Fire forming 260AI from 260

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gillamboy

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New to the AI's so looking for some advice. I have 260 lapua brass that I wish to fire form to a 260ai. Where do you go for your starting load to ensure good shoulder forming but still on the safe side for starting load?
 
gillamboy said:
New to the AI's so looking for some advice. I have 260 lapua brass that I wish to fire form to a 260ai. Where do you go for your starting load to ensure good shoulder forming but still on the safe side for starting load?
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I fireform brass for several AI chambers, and do not normally use a regular loaded round to do so.
Keep in mind that a properly made AI chamber will have a bit of "feel" as you close the bolt on a new factory case.

I prime the case, put in 12 grains of Bullseye, fill with cream of Wheat, and put a small wad of toilet tissue in the neck to hold everything in place.
Pointed in a safe direction and fired, you should have a perfectly formed AI case, without any throat wear in your rifle.

If the shoulder still seems too rounded, simply add another grain of Bullseye.
Now you can proceed with load development with perfectly formed AI brass.

Be sure to clean your rifle before firing regular ammo.

Regards, Eagleye.
 
Jam the bullet into the lands and use a starting 260 load. If the shoulders don't come out nice and sharp, increase the powder. Or use the COW method as above.
 
I use the usual 140 gr match bullet, 45 gr of 4350 and shoot for score. The velocity is not as high as my Ackley load, but accuracy is superb. As good or better than the regular load. i use these fire forming rounds for short range (up to 600 yards).
 
To add to the already excellent advice, CONFIRM that there is contact between the brass and chamber BEFORE fireforming.

There should be light resistance when you close the bolt. Like you have when you have a "fat" case that needs a bit of sizing. Then ensures that the brass is full supported under pressure and will not become a banana or worst, develop a crack.

I used the COW method but subbed cornmeal (no, the letters would be rude :) )

If there is no contact, neck UP the brass then size down to form a secondary shoulder enough forward to cause chambering to be a hint stiff. Not all chambers and brass are the right fit.

Good luck,

Jerry
 
I fire form a lot of 243 to ackley version, I use the cream of wheat process Bullseye, cream of wheat and tissue paper to keep it all togather. Eagleye is correct start low and work up until you have the properly formed shoulder. Plus no wear and tear on the bore.
Bill
 
Terry's Tactical Two-Sixty AI
King of the Hill in Tactical Comps
http://www.6mmbr.com/gunweek046.html

"Cases are primed with Federal 210M primers and charged with 47.0 grains of H4831 or H4831SC. Lapua 139 Scenars are seated to 2.820" OAL. This load produces very well-formed "Ackleyized" cases while maintaining groups of 0.500" or better. Running about 2780-2800 fps, these fire-forming loads are good enough to shoot on some courses of fire and during short-range practice."

The link above has "everything" you ever wanted to know. ;)
 
I do it a few ways. I've used COW with Unique. Trailboss plinking load and a full power load using H4350. Used the Full power H4350 load today and of the 3 groups I fired not one was over 1/2 MOA so I may use that more as an expedient practice round.
 
I've only done it for one rifle and I picked Hodgdons max load with the powder/bullet I had on hand. I sighted in my scope and shot some nice groups.
 
PO used to recommend to his customers, to use a max load for the parent cartridge and just go and shoot it like normal. IF the chamber is done correctly the factory ammo or new brass should headspace perfectly, but this is a big "IF" and needs to be confirmed with your particular chamber. Not all smiths know how to properly headspace an Ackley Imp chamber and not all AI headspace gauges are even correct.
 
When going the full charge of the parent cartridge route.... does the bullet need to be touching or jammed into the lands? Seems like this may cause some very high pressure spikes? I am going to be using some H4350 and 140 gr bullets for the process.

Just curious as I will be firforming some 260 AI in the coming weeks.

Thanks for the advice.
 
I have a 260 Improved I am shooting, it is not a true Ackley however as mine has a 35 degree shoulder where I understand the Ackleys have a 40 degree shoulder. I have fired about 75 rounds now, all being near max loads for the original 260 with Lapua brass and Lapua 139 grain Scenars. This method has worked very well, but I am burning up good powder and bullets and burning up the barrel and I still have done no load development for it yet. I am going to try the COW method for the next batch to see if there is a difference in the quality of the fireforming of the brass. If I still get nice sharp corners I will switch over to this method for the remainder of my brass as I still have another 125 pcs to go. I have Lil' Gun on hand so will likely try that powder and see what I get.
 
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