Lately I've been thinking rechambering my Mauser custom to .243 Ackley Improved might be interesteing. The rifle is great as is, but I like to tinker and its cheap/easy to go AI.

Who is shooting a .243AI? How much gain did you see over the standard .243 Win? Would you opt to do it again?

You don't gain a ton of velocity as you only get about a 5% increase in case capacity which with the 4 to 1 rule figures out to about a 1.5% increase in potential velocity at same pressures. At a nominal 3000 fps for the parent case that's only 45 fps more and most loads for the .243 with 100 grain bullets are held to the 2900 fps area.

But it tames the propensity for wider pressure variations in a given string. Because of that little quirk in the standard .243, factory velocities have been lowered over the years as the max average pressure was lowered. Now this is just my subjective opinion, but what I believe the AI does is let you get back up to the original listed velocities of the .243 quite safely. A lot of claims for AI velocity gains are due to loading them to higher pressure, but in this case I think it's an allowable goal as long as you don't go hog wild about it.

What you also get is a slight decrease in the rate of throat erosion, but even that's only about 10% less by my one and only experiment with a standard .243 in a new barrel and an AI in the same barrel, measuring after the same number of rounds fired. I'd have to go dig out my actual numbers somewhere, but 600 rounds of .243 in a new barrel increased distance to lands by X, AI'ing that barrel and then firing 600 more rounds increased distance to lands by .9X.

Plus, it lessens case trimming but I've found that neck sizing only lessens that a lot in any chambering.

After having gone the AI route in a couple of rounds (and two separate .243 AI's) I'm no longer an AI fanatic but IMO it's certainly worthwhile in this particular chambering.

I've done the AI with my .223, and I couldn't ask for better results. I am not looking for huge gains in speed, but little never more hurts.
If I can a bit more FPS, less hassle with trimming, and also a fresh throat in the process I would be happy.

Thanks.

If going with a new barrel, sure, improve it. But not worth the time,money, and hassle on something already set up.

Take some of the cash you would have used on the rechamber, and buy a WFT trimmer. Case trimming issues solved.

Think of a 24" SAAMI 243 as performing similar to a 22" 243 AI.

If you want it, go for it. It's fun and worthwhile if you like getting a bit more speed, dislike trimming brass, and think it looks cool

I don't shoot heavier than 70's in mine. But an AI shoots 70's as fast as the std. 243 shoots 60's......or faster.

That's just 'too correct' thinking!
It's akin to something I read a LONG TIME AGO, in a real, paper magazine about HUNTING.
The guy said, "If a 24" bbl. is too long, and you think you need a 22" bbl., HELL! STEP BACK TWO INCHES!"

NO KIDDING!~Really?!
That's just TOO LOGICAL!

Powder UP.
Step BACK!
PULL THE TRIGGER ON THAT CRITTER!

Now, we're talkin'.

Barrel twist would play a huge role in my decision. If your tube is twisted fast then I would go for it. The AI shines with the heavier weight bullets.

Plus it is a really cool looking round, LOL

The rifle does well already with heavies. I am leaning toward towards going for it. It's cheap to do, and I guess I just don't see any real drawbacks.

If you a screwing on a new barrel then Id Ackley it but if you are just going to Ackley your original barrel I wouldn't waste the money (this coming from a guy who wastes money doing meaningless real world things to my rifles).

While the 243 improved may offer some gain you will have a real nightmare getting it to feed well in any Mauser action!!!

Yessir, Ackley improved feeding in Mauser actions can be less than stellar, to say the least.

Hmmm glad that was brought up. I hadn't even thought about that.
Back to the drawing board...

I don't believe going to the Ackley Improved gives you any real or large advantage.

In fact, IMHO, it is a disadvantage in many respects.

Stick with the standard cartridge.

One other thought for AI..you have to fireform the cases one way or another and that takes time and effort regardless of which you way you fireform. I have several AIs and I am slowly inching away from them. If I want a particular bullet to go faster I step up to the next larger cartridge...

Bill

I've never seen fireforming as a negative. Actually I kind of enjoy it. I just spent a good portion of a Saturday morning out in the desert banging gongs and forming brass.

After so many AI posts, hard to believe some people still think this way and just don't know any better.

Not following your post at all.

THOMASMAGNUM, this may not help much but I do have 243AI. It has 1/10 twist Hart barrel @ 27" something I could use for antelope etc.

My first AI I used existing barrel and had data from that and I did get increase velocity over that data with the AI. I think you mention same going from 223 to 223AI.

I would think your going to get some increase in velocity but how much couldn't say. I try and stay out of comparing reason I have 243 that got new 60's and latest barrel is 24" and don't load same bullet/powder and I also have 222AI and 222 I put different twist in those.

Well good luck

This was my first thought as well.

While well short of anything I'd characterize as "nightmare" my 257 AI took some tweaking even though the standard Bob case fed smoothly.

If it were me and I had a well functioning Mauser in 243 Win but wanted to play w/ the AI I'd get a Ruger American & have Dave @ IT&D punch it.

I am with you though. Never for the life of me could figure out why fire forming for a hunting rifle could be anything but a pure pleasure. I just received a 280 AI (my 2nd AI ever and certainly not my last) and am looking forward to crafting an accurate fire forming load, setting up the steel in a local hayfield, and keepin it swinging several Saturdays in a row this summer in preparation for the main event in Wyoming this fall!

I've not fed anything shorter than a 7x57 AI into a mauser, so cannot speak to the 08 case.

The 7x57, 280AI and 06AI all fed beautifully into mausers here--may have a bit more to do with the Smithy...

Jim Kobe, on this board, did the fix for me on a 30-06AI with a full-length box and throat, and it feeds just as well as any standard.

I hadn't even thought about the complication of CRF feeding and AI, but I can clearly see it where it woudl be an issue. The rifle is a gem and feeds perfectly now. I don't want to chance screwing it up. I will hold off on the .243AI for now, but I might think about doing one later.
I DO however have another AI project the pipeline. I have a Ruger tang safety that will getting barreled and chambered to .280AI later this summer. It should be a neat one when its finished I think.

My .223AI is just as accurate with fireforming loads as it is with formed AI loads. I've hunted, shot gongs, busted rocks, etc. with firefroming loads. Any trigger time is worthwhile to me, and I certainly wouldn't call it a chore.

I built a 257 Roberts Ackley Improved in 2002 on a VZ24 Mauser action with a Lothar Walther light varmint chrome moly barrel.

I built a 257 Roberts Ackley Improved rimmed in 2012 in a Uberti clone of a Win 1885 falling block with a Shilen Select match #3 taper stainless barrel.

I am an amateur gunsmith, only building rifles for myself. I have ~ 2 dozen reamers and only one is an Ackley. I am not buying any more Ackley reamers, as the fire forming is too much trouble.

If you want a 50-75 fps gain (at most without getting stupid in your loading), an AI'd cartridge based on the '08 case is a good option to consider rather than going to a long action or a wsm. I've had a 7-08AI for about 7 or 8 yrs and it's the wifes gun and she loves it. In that amount of time, been able to build up plenty of fire-formed brass, and I'll bet I've trimmed less than a dozen cases. Pros and cons. No feeding issues in a Rem 700.