rechamber a 243 win to a 6mm AI

[HMH]

I know this question has been asked before, but I have a slightly different situation. I have a 243 win short chambered barrel that I received as a gift and I was wondering if I could rechamber to a 6mm AI without having to remove some of the chamber? I am also looking for a good cartridge diagram of a 6mm AI.

Thanks,

 

[1000yardstare]

The Sierra manual has a 6AI diagram, page 316.

There have been several threads concerning rechambering recently in this forum. I am currently contemplating going from 7mm-08 to 7AI, basically the same move as yours. From my `smith and other forum members I see these concerns.

The barrel has to be set back at least one turn to make sure the 6AI reamer cleans up the rear of the .243 chamber.

The 6AI will be longer than the .243 and in a short action this could lead to magazine and ejection difficulties.

The 6AI is a fatter case which may lead to feeding problems with the magazine rails.

I have a 6AI built on a short 722 action. It is an F Class target rifle which is single loaded so magazine difficulties are irrelevant.

But in a hunting rifle all of the above could be problematic.

 

[JohnnyJohnson]

Very little to be gained in 6MM AI over 243 AI but brass including quality brass is much easier to find in .243.

 

[1000yardstare]

Good point about the .243 AI.

A problem with rechambering that has been mentioned in another thread concerning the .243 AI concerns an off-center factory chamber. If the longitudinal axis of the factory chamber is not coincidental with the axis of the bore, then a rechambering reamer will just follow the axis of the old chamber and you still have an off-center chamber.

I leave it to others with more machining knowledge than mine how you would get around this problem. My `smith talks about live centers and longer than normal reamer pilots but it is a reality that must be considered.

 

[HMH]

The action is a large ring mauser 98 that was chambered in 8x57 so I don't see any length problems or feed problems for the 6mm AI. This is not going to be a competition shooter just something pretty to take out every oncey in a while probably wont see more than a 100 rounds a year. I have to many guns and not enough time to shoot all of them. I would like to go with the 6mm AI unless it is just to much hassel, then I will take defeat and the 243 AI which I am sure will work fine for my purposes.

Thanks,

 

[Ackman]

I know this question has been asked before, but I have a slightly different situation. I have a 243 win short chambered barrel that I received as a gift and I was wondering if I could rechamber to a 6mm AI without having to remove some of the chamber? I am also looking for a good cartridge diagram of a 6mm AI.

Thanks,

A short chambered barrel.....or done with a roughing reamer? Sounds like an Adams & Bennett barrel. I don't know what they actually use but many years back had a 223AI done on one of those. A std. .223 case wouldn't chamber, it hit the body taper before even getting to the web. Measure what you've got, better yet do a chamber cast. You want to know the big end dia. and neck dia. of the chamber, then just compare with the 6mmAI reamer that'll be used. Make sure you'll be cutting everything new in the chamber.

 

[HMH]

I did a chamber cast and measured the reamer it will clean out the entire chamber so the answer to the question is yes this will work thanks to all who replied. My next question is when finishing the chamber the standard 6mm rem is 1.8822 to the start of the shoulder where the 6mm ackley is 1.878 or so my diagram is a little blurry with that last number. So do I need to headspace the 1.8822 in order to get the standard 6mm rem to fireform or will they still fire if headspaced to 1.878 ?

 

[1000yardstare]

The only part of the regular 6mm Rem shoulder making contact with the 6AI chamber is right at the junction of the neck and shoulder.

The 6AI is headspaced a little shorter so that the 6mm Rem case is a crush fit when chambered.

If the 6AI is headspaced with a regular 6mm Rem headspace gauge then the 6mm Rem case may be too far forward in the 6AI chamber for a good firing pin contact on the primer.

My `smith discussed all this with me when I had my 6AI F Class rifle made up. He gave me a crush fit and I have had no problems in fireforming.

 

[HMH]

I'm sorry I don't have any experience with AI cartridges any other tips or advice would be greatly appreciated? How tight does a crush to fit feel when you are closing the bolt?

Thanks,

 

[1000yardstare]

"Crush fit" means the regular 6mm Rem case is firmly supported by the bolt face and the 6AI chamber`s shoulder.

You are not going to be hammering the bolt closed. You should feel a firm bolt closure but not excessively so.