Lands & Grooves...

[BCB]

Picture of an RCBS 45-270-SAA…

Note: The grooves are narrow at the top and wide at the base…

The lands are wide at the top and narrow at the base…

Is this an indication of a boolit “skidding” (don’t know if that is the correct terminology?)?

If so, does it mean the alloy is too soft or is the velocity/pressure to high for that alloy?

Hope you can see the details in the picture…

Thanks…BCB

[405]

Hard to say. Figuring out what happened to a bullet while in the bore after it deforms at impact is usually tricky at best. The hard part is decelerating one slowly enough that it doesn't deform. Just looking at the base drive band land engraving.... looks fine. Almost looks like the "widening" of the land marks toward the top could be just an artifact of the overall expansion of the nose portion on impact..... just a first impression tho.

[44man]

You are reading the boolit wrong. The rifling land marks on the boolit are the grooves in it. They will be larger at the front as the boolit starts into the rifling and is fairly normal. A little skid. But the marks at the base should be the same size as the lands and grooves of the rifling. You need a good seal at the base to prevent gas from going around the boolit.
If the grooves from the lands are too large at the bottom, or the high spots are too narrow, then the lead is too soft or the powder too fast.
From what I see in your picture and not being able to fit or measure, the boolit looks fine to me.