Skip to main content

Ackley Improved Cartridge Headspace

With the help of two longtime reloading mentors and one R&D manager, Lane Pearce clears up the murky situation of Ackley Improved cartridge headspacing.

Ackley Improved Cartridge Headspace
Lane learned something new while trying to correct his misstatement concerning .280 Ackley Improved cartridge headspace and felt compelled to share it. (.280 AI Cartridge drawing courtesy of Nosler)

Reader Patrick Ryan pointed out a probable error in my June 2019 column on the .257 Roberts Ackley Improved wildcat that I’d like to address here. I had stated that when Ackley developed the improved version, he “maintained the shoulder headspace datum of the parent factory round.” I recognized Patrick’s name as someone who had worked for Redding, and I’d previously talked with him several times. He stated that the Ackley Improved cartridge “…shared the same dimension (as the parent round) from the boltface to the junction of the shoulder and neck. This is what allows the parent cartridge to be fired in the improved chamber.”

I had his email address, so we messaged back and forth about this and other shooting topics, and I could only conclude that my understanding of AI/parent cartridge headspace was flawed and that I had misspoken.

The editor was concerned because another “The Reloader” column on the .30-06 Ackley Improved was about to be published, and it contained a comment similar to the one described above. This time I’d stated: “One key feature of the AI chamber is that it maintains the same headspace as the parent cartridge. That means factory ammo can be safely and reliably fired in a rifle chambered for the AI cartridge.”

I promptly pulled out various reference materials, including cartridge illustrations from Wolfe Publishing (1993) and RCBS (circa 1986) and Ackley’s two-volume handloading manual (1962) to investigate the situation. Comparing illustrations of the .30-06 standard dimensions to the AI version seemed to refute Ryan’s observation.


Now What Could I Do?

I decided to call upon the knowledge of two longtime reloading mentors (ST columnist Allan Jones and former ST Rifles/Reloading Editor Rick Jamison) and the Nosler R&D Manager Mike Lake (Nosler sells factory-loaded .280 AI ammunition and rifles chambered for .280 AI). Allan promptly pulled up SAAMI drawings of the .280 Remington and .280 Ackley Improved. The latter is the only Ackley wildcat that has “official” status. He compared the shoulder-neck dimensions and promptly remarked, “They don’t match either.” Rather than help my situation, that puzzled me all the more.


I pulled up the .280/.280 AI SAAMI specs and noted they have the same Basic (i.e., theoretical) headspace datum (the place where a 0.375-inch-diameter ring gauge should touch the shoulder of either cartridge). On the .280 Rem. (with a 17.5-degree shoulder angle) that is 2.1042 inches from the cartridge base. The corresponding .280 AI dimension (with a 40-degree shoulder angle) is 2.1437 inches. That’s nearly forty thousandths of an inch longer. And the neck-shoulder dimension of the .280 Rem. is 2.1993 inches compared to the .280 AI’s at 2.1795 inches. That means the standard round coordinate can be nearly forty thousandths of an inch longer than the AI cartridge’s.

When I posed the same inquiry to Rick, his response was, “A standard round headspaces at the base of the neck in an Ackley chamber, at least enough to fireform the case. Just fire standard rounds in the Ackley chamber. If you have an Ackley chamber, all you need are loading dies and you’re in business. The setup is simple and virtually trouble-free. Ackley sold both chambering jobs and dies. As a customer, it’s an inexpensive way to get higher performance. You don’t need a new barrel, and rounds will feed and fire without further action adjustments or other gunsmithing required.”

I pointed out that the Wolfe Publishing drawings indicated the neck length of the .30-06 case was 0.388 inch and the .30-06 AI case neck length was 0.419 inch, meaning the parent round’s neck was thirty-one thousandths shorter than the AI version. We concluded that sounded reasonable. The standard round’s sloping shoulder could never touch the AI chamber shoulder before firing. So the neck-shoulder junction of the parent cartridge must reach the AI chamber neck-shoulder with at least a slight crush so it would reliably fire.

While discussing the matter with Mike, he reminded me there were many versions of the wildcat “improved” .280 Remington, including several labeled “Ackley Improved.” To add to the confused situation, even the tooling makers’ drawings differed! Nosler decided to follow Mr. Ackley’s intent as closely as possible—to design the chamber so a full-pressure .280 Rem. factory round could be safely fired in SAAMI-compliant .280 AI rifles.


Nosler compared the maximum and least material conditions, i.e., assessed the effect of the required tolerances that must be allowed for both the cartridge and chamber configurations. Accordingly, the company determined the amount of crush versus clearance at the neck-shoulder junction could range from 0.009 to 0.016 inch respectively. Statistically speaking, rarely does either extreme occur because the multiple manufacturing tolerances will average out. So that’s why a .280 Rem. factory round typically fits into the SAAMI-spec .280 AI chamber with just a slight amount of crush.

