Gunsmithing .280 AI SAAMI questions

[goodgorilla]

I've been doing some reading and I am a little confused about a few things about the .280 AI. There are 2 different versions of the .280 AI? There is the traditional .280 AI which will not fire form factory .280 brass, and the .280 AI SAAMI which can fire form brass using factory .280? Do you have to specify that the .280 is the SAAMI version, or are all the new reamers now SAAMI? Like all the new ".280 AI" are now SAAMI?

 

[sandwarrior]

I've never seen a .280 AI or other improved version that did not fireform from standard brass. Can you describe what it is not doing?

 

[goodgorilla]

I've never seen a .280 AI or other improved version that did not fireform from standard brass. Can you describe what it is not doing?

280 Ackley Improved Alert | GunsmithTalk
This page said that there was no SAAMI standard until not that long ago. Something like the SAAMI chamber is slightly different from the first AI's that came around, and reloading dies for that matter are not the same either. I read somewhere that one guy had the wrong version and it screwed up his brass. I'm considering a .280 AI in the future, and I'm just confused after a few articles like the one listed.

 

[slayer_21420]

If you buy a newly manufactured reamer and /or dies they will be made to SAAMI specs. If you are concerned about the issue just give a quick call to the manufacturer and they'll fill you in.

 

[sandwarrior]

goodgorilla,

Leave it to Remington to "F" things up again. Only this time they drug Nosler in on it too. When you fireform an Ackley (or other similar type improved case) you shorten the headspace in the chamber by about .004" (four thousandths). This allows the shoulder of the case to crush against the top of the chamber creating a tight brass seal. When the cartridge is fired, the brass flows out to meet the chamber size. .459" wide at the shoulder and 40 deg.

What was done when Nosler built it's brass off the Remington specs was assume they needed to shorten the chamber more, by .0143" (rounded it is fourteen thousandths). And this is how Nosler built the brass. By being .014" short, you have a lot of expansion in the case that is uncontrolled. Not even belted magnums have that much room to expand (remember they headspace off the belt). So, yeah, there is a bad difference in the way things got done with this. A dangerous thing that Remington (read retarded) left unchecked.

But, I do thank you for this. I have, and many of my friends have, owned .280 AI/improved rifles. This could be a very dangerous thing. The ignition/explosion is somewhat directed at least, but not controlled.

 

[OF&B]

According to the SAAMI drawings, the 280 Remington headspace is 2.100" min, 2.110" max
For the 280 Ackley Improved, SAAMI gives 2.140"" Min, 2.150" max. at the same 0.375" datum diameter.

That's Forty thousandth's difference, not fourteen. 14 is within the range of typical maximum allowed difference between cases and chambers and not worth hysterics.

A detail that is also omitted is the 280 Ackley is rated for 65,000 psi by SAAMI, and the 280 Remington is only rated at 60,000. If you wanted to make 280AI brass, 270 would be a better source and the usual conversion practices would need to be applied. Jammed bullets, false shoulders, COW, etc..

It looks like the neck-shoulder junction was moved from 2.1993" on the 280 Remington case to 2.1795" on the 280 AI case, so the bolt won't close on the Remington case in the AI chamber.

It appears that the AI "can still shoot parent case ammo" concept was deliberately lost when they decided to make brass for it. It should be the 280 Remsler, not Ackley.

 

[goodgorilla]

When you fire form the brass, is the ballistics for that round the same as a round using fire formed brass?

 

[gewehr]

When you fire form the brass, is the ballistics for that round the same as a round using fire formed brass?

No, typically it is 100-150 fps slower than a standard round, for example firing a 280 round in a 280 ackley chamber will be 100-150 fps slower than the speed it would be in a standard 280 remington

 

[Hookturnr]

I have read a ton of arguments on this topic over the last couple years. When I had my current 280AI chambered I also discussed this with my smith. From what I have gathered, all of this confusion is based on the SAAMI spec drawing dimensions having been taken from a different position than the Ackley drawing dimension location. In reality, there is no difference. Mine is chambered at SAAMI minmuim, fires nosler brass with nearly zero change in brass dimension. I have also run factory remington 280 rounds through the gun to fireform with zero issues...it just spits out a nice 280AI case. Get yourself a barrel, chamber it with the min. SAAMI reamer and throat it for 168VLD's and SMILE!

 

[goodgorilla]

No, typically it is 100-150 fps slower than a standard round, for example firing a 280 round in a 280 ackley chamber will be 100-150 fps slower than the speed it would be in a standard 280 remington

Can you be precise using the 280 in a 280 chamber? Does the velocity change around 50 fps between 280 shots, or is that just the velocity change between loads?

 

[M.rolen]

On the last 280 AI that I built it had great accuracy at the 100 yard line fire forming factory hornady 280 rem. But I dont think the velocity would be consistent enough while fire forming to be precise at long range. Just fire form, reload, then start your long range work.

