At the range this weekend I was fire forming some 338-06 cases to 338-06AI. I was using 200 grain nosler bullets with 59 grains of 4350.
Most of the primers were backing out. No other negative signs. The primers were not flatened, just backing out. I'm not sure what it means.
Any help?

Any soot on the shoulder and body of the shell?

I'm just asking because it sounds like you have too little pressure in your load for the case to expand properly.

Option two is, that the headspace of your gun is too large.

To properly fireform my 257AI I have to seat the bullet to engage the rifling to get proper headspace, otherwise the primers back out or the cases develop streatch rings at the base. The AI chamber is supposed to contact a regular round on the shoulder to headspace. If it is a hair too deep this doesn't happen and primers back out and streatch rings develop. Sounds like you have the same problem.

Jerry Liles

McFox,
Soot on the neck and top of shoulder. Could this be because it is forming to AI shoulder?

Jerry,
How do I seat the bullet properly to contact the rifling? Do I seat a bullet long and force it into the chamber?

Insert a boolit in a spent case and chamber it carefully. That will give you the max length of a loaded round. For fireforming load the shells with the boolit a smidgen longer and "seat" them on chamber closing. That way the rifle will hold the casing back towards the bolt face, when you push the button.

A true AI chamber should be a crush fit on a factory case. Meaning you will feel pressure as you close the bolt. Way too many AI chambers were cut by simply running the AI reamer into a std case and not setting the barrel back before cutting the chamber. This will leave you with too long a chamber.

From what you state this sounds like your problem. YOur chamber sounds like it is too long. The primer drives the case forward ignition drives the primer to the rear. Your load calculates a pressure of only 43,000 in a std chamber it will be less in an AI probably not enough to stretch the brass. Leaving blow by in the neck shoulder area.

As stated if the case is long and you move the case forward even if you have enough pressure to stretch the brass you are thinning your brass in the rear. Not a good thing.

You want the shoulder to simply expand not stretch the brass. As Dane stated you could use the bullet to headspace. Or neck the brass up to 358 then adjust your 338 die to give you a false shoulder to space against. Either way you don't want it so tight you need to hammer the bolt shut but you do need to feel resistance as your close the bolt.

Exactly what Ramrod said.

In my philosophy, there is no such thing as a chamber that is too long, only brass that is too short (since it is much easier to make the brass longer than make the chamber shorter!)

Your most certain approach is, as ramrod said, to expand your necks a caliber larger, then resize them for .338, but only run them into the resizing die as far as necessary to allow the bolt to close on them with a firm "crush" fit. In my experience, the firing process allows the shoulder to reform in a manner that the second time the brass is inserted into the chamber it will no longer provide the same resistance in closing the bolt.

One of the best ways to go about this is to start with .35 Whelen brass, but if you already have a significant supply of .30-06 resized to .338, then it will work also.

If you oil the case when fire-forming the
shoulder will fill in the case will come back
over the primer, and you will avoid the stress ring. If the primers protrude you havent fully formed the case and still have head space.
An Ackley improved chamber is supposed to be a tight fit, but many aren't.