I recalled that when my gunsmith, John Gallagher, rechambered my Savage .30-06 rifle he told me he used a .30-06 go gauge as the Ackley chamber’s no-go gauge. He had learned that trick from Dave Manson, maker of chamber reamers and other precision gunsmithing tools. The .30-06 AI go gauge is precisely machined to measure 0.004 to 0.006 inch shorter than the parent case go gauge. He recommends setting the barrel back one turn when rechambering to ensure proper headspace. John did so, and my rifle reliably feeds and fires standard .30-06 and .30-06 AI rounds interchangeably.

In either case, as Patrick pointed out, my first statement was wrong. The headspace datum location on the case body of a standard round compared to an AI version can’t be the same because the shoulder angles are so different. However, my similar statement in the subsequent .30-06 AI column is less specific, so it more correctly describes the relative headspace between the parent and the AI versions.


I don’t know if I’ve completely cleared up the misunderstanding, but I have a better handle on the topic. I guess you’re never too old to learn something new.

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

See More Recommendations

Popular Videos

The Glock 21

The Glock 21

Frank and Tony from Gallery of Guns spice up the Glock test using their non-dominant hands.

Black Hills Evolution of Rifle Cartridge: .308 Win. 175 Gr. Match

Black Hills Evolution of Rifle Cartridge: .308 Win. 175 Gr. Match

David Fortier talks with Jeff Hoffman of Black Hills Ammunition about the evolution of the .308 Win. 175 Gr. Match bullet.

Pinging Steel At Over A Mile Away

Pinging Steel At Over A Mile Away

Big bore semiauto or a lever gun? We look at the futuristic .450 Bushmaster and how it compares to the tried and true .45-70. ISS Prop House gives us the rundown on the guns used in Enemy at the Gate. We ping steel with a .300 WinMag at over a mile.

Tactical Solutions Introduces New X-Ring Takedown SBR Rifle

Tactical Solutions Introduces New X-Ring Takedown SBR Rifle

Keith Feeley of Tactical Solutions sat down with Michael Bane at SHOT Show 2018 to talk about the new X-Ring Takedown SBR .22LR rifle.

See More Popular Videos

Trending Articles

The heart of the newest Model 70 is, of course, its action.Winchester Model 70 Extreme Weather SS Review Rifles

Winchester Model 70 Extreme Weather SS Review

Greg Rodriguez - September 23, 2010

The heart of the newest Model 70 is, of course, its action.

The Winchester .350 Legend is a no-nonsense whitetail thumper tailored for rifle hunters in the Heartland.Winchester .350 Legend Rifles and Ammo Available Right Now Ammo

Winchester .350 Legend Rifles and Ammo Available Right Now

Payton Miller - August 21, 2020

The Winchester .350 Legend is a no-nonsense whitetail thumper tailored for rifle hunters in...

The Winchester Model 52 is a fine, handbuilt smallbore match rifle that was once known as the king of the .22s among competition shooters.Winchester Model 52 Review Rifles

Winchester Model 52 Review

Joseph von Benedikt - July 20, 2020

The Winchester Model 52 is a fine, handbuilt smallbore match rifle that was once known as the...

A half-century in the making, the new DGX Bonded is Hornady's best-ever dangerous-game bullet.Danger Tamed: Hornady DGX Bonded Hunting Ammo Ammo

Danger Tamed: Hornady DGX Bonded Hunting Ammo

Joseph von Benedikt - May 23, 2019

A half-century in the making, the new DGX Bonded is Hornady's best-ever dangerous-game bullet.

See More Trending Articles

More Reloading

The bottleneck 7.62x25 Tokarev is a fun cartridge, and handloading it increases the round's versatility.Handloading the 7.62x25 Tokarev Reloading

Handloading the 7.62x25 Tokarev

Brad Miller, PhD - April 03, 2020

The bottleneck 7.62x25 Tokarev is a fun cartridge, and handloading it increases the round's...

Because case prep is the most time-consuming step in the handloading process, we say any tool that makes it easier is a bargain.Case Prep Made Easy Reloading

Case Prep Made Easy

Lane Pearce - May 29, 2020

Because case prep is the most time-consuming step in the handloading process, we say any tool...

The industry has a lot of cool new products for handloaders in 2020. Here's a close look at three of them.New Reloading Products for 2020 Reloading

New Reloading Products for 2020

Lane Pearce - June 22, 2020

The industry has a lot of cool new products for handloaders in 2020. Here's a close look at...

Starting the handloading process with clean brass allows the cases to be better inspected, and that enhances safety as well as the loads' performance.Reloading Tip — Start With Clean Brass Reloading

Reloading Tip — Start With Clean Brass

Lane Pearce - September 18, 2020

Starting the handloading process with clean brass allows the cases to be better inspected, and...

See More Reloading

Magazine Cover

GET THE MAGAZINE Subscribe & Save

Digital Now Included!

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW THIS MONTH'S ISSUE Arrow

Buy Digital Single Issues

Don't miss an issue.
Buy single digital issue for your phone or tablet.

Buy Single Digital Issue on the Shooting Times App

Other Magazines

Special Interest Magazines

See All Special Interest Magazines

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Phone Icon

Get Digital Access.

All Shooting Times subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit mymagnow.com and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now