Could you explain the mechanics of why a barrel setback is necessary after an AI reamer has been run in a factory barrel?
Thanks
Jim

If the headspace is not on a rim or Belt, you have to set back...

An Ackley go gauge is shorter than a non-Ackley because the headspace moves from the shoulder to the should neck junction.
and it needs to be tight... so you can still fire non-Ackley improved in the rifle.

I.E. you are blowing Out the should when the AI reamer removes the metal, which can make too much headspace, or the thing may not even fire non ackley brass right.
This picture helps.



You can read the whole page here.
https://ackleyimproved.com/headspace-and-ackley-improved-cartridges/

I'm not a gunwriter, but I believe there is a recent thread on this topic. Search for it.

The bottom line is that the improved reamer must be run further into the existing chamber in order to "clean it up" . The barrel must then be set back a bit in order to do this and still maintain correct headspace.

Some unscrupulous gunsmiths simply run the reamer into the chamber without removing the barrel from the action in order to save time. You end up with a chamber that is longer than specifications, and you have your own unique improved chambering. When this is done, the bolt will close on a no-go gauge, and headspace is too long. I have gone through this with two Ackley Improved chambers and such gunsmiths.

Notice the base to the neck shoulder junction distance...

Have seen more than one AI rechamber job fail to fire factory ammo--and even when "set back" they can fail to fire brass previously-fired "standard" brass, because it lacks the slight "crush-fire" radius at the juncture of neck and shoulder.

Just go buy the cartridge whose performance you are trying to attain and save the grief. JMO

I'm attempting to find how to rechamber a 6.5X55 TC Encore barrel in 6.5X55AI. According to the material Spotshooter has provided https://ackleyimproved.com/headspace-and-ackley-improved-cartridges/ it's not viable. A "setback" would necessitate a removal of the barrel mounting lug and rewelding it. Have a growing suspicion that it (6.5X55 to 6.5X55 AI) with a TC Encore barrel has been done.

Well, yeah....

A related factor is that a lot of newer cartridges are ALREADY essentially AIs, with nearly parallel body lines and steep-angle shoulders.

If you want a 40 degree shoulder on a 6.5x55 TC where you can't set the barrel back you just have to build 6.5x55 Improved, not an Ackley Improved. To form brass you have to open the neck to a larger size and the take it back to 6.5 and form a false shoulder for the case to headspace on. After that you can just use a set of 6.5x55 AI dies just being sure you you set up the dies so they don't push the shoulder back too far, There are a lot of improved cartridges that don't use a crush fit to be able to shoot factory rounds. Off the top of my hat the Gibbs line of wildcats come to mind.

Rug,

You can get the appropriate headspace guages to figure out if it’s too deep.

If it is - Blueberry or EABCO barrel works could fix it for you.. by shaving some off the face of the barrel and moving the lug forward a few thousands... but first I’d do the gauge testing to see how far forward it is.
** remember 10 thousands is the max headspace you’d want, so you are probably a bit longer than you might want it but not to 10 if someone just ran a AI reamer in the standard chamber ... that is unless they moved the neck shoulder junction forward much.. Frankly when cutting a chamber you almost can’t feel a thousands or so unless you know what you are looking for and what you are doing, it’s the slightest of cuts.


OR

You can just not shoot standard brass in it and deal with the slightly longer head space by by neck sizing, and only bumping the shoulder...

Can you also load long, into rifling to hold the standard case against to blow of the firing pin to fire form AI cases?

That’s a question, not a statement.......

Blacktail53,

You can, but whether it works correctly or not depends on how firmly the case neck holds the bullet, and how hard the firing pin whacks the primer. Generally find it much better to have the chamber correctly cut for a crush fit on new brass, or to neck up and then neck down again to get a crush fit.

These days, however, I find the easiest solution is to use a factory round that produces the desired ballistics. There are so many out there these days, especially those with steeper shoulders to begin with, that I really don't see any point in fooling with "improved" cases.

I'll throw this visualization into the fray. I drew this up in AutoCAD. The Ackley Improved Dimensions are from Ken Howell's book and are based on dimensions from the Speer No. 4 Manual. I believe this was before SAAMI standardization. If you don't set the barrel back you will end up with a fire-formed cased that has two shoulder angles (ask me how I know).

