Thread: My 260AI Load Development Begins

Originally Posted by outdoorlad

KG, can you explain the reasoning behind this?

How do you get it hard into the lands when you don't use a projectile? What difference does FF the case have with or without a projectile?

If the brass isn't hard onto the bolt face, when the firing pin hits the primer it pushes the case forward as far as the extractor or chamber will allow.

Then the powder ignites & the shoulder pushes forward & grips the chamber then the case head finds it has nothing behind it so slams back against the bolt, usually the primer has also backed out against bolt, then gets completely flattened looking a lot like an overpressure situation.

This sort of thing also happens when brass is too short for a chamber because of over sizing or sloppy Gunsmithing with long head spaced chambers.

This stretches the brass usually right where case wall meets the web.

With "proper" AI (Ackley Improved) chambers the neck shoulder junction is slightly shorter than the brass so it is reasonably firm against the bolt face.

Some brass is a bit short & some chambers are a bit long so this doesn't work sometimes.

There is a difference between AI & improved chambers.

A false shoulder is the way forward for an improved chamber.

How much of a gain are you to expect over a standard 260? I've just done load development on my new 260 with 140VLD's, would interested to know if the extra effort in AI or improving pays off in the end.

Originally Posted by Kiwi Greg

If the brass isn't hard onto the bolt face, when the firing pin hits the primer it pushes the case forward as far as the extractor or chamber will allow.

Then the powder ignites & the shoulder pushes forward & grips the chamber then the case head finds it has nothing behind it so slams back against the bolt, usually the primer has also backed out against bolt, then gets completely flattened looking a lot like an overpressure situation.

This sort of thing also happens when brass is too short for a chamber because of over sizing or sloppy Gunsmithing with long head spaced chambers.

This stretches the brass usually right where case wall meets the web.

so your saying by jamming the projectile it keeps the rear of the case against the bolt head when firing allowing the front portion of the case to form out.

Surely thats no different to a normal cartridge reload situation though, I'd have thought with a custom built chamber it would be a lot less likely?

So how does using a filler instead of a projectile work when there's no jamming to force it back?

Won't know til I can work up a load in the FF brass...but started this thread to share.

The brass is 260 brass the chamber is 260AI. The first firing will blow the shoulder out to fit the chamber.

The other way to do it is to open the neck up to 7mm and then form most of the neck back down to 6.5mm. This way the last part of the neck forms a false shoulder. When chambering the brass there should be a slight resistance. This is what you need to do if using the cream of wheat/fast shotgun powder method to for the brass.

I am reading this with interest as I'm also getting my Tikka and my Blaser R93 re-barreled in .260AI both with Hardy wrapped barrel.
You can FF with out a projectile and hold the case against the bolt face, by running the case through a .277 or .284 die first.
And then through the .260 die to form a false shoulder this will hold it in place and is the way I might go to form my cases.

Shit sorry Stug you beat me.

Might do that after running barrel in with these loads.

im about a month out from building my 260ai. well might be longer than that in the end. have everything here but just moved house and have to move the lathe in and re level the thing. what length barrel?

24"....thought about longer, but decided against it. Has a Hardy Gen 5 suppressor that goes on as well.

Have had a .260 imp for a while now and think I have my forming and loads as good as I can get them.

Have formed Lapua, Rem, Norma and Nosler .260 brass.
Rem and Nosler work best in my rifle.
I run a 7mm button on my sizing die in enough just to expand the last 3-4 mm of the case mouth.
I prime my cases and fill with an amount of AS30N shotgun powder.
I then get a 1 x 1 M16 cleaning patch and cram into the case.
Fire them off. I end up with a formed case with a reasonably sharp shoulder.
I load up my pet load and shoot them.
I get excellent accuracy on the first firing and scary accurate on about the 3rd. Have not had to trim a case yet and only FL size on about the 5th firing.
I have not shot any Nosler brass to the point I have had to bin them but got around 8-9 goes out of Rem brass.

RL17 worked really well in my .260imp but I have sacrificed a little velocity by using 2209 which is more available imo.
140 class bullets are 2900 fps and 130 are 3020fps. I can get them going faster but case life reduces.
24" barrel on an R93.
Having owned one for a while I have to say I really like the caliber.
My barrel is luckily very accurate and has consitant velocities.
But given the choice again of its parent case or going improved I would probably just go standard.
Nothing I have shot with it couldn't have been done with a .260 Rem.





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But those AI cases just look cool, that's a good enough reason! Lol

Originally Posted by outdoorlad

But those AI cases just look cool, that's a good enough reason! Lol

That's sounds like someone I know.......Toby

Originally Posted by outdoorlad

But those AI cases just look cool, that's a good enough reason! Lol

True.




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Nice Rifle.

Hardy Custom?