I have some new brass, in both .270 and .22-250 that I want to fire form in my chambers. Now I know that almost all rifles exhibit a small amount of headspace and that the brass will stretch just ahead of the web area to take up the slack. I would like to do this without this happening. My thoughts are this. If I load the bullet so that it is jammed into the lands, would this push the case tight against the bolt and then stretch the shoulder out to fill the gap instead of vice-versa? If this would work how much should I reduce my powder charge. Would the recommended starting charge be safe or should I reduce it futher?

If the bullet is touching the rifling, you would be creating excessive pressure in any but the lightest loads. I don't know about your idea, but If you 'do' it, make sure you have a reduced load...

reloader-1

I question why you would want to go to the trouble. If headspace of your rifles is with safe tolerances, the stretching in the web is insignificant.

I see no use for such "fireforming" unless you are dealing with "improved" or wildcat cartridges that require the shoulder be blown forward.

Yes, you can, in effect, headspace on the bullet by engaging the rifling. This is sometimes done when a chamber requires fireforming and the base-shoulder dimension is much longer than the parent(like a .30 Gibbs from .30-06). I'm not sure that there's not some bit of "slip" using this method when the firing pin strikes the primer, creating some headspace anyway. As one poster warns, engaging the riflings with the bullet can cause and increase in pressure (although not as rumor would have it), so reduce from full power loads if using this method. A real drawback to bullet-headspacing is that you may not be able to open the bolt and withdraw the unfired cartridge without the bullet sticking in the lands.

A surer way of creating minimum headspace is to expand the necks of the new brass to the next-larger caliber, then resize with the proper die until the case is a "crush" fit in your rifle's chamber. This method creates a "false shoulder" on which the case will headspace, and has none of the (percieved or real) drawbacks of the bullet-headspacing method.

Unless your chambers are overly generous (and I would almost guarantee it if they were belted magnums), I would agree that there's not much to be gained by "pre headspacing" since the initial stretch of the case on first firing is not likely to be excessive.

Yes, it can be done and exactly as you describe. The only word I would change is the bullet "jammed" into the lands. If you load with the bullet long enough that the bolt has some resistance, the bullet is far enough to do the job. This is exactly the way it is done to fireform improved rounds. I would go with a light to moderate load of the fastest powder you have that is listed for the 270 or 22-250 from a reputable manual.

Now the drawback. Unless you want to do the fireforming a lot, you will need to neck size only for those cases from now on. If you full length size after going through this process it will undo it. You must also make sure you catalog the brass so you don't shoot it in any rifle other than the one it is sized for. After a few firings, the brass may require slight force to extract at which point you either need to full resize and start again, or throw it away and begin again, but that may take several firings. I would also agree woth the others above about it not being all that necessary. I would think accuracy will not improve that much and if you just start neck sizing only, it will accomplish the same thing.

I think you would be spinning your wheels, so to speak. Unless your gun has excessive headspace to start with, or if you are oversizing your brass. What you are referring to is Fire-Forming. This is done for Improved versions of the same chamberings. Resize your brass only enough to chamber without restriction, or neck size only.