 

[goodgorilla]

What do you use to fire form? Do you use less grain bullets and loads? Does the fire formed brass that you make perform the same as purchased AI brass? I'm thinking it would be cheaper to buy the fire formed brass considering you got to spend on the other cartridge components and barrel wear.

 

[nhm16]

On the last 280 AI that I built it had great accuracy at the 100 yard line fire forming factory hornady 280 rem. But I dont think the velocity would be consistent enough while fire forming to be precise at long range. Just fire form, reload, then start your long range work.

What do you use to fire form? Do you use less grain bullets and loads? Does the fire formed brass that you make perform the same as purchased AI brass? I'm thinking it would be cheaper to buy the fire formed brass considering you got to spend on the other cartridge components and barrel wear.

Fireforming is not a waste of barrel and bullets if you do it while shooting matches, etc. I shoot F-Open with a .284 Win. based wildcat called a 7mm Walker that is basically a .284 Shehane (another .284 based waildcat) with a 40 degree shoulder. Some of my highest scores were shot while fireforming brass. In fact on my current gun and barrel, I'm in the middle of fireforming ~500 pieces of brass for my new gun, and my scores have never been better at 1000yds.

I had previously fireformed by working up a fairly stiff load with the bullets seated firmly into the lands (0.015" or more).

This time around, I used the false shoulder method (neck Lapua 6.5-284 brass up to 7mm with an expander mandrel, trim, neck turn being sure to remove the donut at the neck-shoulder junction, expand neck up to .30cal, use FL die to partially neck the case back down and forming a false shoulder), so that I can fireform using a gentler load with the bullets jumped, on the theory that this lower initial pressure will be better for brass life.

 

[sandwarrior]

I have read a ton of arguments on this topic over the last couple years. When I had my current 280AI chambered I also discussed this with my smith. From what I have gathered, all of this confusion is based on the SAAMI spec drawing dimensions having been taken from a different position than the Ackley drawing dimension location. In reality, there is no difference. Mine is chambered at SAAMI minmuim, fires nosler brass with nearly zero change in brass dimension. I have also run factory remington 280 rounds through the gun to fireform with zero issues...it just spits out a nice 280AI case. Get yourself a barrel, chamber it with the min. SAAMI reamer and throat it for 168VLD's and SMILE!

This is correct. When I first posted I had not read the follow up article.

Suffice it to say:

The Rem 280 has a datum point on the shoulder. Even though the reloading manuals don't give that, they give the shoulder/neck junction of 2.199"

Ackley shortened the 2.199" neck/shoulder junction .004" to create an interference fit (even though reloading manuals give 2.175"....024" shorter than the parent case...datum point shown wrong?). This is the only way to maximize and evenly allow the case to expand. If you crushed down on the middle of the shoulder on a datum point, excess brass would flow up the neck. And, there would not be adequate brass to fill out the shoulder/body junction.

Fast forward to the SAAMI version. SAAMI standardized having a datum point on the shoulder, as it's easier to create an interference fit to make the round fit tightly in the chamber. So, they took the final (accurate) measurements of the fire-formed Ackley case and put the datum line on the shoulder .014" down from where you would see Ackleys' point of measure.

Now, trying to research this, none of the numbers matched up. All the reloading books show the Ackley .024" shorter than the standard .280 Rem case.

All I can say is I never had any issues using Nosler brass in my .280 Ackley rifle. When I get a wildcat round of any nature, I always check the brass that I'm using for interference fit somewhere at the top of the chamber.

 

[sandwarrior]

nhm16,

I'll agree with what you say about accuracy being tight while fire-forming. A tight headspace off a trued bolt is a pretty good start to accuracy. FWIW, one case that does this, that is not a wildcat, is the GP11 in a K31 (Swiss rifle from 1932-1957) The chamber in that rifle is cut bigger than the other chambers for some reason. Handle grit on cases? In any case a GP11 round is .440" at the shoulder while a fired case is .469". Typical of the Swiss, and their precision minds, The face being true perpendicular to the bore, allows this rifle to shoot as well as it does. Along with their little bullet secret. Suffice it to say there is a lot of room in that case.

As far as fireforming and saving barrel life, I would not worry about that using a faster powder/stiff load. The expansion of the case gives enough pressure buffer to ease life on the barrel. Also, if you don't use a stiff enough initial load the case won't fully fire-form. Thus, giving you tendencies for the brass to not remain true to the chamber it's fireformed in. I typically fireform with no slower than two powder speeds faster than my planned load. Say, I plan on using H4350. Then I form with H4895. You don't need to go max, but use a stout load. Just so the load quickly pushes the brass out to the far recesses of your chamber. Move it as much as you can while it's the softest. Each firing will harden it some.