I chrono'd some recent SP and E3 loads, with weird results

[vnboileau]

These were all loaded on a Dillon 550c, with range brass, Win SPP and Acme 124g RN bullets (OAL 1.065) in 5 shot strings. 

 

I started with factory ammo, and then another load I just happened to have on hand

124g Blazer Brass  1121  36 ES  13 SD

3.8g HP38  1058  12 ES  4 SD

 

Then the Sport Pistol

3.5g  1031  16 ES  6 SD

3.7g  1056  7 ES  3 SD

3.9g  1078  8 ES  3 SD

 

And the E3

3.2g  1036  50 ES  17 SD

3.4g  1038  29 ES  11 SD

3.6g  1097  62 ES  22 SD

 

I was pretty impressed with the consistency of the Sport Pistol loads, and shooting some offhand groups later, they were the most accurate as well.

 

But I'm really confused by the E3.  I was measuring every 10th round or so and they weren't off by more than .1g.  But clearly they weren't very consistent.

[IDescribe]

When the powder ignites, it blows the case walls out against the chamber walls and the pressure creates a seal.  If that pressure seal doesn't happen fast enough, burning and unburned powder will blow out around the case, between the case walls and chamber walls and back into the pistol.  This leads to very inconsistent loads AND inconsistent and typically small incremental jumps in velocity as you increase powder.  To look at your e3 load, my guess is that you're not getting a timely pressure seal until somewhere between 3.5 and 3.6gr, and maybe not even then.

So THAT could be a contributing factor.  

 

Could also be that your powder drop doesn't like e3.

Could also be that your 3.2gr charge really averaged more like 3.25 and your 3.4gr charge averaged more like 3.35 and your 3.6 gr charge averaged more like 3.65.  So what looks to you like +.2gr and +.2gr is really more like +.1gr and +.3gr.  

You add up those possibilities and mix in the +/- .1gr differences from one drop to the next, and your results may well be explainable.

 

Also, when you check charge weights, make sure to take ten drops, then divide the total by 10 to see a single charge weight.  You'll get a number more representative of your 'average' drop that way.   

And if you want to check it out further, do another ladder at 3.3, 3.4, 3.5, 3.6, and see what you get.

 

[zzt]

Since you are getting good SDs with the SP loads, your chrono and loading techniques are good.  That leaves the powder drop, and to a lesser extent a variable in the brass mix.  I originally had problems with e3 in my Dillon measure.  I cured that by disassembling, polishing and deburring.  After that I had no problem.  One thing I do know is e3 does not do well at low pressure.  When I tried to make bunny fart loads, one side of the case would be blackened.  Not enough pressure.  So I increased the load until the case was clean after firing.  Then I continued to increase until I found a load the gun liked (accuracy and consistency).

[Hi-Power Jack]

What was velocity with the E3?

 

I never trust a 5 shot reading thru the chrono - I will start with 5 to get 

"in the neighborhood" but then rely on a 20 shot thru the chrono for

final results