Charge drop variations and Other causes of SD

[Clint007]

Ok here's one quick set of data using the spring. I did NOT weigh powder charges here, I just ran about 20 rounds through, checked multiple times that the weight was 4.8 gr of BE86, and then loaded 20. I will say that each of the few I had measured before I ran  this 20 was within half a grain of 4.8, so the scale range was like 4.75-4.85. (I have that high precision scale from UniqueTek).


BE86 using a 124 gr plated round nose from Berrys, all in fps. All new starline brass with WIN SPP. 1.115"

I ran the Mark 7 at 2100 per hour, with bottom dwell of 1, index speed no reduction. I use the little rubber discs on the locator pins to reduce wobble, so there is no spillage influencing these figures, and I cleaned and watched each round.  This is WITH a return spring on the powder bar.

I did NOT weigh all these drops, however. I just loaded and chrono'd with my LabRadar.

16 shots

max 1079

min 1015

ES 64

Average 1048

SD 20
 
Concordant with Wobbly's comments about the value of the spring, I have long noticed that if the  system sits still for awhile (meaning more than a few minutes) the next charge is often higher than it is during continuous run. I assumed it was because powder was settling in the bar from the hopper, and that was the reason the return spring helps, but maximally settling things so it can't settle (fill the powder bar) any more?

Still not impressed with this SD and ES.


C

PS here's the individual shot data. V0 is muzzle, V10 is 10 feet, using the LabRadar indoor range, about 70 degrees, dry, no wind.

V0   V10
1022   1015
1059   1051
1063   1054
1067   1057
1082   1072
1081   1070
1072   1062
1087   1076
1050   1040
1089   1079
1045   1035
1047   1040
1050   1041
1036   1028
1038   1029
1027   1020

[Wobbly]

I have long noticed that if the  system sits still for awhile (meaning more than a few minutes) the next charge is often higher than it is during continuous run. I assumed it was because powder was settling in the bar from the hopper, and that was the reason the return spring helps, but maximally settling things so it can't settle (fill the powder bar) any more?

I wonder if this "wait" issue is due to the efficiency of the Dillon baffle ?

[Clint007]

Don’t know
I have the UniqueTek baffle
I filled the hopper just before this

[Wobbly]

I have the UniqueTek baffle

Didn't know they had that. Didn't know YOU had that.

Words can't express my envy. I'm trying to think of a suitable punishment for getting ahead of me like that. I was considering a 30 day forum suspension, but that's not good enough. Instead, I finally decided on the digital equivalent of Dante's Inferno. We're going to make you a Moderator !

 

[Clint007]

A fate worth that death, or even exile to Kalifornia perhaps.  Sorry, I just cant' believe they are posturing to jail waiters who give out a plastic drinking straws unless the customer pointedly asks for one. Don't they have more important things to do?  https://www.usatoday.com/story/money/nation-now/2018/01/29/plastic-straws-illegal-unless-requested-under-california-bill/1074610001/

I have just completed a painstaking process of loading 10 rounds with EXACTLY 4.72 gr of BE-86 each, taring and weighing each primed case then filling flake by flake (mostly) to that number.  OAL is 1.12" within 0.005 of that, and crimp OD is .377" on all. 

If my numbers are tight, at least I've ruled out my gun as the problem....

C

[Wobbly]

I don't recommend copper plumbing  or any other non-electric ground wire hook-ups.  If the outlet box is grounded a snug screw connection to that box is adequate.

In desert climates, the dry soils require a dedicated ground.  Copper pipes running under the soil, may or may not be grounded.

As a complete aside...

Water content in the soil is what determines whether a metal water pipe or electrical ground stake will work in any part of the country. In my locale, where it has rained 3 days out of every week since Jan, both those metal objects work great for electrical grounding.

When I worked on self propelled radar systems to be used at China Lake in the Mojave Desert, we had an especially hard time achieving electrical ground for the portable generator sets being used. So we had to write into the procedure for installing the ground stake that after the stake was driven that the operators should pee on the stake.... preferably before starting the generator.

Maybe 1SOW simply needs to train his dog where to urinate !!

 

[Clint007]

Here are the numbers after painstakingly loading ten rounds with 4.72 gr of BE-86. These are velocities at 10 feet using a LabRadar.
Is this a 'good' SD/ES? I expected it to be 'tighter' given that I was meticulous about the charge weight for all 10 rounds.