Don't know about this one but years ago, I had a 7x30 waters TC barrel redone by JDJ and turned into a 7x30 JDJ. New dies and the whole nine yards were required for the new chambering. It was supposed to be the greatest thing sense slice bread. I had to send the barrel back 3 times because it would not fire or chamber factory 7x30 waters rounds. After all the work and money spent, I got a massive increase in speed of 7 FPS over the factory rounds!

I cut my losses and sold everything.

Thanks, John......and I whole heartedly agree.

I’m not convinced that there’s much reason to AI anything these days, unless you just want to...
Instead of chasing velocity to flatten trajectory, one can just spin a turret now days.
Of course there’s other reasons to go AI, if one wants.
I’ll spend the money on scopes and components instead.
But that’s just my take, and everyone is entitled to their own.....😎

Less case trimming, but don't let that slow your roll.


The 7x30 Waters makes zero sense, since it headspaces on the rim.

I was thinking case stretch, but with a 25° shoulder he's in good standing with most standard cartridges.

John
My thinking is that concerning rifles you forget very little and you probably forgot more about rifles in your sleep last night than I'll ever know. I highly respect your knowledge.

What I'm looking for is not necessarily what little I would gain velocity wise. The 6.5/284 would be a viable consideration. Or several others. I have a TC Custom Shop 26" barrel in 6.5X55. Loaded tight it will get to 3100 with 120 gr TTSX. It's fine as is. I'm looking to do some experimenting. I've had wildcats and AI rifles. Realizing not much is gained by going to Ai except maybe decreasing case stretch which the 6.5X55 is plenty capable of.
I'm looking at the hobby thing. I enjoy changing things, the puttering required to load for the AI, running the changed things across the chronograph, seeing how it touches the target and the satisfaction of using it on game. I'm looking at the hobby thing, thus the questions. What I have to gain is the FUN and challenges of doing it.
I greatly appreciate the input from all here. Sure is a pleasure to learn things. Also appreciate the PMs that came my way about this issue.
Thanks
Jim

And a lot of the newer rounds have 30-35 degree shoulders.

Hey John.!


I think it's great to finally have those newer cartridges with accompanying angles since we all know the earlier ones never worked on game or targets...especially the Swede.😁

My last $.02 and then I’m broke.......
I’ve owned both Ackley handbooks since forever and schemed and dreamed of personalizing several of my own rifles. Three thoughts have always kept my money in my pocket....

Initial cost/setup/dies/etc....
resale, if I decide to move it....
and inheritance- neither of my sons reload or are very interested in hunting. Any AI’d firearm I left them would be an albatross.....

I’m better off to spend the money on a hunt somewhere.

Good points.

My perspective comes from owning or testing rifles chambered in some of those exotic rounds, including improved rounds such as the .22 K-Hornet, and several "Ackley Improveds," (even though Ackley himself did not include some of them in his books) including the .223 Remington, .257 Roberts, 7mm-08 Remington, .280 Remington and .35 Whelen. What I found is that none of them made any noticeable difference in ballistics, when their "parent rounds" were loaded to the same sort of pressures. Oh, you could sometimes see another 100 fps on a chronograph, but there was zip difference in the field, even before we started twisting turrets.

The only difference I could actually see was less case stretch, but as noted earlier that advantage pretty much disappeared as newer cartridges started featuring steeper shoulders.

Many years ago I asked Vern and Arnold Juenke why they used a 45 degree shoulder for their Saturn Custom line. They both said that the high pressures and velocities stretch cases, and case life was the real consideration. Hype and competing with Roy Weatherby's marketing was the "lure" pulling in buyers. Saturns were the king of hyper velocity then. The barrels and chambers had a long jump and slow twist rates to achieve the velocities they claimed, and they were honest figures. I owned a 25-270 ICL Ram that I used to take my desert bighorn and had a sweet 7X57 ICL Tortilla for a while. I replaced it with an HVA 7X57 AI my friend the pawnbroker sold me for a song; it has a faster twist, and I like 150-160 gr bullets in a 7mm.

Case life for those who blue-pill is the only honest rationalization for "improving" old standards. Back when the 300 H&H was a hot item the ICL/AI/Weatherby shoulders made sense.

