Semi Custom Kimber Montana 280AI

[shortgrass]

You can run the numbers all you'd like, but the shape of the cases is what's making the difference. I have the last rifle I built under my 07 Manufactures license (I have a 01, now) in my shop and use it as a "display model". It's chambered in .280 Nosler AI. I stripped the bolt of the ejector and firing pin assembly (Rem. 700 LA) and dropped the "GO" gauge into the chamber. I could slightly 'feel' the gauge as I closed the bolt. Then I dropped the "NO-GO" Nosler gauge in. The bolt wouldn't even think about closing. Next, I dropped the .280 Rem. "GO" gauge in, the bolt closed without any resistance. I then inserted the .280 Rem. NO-GO gauge and I could 'feel' the gauge , ever so slightly, as I closed the bolt. I have some new Winchester brand .280 Rem. brass in the shop, so I tried a couple of those. Bolt closed without resistance. I have some new, factory loaded, Remington brand .280. Rem. ammo on the shelf, so I tried a couple of those. The bolt closed without resistance. I, also, have several boxes of new, Nolsler brand, .280 Nosler AI cases, so I got into an open box and tried a couple of those. The bolt closed without any resistance. My reamer and gauges are all clearly marked, so I didn't mis-read anything. I've done this a half dozen times to assure myself that "I'm not seeing things that aren't there". On average, I cut 75-80 chambers, on a professional basis, yearly, and I've been chambering since 1992. Put a 'parent' case/ammo in an Ackley chamber and close the bolt on it, without having any resistance and you are creating an excessive headspace condition. To learn more about the Original Ackley rounds, I'd suggest reading "Handbook for Shooters & Reloaders", volumes one and two, by P.O. Ackley.

 

[yawn]

yes I have read Ackleys books thanks .

So just to clarify, you are saying that the new nosler SAAMI spec is actually LONGER than the original Ackley ?

 

[shortgrass]

The .280 Nosler AI is the anomaly as it has been standardized by SAAMI. It uses no 'trickery' with gauges as the Original Ackley Improved cartridges do. PT&G does make "GO" and "NO-GO" gauges, in "Ackley" form, for those who'd prefer not to use P.O.s' method of gauging.

 

[yawn]

It looks to me as if you are claiming the saami spec to be longer in headspace than the original. Can you please confirm this is your opinion?

 

[MudRunner2005]

IF there is actually a difference it is the reverse of the above. With the nosler SAAMI spec being supposedly .014 shorter then standard 280 rem will be tight in that chamber , not loose. And if that is the case then you should feel at least reasonable resistance closing the bolt if not very hard resistance.
I say "IF there is a difference because" after physically checking quite a few different rifles Im not seeing anything like .014 difference. Not saying there isnt a difference just that Iv yet to see it.

Mudrunners advice on firing some standard brass in both rifles and comparing is a good idea. Posting the results here would be very helpfull.
Ill just add that Iv had a cooper 280ai for many years and fired nosler 280ai brass with over 10 reloads with no trouble at all. It does not stretch .014 as the theory suggests it should In fact it dosnt stretch at all.
Head space on the brass is the same fired as it is new out of the box.

You are correct that they claim the Nosler/SAAMI spec chamber is .014" shorter, therefore it would be very difficult to close the chamber. I haven't owned a .280 AI yet, but will be sooner or later to help complete my '06 Ackley chamberings.

My brass (when forming) doesn't have any body-stretch at all. The neck a tually gets about .020" shorter, because the shoulder and walls blow out.

 

[shortgrass]

If you'll go to the SAAMI web site it clearly shows that the minimum headspace dimension for the .280 Rem. is 2.100" and the minimum headspace dimension for the Nosler .280 A.I. is 2.140", the .280 Rem. being .040" shorter. The .014" you're speaking of is the difference between the Traditional Ackley and the Nosler Version, which has absolutely no bearing on fire forming .280 Rem. to the Nosler A.I. chamber. Headspace, on these rimless cartridges is measured from the bolt face to the datum line on the shoulder of the chamber (the datum line is where the diameter of the shoulder measures .375"). The .280 Rem. cannot contact the Nosler chamber or the Traditional Ackley chamber at that point because the diameter of the Nosler chamber is bigger and the shoulder angle is different than the .280 Rem. That makes all this comparison of headspace dimensions irrelevant. The important thing is, does the .280 Rem. have a 'crushed fit' in the Nosler chamber like it does in a Traditional Ackley chamber(that is reamed to the proper depth)? My experience with the Nosler .280 A.I. is that factory loaded or hand loaded ammo (to the OAL specs in the loading manual for the bullet being used) does not 'crush fit'. If using hand loads, the bullet must be seated 'long', jammed into the rifling. This insures that the round being fire formed will be firmly against the bolt face and will do all of its 'stretching' at the forward end of the case, not at the head end. The current Nosler Reloading Manual clearly states that to fireform .280 Rem. in the Nosler .280 A.I. chamber that the bullet should be 'jammed' into the rifling. When fire forming .280 Rem. in a Traditional Ackley chamber the .280 rd. has a 'crush' fit between the junction of the neck/shoulder and the bolt face.

