N320 sensitivity or chrono off?

[MNshooter]

I’m getting odd results from the same lot of ammo from two large matches and my personal chrono. Is this reflective of the sample size; lighting conditions; bad chrono; temperature; or combination? I QC’d this ammo very closely so I have a high degree of confidence in the OAL and consistent charge weight but I could be the factor, of course.

 

My results are also very different than my experience with N320 in 9mm - always very consistent. I’m nervous to head to Nationals and not make PF. Given my charge weight, I’m equally nervous to increase further. My load is a 180 grain coated lead ACME FP at 1.185” and 4.9 grains N320.

 

Section match: ES of 34, avg PF 167, ~74 degrees, 3 shots, actual bullet weight 178.6 grains.

Area match: ES of 3, avg PF 176, ~94 degrees, 3 shots, actual bullet weight 180 grains.

My chrono: ES of 108, avg PF 172, ~39 degrees, 20 shots, assumed weight of 180

My chrono: ES of 93, avg PF 168, ~64 degrees, 20 shots, assumed weight of 180

 

My tests at lower charge weights were more consistent but still much poorer than when I loaded 9mm.

 

Thoughts?

[pjb45]

Ha, I have chrono issues.  So my first response is the chrono.  VV320 has been very consistent for me over the last 15 years.  Yes I had National and Area Chrono results and use that ammo as a control.

 

The only time VV320 ran slow for me was a Tulsa Nationals for L10.  It made major but barely.  Two days later at Limited no problem.  L10 was very cold.  L was normal.  At 39 degrees I would expect a lower PF not higher.  Check your chrono if you do not have any control ammo to compare.  

 

If you have watched the Chrono guys using two chrono, generally you will see two different velocities for the same shot.  Chronos are just weird.  

[Hi-Power Jack]

5 hours ago, MNshooter said:

 

Section match: ES of 34, avg PF 167, ~74 degrees, 3 shots

Area match: ES of 3, avg PF 176, ~94 degrees, 3 shots

 

My chrono: ES of 108, avg PF 172, ~39 degrees, 20 shots

My chrono: ES of 93, avg PF 168, ~64 degrees, 20 shots

 

The match results are based on 3 shots - not a statistically reliable measurement.

 

But, they assured the match director that your load made Major.

 

Your own chrono of 20 shots each is a good sized sample, and you

are getting fairly consistent results (PF 168 - 172).

 

I like to fire 20 shots over the chrono, and make sure that ALL 20

shots make PF - that usually translates into an average of about

172 or so.  Personally, I'd bump up that load of yours by 0.1 or 0.2

grains because I feel a little uneasy about PF 168, especially if

I'm travelling to a match.

 

Good luck with it      

[perttime]

Doesn't the ES figure look a little high on the own chrono tests?

Are you using sorted or mixed brass? Have your powder drops been consistent?

[MNshooter]

Agreed ES looks very high ... and not at all consistent with my prior experiences with N320 and 9mm.

I’m using mixed brass and a dillon powder measure. I checked individual and average drops several times and they were consistent. So, I was feeling pretty good about the powder charge but acknowledge that the dillon drop does have a margin of error.

[perttime]

Different case head stamps may have different internal volumes. That would cause some extra variation. N320 gives good consistency from my Dillon too. The first charge after a break is often slightly high, so I discard the first one when I get started again.

[bradthegunmaniac]

I would just buy some WWB and call it a day!

[MNshooter]

Ha, I have chrono issues.  So my first response is the chrono.  VV320 has been very consistent for me over the last 15 years.  Yes I had National and Area Chrono results and use that ammo as a control.
 
The only time VV320 ran slow for me was a Tulsa Nationals for L10.  It made major but barely.  Two days later at Limited no problem.  L10 was very cold.  L was normal.  At 39 degrees I would expect a lower PF not higher.  Check your chrono if you do not have any control ammo to compare.  
 
If you have watched the Chrono guys using two chrono, generally you will see two different velocities for the same shot.  Chronos are just weird.  

You are correct. I’m getting lower PF in the cold.

We’ve had terrible weather in MN so once again, the temp was cold when I chrono’d this morning (35). Similar velocities as last week and slower than 94 degree A4.

I have a load that I’m comfortable with at 35 - 40 degrees and should be GTG for warmer temps of FL later this month.

I still haven’t ruled the chrono out. I’d like to run two at once.

[MikeyScuba]

Got chrono'd at the IRC last week, last squad to chrono @ noon with temps 102? (or more....).  Both of our guns were 132!  We use 160gr with N320.  I've never got that high, 128&123 at a match early Sept, temps ~50.  I think the IRC was a few thousand feet higher too.  At home range on a Labradar ~124-126.