Awhile back I had posted a question about seating a bullet out so as to be in hard contact with the rifling. I wanted to do this so that with new brass it would headspace on the bullet and prevent any streching in the head area.

You suggested that I create a false shoulder by necking up to the next larger caliber and then resizing in the proper die so as to have a crush fit in my rifle.

This sounded like a good idea so I tried it with twenty new cases. I removed the firing pin and ejector button from my bolt and sized them so they would close with moderate thumb pressure (maybe thats to much) Any how, after measuring case length after doing this the cases are .010 shorter than before. New cases are 2.530 and now they are 2.520.

Now for my question. When loaded and fired in my chamber will the shoulder blow out and remove the false shoulder and will the neck grow that .010 that I had lost. My actual chamber length is 2.572 and I would prefer to shorten than .052 gap that I now seem to have.

I don�t know what kind of cartridge you are reloading for, missed the post you are refering to, but if you move the shoulder forward during fireforming, wether it is for a long chamber in a standard rifle or if its a wildcat you will loose some overall length. If possible start with a longer case, reforming it to your caliber. For instance I use .300WM/.308NM to form 7RM cases so they will fit my chamber. Original cases are about 0.040" short.
Tron

Sorry about that.

I'm loading for a .270 Win. and 22-250 Rem. using standard brass.

It's quite common for fireformed brass to be shorter than before fireforming in a chamber larger than the brass. The brass has to go somewhere and usually the necks shorten up.

The false shoulder should disappear at the fireforming if you use enough of a powder charge to blow it out well. After the first loading the shoulders will sharpen up a bit more. It's likely your brass will shorten up even more at that time.

With the .270 you�re kind of stuck, I think, unless there are longer cases to reform from (.280 Rem?) With the .22-250 you can reform cases from a longer case (.243 Win?), trim to the length of your chamber, you probably have to turn necks though.
Tron

If your rifle will not give it's best groups with the bullets seated into the lands why bother. Any standard case reformed to the AI version will stretch the least after firing. I own one rilfe that likes the bullet seated just touching the lands for best accuracy. My goal is accurcay not how often I must trim my brass. Neck sized once fired cases give good service and should give you the best service. Most brass will last about ten to twelve loadings. Only the PPC cases last longer because they are so strongly made. Bullets seated against the lands can increase chamber pressure dramatically if the rifle does not like the bullet seated there.

Turkeyshooter:

Been away and just now found your post.

Most of the comments here are fairly accurate. Your shoulders will iron out nicely when fired with full or near-full power loads. You will also experience some overall case lengthening due to the shoudler "ironing". I don't know how much your cases will grow, but it would seem nice to have them starting short enough that it will be several firings before they might require trimming. Let us know how things go.