Chronograph Data Analysis?

[CastIronSkillet]

Hi All, long time reader and lurker here, most questions I've had can usually be solved with a search so not much posting, maybe that will change.

I'm working on a new Rem 700 5R 300 Win mag load and I got a few data points that seem odd and would like some other opinions. The starting load data is below. 71 and 72 grains were re-shoots due to good groupings on a previous outing w/o the chrono, .6 and .7 ish respectively and I wanted to get velocity #'s this time out. There was some powder movement with these two which is probably why the STD Dev and ES weren't too good. 72 grns had a chrono error on the last 4 shots, sorry no data there. I did not re-shoot 73 because it was about a 1.6 previously and I thought I could slide back into another node if I went past it at 73.5.

1st data point question, I did not anticipate a 159 FPS jump from 72-73.5 this quick, what do you attribute this to? No pressure signs on brass... slightly rounded primer, no ejector or extractor marks, easy bolt lift, etc. and inside max published data.

2nd question: As the case started filling more on 73.5 and 74 the velocity, STD Dev, and ES stabilized quite nicely except for one low reading each, exclude that data point and #'s look great. Any thoughts on this? 73.5 was about a 1" group and 74 was a .6. Do you just re-shoot 74? work up and down in .2 or .3 grns?

I'd rather not re-shoot the same load if I don't have to. It is a pain dragging all my crap to and from the range and setting up during a cease fire to have the chrono malfunction after 6 shots...

Load Data
Federal FC brass fire formed and shoulder bumped .005"
Trimmed to. 2.610", uniformed primer pockets, de-burred flash hole.
Powder: IMR 7828 SSC
Bullet: Hornady 208 ELD-M
Primer: Fed 215 match
.040" off the lands
OAL: 3.608

 

[BallisticsGuy]

Why are you pushing the shoulder back so hard?

Anyway, in general you'll find that full cases (without getting into compressed loads) perform the most evenly. Less air gap, less unpredictable stuff going on.

It looks from your data like you just weren't getting up to full steam at 71 grains. You get really good velocity stability at 73.5 and the ratty ES at 74 suggests that you've found a good stopping point at 73.5. Work a test with seating depth and see what happens. I've had good luck running a set at .010 jump, .040 jump, .080 jump and .120 jump. You'll probably see a trend. If it likes a little less jump then it might want another couple tenths of powder.

I would personally check out 74.5 and see what it thinks of that. Might come back a bit hot, might not. Might just squish in those SD's a bit and give you that tight group you're looking for. Don't take that as pressure in the face of the reality on the ground. Use good judgement.