Topic: Tell me about fire forming brass please.

[technique]

I wanna know all about it but my main question is:

I'm under the impression that with say my bolt guns, I can fire some new factory ammo and that brass is now fire formed to my chamber. I am also under the assumption that these pieces of brass do not have to be re-sized because they are now sized to my chamber, is this correct?

Would they need to be trimmed? Or maybe not because I didn't re-size?

Please give me the run down. Thanks.

[fj40mojo]

At that point you can neck size only. You shouldn't have to full length size for 3-4 more firings and trim then as well if needed. Your full length sizing die can be set up to size the neck and body of the case with out bumping the shoulder back which will limit how much the brass is worked in the overall length, ie leaves the case headspaced for the chamber it was fired in. Of course that ammo will likely only work in that rifle now.

[popsgunner]

+1 FJ, spot on info, Sort your brass as well, all same headstamp, lot, year etc... thats the best gain for accuarcy.

[Nomad]

 Get a set of mics and use them as well and after you neck size only check to make sure
that the brass will fit your chamber sometimes you get little surprises when you dont
want them.........Luck

[technique]

Cool, I'mma give it a shot with my .243 and see how it goes. Later on, when I have my 5R, I'll try it with .308.

[agunforeachhand]

Does this apply to all firearms? Or just rifles?

[carharttfarmer]

just rifle cailbers

[RGinIdaho]

Heed Nomad's warning. Particularly if you choose to neck size with a full length die. The die will resize/squeeze the body partially and may cause the shoulder to move forward. I've seen partial sizing result in shoulders pushed forward enough to prevent bolt guns from closing.

Best bet is a dedicated neck die. Don't forget to pick up one of the Stoney Point/Hornady guages so you can check "headspacing" on your fired brass and then again after sizing.

[High Wall]

Does this apply to all firearms? Or just rifles?

It applies to bottleneck cartridges (including belted cases), whether rifle or pistol.  If you don't set the shoulder back enough, you will get hard chambering, or it won't chamber at all.  Set the shoulder back too much and you will get incipient head separations at some point on subsequent loadings.  In pistols, the Contender is particularly picky about this.

[J Mack]

Most of my shooting would be considered varmint hunting or tactical type and I always bump my shoulders at least .002” for reliability and my ammo will shoot sub MOA reliably. FJ just shot ¾” group @ 200 yards from some ammo that was loaded on a Dillon 650 progressive press in less than perfect conditions. My point is don’t get too twisted around the axle trying to make unreliable benchrest ammo if reliable tactical/hunting ammo will get the job done.   

For a better explanation this is a quote from Sinclair:   
Ideally, the amount of sizing you want to have occur for most hunting and varmint rifles is approximately 0.002” to 0.003”. Benchrest shooters and other competitive shooters will normally only “bump” the shoulder back approximately 0.001” so there is minimal case movement in the chamber. The balance that a benchrest shooter tries to achieve is the minimal headspace change he can achieve that still allows the cartridge to chamber without requiring too much effort to close and open the bolt, thus not disturbing the rifle’s position on the rest and sandbags. Some benchrest shooters will not even use a full length die to set back the headspace but will use what is called a “bump die”, which only adjusts the shoulder position and headspace while leaving the body alone. Some of these “bump dies” do have provisions for using bushings to size the neck. This same headspace balance is also important for a position shooter (prone or standing). You want the case to be well fitted to the chamber but you don’t want to have to force the bolt open each time with hot loads and disturb your position and “Natural Point of Aim”.

Full article; http://blog.sinclairintl.com/2009/02/19/setting-up-a-full-length-sizing-die/

[RGinIdaho]

don’t get too twisted around the axle trying to make unreliable benchrest ammo if reliable tactical/hunting ammo will get the job done. 

+1

The best thing you can do if you are going to play the case tolerance game is to learn your rifle. How it shoots and how it likes to be fed. Find a load that shoots well full length and neck sized. Learn when your rifle wants the shoulder set back. I can get 5 neck only trips in my tactical bolt but opt to bump back .002" on the 4th for reliability. Hot or cold, it shoots great that-a-way.

The only exception might be extreme long range. Then, SD in an overall accurate load probably makes a greater difference than concentricity. Unless we are talking a really crappy chamber and throat or grossly out of round handloads.