I've recently converted some LC 7.62x51 brass into 7mm-08 for a rifle I'm working on.  I have a statistically insignificant sample that brass that has been fired at least once in the 7mm-08 is more accurate than freshly converted brass.  It's more of a feelz thing.

If I want to fire form this brass with a minimum investment in components, how would I go about doing it?  The cheapest bullet I can find and pistol powder?  Just for grins, I used a 100 gr bullet and Quick Load wouldn't even predict a pressure for Bullseye powder until I 'used' 10 grains because the starting pressure was too high.  At 10 grains, the predicted max pressure is 20,645 psi.  It'll take around 15.6 grains to get up to 40K psi.

So I guess my questions are how do you fire form brass, what's your load to do it and how much difference do you think it makes?

FWIW... I had some new Lapua for my 308Win and wanted to expand a few out to within .002" short of the max headspace for the rifle as a test.  I think I needed to go from 1.621" to 1.627".  Anyway, I used 150gr bullets and a load near recommended starting load, that only got me to like 1.624".. had to go up to near max to get them to expand out to 1.627".

As for how much difference it made.. jury is out.  I've changed a lot of equipment & procedures lately so basically starting over.

Just load and shoot them without any particular fireforming step.  Fireforming costs bullets, primers, powder and barrel life PLUS, QuickLoad is warning you that you're on the wrong path (high pressures indicated).  What would be the cost of a KABOOM?

Could you give me more details on this?  I understand there would be a chance of a double charge using 15 grains of pistol powder but other than that, what issue do you see with 40K psi in a cartridge rated for 60K psi?

I guess that was the original question.  The load I'm currently shooting is predicted to be around 54K psi.  What would the minimum pressure be to fire form my the LC brass?  I'm with you on the cost which is why I wanted to use a bullet that cost half as much and a pound of Green Dot that I have no other use for.  (Originally bought for a special effects device for a vacation bible school skit)  I also wanted to save some barrel wear by not pushing the bullets as fast.  But I want my loads to be as accurate as possible when I go to a bang steel class later this year.

Unique and Cream of Wheat.

Good article here:

Fire Forming

That said, since 7mm-08 is just a necked down 308 (or 7.62), all I've ever had to do is size the 308 brass with the 7mm-08 FL size die, being careful to make the headspace tight.  Prep, load, and you're done.

The first firing will provide perfect cases.  The 7mm-08 is just the 308 with a smaller neck.

Yes, but how much benefit do you see using fire formed cases vs just resized from .308 cases?

I misread your point on the subject of pressure.  

Still, I'd say just shoot them due to cost.

In the one instance where I bought into a wildcat cartridge requiring brass forming, a 6 XC, I just formed and shot the brass using full power loads.  I monitored the case dimensions before and after firing until the headspace settled down.  It took about 3 firings before all cases were at the same dimension.  The point is, it will likely take more than one firing even at full pressure.  One firing gets you really close but not all the way.  

You are re-forming shoulder and reducing the neck diameter by about 0.025", correct?...  

Just load and shoot.  A small inaccuracy is most likely trivial unless you are doing benchrest matches.

I've always just used a load for the finished case I'm making when I've converted to 7mm TCU. I never bothered with the whole cream of wheat idea. Using a pistol powder for a rifle case is down right crazy IMO

If you are creating an Ackley-Improved case or some radical reforming of the case body, shoulder and neck, then a range trip to fire form might be warranted.  But he is just resizing the case neck, necking it down by 0.025".

I'd highly recommend reduced Trail Boss loads for 100 yard shooting - or with recoil sensitive shooters.  They're quite fun.

In certain particular cases it works.

The 'cream of wheat' loads can use pistol powder in some cases.

The weight of the cream of wheat 'bullet' is vanishingly small.

I have a couple of AI chambered barrels (.22-250 AI and 6 mm Rem AI) for my Panda action varmint rifle.

Both require 100% neck turning.
A factory parent shell will not fit in either rifle.

I agreed with Kelbly's that if you make a tight neck make it tight enough factory brass will not fit.

It prevents dumb mistakes.


When done carefully I can obtain excellent accuracy and well formed cases on the first go round.
I do not load down but load around the middle of recommended.

Across two barrels I have only had a single split case during forming (one .22-250).
No chamber damage visible.

Under a borescope I could not locate the split location after the fact.  And I looked hard. At the
highest magnification I could get.
And have formed many hundred cases.

Accuracy was excellent.  Better than 1/2 inch 10 shot groups at 100 yards.
The barrels hit about 1 inch horizontally different and barely 1 inch vertical at 100 yard.
It was repeatable enough to change barrels, adjust the scop, and be on with teh first shot on the 'other' barrel.

It was better with a formed case but still good enough for around 200 yard varmint killing when I did my part on range and wind.
Fields of soybean plants are an incredible wind flag.  You can see the 'waves' in the breeze.

The .22-250 barrel has been set back once, the 6 mm twice.
Still better than my Swift barrel.
More rounds,  better accuracy, and brass life.

Mostly groundhogs so not the smallest target but after forming out to around 400 yards with the 6 mm.

It was scary accurate from the start.

From .308 to 7/08?In a typical production run rifle?
Very little,if any at all.

There were loads published in one of the NRA magazines years ago that used "light for caliber bullets and Unique powder.

I've used this many times in a few different calibers.

People who fire form brass for wildcats have been doing this for ever.

Your 100gr bullets will work fine. I wouldn't use Bullseye though I'd use and do use Unique.

Or if you want use Trail Boss. With it you can't double charge.

Some of the loads are very accurate. My 55gr FMJ load I use to fire form brass in our 22-6mm AI shoots groups any AR shooter would be proud to post photos of.

Motor

Tite Group is listed as a reduced load powder for several calibers as it isn't dependent on case position for burn (supposedly).

In 308, 8 gr. under a 168 SMK produces 25k PSI. Not sure if that would be enough. I imagine it could be adapted to 260 without too much pucker factor.