 

[yawn]

If you'll go to the SAAMI web site it clearly shows that the minimum headspace dimension for the .280 Rem. is 2.100" and the minimum headspace dimension for the Nosler .280 A.I. is 2.140", the .280 Rem. being .040" shorter. The .014" you're speaking of is the difference between the Traditional Ackley and the Nosler Version, which has absolutely no bearing on fire forming .280 Rem. to the Nosler A.I. chamber. Headspace, on these rimless cartridges is measured from the bolt face to the datum line on the shoulder of the chamber (the datum line is where the diameter of the shoulder measures .375"). The .280 Rem. cannot contact the Nosler chamber or the Traditional Ackley chamber at that point because the diameter of the Nosler chamber is bigger and the shoulder angle is different than the .280 Rem. That makes all this comparison of headspace dimensions irrelevant. The important thing is, does the .280 Rem. have a 'crushed fit' in the Nosler chamber like it does in a Traditional Ackley chamber(that is reamed to the proper depth)? My experience with the Nosler .280 A.I. is that factory loaded or hand loaded ammo (to the OAL specs in the loading manual for the bullet being used) does not 'crush fit'. If using hand loads, the bullet must be seated 'long', jammed into the rifling. This insures that the round being fire formed will be firmly against the bolt face and will do all of its 'stretching' at the forward end of the case, not at the head end. The current Nosler Reloading Manual clearly states that to fireform .280 Rem. in the Nosler .280 A.I. chamber that the bullet should be 'jammed' into the rifling. When fire forming .280 Rem. in a Traditional Ackley chamber the .280 rd. has a 'crush' fit between the junction of the neck/shoulder and the bolt face.

This is muddying the waters some what but OK.
yes the .014 is supposedly the difference between the traditional ackley and the new saami version. The discusion revolves around the new Saami spec being .014 shorter in head space when fired in a tradional chamber, ie the brass gets .014 longer after firing.
The points you raise are correct when looking at the designated datums on the drawings but that's not where the physical contact occurs when chambering a standard 280 round in an improved chamber.Because of the 40 deg shoulder it contacts much closer the to the neck shoulder junction at which point the standard .280 rem is longer at 2.192 than the saami ackley at 2.174 creating the light crush.
What's happening in your chamber I have I no idea.

 

[yawn]

Heres some discussion on the topic

280 Ackley Improved Alert | GunsmithTalk

some interesting reading in the comments

followed by some actual physical testing

https://gunsmithtalk.wordpress.com/2012/07/17/280-ackley-improved-emperical-headspace-test/

 

[shortgrass]

This is muddying the waters some what but OK.
yes the .014 is supposedly the difference between the traditional ackley and the new saami version. The discusion revolves around the new Saami spec being .014 shorter in head space when fired in a tradional chamber, ie the brass gets .014 longer after firing.
The points you raise are correct when looking at the designated datums on the drawings but that's not where the physical contact occurs when chambering a standard 280 round in an improved chamber.Because of the 40 deg shoulder it contacts much closer the to the neck shoulder junction at which point the standard .280 rem is longer at 2.192 than the saami ackley at 2.174 creating the light crush.
What's happening in your chamber I have I no idea.

