260 Ackley Improved 40 degree

[zerobarrier]

Ok this is probably a stupid question but I do not understand the whole Ackely Improved thing. I never owned one or knew anyone who did. I have the opportunity to purchase a Rem 700 chambered in this with a 24" m24 match barrel.

What is the difference between the Ackely and regular 260? What different reloading steps do I have to take?

I know I need special dies. Redding makes a 3 die set for 260 ackely improved 40 degree. Other than that do I need anything else? Do I just use regular 260 brass and use the FL sizer that comes in the Redding set?

Any info on this would be helpful.
Thanks

 

[Cemetery21]

You could probably Google up some pictures of the differences in the shape of the brass after being fire-formed in an Ackley chamber. Basically, most of the taper in the sidewalls is blown out and the shoulder angle is sharper, from 30 something degrees to 40 degrees. The result is a little more powder capacity.
I'm not familiar with the 260, but other Ackleys gain 8-10 percent more powder capacity. Also, the design is such that normal caliber brass will chamber and fire normally, resulting in a "blown-out" case that fits the Ackley chamber. In my experience, fireforming normal loads got excellent accuracy, so you are not wasting components to form the brass. Then, after the first firing, the brass is now "Ackley" and you will need those specific dies. For a bolt gun, you should not need to full-length size until after the 3rd or 4th firing. Just neck size when reloading until the bolt gets hard to close, then full length size.

 

[Cemetery21]

I'll add that I can understand both sides of the issue about whether to modify a "factory" cartridge.
One, if you want more performance, just buy a bigger gun.
But, P. O. Ackley was an interesting man that did a lot of experimenting with firearms of his day. He documented a lot of his work and several writers of the day also recorded his attempts.
I think it's partly because of the history that I enjoy the 2 Ackleys I shoot. Interestingly, look at the shape of the new short magnums and many benchrest specific cartridges - very little sidewall taper and sharp shoulders.

 

[zerobarrier]

I did google some pics and can see the difference. I was unsure if you still get good accuracy while fireforming or if it was just a waste of the components and barrel life. I read about the cream of wheat approach.

 

[Cemetery21]

Mine are both prairie dog rifles. 1200 rounds were fireformed in one trip and the accuracy was up to the task. You do lose a little velocity in the first firing and the POI will likely be different when you shoot the brass the second time with Ackley loads.

 

[taliv]

I won two 1000 yard nra hp prone matches while fireforming. It's plenty accurate.

The important things to know are that you have to fireform but once that's done you'll probably never have to trim. I've had 15 firings on brass before and never trimmed a single 260ai. Total about 15500 rounds and 8 barrels.

You will get 1800-2400 rounds on a barrel depending on how fast you run it.
You can push Berger 140g hybrids over 3000 fps which is 6.6 mils to 1000 yards at 2000 da and about 1.5 for a 10 mph full value wind.

You can use 308win magazines and a ton of companies make 260 brass and 243 brass which you can neck up.

 

[taliv]

Btw make sure you find out the round count on that barrel and who chambered it and what reamer they used. It sure didn't come from Remington that way and if they put 1000 rounds on it you may as well knock $600 off the price to pay for the next barrel.

 

[greyling22]

I have a 257 ackley, and I get fine accuracy firing regular 257 roberts rounds out of it. Personally, I never bothered with the cream of wheat thing. I just load and shoot a medium powered roberts round sized with the ackley die. Seems to work for me.

 

[Seabeeken]

I found my fireforming loads in my 243 Ackley super accurate. Much more than the loads after forming the cases.

 

[Jim Watson]

Saw that once here. A guy got all enthused over the 7mm STW and had his 7mm RM rechambered. For some reason his only decent accuracy was with the first firing after the 8mm RM brass was necked down. After it was fireformed to his chamber, performance was fair to poor. And that was not much fireforming.

 

[taliv]

it's important to do fire forming right. because the 260rem is tapered and the chamber is much less so, the case will naturally lay in the bottom, if not for the fact that the ackley is supposed to be .004 shorter which means that when you put the parent cartridge in there, if your gunsmith did his job properly, it should be difficult to close the bolt because you are crush fitting it in the chamber. essentially, bumping the shoulder almost those 4 thou, minus clearance.

if your smith didn't do his job right, then you can seat the bullet out well into the lands, in which case the case will align by virtue of the bullet being stuck in the lands. not ideal but it can work.

if you don't do either of those, then basically the case is laying on the bottom when you pull the trigger which means you're fire forming the neck a lot more on one side and your runout is gonna suck forevermore.

 

[Curator]

Taliv has it exactly right. The "devil is in the details." Fire forming incorrectly will not yield the accuracy you expect. I learned this the hard way with .30-30 AI and again with .35 Whelen AI. When I got my hands on a .257 Bob AI, I did it right the first time and have been very happy with the results. Most Ackley Improved cartridges will give from 5 to 10% extra velocity from increased powder room. The advantage with the .35 Whelen AI is extra velocity/lower pressure and longer case life. .30-30AI might not work well in your lever action rifles but bumps up .30-30 ballistics in bolt or box-fed rifles with pointy bullets.

 

[spitballer]

I'll bet the angle of Ackley shoulders affects area of turbulence in the throat also.

 

[zerobarrier]

Ok, thank you guys. After doing more research and listening to what you guys have to say I believe I am not going to purchase an Ackley. I will just continue to save my money for my 260 build.