Ackley Improving

MarinePMI

MarinePMI

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Minuteman
Jun 3, 2010
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#1
Interesting discussion on the Ackley improvement of cartridges during the latest podcast. I can't say I agree with all the things stated (like it being a 40* shoulder, since several of his cartridges were made with 30* shoulders too; e.g. 17AH).

Also, as I understand it from a buddy that apprenticed as a gunsmith under one of PO Ackley's protege's, the main reason for AI'ing a case at the time was two fold.

1. A limited number of factory chamberings at the time

2. A limited number of available powders (most were military surplus canister grade powders).

Ackley created the cartridge conversions so users could utilize an existing (albeit not optimal) chambering, and perform the conversion without sacrificing the factory barrel, and also so that more of the courser burn rate powders could be put in the case. Today we just change the powder, but back then, the limited variety of powder available was the powder available, so a change in the case was the only option for most, to increase performance.

With the plethora of chamberings available today, and the number of powders available to fine tune for a specific case's unique case capacity/bore capacity, I'd think the AI is just not really a viable thing today unless you just want an "AI" chambering. Too many other cases today are available that come close to upping case capacity of an "AI" case, and avoid feeding issues (which many with 40* shoulders suffer from). Granted, detachable magazines today allow less of a feeding issue, but it's still there.

At any rate, it was a good discussion (still listening to the final part of the podcast), but figured I'd chime in and maybe get some discussion going....
 
#2
Biggest asset of an AI is limiting case stretch. Second would be modifying the shoulder angle for the torching effect to the throat slowing down the erosion process. Using a standard case to run inside of 100fps to a magnum case with obviously less powder allows a few more reasons. The same advances in powder that improve the parent case also improve the AI version. 243 win doesn't run H1000 well. An improved 243 be it the Ai or comp match etc all can run H1000 a single base powder which provides much longer throat life. The straighter case also grips the chamber better to be able to run much higher pressure before similar to many modern cases. In a tactical situation the ai isn't optimum due to feeding. However in various target and hunting situations it can help to have much more stable brass that doesn't dimensionally change. Being able to put five instead of 2 or 3 in the box without giving up any ballistical advantage never sucks either
 
#3
The torching effect isn't driven just by the shoulder angle, but also the length of the neck. Case stretch is a valid argument, but really, how much stretch do we get when we properly set up our dies?

As to powder advances supporting increases in both cases, it's six in one hand, half dozen in the other IMHO. And brass is dimensionally stable once it has been formed/fired in your chamber.

I'm not saying AI'ing a case is bad. Just that it has very limited applicability in increasing performance these days.

But hey, if folks want an AI'ed case? Go for it. I went down the wildcat rabbit hole in spades as a younger shooter, and it was fun and enlightening. Many would learn a lot from the experience, and there are some cases where you have no choice but to go that route (lack of factory chamberings in the bore size/case size you desire for a given need). But those are far and few between these days. Most of the wildcats I played with now have a factory equivalent these days (17Mach IV = 17 Fireball, 17 Ackley Hornet = 17 Hornady Hornet, 20 Tactical= 204 Ruger, 300Whisper = 300 Blackout), so I no longer deal with the headaches of time, expense of forming dies and reduced barrel life from it. Some I still deal with, but they are easier cartridge conversions (9.3x57mm for example).

JMTCW...
 
#4
Some good points brought up I have to say I lean towards ubetchas view though.
With the addition of the ability to use the same Bolt face in certain situations too like 223ai without having to change to a ppc or 308 to jump to something a little peppier.

Also I would make the argument that so many of the new choices are un-needed in a lot of situations.
6.5 creedmoor always bless my mind since we had 260, but....
It took over.
More choice is always good though, pretty fortunate to have something to fill every niche.
 
#6
If you’re really into these type of conversions, I’d highly recommend finding copy of this. Well worth the expense, and shows much evidence that there really isn’t much new.
 
#8
The slowest powder that P.O. Ackley had available to him was 4831.

The reason the 40 degree shoulder became the standard was because that: A) It is where the point of diminishing returns on brass flow was reached. B) That was the shoulder angle that would clean up the shoulder of every existing factory round at the time.

