Home Forums Hunting & Shooting Custom Rifles & Wildcats 243 AI questions

Been digging up some new rifles ideas the last couple of week.

Ran up on a sako L579 in 243 that has been “Ackley Inproved”. As I understand it they neck down the cartridges to allow for more powder (hotter load) to it will have better speed.

Questions:

- is any work actually done to the action? I may build off of it down the road
-can it shoot factory loads if I get tired of reloading?
-would rebarreling take it back to a 243? Or another caliber if I chose ?

An “Ackley Improved” cartridge is identical to the parent cartridge except with reduced body taper and increased shoulder angle. At equal pressures there’s limited gain in performance and increased brass prep because fire forming is required.

An advantage of Ackley improved cartridges is reduced brass trimming.

All told I don’t have any rifles chambered with an Ackley chamber because it’s not worth the extra effort.

No work is done to the action.

Yes, you can shoot factory ammunition from an Ackley chamber. All “proper” Ackley chambers will chamber the parent cartridge ammunition. This will make Ackley brass. You could then reload the brass and it would match your chamber.

A rebarrel will revert back to the parent cartridge or any short action standard bolt face cartridge.

Some of the older/tapered cases (250Savage Improved, 257 Roberts Improved, 30-30AI) see a good increase, but the 243 has a modern case shape.

my buddy did a build on a sako action, he said they have a lot more flex to the action and aren't that great of a platform for custom builds especially those with very heavy barrels.

If I rebarrel it will be back to a regular 243 or possibly a 7mm08/260

Fire forming is no big deal, just shoot standard ammo, it will fire form to A.I. then resize neck and go on and reload, it's no big deal. Rio7

My opinion too. My 250ai is a laser with 85gr Barnes X bullets.

Your "buddy" is wrong.

If you look at the amount of steel on the bottom of the old Sako actions ... they are stiff.

You'll gain right at a 5% increase in powder capacity which translates to perhaps a 1.5% increase in velocity at same pressures. Assuming 3000 fps for the parent case that gives 45 fps more, hardly worth writing home about. Rate of throat erosion will be reduced by around 10% which is good considering the .243 eats throats. You will also rarely if ever trim cases. I trimmed a batch of cases right after fire forming and over 25 firings they never needed trimming again. When I finally tossed them at 25x they had only gained around .005-.006" in length.

Getting back to the velocity increase. Lots of AI shooters claim greatly increased velocities because they load to higher pressures. In the .243 I think that might be somewhat valid. The .243 shows a wider variation in pressures in a given string so it's max pressure was lowered some time ago. The 40 degree shoulder of the AI tames that bad habit so one could load back up to the original pressures. Doing that combined with the velocity increase provided by increased case capacity could net you maybe 75-100 fps more. That's just theoretical discussion which I wouldn't personally condone unless you know the pressure specs of the original loading, have very good pressure testing equipment and know how to use it.

But the increased throat life and lack of trimming are the main benefits for the .243 AI.



Now all that said, I've had two barrels so chambered and if you like to mess around with such things they're fun and something interesting to work with. I certainly learned some things as a hobbyist so they were worthwhile projects. If you just want practicality get a 6mm Creedmoor and be done with it.

Your buddy has no clue what he is talking about Sako is one of the better factory actions for a custom build, I have several including an L579 that the OP is asking about.
The 243AI gains you very little compared to other Ackley chamberings because you are mostly changing shoulder angle, the body has very little taper to start with.
Never really found the claim that Jim in Idaho makes of increased throat life to be valid in any of my Ackleys but less trimming for sure
As for the OP's last question, yes you can rebarrel it back to 243 or any cartridge you choose that has the mythical .473" bolt face, The L579 is a short action so you could go 22-250 to 308 and still use the magazine

An important consideration when rechambering from a standard to an Ackley chamber is the need to set the barrel back, usually a complete thread so the writing, sights, etc. are all facing up. If the Ackley reamer is run in until the old chamber is cleaned up there will be excessive headspace when firing factory ammunition. The go gauge becomes the no-go gauge & if a go gauge is required will be approx. .004" shorter than the standard go gauge.