AVerage is 1025
Hi 1045
Low 1011
SD 11.4
ES 34

1019
1025
1011
999
1012
1007
1024
1013
1001
1033

I confess I did not do that little 'point the muzzle up and tap the gun to settle the powder back' maneuver.  I mean I'd read it and seen it done at chrono checks at matches, but never really emraced that idea. Something about having the powder back against the primer. Does this matter with 9mm? Not much air in these cases with 4.7 gr of BE86 and a Berry 124 gr HBRN, but there is SOME air, compared to loading with some others...  Bottom line, I did NOT do this for these values, and a guy with me said that might reduce the SD a bit. So I'll do that again with another 10 rounds later, and see.

C

[1SOW]

Can't vouch for it personally,  but I have read where very small amounts of powder volume in the case can produce differing pressures / .bullet speeds depending how the powder is dispersed and the flame throw of the primer used.
Truth or fiction,  I don't know.  Sounds good.

[IDescribe]

Having the powder sitting in the case the same way at each ignition will increase consistency.  If you are going to tilt it back, you should do it for every shot.  I do not do this.  What I do — after I load the mag, I tap the mag a few times back down to loosen up powder. Then insert mag and assume that the clambering of each cartridge with loose powder will leave similar powder columns. After I started doing that, my “first shot” anomalies disappeared.

Tap the mag a few times, that’s all it takes.  My ES and SD numbers are typically excellent.

[Wobbly]

I confess I did not do that little 'point the muzzle up and tap the gun to settle the powder back' maneuver.  I mean I'd read it and seen it done at chrono checks at matches, but never really emraced that idea. Something about having the powder back against the primer. Does this matter with 9mm? Not much air in these cases with 4.7 gr of BE86 and a Berry 124 gr HBRN, but there is SOME air, compared to loading with some others...  Bottom line, I did NOT do this for these values, and a guy with me said that might reduce the SD a bit. So I'll do that again with another 10 rounds later, and see.

I never consider that with any 9mm loads, only things like 38 Spcl with that cavernous case.

 

[Clint007]

Thank you.

I'm still getting a dissatisfying ES and SD with these loads. Did another set today, SD of 15, ES of 45.  And that's with me measuring each case before and after powder drop and testing only those within 0.05 gr of my goal charge weight.

can a too-tight crimp cause this problem?  I'm mostly at 0.377..could this be a tad too tight?  Maybe Maybe I will untwist the Lee crimp die just a skotch and go for 0.380?  Or the least amount of crimp (de-belling) that reliably chambers?

And I'm setting up the 550b for 9mm (since I have a plethora of dies I don't have to defrock the 1050) also, to see what that gets me.

C

[1SOW]

JMHO:  .377 is not too tight with 9mm Starline brass using BRY 124 plated bullets.
With BRY TP bullets this is my max. crimp,  .3775-.378 is my preferred average with WIN or R&P brass. .

[IDescribe]

Clint, your ES and SD problem is very likely the result of your exceedingly light load.  Two things going on -- your fuel-air mixture is too rich -- Wobbly and/or James can explain this with some detail; I can't    --  and on top of that, you are getting a late pressure seal and losing some expanding gases and powder as they escape between the case walls and chamber wall prior to the completion of the pressure seal. 

I expect to see poor ES and SD numbers at the bottom of load windows for those reasons noted above, and YOU aren't even at the bottom of a load window for that bullet with BE-86.  You're well below the load window.  The most relevant data I see for a 124gr plated RN is Alliant's data for a 124gr FMJ at OAL 1.12, and that data is 5.2gr - 5.8gr for 1167 feet/sec.  Your 4.7gr and 4.8gr loads are WAY light.    

Wobbly tested this powder with a PD 124gr JHP.  To MY eye, looking at his data, it looked like he started getting a decent pressure seal and efficient burn at 4.8gr.  But that's with a JHP, which typically has lighter charge windows than plated or jacketed RN.  I'd expect your 124gr Berry's RN SD and ES to clean up somewhere around 5.2gr, give or take, depending on what OAL you're using.

Good luck. 

[mrcabinet]

I feel kinda stupid that I read that 4.8 grn.s, like everybody else, and didn't even think about the sealing issue. I know that with BE-86 and 124 grn. coated I had to get to 5.1 before I got a decent seal.

[IDescribe]

That’s why they pay me the big no bucks.