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Fire forming brass?

25 Apr 2022
@ 01:58 pm (GMT)

David Kopp

Hi all,

I'm in need of knowledge regarding new brass to be formed for the chamber and have been looking at options.

1. use trailboss and seat in to the lands
2. use a powder for the caliber with low to medium powder charge and seat into the lands.

Which would have best effect? How much trailboss to start with.
It's for a 7mm-08 and I have 150gr win pp to use.

For a 6.5 swede same thing but I cannot get to the lands. I'm opting to size the to a 270 and resize until the brass fits the chamber.
What would work best for this trailboss or h4350 using 140gr bullet?

Any thoughts or experience would be greatly appreciated.
Thank you


26 Apr 2022
@ 10:42 am (GMT)

Nathan Foster

Re: Fire forming brass?
Hi David, will try to simplify. Trail boss will 'mostly' form the case and help make the case / neck concentric. Putting the bullet on the lands helps to build pressure a wee bit with this mild powder and keeps everything aligned to the bore.

A mild load with regular powder will give more form to the case. The shoulder will however still spring back a few thou (up to about .004") so if you develop a load based on these cases and then neck size, they will need to be rechecked at the range, just to make sure pressure / velocity / accuracy is still the same. If not, a final tweak with +/- a half grain will finalize.

A near full pressure load with regular powder will fully form the cases, though some spring back (say .002" may still occur). As always, recheck everything at the range.

Much will of course depending on brass versus chamber specs.

This should be enough info to start with. Further info may only confuse matters.
05 May 2022
@ 10:08 am (GMT)

David Kopp

Re: Fire forming brass?
Thanks Nathan, I will start with the trailboss due to do getting a couple albs and use better powders after cause of the supply shortages that we all are feeling. Will this be ok to help break in the barrel or due I need more powerful charges for that?
07 May 2022
@ 08:53 am (GMT)

Nathan Foster

Re: Fire forming brass?
Hi David, it can take a bit longer to break in this way, but if you have a good number of cases to form, the round count and cleaning will give it a good work over. In any case, this is something you will be able to observe (rate of copper fouling etc) and monitor for yourself as you work through both the slow and fast loads.
09 May 2022
@ 01:33 pm (GMT)

David Kopp

Re: Fire forming brass?
Hi Nathan, yeah I have a 100 brass to form. I figured that using trailboss and 139gr interlock bullet would work nicely. The rifle is a remington 7mm-08 with trigger tech trigger and a sps hogue stock for now till I can bed it. After that I would load up with Win. PP 150gr to use and keep within 300yds max, those bullets only have .373 bc (if anyone was curious). From there work into the 162gr eld m's.

I'm not sure how fast I will get all that worked out but that was the plan.


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