I have to smile when people that have never owned one regurgitate what they've read or heard. I've worked extensively with 4 different Ackley chamberings & each one has been just a wee bit different. Two of them (257 Roberts & a 30-06) fireformed factory brass without a hitch. The 3rd one (338-06) even though chambered properly as noted above refused to do so, developing that bright ring at the web that tells us the base will soon separate from the body. Brass was successfully formed with 16 gr. of Unique, a case full of cornmeal & a wad of TP fired straight up into the air in the backyard. I dont know why, but it's how that rifle worked out. This chamber is a tad rough... bolt lift is fine but extraction isn't so good, so that could be part of the problem.

The 4th (22-250) was a trade-in & apparently just had the reamer run in to clean up the chamber (& then some) giving somewhere between .020 to .035" excess headspace. Brass was partially separating on the 1st firing, so now is expanded from .22 to .25 then resized in a standard 22-250 die with a secondary small shoulder to chamber very snugly & fired with a stiff standard 22-250 load. This one is not a true Ackley. It's an Ackley long maybe. Using Ackley dies kept way off the shellholder I'm just now retiring some 30 year old brass that was loaded 10 or more times (a 53 gr @ 3975 fps), that's finally age-splitting necks. Primers still fit snugly.

I like all of my Ackleys & run them on the warm side, because that's what they do best. If primer pockets stay tight for 4-5 (or more) firings it works for me if the accuracy is good.

Jeezus Fhuqk,you CLUELESS Droolers are a hoot! Hint. Congratulations?!?

On the presrcibed platform,I'd go Seex Kreedmire and at least 8" RPM. It's too trite in COAL,to make a 260/260AI or 7-08/7-08AI shine and likely outta room in 243/243AI(though certainly suffering a Retard Twist rate). Hint.

Rest fhuqking ASSURED that a 250AI with an 85gr of any flavor,is certainly no "laser",with the schit aero form and pedestrian velocity. Though in fairness a 224 Speedmire stoked with an 88 ELD and it's .585BC at 3200fps,most certainly is. You gals will haveta' pardon my shooting it all and then some. Hint.

There is no "extra" "effort" required with an Improved case. They utilize a like number of ram strokes to load,which will only come as a "surprise" to Drooling DUMB Fhuqks. Hint.

You Magnificently STUPID Fhuqks,never disappoint,by simply doing your best. Hint.

Bless your hearts for trying though.

Hint.

LAUGHING!............

What 'Stick said.

I have a 243 AI with a 8 twist and 350 formed and loaded brass, and it wasn't rocket science to form the brass.

I also agree that if I were to do it again, I'd just go 6mm Creedmoor.

I have shot the 243 AI since the mid 80's. Today, I would go the 6 Creed, and Stick is spot on. Get the toughest brass there is....pick. Spend some time on throat geometry design.

Many wonder what the 243 AI will do. I hunted coyotes with many 243 AI's. 70g Nosler ballistic tips at 3800 shooting tiny bug holes is normal, not the exception...zero freebore reamer left room in the Remington magazines, barrel set back at 1700 rounds if you use ball powder, otherwise, no.

I fire formed killing stuff, 70g Noslers at 3700.

Keith went through a whole sh#tload of barrels too.

As another post said, the chamber in that 243AI needs to be checked for headspace, as some gun mechanics would just run an Ackley reamer in without setting the barrel back to achieve correct (tighter) Ackley headspacing, at least with rimless case rounds. I’ve had a few Ackley rifles and enjoyed tinkering with them. It helped to have my own machinery (lathe). I have kept a favorite- Shilen barrel 250 AI, a favorite of mine.

The .243 AI rifle the OP bought was one I bought from a campfire member back in 2013. I went back through my records and this is what the original owner said about the rifle and the smith that did the work on it'

"Action is Sako's L579 and the barrel is a Sako sporter take-off re-chambered by Larry Cribbs of La Grande. Twist rate is 1-10, barrel length is approx. 23" muzzle to chamber, muzzle diameter is .640". Stock is a lightweight Brown Precision with a 14 1/4" length of pull and krylon earth color. Stock trigger, no sights."

