subsonic fireforming?

[mstarling]

Hi Guys,

Mentioned that I finally got cases that would fit the cartridge gauge and chamber in the rifle. Required using a small base .223 sizing die before forming the neck of the case with a FL 300/221 sizing die.

I loaded a few rounds of one fella's subsonic recipe for 147 FMJ BTs ... 8.3 gr of H110 (WW296).

Rounds chambered easily. After firing w the gas system closed the cases extracted easily with just the charging handle.

Interestingly, the shoulder was not fireformed with this combination.

What is a minimum kind of load that will fireform cases?

Thanks,

Mike

[amafrank]

The load required will vary considerably with the type of brass you are using. Thin brass made from .221 will require much less pressure than brass made from military 5.56 so its not a simple answer. I find with my rifles that winchester commercial .223 brass will fireform quite easily with .220gr matchkings and 9.2gr of N110 or H110. I don't normally shoot the lightweights subsonic so I can't give you a load for that. The same load fired in lake city brass will usually fireform though sometimes it doesn't quite blow the shoulder out all the way. One shot loaded supersonic will usually take care of things regardless of bullet weight.

I've really not been all that concerned with the fireforming other than making sure we don't shoot first time brass for testing accuracy in rifles. I've never had any problems fitting sized cases into any of our chambers so the small base die you are using raises questions in my mind. We don't fireform to fit brass but rather to make it consistant with the rest of our brass. It sounds to me like you've got some problem brass to start with or else your chamber is at the very small end of spec.....maybe under spec.

Not sure what else to tell you on this. Post some pictures of your brass before and after sizing and buy some new unfired commercial winchester or federal brass and see if you need to really squish it down to get it to fit like you have been with whatever you're using.

Good luck
Frank