Fire forming brass changing results.

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Fire forming brass changing results.

Post by Diddums » 28 Apr 2019, 11:42 pm

I did some load testing with new un-fired winchester brass for my 300WM and I had a good group of about 1/2 inch.
Now all the brass is fire formed and grew by about .160 of an inch.

Anyway, I took the good load and went to narrow it down and see if I could replicate it and the results were completely different, I just had a string going up and left.

Would having the brass stretch from fireforming be enough to completely change the results I had with new (shorter) brass?
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Re: Fire forming brass changing results.

Post by deye243 » 28 Apr 2019, 11:49 pm

So was this a .5" average of 5 x 5 shot groups
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Re: Fire forming brass changing results.

Post by duncan61 » 29 Apr 2019, 12:14 am

I found with factory loads and new brass you fired it once then neck trimmed back to length then did not have to trim brass again.I would spin 10 or so every new reload batch and no new material came off even after multiple firings.I have concluded that once brass is formed to the individual chamber and trimmed it stays uniform from then on.I have found some reloads wont chamber in others rifles.This result has been uniform with .222 .243 and 7mmRem Mag brass.If you anneal the brass it could affect this
.22 winchester .22hornet .222 .243 7mm rem mag cbc 12g
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Re: Fire forming brass changing results.

Post by Diddums » 29 Apr 2019, 7:16 am

deye243 wrote:So was this a .5" average of 5 x 5 shot groups

No, only a 3 shot group as I was doing .5 grain steps.
The group's before an after started opening up.
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Re: Fire forming brass changing results.

Post by bladeracer » 29 Apr 2019, 8:40 am

Diddums wrote:
deye243 wrote:So was this a .5" average of 5 x 5 shot groups

No, only a 3 shot group as I was doing .5 grain steps.
The group's before an after started opening up.


You're making load development decisions on a three-round group?
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Re: Fire forming brass changing results.

Post by bladeracer » 29 Apr 2019, 8:53 am

Diddums wrote:I did some load testing with new un-fired winchester brass for my 300WM and I had a good group of about 1/2 inch.
Now all the brass is fire formed and grew by about .160 of an inch.

Anyway, I took the good load and went to narrow it down and see if I could replicate it and the results were completely different, I just had a string going up and left.

Would having the brass stretch from fireforming be enough to completely change the results I had with new (shorter) brass?


As for fire-forming, yes it can have significant effects depending on how much difference you have in capacity before and after fire-forming. In a "smaller capacity" full-length sized case you'll have higher pressure and velocity than with a case that fits the chamber.
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Re: Fire forming brass changing results.

Post by Member-Deleted » 29 Apr 2019, 9:08 am

Diddums mate I fire form for a Ackley 22-250 but its a little bit more extreme than what you are doing but I also find that fire forming produces a different outcome so I fire form with a light load so as not to stretch the brass too much but you're only forming the brass to your chamber a little less than the Ackley I find that to find a good hand load its best to use fire formed brass as much as possible then once I have a load I use that in the new brass as well you'll find there won't be much change after that if you have a light barrel the more you shoot in succession poi may change as the barrel heats up :thumbsup:
Last edited by Member-Deleted on 29 Apr 2019, 9:39 am, edited 1 time in total.
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Re: Fire forming brass changing results.

Post by on_one_wheel » 29 Apr 2019, 9:26 am

There's a chance that your .5" 3 shot group was a "fluke" group

Personally I prefer to rely on 5 shot groups.

And if the best group can't be replicated then it's considered a fluke group.

I wouldn't bother developing a load unless my brass was all at least once fired, trimmed, annealed, cleaned and sorted by volume or weight.
Doing this will remove a few variables.
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Re: Fire forming brass changing results.

Post by marksman » 29 Apr 2019, 3:59 pm

IMHO you will not get good information on your reloads till you have fireformed your cases, some case's will need more stretching or filling out than others so there can be a big difference in volume

as far as how many shots to be able to asses a good or bad group when testing, that's up to you
I usually test with 3 shot round robin groups then verify good groups with a 5 shot or 10 shot group,
but understand this that if your first and second shot are 2-3 inches apart there is no benefit in shooting again, is there so why would you keep going to 5 shots
once you have found your sweet spot you should be able to still get a good group with a bit of variance in reloads

I would suggest you fireform your cases and then do your testing using an ocw test
http://optimalchargeweight.embarqspace.com/

understand though that there are other things that can make your .5 group different than internal volume
hope it all works out for you :drinks:
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Re: Fire forming brass changing results.

Post by RoginaJack » 29 Apr 2019, 4:26 pm

Yes, spot on "Marksman"...
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Re: Fire forming brass changing results.

Post by SCJ429 » 29 Apr 2019, 6:57 pm

Now you have once fired all your brass, trim them and do your usual match prep. Get your favourite 180 grain pill and get it going at about 2950 fps. You now should be close to your accuracy node. Sounds simple enough, never works out that way.
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Re: Fire forming brass changing results.

Post by SCJ429 » 29 Apr 2019, 7:32 pm

2950 is a good speed for a 180 and then you just need to get the thing to shoot. A friend had a 300 Win Mag fly rifle about 15 years ago. We would get the speed we wanted and then tune it. You could try for a higher speed if you think you can produce it but with a factory rifle 2950 is a nice achievable speed.
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Re: Fire forming brass changing results.

Post by marksman » 29 Apr 2019, 11:15 pm

I used the ocw to do testing on my last 300wm
after finding a brilliant load I chronographed it and it was doing 2950fps with an es of 7fps with 180gr accubonds
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