Larry Cribbs competes in and builds rifles for NBRSA so he did a precise job on the barrel and the smithing. Whoever did the stock work was less talented but the rifle shot very well so I left it alone, I had never owned a Sako before so it scratched an "itch" for me. I reloaded for it and it came with 80 fireformed brass and 20 new cases and Redding 243 ai 40 degree dies. The OP doesn't reload and didn't want the dies or brass. I pretty much only shoot, .22, .223, and my Dad's rifle for hunting nowadays so I didn't use the rifle like I planned to and sold it. I would be surprised if the rifle doesn't do fine with factory ammunition before the OP eventually re-barrels it which he said was his longer range plan for it. That said, I have a .223 AI that was smithed by I,T, & D and with some of the re-manufactured ammo based on military brass the cases will show incipient case-head separation. It fire forms fine with factory new ammunition and I get good case life.

A big area of concern is remaining barrel life on that Sako... how many rounds were sent down that barrel.since barrel life on a 243 is relatively short. Another concern is twist rate.

Otherwise it might be better to invest in a 6 Creedmore.

I built a 243AI back in the day as well, great accuracy and fire forming was very accurate as well, so you could hunt while fireforming, win/win.
Now I would not build another one, just buy or build a 6mm Creedmoor and call it a day.

THIS!

You Nailed it SuperCub. That's about the best explanation I've heard. I have one AI and that's a .257 Roberts. I went with the .257 because for years I always heard the .257 showed good gains. However, one thing puzzles me. The .30-06 case is old fashion also, but the AIs I've read about it were minimul of any gain which leads me to believe there are other factors involved. Maybe amount of overbore has something to do with it.

My .257 shows gains with 115 grain bullets of up to 200-300 FPS over the standard .257 Roberts depending on propellant used. I've had the best gains with the 115 grain bullets using RL-17. However YMMV.

I have to add that my .257 AI has a 26" barrel which helps maximize gains.

How many of you, have shot out the barrel of a .243 A.I. 1x8 twist with 105 to 108 gr, bullets ?? Rio7

[quote=Filaman]


You Nailed it SuperCub. That's about the best explanation I've heard. I have one AI and that's a .257 Roberts. I went with the .257 because for years I always heard the .257 showed good gains. However, one thing puzzles me. The .30-06 case is old fashion also, but the AIs I've read about it were minimul of any gain which leads me to believe there are other factors involved. Maybe amount of overbore has something to do with it.

Re: 30-06 Imp.: 'Tis a confused mess of opinion, preconceived bias, or hearsay, mixed with maybe overly judicious handloading & a low SAAMI pressure for the old 06. Most of my data is from the early '90s with IMR4350, WW brass, & WLRs, but have safely reached 3300fps with 150s, 3200fps with 165s, & a tad over 3000fps with 180s with reasonably good accuracy (all either Nosler Solid Base or Ballistic Tip) in my 30-06 Ackley. It has a 26" barrel. Fully formed cases hold c.10% more water than standard 06. Temps were mostly around 75*, but there were some 30* days in there as well. That's knockin' on, but not quite, 300 H&H velocities. I also started development with RL19 & 150s with slightly better accuracy stopping about 100fps less (max pressure) than the 4350 loads. RL19 peaked out before 4350 with 165s & 180s even sooner. Never did get around to trying RL22 back then. The brass all lasted for 5 or more reloads & some is still loaded in MTM boxes ready to go if the necks dont split after 30 years. Will probably seat the bullets a few thou deeper to break the weld if there is one.

Using Sierra VI data, I recently tried some RL17 matching their speeds rather closely in some of these same old cases. I am curious what pressure Sierra held their loads to as they stop at 2900fps for the 180s in the Ackley, but also show 2900 as max velocity for the standard 06 while showing only a small gain for 150s & 165s with the Ackley. I may continue ever so slowly upward with these but will likely just stick with what is already known to work.

I’m rebarreling my rock 1-8” twist 243 after approx 1500 rounds. Vast majority of the mileage was firing 105 bthp using RL17.

That's the best by far I've ever heard about the 06 AI. With performance like that, who needs a magnum?

woodson, Must be a lousy barrel I have 3 .243A.I. with over 4000 rnds down the tube on each one, and all will shoot dime sized group at 100 yrds, hope you get a better barrel this time. Rio7

The internet strikes again....

I can pee farther than you can.

Ordered another Rock barrel. I don’t feel as though 1500 rounds is unreasonable out of a 243. Grats if you’re getting 4K+ out of your AIs.

