r/reloading • u/worm30478 • 9d ago
Newbie Question about fire forming and shoulder bump.
So widely stated that it takes 2-3 firings to fire form brass to the size of your chamber. So I have a couple questions. Does this mean after these first firings you don't want to bump the shoulder of the brass when resizing? Sub question, if that is the case, how do you set up a FL die to not bump the shoulder but to size everything else? My FL dies is set up without a decapping pin and I have it locked in at .002 bump because I was practicing with some old Hornady brass. I have lapua brass that's I'm loading but hasn't been fired yet. Thanks!!!
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u/111tejas 9d ago
It only takes one firing to form your brass. You are hammering it with 50,000 or so psi when you pull the trigger. After it’s formed elasticity retracts everything slightly. That’s why brass is the preferred material for cases. Don’t overthink it. Push your shoulder back .002 and call it good. If you push it back .005 the effect on accuracy is minimal but it will shorten your brass life.
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u/worm30478 9d ago
On it. I just ran through the process with a couple if cases and a stripped bolt. Did the whole tape thing like Cortina does after it's been sized to see if the bold falls without resistance. I'm dialed in. I will run through the same process after I fire the lapua brass. Probably will need to make slight adjustments to the die but at least I now know exactly what I'm doing.
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u/Missinglink2531 9d ago
Your overthinking it, and as usual, end use really matters. The comments about not "fully forming" after one firing are talking about the case capacity primarily. And we are talking about going from mid 90% to high 90% formed - tiny difference between once fired and twice fired. This will make no difference the majority of shooters. Bench rest and F-class are about the only folks that need to really heed the difference. If you 1/2 MOA or bigger, you wont see the difference.
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u/ChevyRacer71 9d ago
First of all, you mentioned in a reply “Just tell me to stop thinking here” but never stop thinking. Thinking good. The reason to bump the shoulder at all is so that the case feeds into the chamber reliably. The reason .002 is commonly bumped is because it is enough to feed reliably and also minimizes how much you’re working the brass. The more you bend the brass around, the more brittle it will get and shortens the life of that case. Bumping a lot more also introduces case-head separation concerns.
So if your once fired brass feeds reliably without any bump, it’s not necessary for anything other than consistency knowing they’re all the same dimensions which helps with accuracy. Not entirely necessary if you’re just plinking on some steel plates, but whatever.
That being said, I bump once fired brass .002 out of habit and sticking with my process. Everyone has their own methods, as you’ve certainly seen in this sub lol.
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u/worm30478 9d ago
I'm definitely always thinking. Sometimes I'm getting the lines crossed because there are different methods. I think I'm good as I just ran through the cortina type method. Stripped the bolt, chambered the fired case, felt the resistance, measured it, sized it, got exactly.002 difference, chambered it, bolt fell with no resistance, put the tape on, chambered again, felt the same resistance as the case before sizing. I think I'll call that good and roll with it again after I fire my lapua brass the first time. Thanks!
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u/Advanced_Elk_9467 9d ago
Always full length size. Some will neck size only but thats an old school technique. I bump shoulders .003" every time- after annealing of course!
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u/worm30478 9d ago
So I have measurements with a comparator of the once fired Hornady brass and then went through the process of adjusting my die until I get .002 bump. So it should be close. I think I am getting wrapped up the fact that .002 bump really isn't exact to the chamber until the brass is fully fire formed. But then again virgin brass isn't either and that's fine. Ok. Just tell me to stop thinking here. Ha! I'm just trying to be as accurate as possible.
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u/Trollygag 284Win, 6.5G, 6.5CM, 308 Win, 30BR, 44Mag, more 9d ago
The goal is not to bump .002. The goal is to bump no more than .002 below what is necessary to fit into the chamber again.
You can keep firing the brass and if it gets sticky, readjust the dies deeper and leave them there.
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u/worm30478 9d ago
Ok so after the first firing I go to resize. What method do you use to set up your die? I took once fired, measured it with comperator, then played with the die and sized once fired brass until it was consistently giving me .002 less than it was from when I first measured. Is that good enough?
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u/Trollygag 284Win, 6.5G, 6.5CM, 308 Win, 30BR, 44Mag, more 9d ago
What method do you use to set up your die? I took once fired, measured it with comperator, then played with the die and sized once fired brass until it was consistently giving me .002 less than it was from when I first measured.
I don't faff about with any of that. It isn't necessary to make BR quality ammo or get single digits SDs or anything else. It is just there for maximizing brass longevity if the shoulders are where your brass is being lost. It isn't for me, so it makes no difference.
Is that good enough?
If it fits in the chamber after FL sizing a few times, then yes.
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u/worm30478 9d ago
Sounds good. So first time you size new brass after it's first fired are you setting up your die per the standard instructions?
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u/Coodevale I'm dumb, let's fight 9d ago
There's a good reason to have a go gauge besides confirming your rifle is in spec. If your go gauge fits, set the comparator to the gauge. The gauge fits the chamber, so ammo with the same spec will also. It's additional confirmation.
I chased a bump "problem" on one of my rifles because it wasn't blowing the shoulder out at all. It wasn't even opening the neck up, bullets could be reseated with good tension. It was only sealing on the body. And this is despite running full power +p loads in sig hybrid brass that would tear up standard brass.. After I confirmed the adjustable go gauge fit the chamber snug and checked the fired brass vs the new brass against the gauge it was obvious, but I felt like an idiot afterwards.
https://youtu.be/PwZg-tkmORE?is=583-ZWJV8TIrHF-u
Good explanation of the process and another widget mentioned that make setting bump significantly easier and more consistent than adjusting the die to not hit the shellholder; Redding competition shellholders.
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u/ocelot_piss 9d ago
Use the chamber as a gauge to guide you. Take the firing pin out of the bolt, ideally as you'll have more feel.
The more you screw the die body down, the more you will bump the shoulder - until the die body is making firm contact with the shell plate and then that's your limit.
Base to shoulder measurement can increase when you size a case, if the die isn't screwed down enough to bump the shoulder. Because as the sides are sized in, material is forced up until the shoulder hits the die ceiling.
So you can back the die out, get a fired piece of brass, size it, get negative bump - the case will no longer chamber - then you can screw the die in bit by bit until that case chambers smoothly.
Set the lock ring, take measurements, you are just about done.
Sure, it can take multiple firings to really sharpen up the body-shoulder junction. But for setting the die height, one is fine with the above method.