Fire forming 243AI

[Tiny Tim]

First semi-custom, first premium barrel, first AI, so this is new territory for me. Rifle is trued and "printed" Remington 700 SA, 243 AI w/ 26" Rock creek 8tw, 5R cut barrel and Wyatt's extended box. Loading 43 gr RL-22 behind 105 AMAX (because I have some left over and want to use up). Using new Nosler brass. Getting a 10 shot average of 2936 fps. ES on first 5 was 58fps, and next five was 26fps. These are my first ten shots and I was wondering if the large ES is due to fire-forming or break-in? It seemed to get better as I shot. Data on this powder- bullet combo is wildly varying from source to source (some have max @42.5 gr and others as high as 46 gr for 243). No signs of pressure and shoulders are slightly rounder than Hornady American Whitetail factory ammo. Should I continue with this load or go up a bit? Will ES stabilize as barrel gets broken in? Or is this a fact of life whilst fire-forming? Could it Just be an erratic "node"? Again, all new territory for this shooter. Sorry for such a long post. Any insight/suggestions would be most appreciated.

 

[JMW67]

fire forming I like to use a little faster powder in my 243ai I use imr 4350 and a pretty stiff charge for the parent case gets me better results and I seat the bullet into the lands

 

[Tiny Tim]

Would have liked to use a 4350, but none around. Thanks.

 

[Dmagna]

Don't worry about keeping track of anything during the fire forming process. You will gain case capacity and will have to add powder anyway. You should probably load faster powder to get the harder explosion in the case. I would load close to a max .243 charge, And send it. I would do 50 or so cases, then start load development.

 

[MagMan]

I fireform with 46.5 grains of RL25, 210 and a 115 DTAC. Shoots well with forming loads.

.010 off