The 40 degree shoulder actually builds pressure just a bit fast when compared to an optimal shoulder angle of 30 degrees.

Why 30 degrees? Because that is the maximum angle that you can get high pressure gas to follow a contour without excessive flow turbulence. This is why many suppressors use 30 degree cones in the baffle design.

The theory of the case gripping the chamber walls better is a myth. At 60K+ PSI, the brass is plastic. It does nothing to alleviate bolt thrust.

If you want to read more about this from the horses mouth get "Handbook for Shooters & Reloaders" Vol. 1&2 by P.O.Ackley.
 
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#9
Those books also have some (dated but) interesting reading on terminal ballistic performance. Like Hatcher's Notebook, Ackley's books should be required reading for those who do anything beyond normal reloading (drop powder, stuff bullet and bang).
 
#10
I cut my reloading teeth, so to speak, on the writings of men who pioneered before I was born. I collect works by the old guys like Warren Page, P.O. Ackley, Ken Waters, etc....as well as old reloading books that have some of thier articles.

Some of it has proven erroneous or incomplete in light of modern discoveries and better technology. Other parts have stood the test of time amazingly well. All of it interesting to me.
 
#11
I should actually amend one statement. At lower pressures, chamber gripping by the brass IS a thing (think pistol pressures). In fact, the Seecamp pistol uses an unusual method of delayed blow-back operation based on this.

A slight annular groove is cut in the chamber for the brass to expand into upon firing. This slows the case extraction just enough for the pistol to function correctly. When the brass is extracted, the bulge is ironed out of the case and looks fairly normal. You can just tell something is odd if you look at the wear patterns on the brass.
 
#13
You're not blocked, Diver had the same issue a while back. I'll have to see if I can figure out if it's a setting I need to change. PM inbound.
 
#14
IIRC, MP-5's are the same way; fluted chamber to cause the case to "stick" momentarily and retard extraction.

As to the books, we'll have to compare notes, as I have a lot of old/collectible books as well (Pope & Mann, Howe,, etc.). Even have a first addition "The Woodchuck Hunter"...
 
#15
MP5's do have a fluted chamber, but it is to aid extraction. The chamber pressure pushes the roller bearings into a recess that holds the action shut until pressure drops.
 
#16

You are correct, I wasn't quite awake yet when I posted my response. Thinking about it now, I recall them shearing rims off the cases until they fluted the chamber to aid in extraction.
 
#17
The 280 ai outsells the 280 and the 7rem mag. Rich Sherman's sherman short's have less body taper than the saum case with less volume and can run more powder without showing the same pressure signs. Ie case head expansion swipes heavy bolt life. At the same pressures it's out running the saum noticeably. Rich has done the same things with a 270 case for his long action rounds and runs velocities in excess of the 264 win mag, 3250 with a 150 matrix. He had a customer that is running the 195 berger at 2950 in a 7ss. That's where a saum runs the 180. They are seeing 2800fps in the 338 ss with the 250 berger. That's faster than the 338 win mag can and right with the 340 wby. At less than 3.0 coal. Another has the 300ss and has wacked 2 bucks in consecutive years over 1100yds delivered I believe a 225eldm north of 2900fps. Not ai per say but along the same principals of straighten and sharpen the case. He also adds neck length something the gibbs lacked.
I'm a fan of a few not all because there are many cases of just moving to a new case is better.
As much as I like the 243ai for my dog pounder, I think a 6xc with the 105 amax is a better option and you can substitute the 6 creed there if you wish.
Another way to look at it beyond need. One of my boss's is looking for a new boat. His 55'er will do it all in spades. His next one will just cost more money to look a little cooler doing the same thing.
 
#18
I went full tilt on the AI cases when I first started building my own rifles 15 or so years ago. I'll always have a soft spot for the 22-250 AI using heavier bullets, but mostly I just don't think fire forming is worth the hassle unless it's done in a prairie dog town. I'd rather have my rifles running the finalized load ASAP.

Can't say I've tried the 280 AI with off the shelf brass, though.
 
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