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243ai "trim to" length

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Unread 05-17-2014, 08:58 PM
Bronze Member
Join Date: Apr 2009
Location: rochester mn
Posts: 54
243ai "trim to" length


I have a question I am hoping some of you .243ai shooters may know the answer to.

I finally got my brass fire formed and am prepping to load as an AI round for the first time and when I got to the trimming them to the same length phase, I realized that there is no "official" trim to length. I was just gonna go with matching them all to the shortest piece but most of them measured 2.022(avg) which btw, I notice is a good bit shorter than the standard .243 trim to of 2.035. Is this an issue?

The shortest piece after trimming measured 2.006(neck was not square and I trimmed very slowly until I could see it was squared up...this appears to be the only piece like this so I tossed it).

Any advice, ideas or thoughts on this?

Thanks for your time fellas,

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Unread 05-17-2014, 09:16 PM
Platinum Member
Join Date: Jul 2012
Location: North Central Valley California
Posts: 2,249
Re: 243ai "trim to" length

I believe you'll find that the AI case length is no different than the .243 (2.0449 - your chamber may vary). The only difference I'm aware of is the shoulder angle and a straightening of the body of the case to provide more volume..
I could be wrong ... if I am, somebody please put me straight (with supporting documentation of course)

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Unread 05-17-2014, 09:47 PM
Platinum Member
Join Date: Oct 2008
Location: Alabama
Posts: 9,995
Re: 243ai "trim to" length

The AI cases and their SAAMI counterparts both have the same case OAL.

However, with most AI's when the brass expands in the new AI chamber, the neck will shrink around .0200" because the case is scavenging brass from the walls and neck to form the new sharper neck that is pushed farther forward, and the walls expanding.

For example, Alot of people use .25-06 brass for their .25-06 AI. The SAAMI case length for both is 2.494". When you fire-form regular .25-06 brass in the AI chamber it shrinks to 2.474". It doesn't hurt anything, and the brass will eventually stretch back out after a number of firings.

However, I am very OCD. I reform .270 Win brass because it has a longer neck. I FL size .270 Win brass in a FL .270 Win sizing die, then I run them through my .25-06 AI FL sizing die. Then I trim the brass to 2.514". Then I chamfer and deburr the necks. Then I load them up. That way when I fire them in my .25-06 AI chamber, the brass comes out fully formed, and is a perfect 2.494" in OAL...Plus or minus a couple thousandths.

Like I said, I do mind that way, but that is because I'm extremely OCD about my ammo and when I reload.

And there is absolutely nothing wrong with shooting AI formed .243 brass that is .020" short. It won't hurt a thing.
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