Confused as usual; .243 AI head space gauge

Mram10 said:
I might have read it wrong, but the ai gauges should be longer than the parent cartridge. Example: a 280ai gauge is between 2.140-2.150. The parent is 2.100-2.110. Makes sense since you do it to get more powder. I also have a 243ai reamer if anyone is looking ;)
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It's really just the opposite. The ai gauge is shorter, giving a crush fit of the parent case in the ai chamber. This is meant to hold the case firmly against the bolt face when the pin strikes the primer to keep from having the case stretch in the Web area when fire forming them.
 
mwezell said:
It's really just the opposite. The ai gauge is shorter, giving a crush fit of the parent case in the ai chamber. This is meant to hold the case firmly against the bolt face when the pin strikes the primer to keep from having the case stretch in the Web area when fire forming them.
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Check out the saami book for headspace length between 280 and 280ai cases. The values are as I posted so I am confused by your statement. If it were the opposite, wouldnt you lose powder capacity?
 
Mram10 said:
Check out the saami book for headspace length between 280 and 280ai cases. The values are as I posted so I am confused by your statement. If it were the opposite, wouldnt you lose powder capacity?
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I'm familiar with the prints. That's why a SAAMI 280 ai is so confusing and is a bad example to use when discussing Ackley cartridges, in general.
The gained capacity is from the straighter case wall and the 40° shoulder of the AI vs the parent case. The ".004" crush is inconsequential to capacity.
 
If you don’t Chamber the case to match the headspace gauges, you don’t get the increased capacity. There is .040” difference that cannot be changed to have a shorter headspace gauge for the ackley. That doesn’t make any logical sense to have a shorter headspace gauge for the ai. Do the math and you’ll see. You lose case capacity. The .375” datum point is a constant that shows a safe headspace distance. You can make your own variant and headspace as you wish, but shouldn’t confuse people with what the saami spec calls for.
 
Mram10 said:
If you don’t Chamber the case to match the headspace gauges, you don’t get the increased capacity. There is .040” difference that cannot be changed to have a shorter headspace gauge for the ackley. That doesn’t make any logical sense to have a shorter headspace gauge for the ai. Do the math and you’ll see. You lose case capacity. The .375” datum point is a constant that shows a safe headspace distance. You can make your own variant and headspace as you wish, but shouldn’t confuse people with what the saami spec calls for.
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Let me ask this..I can't put my hands on them at the moment but I have a factory new 280 remington and a factory new saami Nosler 280 ai loaded round...and a chamber cut .004" shorter than a 280 rem go gage. I marked both cases up with dykem and chambered them in the rifle. Both contact the chamber at the neck/shoulder junction. How can that be, based on the print and data you provided? If I can find them, I'll post pics of the cases. In the meantime, this is a very good explanation of the issue and why the confusion...with pics.. I know it's confusing but that's my point, exactly. I'm not giving bad info. There is plenty of that out there already.
https://gunsmithtalk.wordpress.com/2012/07/17/280-ackley-improved-emperical-headspace-test/
 
Mram10 said:
If you don’t Chamber the case to match the headspace gauges, you don’t get the increased capacity. There is .040” difference that cannot be changed to have a shorter headspace gauge for the ackley. That doesn’t make any logical sense to have a shorter headspace gauge for the ai. Do the math and you’ll see. You lose case capacity. The .375” datum point is a constant that shows a safe headspace distance. You can make your own variant and headspace as you wish, but shouldn’t confuse people with what the saami spec calls for.
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On an AI chamber you just blow the shoulder out to 40* . That gets you a little more powder room. If you lengthen the case then you have a wildcat cartridge.
 
Sdean ,
Case length and headspace length based on datum point of .375” not the same.

As to the topic at hand, I agree there is a ton of bad info out there. That is why saami is there and simple math. Make a couple triangles with the shoulder neck junction going back toward the case head. One with 40deg shoulder and the other with 17.5deg. It clearly shows the length from base to .375” datum MUST be longer for the ai. Normally I wouldn’t care, but new guys are getting dangerous info here and could ruin barrels or worse, get hurt.
 
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Mike,
To add to the confusion, the shoulder/neck junction on an ai is .016 shorter than parent 280. Doesn’t matter with regards to headspace, but still interesting. You think you’d blow out the shoulder to 40deg and keep the shoulder/neck junction the same, but no.....
 
