How critical is case length to accuracy?

[Les in Wyoming]

In trying to find bullet jam, I de-primed several fired cartridges and put bullets in long. Each one measures very different. In re-doing this with the same cartridges, I noticed that each cartridge measured the same each time, but they were all different in CBTO measurement. So then I measured case lengths. They are all different. But how should this affect the bullet jam measurement? After all, we are still measuring from the base to the ogive. So the case length should not matter . . . . . should it? And how critical is case length to accuracy? How much can they vary? Thanks for the help.

 

[bassassassin104]

I just finished reading through the thread about finding the Lands with a bullet. I believe your question ended up getting answered there, but I will share what I believe to be true. I have not tested this, I don't have the time or components to do what it would take to verify this. In theory, varying case length could mean varying neck length, which would cause the bullet to release inconsistently. In my mind, it would be like having varying neck tension from shot to shot. As far as the varying CBTO, it could also be due to neck tension variance from one to the next. What type of resizing die are you using?

 

[Les in Wyoming]

I just finished reading through the thread about finding the Lands with a bullet. I believe your question ended up getting answered there, but I will share what I believe to be true. I have not tested this, I don't have the time or components to do what it would take to verify this. In theory, varying case length could mean varying neck length, which would cause the bullet to release inconsistently. In my mind, it would be like having varying neck tension from shot to shot. As far as the varying CBTO, it could also be due to neck tension variance from one to the next. What type of resizing die are you using?

This sounds like a reasonable theory. I have been leaning that way myself. So I am working on uniform case length at this moment. Thanks.

 

[rsnell]

You must use the same bullet and case when trying to determine how repeatable your measurement is. Bullet length is the biggest variance with bullet ogive the next.

If you want to keep everything simple, use the Sinclair bullet seating tool. This measurement will determine the length some ware between touch and jam. Subtract 0.050 inch from this measurement and seat the bullet. This will give you a good hunting load. I have done this for six different rifles from 22-250 Remington to 30-06. I do not worry about headspace on the 300, 340 and 378 Weatherby rifles since it is impossible to reach the lands on these rifles and I use bullets with a cannelure.

 

[Beluebow]

They are all different. But how should this affect the bullet jam measurement? After all, we are still measuring from the base to the ogive. So the case length should not matter . . . . . should it? And how critical is case length to accuracy? How much can they vary? Thanks for the help.

That is correct....case length has zero to do with jam/touch.

 

[Mikecr]

Case length is not significant to shooting results either.
It is beneficial to set trim length close to chamber end though (~5thou). So you can do this later when appropriate to do so.