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243 AI headspace gauges

Specifically there is supposed to be a .004" interference, so purchase two "Go" gauges and grind one .004" short. That is your Ackley "Go" and as above the SAAMI Go becomes your no go. Grind the .004" off the bottom square edge.
 
Specifically there is supposed to be a .004" interference, so purchase two "Go" gauges and grind one .004" short. That is your Ackley "Go" and as above the SAAMI Go becomes your no go. Grind the .004" off the bottom square edge.
Yes. I mis spoke in my post above and corrected it. Another way is to set bolt clearance to .010 and chamber per usual, using the parent go gauge. Then take .004 from the barrel shoulder. This should yield .006 bolt to bbl clearance and .004 crush fit of the brass in the chamber. Sounds like a lot of interference but it's not, due to the parent brass will only contact at the neck/shoulder junction until fire formed. That area will "move" much easier than the full diameter at the datum.
 
Yes. I mis spoke in my post above and corrected it. Another way is to set bolt clearance to .010 and chamber per usual, using the parent go gauge. Then take .004 from the barrel shoulder. This should yield .006 bolt to bbl clearance and .004 crush fit of the brass in the chamber. Sounds like a lot of interference but it's not, due to the parent brass will only contact at the neck/shoulder junction until fire formed. That area will "move" much easier than the full diameter at the datum.

Yes sir, and it's a good way to do it especially if you don't want/need to buy a separate gauge to grind on. I do quite a few so I just modified the gauges. I would do it that way if I was only doing one or a few a year. Some customers are not happy unless I show them the action close on a gauge.
I always explain headspace with reserve because many folks will jump in with their "2 cents" and confuse others with "clever" word play. It's bad enough explaining it without having to go over an Ackley.....haha.
Who was that guy that used to pi$$ with everyone about not moving the shoulder?? Duffy or Luffy??? Where is he when you need him!!!
 
Interesting discussion. I'm late to the party, but trying to understand my 243 AI. Am I correct in thinking that my Hornady case comparator in 243 Winchester contacts the shoulder of my 243 AI case in the same place as my rifles chamber does? If it does, I'm confused because you guys are saying the AI chamber should be .004 less than the maximum 243 headspace. Using the comparator mentioned above, my fire formed brass is measuring .064 over SAAMI maximum of 1.634. Did the guy who installed my E.R. Shaw barrel screw up?
 
It's likely right. Bottom line, the hornady tool is not intended for actual numbers but only for comparison's sake, of your before and after sized brass. It won't contact in exactly the same place as the chamber either and IDK without looking but being a wildcat, the AI may not use the same datum location, which is what sounds like is going on. Easiest test is, new brass should have a slight crush fit in your AI chamber but that contact will be around the neck/shoulder junction with non AI brass in an AI chamber...until fire formed. If you don't feel any resistance closing your bolt,(preferably stripped), put a layer at a time of scotch tape on the bottom of the case until you can't close the bolt with modest effort.
To clarify, new 243 brass will/should contact your AI chamber at the neck shoulder junction until fire formed. Hopefully that answers your question

Just noticed...old thread. Lol
 
It's likely right. Bottom line, the hornady tool is not intended for actual numbers but only for comparison's sake, of your before and after sized brass. It won't contact in exactly the same place as the chamber either and IDK without looking but being a wildcat, the AI may not use the same datum location, which is what sounds like is going on. Easiest test is, new brass should have a slight crush fit in your AI chamber but that contact will be around the neck/shoulder junction with non AI brass in an AI chamber...until fire formed. If you don't feel any resistance closing your bolt,(preferably stripped), put a layer at a time of scotch tape on the bottom of the case until you can't close the bolt with modest effort.
To clarify, new 243 brass will/should contact your AI chamber at the neck shoulder junction until fire formed. Hopefully that answers your question

Just noticed...old thread. Lol
Thanks gunsandgunsmithing, that makes a lot of sense. I'm pretty new at trying to precisely measure things so it's easy to get confused. I too noticed this was an old thread, but hoped someone was out there listening.
 
When headspacing for a 243 AI what headspace gauge must I use to get the correct headspace.I don't have 243 Ai gauge,
The number thrown around is .004 crush, which would be fine if all brass was created equal. But it isn’t. There can be that much variation and more between headstamps and even the same headstamp. My AI’s are set with .010” crush minimum, and some more. Even that, closing the bolt you feel very little resistance
 
The number thrown around is .004 crush, which would be fine if all brass was created equal. But it isn’t. There can be that much variation and more between headstamps and even the same headstamp. My AI’s are set with .010” crush minimum, and some more. Even that, closing the bolt you feel very little resistance
Can you explain .010 "crush"? Is that .010 short off not being able to close the bolt?
 
Can you explain .010 "crush"? Is that .010 short off not being able to close the bolt?
Yes, but not at the normal datum. A parent case in an AI chamber indexes off of the point of contact, the neck shoulder junction, until fire formed. Not trying to be short myself but reading up on how Ackley cases are made and formed will almost certainly help give anyone a better understanding of what that crush is and where and why. Pretty ingenious really. Yes, the most common number used is .004 crush at that small contact patch area...a ring really. Other than a 280, I think all other ackleys are wildcats so there is no "standard" for this but it's very common that .004 is used, even if it provides no crush because it still minimizes it and in the real world, works well the vast majority of the time
 
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Can you explain .010 "crush"? Is that .010 short off not being able to close the

Can you explain .010 "crush"? Is that .010 short off not being able to close the bolt?
As g&g explained, when chambering a factory case in an Acklley chamber to fireform it, the datum line is irrelevant. The factoy case only cotacts the chamber’s neck/shoulder junction as the bolt pushes it forward when being closed. There’s a slight bit of resistance as the case becomes shorter at that very small contact point. The amount shorter it becomes is the”crush”.
 
The number thrown around is .004 crush, which would be fine if all brass was created equal. But it isn’t. There can be that much variation and more between headstamps and even the same headstamp. My AI’s are set with .010” crush minimum, and some more. Even that, closing the bolt you feel very little resistance
The number thrown around is .004 crush, which would be fine if all brass was created equal. But it isn’t. There can be that much variation and more between headstamps and even the same headstamp. My AI’s are set with .010” crush minimum, and some more. Even that, closing the bolt you feel very little resistance
Absolutely right on. Ive found this out playing with lots of different makes of brass. It might be wise to check all your brass and go buy the shortside to make sure you have contact with all the brass. Size accordingly. Or some will touch, some wont. Youd be surprised.
 

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