I quote Dave Manson:
"From the reamer/headspace gage maker's point of view, SAAMI standardization of the 280 Ackley Improved has created problems. Mostly, it's a matter of making sure folks are informed about the change, proper fireforming--if they want to go this route--and which ammo to use in which chamber.
Ackley's intent, with rimless, shouldered cases, was to headspace the improved chamber so that the un-improved parent cartridge could be loaded and safely fired in it--the parent round was held between the breechface and the neck/ shoulder junction of the improved chamber. He advised that the breech-face-to-neck/shoulder junction in improved chambers be held some.004" to .006" shorter than in the parent chamber. Traditionally we, and other reamer makers, have done this, grinding reamers with a MINIMAL RADIUS at the N/S junction for more positive headspacing during fireforming.
Nosler/SAAMI shortened the traditional 280 AI headspace another .014". Additionally, the radius at the N/S junction was specified at .060" +.025". This was likely done because it's very difficult to form 40-degree shoulders with small radii--they're supplying fully formed ammunition, remember.
What does this mean for the owner of a 280 AI?
First, if you have one headspaced the traditional way, don't buy Nosler ammo unless you want to see evidence of excess headspace and risk case separation--its shoulder location guarantees at least .014" excessive headspace. When you need new cases, fireform them from 280 Remington brass.
Second, if you have a SAAMI-spec chamber, you can buy Nosler ammo OR fireform 280 Remington. The N/S junction on the SAAMI chamber IS .014" closer to the breech face, but the .060" radius at this points provides a little more room to accomodate 280 Rem ammo. You may feel a little resistance as you turn down the bolt handle, but it will go and the case will be held securely during fireforming.
Finally, re-loading. Don't use dies made to the old spec to re-size cases fired in SAAMI-spec chambers. The few re-size dies I checked that were made to the "old" spec would not reach the shoulder of a case fired in the SAAMI chamber.
You CAN use SAAMI-spec dies to re-size cases fired in old-spec chambers, but be sure to set the die so it barely touches the shoulder of the fired case. DO NOT set the die so it bumps the shellholder when the ram is up--you'll introduce excess headspace or crush the case.
There are different versions of the 280 AI out there, so this commentary doesn't apply to everyone. If anyone has questions about his specific rifle, I'm willing to try to answer them."
Dave Manson
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Additionally, I add that Redding current production dies are for chambers that are cut to the SAAMI specification are 0.014 shorter in headspace than the original PO Ackley specs and are stamped "280 Ackley Imp". Redding dies made before 2011 are stamped " 280 Rem Imp 40° " and are built to the originally accepted PO Ackley specs. RCBS also has two different dies: Group D 17001 .280 Ackley Improved and Group A 17030 .280 Ackley Imp (Nosler)
Sugar coat all you want, but Nosler created a cartridge with different specs - 14 thousandths is 14 thousandths - or as this say, "It is what it is."
Last edited by Offshoreman; 06/02/20.
