactly why I shoot for 135 pf and make sure my SD/ ES doesn't put me right at 125 if it happens to be on the low end of the stats. Good job keeping your head and actually reading the rule book.

[Hi-Power Jack]

2 hours ago, hermans said:

 

A day or two before the match I always shoot 5 rounds over my chrono. I then delete the lowest and the highest velocities and use the remaining 3 to calculate my power factor. 

 

 

I still like to put 20 rounds over the chrono, and make sure that they ALL

meet PF     

[eern]

so area 5 was a similar issue.  first 3 were just under so he shoots the 2nd 3 ( which actually made it on there own, but I told him he needs to take the best 3.  Same song of not my first time.  I showed his the rule and also the fact that the chrono sheets say right on them best 3 of 6.  Know the rules and be confident, not angry, when trying to get the right call.

[DKorn]

When I eventually start reloading, I plan to weight 50-100 bullets prior to loading, then shoot 50+ rounds of my final load over the chronic and do a capability study to ensure that I can reliably meet power factor with a good Cpk. 

 

But im a Quality Engineer and a bit of a nerd, so my method is probably way overkill. I'll also probably do a full PFMEA for my reloading process...

[rowdyb]

cleaned out powder measure, bell crank and powder bar. qc-ed the rest of the set up. replaced parts as needed. reviewed my old chrono and load data for this bullet and powder combo. then made some new ammo with two different powder amounts.

 

new battery in chrono, set up in shade, 6' from it. 65F, 400' above sea level.

 

3.3 grain Titegroup yielded shots of 917, 900, 914, 915, 899, 904, 894, 908, 896, 908. (mean of 905 fps)

This load gives me a sample standard deviation (s) of 8.19 and a variance (s2) of 67.1 and a 99.9% confidence level nothing will be under 865fps.

 

3.2 grains TG yielded 871, 891, 870, 874, 876, 876, 880. (mean of 876 fps)

Here i get a sample standard deviation (s) of 7.09 and a variance (s2) of 50.14 and a 95% confidence level nothing will be under 862 fps.

 

I'll just stick with the 3.2

Edited April 7, 2017 by rowdyb

[jwhittin]

Rowdy, what's your bullet weight?

[rowdyb]

147

[rondog]

Rowdy What gun ya shooting?  I run the same load. 

[WaJim]

21 hours ago, rowdyb said:

147

 

In your OP you say the Chrono asked what your bullet weight was.....

 

I thought it was protocol for Chrono stage to pull a bullet and weigh.

 

I just got back from Area 1. It was my first III but Like my previous level II matches they physically weigh your bullet.

 

This could change the PF significantly.

 

BTW my 180's weighed 181.6. Still have my little red sticker.

[WaJim]

15 hours ago, rondog said:

Rowdy What gun ya shooting?  I run the same load. 

 

Yeah that isn't all equal either.....

 

I have a Barsto that is ~40fps slower than my back up guns Kart.

 

 

[rowdyb]

My Accu Shadow at this match. I didn't see them weigh a bullet nor was i told what one weighed. I was just stating my weight.

[WaJim]

50 minutes ago, rowdyb said:

My Accu Shadow at this match. I didn't see them weigh a bullet nor was i told what one weighed. I was just stating my weight.

 

Well that's interesting.....they didn't weigh?

 

If the bullet weight isn't physically checked then how can they hold you to the PF?

 

Am I misunderstanding something?

 

 

 

.

 

 

[Ultimo-Hombre]

41 minutes ago, WaJim said:

 

Well that's interesting.....they didn't weigh?

 

If the bullet weight isn't physically checked then how can they hold you to the PF?

 

Am I misunderstanding something?

 

 

 

.

 

 

Nope. 

 

They asked the weight. 

 

Nothing wrong with with a little bit of honor system. 

 

If if you came in at 210 Pf at least your squad knew you were a liar. 

[rowdyb]

Nope, I think your tracking completely.

[jwhittin]

The declared bullet weight is allowed if a properly calibrated scale is not available or an acceptable bullet puller isn't available. See Appx C2 10 and 13. 

[WaJim]

23 hours ago, jwhittin said:

The declared bullet weight is allowed if a properly calibrated scale is not available or an acceptable bullet puller isn't available. See Appx C2 10 and 13. 

 

Now that's what I was looking for....thank you.

[WaJim]

On 4/8/2017 at 5:17 PM, Ultimo-Hombre said:

Nope. 

 

They asked the weight. 

 

Nothing wrong with with a little bit of honor system. 

 

If if you came in at 210 Pf at least your squad knew you were a liar. 

 

The honor system wasn't my point.

 

I'm a little new to the sport (couple years) so bear with me.

 

I've only been chronoed with the bullet pulled.

 

I think its counter productive to hold a competitor's PF to an exact number if the other numbers used in figuring PF like actual bullet weight arent adhered to....

 

Not trying to get in a pissing match but if Chrono doesnt use the actual bullet weight can a shooter that claims a 115 gr 9mm that barely fails PF ask for that bullet to be weighed.

 

Just saying, If the actual weight is say 116.8 then that may make his load meet PF.

 

I'm not arguing ...just trying to clarify.

[WaJim]

An addendum.....

 

Could a shooter before the match weigh his bullet at home and when asked say 116.8?

 

 

Edited April 10, 2017 by WaJim

[MikeBurgess]

Yes when asked the shooter could give whatever weight he beloved to be accurate (or if less honorable a weight he just wanted it to be)

Sent from my SAMSUNG-SM-G935A using Tapatalk

[WaJim]

Thank you...then that makes complete sense to me.