Home Forums Hunting & Shooting Ask The Gunwriters 280 Ackley SAAMI vs. 280 Improv 40 deg pre-SAAMI

Hoping someone can clear this up for me, as my head's going to explode.

I have a friend that took his bone-stock 280 Rem to a gunsmith and asked for it to become a 280 Ackley. The 'smith turned the barrel back one revolution and chambered it (with POA's original .004" crush fit on the datum line shared by both the regular and Ackley forms of the 280).

Will this work--without excessive headspace--with SAAMI 280 Ackley brass, e.g., Nosler?

From what I'm surmising within this Nosler FAQ (which the gunsmith seemed to follow to a "T"), is that the issue is when a 280 Rem is rechambered to an Improved without first turning back the barrel.

Any & all help greatly appreciated.

The correct chambering for the original is not a .004" crush on the datum line but a .004" crush at the juncture of neck and shoulder. It is readily apparent that this measurement can vary with differences in neck diameter and shoulder angle. GD

Yes it will work.

They had it set up the way P.O set it up.

Will work with standard 280 loads/brass as well.

My mistake.

What greydog said.

You don't know if it will work unless you chamber some UNFIRED .280 factory brass. There isn't a vast amount of difference in the Nosler and Ackley chambers, so SOME factory .280 brass will work fine--and some might not.

I emphasize UNFIRED because there can be problems with some fired cases, due to them lacking the slight radius between the neck and shoulder.

John, just to be clear, standard 280 Rem or improved new brass, e.g., Nosler?

Either one.

In general, having messed around with quite a few .280s and .280 AIs, I prefer a little chambering resistance in an AI chamber with any kind of .280 brass.

I am curious, though, how the variance occurs in the first place. The Nosler FAQ implies it has to do with rechambering a standard 280 Rem without turning the barrel back, creating what several say is between .010"-.014" of headspace. Is this the generally accepted rationale?

From my understanding it is largely a difference in measuring the cases from the datum line vs the shoulder junction. I have not shot the Nosler brass in my AI but I would assume that if it has a crush fit it would be fine, if not jam the bullets to fire form. If you are really concerned then neck up and create a false shoulder.

The rifles I chambered with a $37 sammi 280AI go gauge from PTG play well with Nosler 280AI brass.

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."

This explains and clarifies what I was asking on the reloading page last week. Thanks for posting it.

RM

The information from Dave Manson is interesting--partly because the difference in headspace is so small--which can result in something I personally experienced when Nosler first introduced the .280 AI as a factory round.

To promote the "new" cartridge they decided to take a couple of gun writers on a pronghorn hunt in Wyoming, one of them me. Nosler wasn't building rifles then, so I had a Ruger No. 1 chambered for a smaller 7mm round rechambered by a local smith. But there weren't any headspace gauges available, so I took him some unfired Nosler cases--which at the time were headstamped "Norma." He used a .270 Winchester Ackley Improved reamer and a 7mm neck reamer to do the job.

The rifle shot very well with both the factory ammo Nosler sent me (which was loaded by Norma, in the same headstamped brass), and with various handloads. But I also had some .280 Remington ammo on hand from various projects, and decided to see how it would fireform in the new chamber. It formed fine, without a hint of excess stretching.

Thanks for the info on the 280 Ackley. guys. I have a Savage 110 Hunter in 280 Ackley Improved. I bought Remington brand 280 Remington brass and have been fireforming it to get 280 Ackley brass. My rifle's bolt closes snug on this factory brass, which leads me to believe my rifle isn't chambered for the Nosler version, 14/1,000" shorter. Am I right? I guess I shouldn't buy any Nosler 280 AI brass.

Dunno--but do know that .014" is just slightly more than the thickness of the average business card. Have measured to the datum line on a bunch of factory brass, and it can easily vary that much.

So there still are two versions of the 280AI - wonderful.

That is how I check an AI to see if it's done right slight resistance with a factory round. Had several that were not done right,

"Slight resistance" is exactly what I found with my rifle, chambered using Nosler/Norma unfired brass, with unfired Remington factory .280 brass.

That said, after some experience with several "improved" rounds, mostly 40-degree Ackleys in cartridges from .223 Remington to .35 Whelen, fired "unimproved" brass in the same chamber often won't even go band, due to the lack of the little shoulder/neck radius on new brass.

My point is that .014" difference in headspace (IF the .280 AI chamber is reamed that accurately) is a very tiny amount--and a very slight amount of variation in both the chamber and brass can work just fine, whether the chamber is supposedly "original" Ackley Improved or Nosler.

Should also add that the standard allowable SAAMI variation in headspace for most rifle cartridges is plus or minus .007"--exactly half of the difference between the "Ackley" .290 AI and the "Nosler .280 AI." Again, this is typical rifle-loony obsessive minutiae.

Yet another point: Most mass-produced full-length sizing dies tend to size brass to different slightly different headspace when using the standard "screw 'em in until the die contacts the shellholder" directions. This generally varies as much as the headspace difference between the Ackley/Nosler .280 AI rounds, especially when we throw in the differences in individual shellholders and presses.