I've been shoothing a custom 338-06AI this summer and loving the heck out of it! But today, as I sat at the reloading bench, it dawned on me that I don't know the specifics for what the appropriate case legnth is on an improved cartridge. The manual list 2.494 as the desired legnth for the standard 338-06. I fire formed all my cases from 30-06 brass and afterwards they all measure 2.470. And I neck size thereafter.

So, how does one determine the correct case legnth for improved rounds anyway? Or, because the shoulder is blown out, and the case effectively shortened, is this a non-issue? Does it depend?

Someone who knows, please speak up!

Hi Waldog
It is my understanding that as Ackley Improved chambers are able to fire factory ammo that the case length for an AI cartridge is the same as for the non AI cartridge.

When fireforming to AI dimensions the brass will be shorter than before fireforming (as you note).Over repeated fireings the AI case will lengthen but not as much as a non AI case.

I have been dealing with this issue with my 218 Mashburn Bee.In Australia I could not get a Lee case length guage for 218 Bee,I would have had to get Lee in America to make one for me.

The trim length for the 218 Bee is 1.335" and the max length of 1.345".
The 25-20(which are available in oz) has the same shell holder size as the 218 bee and a trim length of 1.32" and a max length of 1.33".

So ,today as it happens,I got the 25-20 case length guage and chucked it into my drill and with a file reduced the .25 thickness to .224 and now I have a 218 Mashburn Bee case length guage.

For my 270 AI I use a Lee 270Win case length guage.

Regards
Deafdog

Waldog,
I would measure the chamber lengh and then trim my cases to be .005-.01 shorter than my chamber length.

Thats why I use 35 Whelen brass to make 30-06 AI.
The cases don't end up too short.