280 AI: SAMMI or Traditional Chambering??

[ChinookTX]

I am about to buy a Cooper 52 in 280 AI. Cooper still uses the traditional AI chambering (i.e., they have not converted to the new SAMMI standard facilitated a few years ago by Nosler and maybe Remington). Cooper assures me I can fire 280 Rem cartridges in this chamber (resulting in fire formed brass for my chamber); also, I can shoot Nosler 280 AI ammo which is sized to SAMMI.

I'm a little perplexed by this new standard that's apparently not being accepted by anyone but Nosler.

Question: Are the two chamberings (SAMMI or Traditional) equivalent when it comes to being able to chamber 280 Rem and 280 AI SAMMI ammo? I'm assuming there's no such thing as 280 AI Traditional ammo as that would all have been fire formed using 280 Rem brass... ??

The standard dimensions of the 280 Rem and 280 AI SAMMI are different, as is the "standard" dimensions of the 280 AI Traditional (if there is a standard for this).

The reason for this question is, "should I buy this Cooper with the Traditional AI chambering or should I find a rifle chambered for the 280 AI SAMMI"?

Thanks.

 

[bheadboy]

if you reload it makes not difference, by the Cooper, fire what every you want and reload using Redding 280Ai dies.

Bob

 

[Smalltruck]

The change seems to be where they measure the shoulder at. Which is where you measure for headspace. It seems like using a datum line on the taper is gaining in popularity.

On smaller cartridges like a .223 that line is a .330 diameter line is 1.5573 from the base of the case. <That is the SAAMI spec. So how do you measure that? What I found was that if you take a .330 die bushing a zero your calipers and then slip it over the case neck you can then measure for case length at the shoulder. That will tell you if you need to bump the shoulder. Case overall length is a different thing...

On my 280AI being built I did the SAAMI spec reamer. It just seems easier to sell if I ever need to that its built to a "standard".

 

[ChinookTX]

Smalltruck,

You are building yours so you can make the choice. If I buy one already built, right now I am choosing between Nosler (SAMMI) and Cooper (Traditional).

If I do the SAMMI, I can buy/shoot Nosler ammo and Nosler brass without a second thought. It seems I'd have a problem shooting 280 Rem in it as the lengths to the neck are different. Even if I get the bolt to close and fire form the brass, wouldn't I have to trim every casing?

If I do the Traditional, I can fire form 280 Rem brass. I'm told I can also shoot Nosler SAMMI, even though there could be headspace issues. I guess I'd have a little more throat since the brass is about .015" shorter.

I was very surprised that Cooper has no plans to convert to the SAMMI reamer. Why would they not change if that were going to be the standard?

I'd make your choice and go with the standard but I'm not sure this standard is going to stick...

 

[ThunderDownUnder]

If you want to use new Redding dies then the SAAMI spec may be the better choice. Pre 2011 their dies were for the 280 Improved now they are for the 280AI which is the SAAMI spec version.

Read this : http://www.redding-reloading.com/tech-line-a-tips-faqs/133-280-changes

Ian

 

[wwbrown]

I went with the traditional chambering when I ordered up the reamer from Dave Kiff, in fact that barrel is in the lathe to be reamed today. This gun will be for F-open and I wanted to use Lapua 30-06 brass due to Lapua's quality so I gained nothing by using the SAAMI chambering.

 

[expiper]

in my case with the 7mm/07- AIMO...I used SAMMI specs. on the case body so that I could use modern Redding .280 AI dies and not be over sizing the bigger Ackely dims (the old dims are wayyy bigger at the .200 line than new 06 brass ),,,,I shortend the case neck dim. so that 30-06 brass would be correct length for the MO (modified overall ) length,,,,it works and shoots great,,,,Roger

 

[oldroper]

Smalltruck,

You are building yours so you can make the choice. If I buy one already built, right now I am choosing between Nosler (SAMMI) and Cooper (Traditional).

If I do the SAMMI, I can buy/shoot Nosler ammo and Nosler brass without a second thought. It seems I'd have a problem shooting 280 Rem in it as the lengths to the neck are different. Even if I get the bolt to close and fire form the brass, wouldn't I have to trim every casing?

If I do the Traditional, I can fire form 280 Rem brass. I'm told I can also shoot Nosler SAMMI, even though there could be headspace issues. I guess I'd have a little more throat since the brass is about .015" shorter.

I was very surprised that Cooper has no plans to convert to the SAMMI reamer. Why would they not change if that were going to be the standard?

I'd make your choice and go with the standard but I'm not sure this standard is going to stick...

Most that have 280AI build understand the choice on reamers myself I had SAAMI 280AI build if I wanted to fireform brass I could of had the other reamer. Your not only one that had to make a choice.

 

[Timgunner]

So I've heard and read contradictory information from several different sources on the difference between the "280 ackley 40 degree shoulder" and the new Nosler 280ai. Can someone set the record strait. Is the case different at all or is it just measured differently thus providing different standard dimensions? From what I understand about PO Ackley's designs they were set to headspace at the junction of the neck and the shoulder this is the feature that allowed factory rounds to chamber safely. If the Nosler 280ai can safely fire factory 280 ammo wouldn't it require the same design and dimensions?

 

[TonyR]

So I've heard and read contradictory information from several different sources on the difference between the "280 ackley 40 degree shoulder" and the new Nosler 280ai. Can someone set the record strait. Is the case different at all or is it just measured differently thus providing different standard dimensions? From what I understand about PO Ackley's designs they were set to headspace at the junction of the neck and the shoulder this is the feature that allowed factory rounds to chamber safely. If the Nosler 280ai can safely fire factory 280 ammo wouldn't it require the same design and dimensions?

Follow the Redding link in Thunder Down Under's previous post in this thread. Redding describes the difference a 0.014 inches of headspace. The Nosler is shorter. I chose the traditional version since I don't plan on using Nosler brass

 

[BillPa]

Here is what Dave Manson had to say....

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
1-810-953-0732