Home Forums Hunting & Shooting Custom Rifles & Wildcats The Ackley Chamber

What is the consensus view of an Ackley chamber? I mean what is it? To me it is a chamber that is increased in diameter(less taper) and shouldered to accept factory loads safely (same headspace dimension) and has a forty degree shoulder.

There are dozens of other improved chambers but am Ackley must be as above right? If not isn't someone elses version.

The minimum taper may be common in improved cartridges but Ackley and std chambers use the same headspace gage and the shoulder is forty degrees. Yes? No?

The headspace IS NOT the same on a rimless cartridge. The standard round in the parent chamber headspaces on a datum line whereas the standard round in the improved chamber headspaces at the neck/shoulder junction before fireforming. A standard go-gauge should not chamber in an improved gun. Ackley's Handbook has a chapter devoted to the subject. Hill Country Rifles built a .280IMP for me with excessive headspace because they didn't understand the concept and it would not form cases properly and had to be set back by another smith because they wouldn't fix it.

In a rimmed or belted round the headspace gauges are the same.

The Ackley versions have almost straight taper on the case walls and a 40* shoulder.The chamber should be cut so as to be a crush fit on the parent case for fire forming.As stated above a 257 go gage should not work in a 257Ackley chamber.If you want to build an Ackley go with someone that knows what they're doing.Ray Montgomery in Colorado is one of the best. powdr

My rimless AI cartridges work with standard ammo just fine and that is one of the differenes between an improved cartridge and a wildcat i.e. the ability to use a standard cartridge in the improved chamber. Example, a properly fitted and chambered 280AI can use normal 280 ammo but if you fired a regular 280 round in a 280 Gibbs or Hawk you would have serious headspace problems, if the rifle even fired the ammo. The Gibbs and Hawk versions (others as well) are true wildcat 284/06 type rounds.

Sortakinda same issue, you ought to see what I am getting for speeds in my 348AI.... Fun, fun,fun!

Many rifles are succesfully AI'ed by simply pushing an AI reamer into a standard chamber without even removing the barrel or fiddleing with the setback. BTDT.

"Many chambers have been successfully AI'd......"

Unless they are rimmed cases, they are all wrong!!!!!

Doc is right if you plan on firing factory rounds in a AI chamber, you need that crush on the brass to hold it against the bolt face.

If however, you are starting from scratch, and understand what's going on, you can live with the added .004" of headspace very easily. You must do something to keep the brass firmly against the bolt when fireforming. A long seated bullet hard into the lands can work. Perhaps a better way is to size the brass up one caliber, then resize a little at a time until you get the same crush fit in the chamber. You also have to properly adjust your sizing die so you aren't pushing back the shoulder excessively.

There are a lot of ways to form brass, but it's not for the inexperienced.

Doc can you explain why the barrel can not just be re reamed? I am new to the AI scene and have been told a 223 ai can be made by re-reaming a 223 rem barrel without cutting it back. thanks

You may have been told it because lots of people believe it. The correct way is to shorten the chamber prior to cutting the new AI chamber. Failure to do so can result in too much headspace when firing factory rounds. 7mmfreak's explanation is more thorough and correct. The factory go headspace gauge should not fit in a properly cut AI.

OK, I looked at piece of 223 AI and 223 Remington brass and see how if you did not re-headspace that could be an issue. I guess were I got confused is I was thinking of a savage barrel where if I am correct you would not need to cut back but just screw in farther.

Of the 14 or so Savage and Rem 223 barrels that I have converted to 223 AI, only two had to have the barrels set back.

After measuring the boltheads, etc, etc, etc...and doing the final calculations, that is where they ended up.

A lot of variables exist when reaming a 223 to a 223 AI chamber. If the original 223 chamber has a sloppy cut or is on the big side of spec, you are better off lopping a little off.

Not too many variables exist. The juncture of the neck and shoulder is where it is. If said juncture is .004" inches short, as it should be in a proper AI chamber,factory ammunition would be a crush fit in the standard chamber. If factory brass was not a crush fit in the standard chamber,the same chamber, when re-cut to AI configuration, will be too long unless the barrel is set back. Like it or not, this is fact.
Now, the juncture of the neck and shoulder will vary according to neck diameter. For example: If we cut an improved chamber with a tight neck so that new brass headspaces correctly, all will be well. If we then decide to re-cut the neck to standard specs,headspace (or more properly, head clearance) will be too great. If we were to establish a headspace figure at a given datum point, the figure would be different for chambers with different neck diameters.
With the standardization of the 280AI cartridge,I would assume we now have a measurement to a datum line. Whether or not this is compatible with the fireforming of factory 280 brass, I can't say.
Headspace gauges for the AI cartridges have been, up until now, standard "go" gauges shortened by .004".
Interestingly enough, Ackley apparently made a mistake in his drawings of the 30/06 AI chamber. Rather than showing the AI chamber as being .004" short in the distance to the neck/shoulder juncture, he showed it as being .004" short to the datum line and all other dimensions were based on this figure. As a result, the neck shoulder jucture was roughly .030" too short. When a chamber is cut to proper AI specs to allow the fireforming of factory brass, the neck is too long. At least brass trimming will never be required! Apparently, nobody noticed this until just a few years back and all reamers were ground with an excessively long neck and continue to be made this way since nobody wants to change.
With a properly cut AI chamber, new brass will chamber with no great difficulty but with a definite "feel".
By the way, because the factory brass is made based on the distance to the datum line and not to the neck/shoulder juncture, one make of brass may work fine while another may not.
Many prefer to fireform using blank loads with or without a filler of some sort (Cream of Wheat seems popular. I imagine oat bran would work nearly as well. Even inedible products such as toilet paper, work out fine!)When fireforming with loaded cartridges, light loads are not a good idea. They will almost always produce a case which is too short. A good, snappy load is best.
There are other fireforming techniques and pitfalls which I won't go into here but, in general, a properly cut AI chamber should produce properly dimensioned AI brass with little difficulty. GD

Powdr hit the nail on the head.

+1
Right on!

I think its important to remember here too that one of the very distinct advantages of the Ackley-ized chamber is the ability to fire factory ammo. If you don't set back the existing chamber you can't do that, and therefore lose this important advantage. You may have a workable wildcat, but it ain't a true Ackley.

I have a 257 AI built on a CZ Mauser action and it shoots the lights out. A huge advantage that I've just discovered after testing out different bullet weights at different levels of intensity is that POI is w/in 6" on just about every load I put through it.

That is to say that I recently zeroed it with a load it loves (50.5 gr IMR-4350, Speer 100 gr HP, 3320 fps) and found that another load yeilding about 3500 fps from a 75 gr Vmax using H-380 hits 3" low, same as a Winchester 117 gr PP factory load while yet another using 117 gr RN Interlocks and IMR-4831 hits 3" high.

With this rifle I can travel on a hunt and if I somehow get separated from my ammo I'll still know that POI will be close enough for quick adjustment on a range.

I love my Ackley!