Yawn,,,, .018" is NOT a light crush! It would take a mallet to close the bolt! .004"-.006" takes some effort. I'll go ahead and say that ammo dimensions are not the same as chamber dimensions, the ammo is just enough smaller so it will fit easily. but not be sloppy. Take even .005" off of the .018" and you're still left with .013" crush, which is an extream number. Go on down to the "GUNSMITHING" section here on LRH. There's a thread titled ".280 AI Concerns". azgutpiles' buddy is having the same troubles many are having. He had a case head seperation and, if fire forming .280 Rem. without "jamming the bullet", the case head swells. This tells me the cartridge doesn't fit the chamber as it should. To expand further, the new Nosler brass in a "Traditional" chamber (the Traditional being .014" longer) is creating an exessive headspace condition. Remember, the ammo/cases are smaller which means the excessive headspace could be .018"-.020". NOT a good situation, any way it's looked at. It is still da*#$@ funny that Nosler, themselves, recommends "jamming the bullet" (into the rifling) if handloading .280 Rem. to fire form in the SAAMI chamber.

 

[yawn]

Yawn,,,, .018" is NOT a light crush! It would take a mallet to close the bolt! .004"-.006" takes some effort. I'll go ahead and say that ammo dimensions are not the same as chamber dimensions, the ammo is just enough smaller so it will fit easily. but not be sloppy. Take even .005" off of the .018" and you're still left with .013" crush, which is an extream number. Go on down to the "GUNSMITHING" section here on LRH. There's a thread titled ".280 AI Concerns". azgutpiles' buddy is having the same troubles many are having. He had a case head seperation and, if fire forming .280 Rem. without "jamming the bullet", the case head swells. This tells me the cartridge doesn't fit the chamber as it should. To expand further, the new Nosler brass in a "Traditional" chamber (the Traditional being .014" longer) is creating an exessive headspace condition. Remember, the ammo/cases are smaller which means the excessive headspace could be .018"-.020". NOT a good situation, any way it's looked at. It is still da*#$@ funny that Nosler, themselves, recommends "jamming the bullet" (into the rifling) if handloading .280 Rem. to fire form in the SAAMI chamber.

There are 2 points here
firstly the saami vs traditional discussion- which involves the new spec being shorter by .014 so if new nosler brass is fired in the traditional chamber it will stretch to fit the traditional chamber. If you search back through older threads on the topic here you will find that Im not convinced there is a difference , one of the reasons Im not convinced is I can fire new SAAMI nosler 280ai brass in my chamber with no stretch at all and yet still fire form standard .280rem with ease .How can there be a difference ? as you pointed out the .018 difference should be to much to close the bolt easily on the standard 280 rem .I have in the past threads raised this and other points. Im more inclined to believe the second link from my post above which shows no difference at all. But either way
( and this is the second point) if SAAMI nosler brass is to short for a traditional chamber as is claimed ( or even the same as Im more inclined to believe ) then given the original ackley is .04 shorter than than a standard 280 rem at the neck shoulder junction to promote fire forming standard 280 rem , how is it possible the saami chamber is to long to fire form standard 280 rem as you claim?
You cant have nosler saami 280ai brass stretching to fit a traditional chamber AND have the SAAMI chamber to long to firefore standard 280 rem. That's a complete contradiction

 

[azgutpile]

I hope this helps...This was posted earlier by "Woods" on 3-21-2011

Here is what Dave Manson of Manson Reamers had to say:

QUOTE

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

UNQUOTE


Now that I know I can deal with it but I do think it is irresponsible for Nosler to sell their 280AI cases or boxed loads without a heads up.

 

[atrietch]

Thanks everyone. This clears it up for me. I think...

 

[yawn]

Yes this discussion has been on going for some years now. If you read the first link in my previous post , more specifically the comments that follow you see a reference to Dave Kiff from pacific tool and guage saying pretty much what Dave Manson has said . But the funny thing is Dave Kiff supplied the gauges and reamers that proved there was no difference in the in the second link. I v followed this for quite a while now and Iv taken every chance to check chambers in 280ai. rifles. Im up to eight now with both factory rifles from kimber ,cooper and custom builds that where set up as traditional chambers using the standard 280 rrem gauges. I am yet to find a significant difference.
The difference as explained in the video is on the drawings and comes from a simple change in datum for the neck shoulder junction when the saami spec was drawn. That is; it is indexed from a slightly different position giving an apparent change in length. On a 40 deg shoulder you only have to shift it .015 (Aprox) along the shoulder to show an apparent .014 difference in length. Even less if the radius is involved.
One thing to keep in mind is to change head space on a case by .014 takes less than 1/4 turn in of a FL die. From my experience very few reloaders actually set up their FL die properly anway.