Fire forming barrel?

[46and2]

I have a 300 wm that is going to get a new custom cut rifled barrel. I have 200pc of ABM brass fired one in the old barrel. Here are my options.

Install the new barrel and continue to load the fire formed ABM brass. Saving barrel life.

Install the new barrel and start with fresh Lapua brass.

Fire form the new Lapua brass in the old barrel, then install the new barrel and use already formed brass

I have spare powder and primers that I don't prefer to use often to form the new brass.

The issue is..
300wm brass headspace increases up to .020 until formed, and developing a stable load just doesn't happen until then.

Barrels can take about 100 rounds to settle in/ broken in.

Components are increasingly costly.

 

[6bra1k]

i think you are over thinking it
is the new and old bbl cut with the same reamer ?
i have some abm brass(500) unfired..but had to sort to be useful in a "target" rifle.
(less than a competition rifle, more than a hunting rifle)
sort that brass if you plan on using it
is this a hunting rifle, a steel rifle or a competition rifle.
never used lapua 300wm, but i would weight sort.

 

[46and2]

I'm the best over thinker!

Steel and hunting barrel.

 

[6bra1k]

use the abm for steel and the lapua, sorted for hunting

 

[buddy.223]

Just an observation I found new Lapua 300 wm brass is v thick compared to the other manufacturers, if you don’t want to neck turn check when specing a reamer .

 

[SKWERLZ]

If it’s the same reamer run the old brass.

My first 100-200 on any new barrels is to get it up to speed and once fire the brass if needed with a mild load.
Those shots are always plenty accurate and excellent practice and fun banging steel.

 

[moondog]

If I'm running in new brass for a caliber, which is usually 300 pieces. I'll fire form on the old barrel, maybe 25-50 on the new barrel for break in and to compare any differences in headspace if it's not my reamer.

 

[wildcatter]

I did this with excellent results, and chambered the factory 243 barrel for the 6mm Remington AI chamber I was building, now have a hummer with that barrel, but do all my fireforming in it. That factory barrel shoots .3" moa all day with 3 different loads.

But to answer your question, I would never load another bullet to fireform brass. This worked great for me and is cheaper than anything else you can doe. I was taking a necked down 8x57 Mauser case from Lapua, much more work than your needing to do and harder to get good results, but this gave them!

I chose to fire form before turning, just used 14 grain of bullseye, and filled my cases with corn cob polishing media, then sealed them with zest bar soap, bees wax, or paraffin. Then turned the neck's with my K&M nk turner w/ inside donut cutter pilot, one step done, after formed, was all within max length, and after the first firing with loaded ammo, trimmed to uniform length of the entire lot of precious new cases!

I will never wast the powder or bullets to fireform any brass ever again. But if your going to fireform to a custom chamber, I suggest paying the smith to use the same reamer and for about 100 bucks have the old one reamed with the same thing your going to waste the powder and bullets to form to.