Thread: My 260AI Load Development Begins

Originally Posted by Tikka7mm08

One hydraulic formed and one FF:



Both Lapua and I can't see the difference. New regime is anneal, form, anneal, FL size. Sounds a bit too it but the longest part is the forming. Lapua seems to respond very well as can be see above. Lost 1 case because FL'd too quick from the annealer and the case mouth deformed a little (useable but not passable for my OCD).

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Wow, they are coming out great now. You should be stoked Sure saves a bit of stuffing around with shotgun powder etc.

Yep thought they were ok before but now will never need to fireform again.

Hydraulic on left and FF on right.

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I find on some brass once fired that there is a minor tightness to chambering, say 2 out of 10. I have body taper die and that doesn't work but a feeler gauge under the case seems to work well to make it like new brass again. Is this the shoulders requiring a bump back? I will drop the load back as it must be slightly hot, and perhaps take some before and after case head dimensions...what is the consensus on allowable case head expansion?

With my AI (6.5SM AI) I find with the 40 dgree shoulder and the only slight case taper I go around 5 firings b4 chambering is a concern and FLS becomes required. Virtually zero brass flow.

Re base measurement - yep did that, took mic to range, recorded movement, if any. Analysed the hell out of it. Discarded checking in the future.

There was a good article on Accurate Shooter quite a while back debunking using base growth as the ultimate pressure guide.

Some chambers (yours would not fit into the category I assume) are a bit "sloppy" so you can get what appears to be excessive base grouth after 1 shot with safe pressure loads. Subsequent loadings of the same brass at the same safe pressures, neck sized only, would see little or no movement. Panic over.

Rule of thumb used to be anything around 1 thou and panic. Or anything that continues to grow.

I have also seen very loose primer pockets with in some cases no proportional change in base diameter.

On my AI I gauge the primer pockets b4 each load as I did have one load that opened up the primer pockets. Depends if you are running hot or not. On the Swede (6.5mm) I get 3010 fps with 142gr projectiles but did take it up to a lot faster/hotter than than that - hence BIG primer pockets. Very annoyed with myself given the effort required to make brass.

Originally Posted by Tikka7mm08

Is this the shoulders requiring a bump back?

Have you got a gauge to measure to the shoulder datum point?
The ones that are tight to chamber are they similarly tight to extract?

No I don't. Also tried some RCBS competition shell holders but seemed to make little difference. I think I will back off perhaps a grain and see how I go. 45.5gn destroyed primer pockets after a couple of firings, so 44.5gn still a bit hot with those couple of cases...so will try 43.5-44.0gn.

Not tight to extract, bolt closure and lift just a little stiffer from new brass.

Originally Posted by Tikka7mm08

No I don't. Also tried some RCBS competition shell holders but seemed to make little difference. I think I will back off perhaps a grain and see how I go. 45.5gn destroyed primer pockets after a couple of firings, so 44.5gn still a bit hot with those couple of cases...so will try 43.5-44.0gn.

Not tight to extract, bolt closure and lift just a little stiffer from new brass.

Yep, cannot ignore enlarged PPs :-)

Normally when I fire form I use a forming load and second rate projectiles. After the first firing I run my normal load (or do serious load development). But with your case forming method the capacity must be close to fireformed size.

Originally Posted by Tikka7mm08

I find on some brass once fired that there is a minor tightness to chambering, say 2 out of 10. I have body taper die and that doesn't work but a feeler gauge under the case seems to work well to make it like new brass again. Is this the shoulders requiring a bump back? I will drop the load back as it must be slightly hot, and perhaps take some before and after case head dimensions...what is the consensus on allowable case head expansion?

I found the same with my 30deg Imp. Bump die with feeler gauge sorted the issue & I backed it off 0.5gr. All the cases seem to be ok now and primer pockets tight. I did stuff 7 cases by running 1gr over where I'm at now, the primer pockets were loose as. Trying too hard as a velocity hound

I hear ya...

Originally Posted by Tikka7mm08

No I don't. Also tried some RCBS competition shell holders but seemed to make little difference. I think I will back off perhaps a grain and see how I go. 45.5gn destroyed primer pockets after a couple of firings, so 44.5gn still a bit hot with those couple of cases...so will try 43.5-44.0gn.

Not tight to extract, bolt closure and lift just a little stiffer from new brass.

I have a forster press so no choice in shell holder as such and had similar issues with my AI

I had to get my redding FL die ground as it didn't bump the shoulder at all in my press.
So now all I do is anneal tumble and bump the shoulder around a thou.
Have not had any issues since.
After around 5-6 uses I need to use a body die then bump to extend the life of the case a bit more.

My primer pockets get a bit loose around 8 goes on a moderate load.

I have changed powder recently so haven't seen if there is any change to case life yet


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Yes it feels like on some cases the FL dies just isn't 'reaching' the shoulders well enough...and have the shell holder hitting the base quite firmly on the cam over of the press.

Originally Posted by Tikka7mm08

Yes it feels like on some cases the FL dies just isn't 'reaching' the shoulders well enough...and have the shell holder hitting the base quite firmly on the cam over of the press.

Just a suggestion, but get your FL die ground a bit so you can bump the shoulder. Body die won't do the shoulder.
If you are worried about case head expansion (I wouldn't worry about a little more than normal in an ackley. In my experience pocket will go first in the .260 AI even with hot loads) get a body die.





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Righto... how much ground off the FL die?

What ever gives you a bump with the feeler gauge.

I got 15 thou off mine iirc.
Adjusted until I got the bump I wanted and locked her solid. Works a treat now😆

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