I've got 2,300 rds on a 6 Dasher that is giving up the ghost.

H1000 Rio?

Whose bbl's?

AA2700 has one of the coolest heat index's of all powders. We shot the AI on p. dog towns, hot and heavy. About .070 freebore growth in 1700 rounds was normal, but cut off 3/4-1.5" and you are into new barrel...not so with many other powders.

I bought one of the cheap digital borescopes off amazon, thing works amazingly well. Good investment if anyone thought that a useful borescope wasn’t out of their price point.

Higginez, my barrels are 2 Wilson 1 Proof research, Bullets 105 Scenar OR 107 SMK, Powder Retumbo, many people are suprised I use Retumbo, but I get 3050 FPS out of 22" barrel and dime size groups. RIO7

before you build a 243 AI

take a look at the 6XC.........

same performance but much less powder........

dies & brass are easy too


https://www.accurateshooter.com/cartridge-guides/6xc/

tikkanut, There are more 6mm chambers than you can shake a stick at and some are very good shooters, but I will stick with the .243 based round, easy to fire form, very accurate you can find ammo almost anywhere if for some reason you run out of reloads, the 6 creed, ain't bad at all, again if you can find ammo anywhere, how much powder a round burns means nothing to me if i couldn't afford to shoot the guns i do and reload for I would take up knitting' Rio7

Rio7,

.243 speeds with slow powders is not really same/same and certainly not an indication of what great barrels you have.

Have a great 4th of July

One could say that in itself is a success. I have shot out more 243 barrels than all others combined at 243 velocities.

Last thing I would want in a p/dog patch would be a 243...let alone an 243 AI

Even a heavy barrel....noise/recoil/heat.....

Many better 6mm choices as even you mentioned

6BR non repeater....30-31 grs....my ole fav the 6XC...37-38 grs

Oh....I don't buy store bought ammo so I don't worry about running out

I have two .243 AI Rem 700 SA rifles, one sporter contour and one Varmint contour. These are factory barrels re-chambered to AI before the 6XC or the 6 Creedmoor existed. I also have a 6mm AI re-chambered factory 6 mm sporter contour barrel on a Rem 700 long action and a 6 Creedmoor Lilja barrel on a Rem 700 SA. I did the AI conversions to eliminate trimming and change the tendency of the .243 to erode throats. Been happy with the .243 AI chambers, but I really like my 6mm AI compared to the .243 AI's , but today, I would do either the 6 Creedmoor or 6XC. My 6mm AI is incredibly accurate and regularly shoots to 800 to 1000 yards on gongs and prairie dogs. My 6 Creedmoor does similarly. Personally, I think there are currently better options than the .243 or .243 AI.

If I was going to build an AI for this caliber, I would do a 6mm Rem AI. Might as well get a meaningful increase.

If you are going to do that, why not a 6x284?

Have shot 6-284 a lot. Probably does not outperform a 243 ai by much although with a lot more recoil noise and powder. Action length might depend on bullet and seating depth. Brass must be formed in a two step process from 284 winchester or one step with 6.5x284.

Back to the original question. If the rifle is priced well I would get it. Have a look with a bore scope first. If dies come with it then better still. If you want to shoot 243 for awhile you will loose only around 40-50 fps in most cases.

Target shooters especially with hot or double based powders like R17 or VV 560 and running heavy VLDs at maximum velocity will loose target grade accuracy in as few as 1,000 - 2,000 rounds. Hunting accuracy could almost triple that.
Only if you did a lot of varmint hunting or target shooting would you burn out the barrel in short order.

So updating here.....original pick up was a Sako L579 forester 243ai

Sold the older aftermarket stock that was included and replaced it with a Boyd’s custom shop hardwood stock cut for this action.

Barrel was pretty used up...replacing with a fluted .284 Douglas barrel in 7mm08.

Dropping in a Timney......at cerokote now and should have in a few weeks

She will wear a Swaro 3-12x50 and kill a lot of things.

All of this^^^

The throat of my 243 AI with a SS barrel is eroding a LOT slower than other 243's I have. That's why I chose to AI a new factory SS 243 bbl, rather than expecting any significant increase in velocity. If I had to do it again I would give the 6mm Creed a hard look.