Chino,
Do yourself a favor and use saami headspace gauge distances (base to datum) to verify. As for the 243 ackley, without doing the math, the base to datum point should be about .035” longer (total guess but close) when changing from 20deg to 40deg ackley shoulder. Find a good trig calculator online or ask any jr high student to help you since you probably forgot it all like I did. I make my own go and no go gauges for personal stuff for many reasons and trig doesn’t lie. Good luck and never trust a rifle that doesn’t work with standard gauges. Ask questions whether the gs is respected or not. We all make mistakes
 
And another thing...... "AI" means something. Specifically ACKLEY Improved. Now PO had a bunch of reasons for his "improvements" but the single biggest driver was NOT "to hold more powder" as has been asserted. And, basic to Mr Ackley's system was the concept of obtaining "proper headspace on factory ammunition" so that you could walk into a local store and buy normal rounds to fire in your "Improved" rifle. Hence "Improved" not "wildcatted"......

And none of this is about "luck"...... I bridle at "good luck" as an admonishment to one who's planning on setting up a 55,000psi deflagration 10" from hissown eyeball.... let's UNDERSTAND this stuff folks if'n we're gonna' opine on the innertube.

In short, in Parker Ackley's own words "An Ackley Improved cartridge will headspace properly on factory cases" and if a person can't visualize, realize and implement the necessary measures to accomplish such, they SHOULD NOT be cutting AI chambers.

Nor should they be advising others on the subject.


al


off
 
Ha. Funny. Please explain what I’m missing. Obviously you know how to read since you’re responding. If I’m wrong in my reading of the headspace measurements, show me and I’ll gladly correct my error.

I realize my post count here is low, so I must not be a good machinist :)
 
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If you don’t spec your 280 ai chambers to the already published saami chamber specs, what do you use?

If I brought a box of parts and said, make me a 280 ackley, what headspace gauge would you use? Do you make your own? Do you use a 280 case? Other than powder increase and longer brass life, why do you choose to make ackley?
 
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OP,
I am no nuclear (new-Q-lerr) scientist.... I digress :)
Here are the saami specs on both 280 and 280 ai. Shows the relation of shoulder angle to headspace. Hope this helps.

Note: headspace has Nothing to do with neck/shoulder junction. Only base to datum. That is the main confusion. Ex: 280rem has longer base to neck/shoulder junction length by .020”. That is why the 280rem “crushes” a bit when placed in a 280ai chamber. Again, nothing to do with headspace gauge measurements. Learning is fun ;)

As a great man said “you can lead a horse to water....”
 

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Mram10 said:
OP,
I am no nuclear (new-Q-lerr) scientist.... I digress :)
Here are the saami specs on both 280 and 280 ai. Shows the relation of shoulder angle to headspace. Hope this helps.

Note: headspace has Nothing to do with neck/shoulder junction. Only base to datum. That is the main confusion. Ex: 280rem has longer base to neck/shoulder junction length by .020”. That is why the 280rem “crushes” a bit when placed in a 280ai chamber. Again, nothing to do with headspace gauge measurements. Learning is fun ;)

As a great man said “you can lead a horse to water....”
Click to expand...

Now, that's funny but what's really funny is that you still just don't get it, yet you are so sure of yourself.
The .375 datum of the parent case does not contact in the ai chamber. It means zilch. It contacts near the ns junction. That's why you can't make sense of the numbers precisely, because the standard gage will contact just a few thousand below it or else neck diameter would change hs.
Imagine for a minute, putting a standard gage in a 40 degree ai chamber. It can only touch at the area I just mentioned.

Apparently you didn't read the link I posted or you think that there must be some conspiracy theory between him and anyone that actually does get it. Just read it, watch the video and read the comments. There are some well respected and qualified people that posted in the comments. One is Fred Zegglin, owner of 4d Reamers. Please, please explain what is clear as day in the link I posted before continuing to try to convince us all of something you don't have a grasp on yet. Until you can explain that, do us all a favor and keep an open mind to the possibility that you might be wrong this one time.

Thankfully, none of this confusion applies to the ops .243 AI
 
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I’ll bite! I just can’t help myself :)
Take a look at those gauges in the pic on the article. Do both noses look to end with a datum diameter of .375” ? Also, the author of that article mentions a headspace of 2.154 on the parent 280 case. No idea where he is getting that since it isn’t on the saami spec sheet.
 
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