Pressure signs...

1

1stmar

New member
Going back over my logs from Fridays shooting I had made a note that 1 round in 10 had stiff bolt lift. the load was 36gr varget, 53 gr Sierra in 22-250. All rounds were chrono'd. I looked at the case today and I measured the shoulder. Sure enough the shoulder is .001 higher then the other rounds and there is an extractor mark. I'm pretty meticulous about my loading procedures. I measure each charge, case prep is the same, measure each bullet, measure the shoulders and mark any that are more then .003 pushed back. (usually neck size but at this point I needed to push shoulders back) if there is anything out of "spec" I will mark the case or bullet with a red marker so I know it prior to firing and can judge the impact of the failure. This cartridge was not marked as any type of failure (oval, headspace, runout , case weight, etc). So I'm pretty confident I didn't miss anything. Here's the other oddity: the velocity was not the highest (3651) and poi was in middle of the group. Sd was 20.7, es 40 and group size was .58. I have fired loads of 36.5 and 37gr with no signs of pressure.

My question is what could have caused the excessive pressure and why didn't it show up in the results (chrono, group size)?
 
1

1stmar

New member
Ok, I think found it. Looking at my shell box, I noticed my notes " case weight variation". I forgot I did this test, I made 5 cartridges with varying case weights to see what the impact would be. I just reweighed and this case in 6 grains lighter then heaviest case in the group. Interestingly though the only noticeable impact was the pressure, the velocity (while at the higher end) and poi were ok.
 
1

1stmar

New member
Right now that's the only connection/conclusion I can draw. I'm not convinced its enough of a difference my average case weight is 159 gr. I use 1.5 grains as my acceptable tolerance so ~ +- 1 gr. cases that exceed this went into another group I had some that were 162 gr on the high side and some that were 156 gr on the low end. That's only 3 gr difference from the avg, but 6 gr from the max. I'm skeptical but can't explain it any other way.
 
M

mrawesome22

New member
Could have been a piece with a softer alloy than the rest.

I quit wasting my time with Federal brass for this reason. Sticky bolt, head marks, loose pockets.... with starting loads. :thumbdown:

sudo passwd root
 
J

jepp2

New member
I just reweighed and this case in 6 grains lighter then heaviest case in the group.
Click to expand...

But the "lighter" case should have had greater case capacity and thus lower pressure.

A water filled case weight would be a more meaningful comparison.
 
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