Has anyone ever ran into this issue??

[Larryh128]

Put together a lightweight 240 Weatherby & have been freezing doing some break in & load developing. My brass is all out of the same lot & all trimmed to exactly the same length. I loaded up 5 rds with 95gr BT's & 5 with 55 gr BT's both at close to max charges. After firing & measuring the lengths, the cases loaded with the 95 gr BT's grew in length what I would expect. .001-.002 after being fired. The cases loaded with the 55gr BT's SHRANK in length about .002. I can't say that I've ever seen a case shrink. Don't know what to think. Any ideas?? Neither load is anywhere close to being a mild load.

 

[Witchhunter]

I would bet that the load that shrunk was the hotter load. Mic the bases of both and see, or look at primers for pressure.

 

[22BRGUY]

I would bet that the load that shrunk was the hotter load. Mic the bases of both and see, or look at primers for pressure.

This sounds right to me also...the 55's developed more pressure forcing the shoulder of the case harder into the chamber walls thereby shortening the neck.

 

[Larryh128]

Sounds like you're probably correct. Primer was OK on both but the 55 gr did look slightly hotter. Too late to mic them as they have been sized & tumbled. Thanks.