223 improved fire forming issues

[Martman]

Recently, I had Shilen re-barrel my Remington 223V to 223 improved using their select match grade blank with a 1 in 9 twist, varmint contour. Having never had an improved or wildcat cartridge I am looking forward to working up loads for a prairie dog hunt next spring. However, after reading various articles and forum comments about the fire forming procedure, I am having case loss problems with fire forming cases. I have used 3 loads as follows: New LC brass, Rem 6 1/2 primers, 25 grains H335 behind Nosler BT 55 grain with a COL of 2.260. I then fired loads used in my Stag Arms HB which is WW cases, Remington 7 1/2, Varget 25.3 grains, Sierra HPBT 69 grain bullet with a COL of 2.260. I also fired Winchester factory 55 grain ball ammo. 28 of the 90 cases show signs of incipient case separation after fire forming. Is this about normal case loss while fire forming? I spoke with a Shilen rep who suggested dropping down to 23 grains of H335 and seating the bullets out to touch the lands. I haven't tried this as yet. I would appreciate any suggestions or comments regarding this issue. Thanks in advance.

 

[LRSickle]

Sounds like you have a headspace problem, (kinda). Your case should be back firmly against your bolt face so the only way your case will expand is forward to the shoulder of your chamber. I'm sure that's what the Shillen rep is trying to accomplish by seating your bullet out enough that it forces the case back against the boltface upon bolt closing. Another way is to slightly deform your case body so it fits tightly in the chamber and forces the case back against the boltface as you chamber the round. Then just fire and the case will be fireformed back to a cylindrical shape again.

 

[Martman]

I thought it might be a head space problem however in checking with a 223 go gauge with the ejector removed, the bolt won't close. So I feel reasonably certain the head space is OK. With regards to slightly deforming the case, could you give me an example of what you mean?

 

[LRSickle]

It just doesn't seem right. I may be wrong so we might both be learning something. When ignition occurs your case expands and grips the sides of your chamber first, followed by your case expanding length-wise. If your case is pressed back against your bolt in the first place, your bolt will support the base of cartridge and keep your web from stretching and thinning out. The only way your case can stretch is forward, which is what you want since your fireforming. I'm pretty sure your unfired cases are smaller that your go-guage which might account for the headspace problem when your fireforming.
As far as deforming your case goes, just tap on the side to make it slightly out-of-round. Just enough so the friction of the case against the chamber walls will force the case back against the bolthead. Just tap the sides lightly with a screwdriver handle.
If your fireforming with reduced loads, I don't think you'll have to worry about high chamber pressures.