Heh... the Ackley Imp. debate continues off topic, yet again, from the original post.

While we're throwing a couple of pennies around, here's mine.

In another life & time I owned & operated a gunshop evenings & weekends, doing gunshows once or twice a month. I picked up a nicely done, but really ugly custom 257 Ackley on a Mauser action in a fancy '60s style really shiny stock with exaggerated rollover cheekpiece, whiteline contrasting forend, swollen pistol grip, etc. for a little more than the cost of an action at a show. At least the bluing was nice. I always thoroughly cleaned & test fired used guns before selling them.
A. to see if they were keepers
B. to be sure there was nothing wrong with them.
The 257 was fun to mess around with & I even bought dies for it. This was B.C. (before chronograph), so no idea of the true speeds, but accuracy was pretty decent at or near full throttle. Someone else wanted it much more than I did so it went DTFR. Buy low, sell high is a good thing if both parties are happy. Besides, it was an eyesore.

At another show a few years later I got, along with some cash, a factory barreled 700V & a 26" Douglas re-barreled Ruger 77 both Ackleyed in 22-250 & 30-06 respectively in a trade for one decent used Remington 700 BDL in 308. There were problems with both other than terribly copper fouled bores, the headspace being GROSSLY excessive in the 22-250 & the '06 just didn't shoot very well. Adapting my loading procedure & some experimenting turned the 22-250 into a 1/4' gun at unheard of velocities this side of a Jaybird or a CHeetah. The '06 came alive as well after removing all the glass bedding material from places it didn't belong (inside the trigger mechanism, etc.). Dies & brass came with both guns, so there's that too. This was all early 80s to mid 90s so there wasn't all that much new & exciting other than 35 Whelen in a factory rifle happening. I decided to rebarrel a Stainless Stalker to 338-06. The 'smith who took on the job wanted to split the cost of the reamer & since the other Ackleys had turned out so well I opted for a 40* 338-06. Maybe a 100 to 150 fps more with 210 Partitions while back then dies for the standard or the Ackley 338-06 were the same price, so no extra cost. The 280 Rem seemed like another good future Ackley project at the time, & maybe even more so now that Nosler has since made it legitimate.

I still have all three. They're paid for. They work very well (338 is a liitle funny). Brass lasts a long time even at the speeds I load them to (Why drive a hotrod in 2nd gear?). I like them, & wont really care too much if the calibers inconvenience whoever inherits them if I'm dead. I'm unsure about spending a pile of $$ to build a new Ackley today, but I think Douglas or your local gunsmith may be affordable. There's no reason to be afraid of buying a used one either, especially if dies are included in the sale. Think of it as an adventure... & it ain't yet another Creedmoor or SAULSD. What's with acronyms for everything these days?

Blacktail,

Like John said this is a viable method, provided you use something like the lee crimp die to make sure the bullets stay put.

If it were my rifle with this issue and I decided NOT to set the barrel back, knowing that crimping & jamming into the lands can raise pressure, I would use a lower powder charge load to fire form the brass into the extended AI range, and then go from there with reloading based on bumping back the shoulder.

Once it’s formed to the chamber as long as you don’t reset the shoulder it would be fine... just bump the shoulder vs full sizing it.

Although, Given I’m a gunsmith I’d reset the barrel anyway...

I’m still liking my .300 Holland & Holland Improved......aka .300 Weatherby and it’s little 7mm brother and a 3rd cousin twice removed .35 Whelen. Happy Trails

^^^^^^
Do this and you have no problems.

I


Spotshooter. I agree.

My old .270 had excessive head space and I didn’t know it. Not until I loaned it and It wouldn’t reliably fire factor ammo. I had no idea, since I just partial sized cases from day one and never had an issue.
I had the head space corrected by Mike Harris and had a heck of a time chambering my left over reloads.
The barrel stamping showed that very little movement was involved in getting it back to specs.
The factory cases in the long chamber would show very slight firing pin strikes, as it just pushed the case ahead.
Making .270 cases from new 30-06 brass would always leave a small donut that gave a firm head space, that would iron out upon firing. All this in a 700..... a controlled feed action probably would have held the case to fire and I’d have never know there was a problem.......