Meaningful information observed fire forming brass

[TrapperBR549]

The background is I am developing hunting loads for an elk hunt this fall. I have a Win M70 300 Win Mag.
I started with a couple boxes of Winchester factory ammo, fire formed and I am making progress towards a satisfactory load. I haven't been thrilled with the Winchester brass and picked up 100 rounds of Hornady new brass over the weekend.
I was wondering if I can gather any meaningful information while fire forming the brass. Is there any reason to try different charge weights and compare groups and/or velocity or should I just load a fairly light load and waste the powder and bullets?
I have a comparator to see how much the case grows and will be checking concentricity after firing and sizing.
Hope this makes sense and thanks!

 

[std7mag]

Your fire formed brass shouldn't be that much different from your new brass.

The difference in volume between your Win brass and Hornady brass may be a larger difference.

 

[TrapperBR549]

I know when I initially fired the Winchester it stretched substantially so I wasn't sure how much difference that would make. I assume headspacing off the belt on the new stuff vs. off the shoulder after fire forming will make some difference as well?

 

[Straightshooter1]

The background is I am developing hunting loads for an elk hunt this fall. I have a Win M70 300 Win Mag.
I started with a couple boxes of Winchester factory ammo, fire formed and I am making progress towards a satisfactory load. I haven't been thrilled with the Winchester brass and picked up 100 rounds of Hornady new brass over the weekend.
I was wondering if I can gather any meaningful information while fire forming the brass. Is there any reason to try different charge weights and compare groups and/or velocity or should I just load a fairly light load and waste the powder and bullets?
I have a comparator to see how much the case grows and will be checking concentricity after firing and sizing.
Hope this makes sense and thanks!

Hornady brass will have less case capacity than Winchester brass and there's enough difference that changes the ballistics some.

For example, in a .308 I've found Hornady brass to have a capacity of ~ 55.4 grs H2O and Winchester brass at ~ 57.7 grs of H2O. If I'm loading with Varget, I'd be getting ~ 40 fps difference.

So, switching to Hornady brass, I'd say you'll need to reduce your charge weights to keep in that same accuracy node.

 

[Bill Norris]

Agree. Winchester brass always weighs less than other brands that I have weighed. Case neck thickness is always less as well.

 

[mikecr]

Regardless of capacity differences, chamber fit will be different(on first firing) and this affects velocities, likely to lower them. It takes energy to expand new cases.

I would not powder develop while cases are changing.
You can do full bullet seating testing while fire forming.

 

[Coyotefurharvester]

If you have a good barrel, using mass production hunting bullets, you will not see much difference in group sizes between 1st,2nd,3rd firings(if all loaded the same). You may have sizing issues after the 3rd or 4th loading.

 

[thatguyshm]

For a hunting rifle I absolutely will develop loads with new brass. If you find a good load chrono it, then try it with the fire formed brass. If the velocity is different, adjust powder charge accordingly, then check group sizes. You may be surprised.

If that doesn't work, set the shoulders back a bit further than normal. It's hornady brass, I've found the pockets will go before you have any chance of case separation.

 

[TrapperBR549]

Regardless of capacity differences, chamber fit will be different(on first firing) and this affects velocities, likely to lower them. It takes energy to expand new cases.

I would not powder develop while cases are changing.
You can do full bullet seating testing while fire forming.

I have a load that shoots reasonably well with the Winchester brass. It is nowhere near maximum pressure, I think I went 2.0 grains higher and still didn't show excess pressure, so are you saying I should do seating testing with that load in the new Hornady brass? I am significantly off the lands at maximum overall length based on the magazine, I think by around 30/1000. What increments should I test, i.e., 3 shot groups reducing OAl by .005?

 

[TrapperBR549]

For a hunting rifle I absolutely will develop loads with new brass. If you find a good load chrono it, then try it with the fire formed brass. If the velocity is different, adjust powder charge accordingly, then check group sizes. You may be surprised.

If that doesn't work, set the shoulders back a bit further than normal. It's hornady brass, I've found the pockets will go before you have any chance of case separation.

What will setting the shoulders back more do?

 

[Coyotefurharvester]

Don't move the shoulders until unnecessary extra effort for hunting, follow Berger bullets seating depth instructions. Innovative technologies belted mag collet die could be your best equipment upgrade.

 

[Ned Ludd]

Trapper - I use virgin brass for load development regularly. My observation is that the necks need some work straight out of the box, so I open the necks first with an oversized expander mandrel, then size them back down with the appropriate bushing. A tuned load in virgin brass can shoot very well. Once the brass is fire-formed, you may need to tweak it a bit from the virgin brass load, or at a minimum confirm it is still working well.

I have used loads in virgin brass on a number of occasions in F-Class matches. IMO - there is no good reason to put a bunch of rounds into the dirt just to fire-form the brass while getting little useful information in return. Prep it carefully and use it.

 

[thatguyshm]

What will setting the shoulders back more do?

If you find your once fired loads don't match up well to your new brass loads, moving the shoulders back to closely resemble your new brass may bring it back around, case life will suffer, but hornady doesn't usually last all that long in the pockets so it can be a wash. It all depends on what you want to do.

 

[mikecr]

I have a load that shoots reasonably well with the Winchester brass. It is nowhere near maximum pressure, I think I went 2.0 grains higher and still didn't show excess pressure, so are you saying I should do seating testing with that load in the new Hornady brass?

Yes, FULL SEATING TESTING. Berger laid out a good process for this (works for any bullets):
https://www.longrangehunting.com/th...-from-berger-vld-bullets-in-your-rifle.40204/

With their process you back off the load to below where you know you'll be,, not just for safety but to be sure you're NOT in a powder node, which would collapse during testing, messing with results of seating (itself).
It sounds like you're backed off for fire forming. Good time to do this testing. It's a good time to do primer swap testing as well (around 2nd or third fire forming).

This would give you a best course seating, and with cases stable in dimension (fully fire formed & sized per your reloading plan), move to powder development. Then with best course seating, best primers, and best powder load, move to fine seating testing. This is merely tweaking within a relatively narrow seating window(~8thou) for tightest group shaping.
You can also go to neck tension testing now. This is done through neck sizing LENGTH.

I know folks are very happy with new brass results, for hunting and competition.
But here we're talking about load development only -without tail chasing.
With many chambers, fire formed brass does not shoot the same or close to new brass. So instead of doing powder testing with tweaks, perhaps at each fire forming, just wait until it's the right time and do it once.
I also recommend that you find best seating off the lands(OTL), prior to powder development, for way less tail chasing in that regard.

 

[TrapperBR549]

Thanks for all the help, it is truly appreciated.