Fireformed 280 AI question.

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hawk-i

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So I just bought myself a Kimber Montana 280 AI.

Stores haven't got any 280 AI ammo or brass so I bought a box of 280 Hornady Superformance 139 sst's and a 50 count bag of 280 rem brass with the idea I could just shoot the ammo and have AI formed brass.

I also loaded up some of the bag of 50 with 162 BTSPs. ...all seemed good at the range but when I got back to the reloading bench I see 1/3rd of the factory ammo has signs of case head separation but all of the hand loaded 280 rem is Fireformed with no case head separation signs.
I always thought you could shoot regular 280 rem ammo and safely end up with 280AI.

Is this not correct.???..on the hand loaded ammo I had the bullet seated out into the lands as a precaution but didn't think it was necessary.
 
Should be able to fireform from 280rem but maybe superformance wasn't the best choice. It's a pretty high pressure load especially when there's that much room for brass to stretch. Just an fyi North pro sports has nosler 280ai brass in stock.
 
As I understand the AI idea, the AI has the same headspace dimension and datum point as does the parent case, but with a different (steeper) shoulder angle. So the distance from case head to root of shoulder is less on the AI case than on parent case - why you can not correctly ream to an AI chamber without setting back the original barrel. I understand that a AI chamber should properly handle parent cases. You should have been able to shoot properly sized factory 280 ammo in a proper sized 280 AI chamber. Head separation signs observed were what? Do you have grooves on inside of the factory cases?
 
Potashminer said:
As I understand the AI idea, the AI has the same headspace dimension and datum point as does the parent case, but with a different (steeper) shoulder angle. So the distance from case head to root of shoulder is less on the AI case than on parent case - why you can not correctly ream to an AI chamber without setting back the original barrel. I understand that a AI chamber should properly handle parent cases. You should have been able to shoot properly sized factory 280 ammo in a proper sized 280 AI chamber. Head separation signs observed were what? Do you have grooves on inside of the factory cases?
Click to expand...

Yes grooves on the inside and on some a visible ring on the outside. ..enough for a fingernail to sag on the ring.
 
Your understanding on how a true Ackley chamber should work is correct... the parent case should be able to be fired in the AI chamber without any issues. In many cases, the accuracy is very good, pressures lower then the original factory loading, perfectly formed cases when ejected.

Problem is that in the Shooting industry, everyone is allowed a range of tolerances both bigger and smaller then a "norm". So you can have a max spec chamber and min spec brass. Now the "jam" that PO Ackley designed into the dimensions is gone and with elevated pressure loading, the stretch in the case web is too high and you have cracked cases.

So unless I controlled the dimensions of the chamber, I assume the chamber is long and size my cases accordingly to have that jam fit when chambered and fired. I also avoid using a bullet and high pressure load, prefering to go with the COW method of forming as it is so much easier on the case web.

Toss any suspect brass.. it is going to crack.

Good luck... it is a great chambering when you get some brass formed properly.

Jerry
 
Just an update....I had 5 rounds of the Superformance cartridges left from the first range trip.
Today I pulled the bullets and dumped the 63.2 grs of powder in each of them and loaded each with 40 grs of Imr4064 then reseated the 139 gr bullets.

They Fireformed perfectly with no case head separation signs....note to self....don't try to Fireformed 280AI from Hornady Superformance 280 rounds.
 
hawk-i said:
Just an update....I had 5 rounds of the Superformance cartridges left from the first range trip.
Today I pulled the bullets and dumped the 63.2 grs of powder in each of them and loaded each with 40 grs of Imr4064 then reseated the 139 gr bullets.

They Fireformed perfectly with no case head separation signs....note to self....don't try to Fireformed 280AI from Hornady Superformance 280 rounds.
Click to expand...

Very Interesting ! So HI PRESS loads stretch the brass way to much it seems but low pressure loads dont seem to ! RJ
 
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