Does anyone NOT bump shoulders on FL resizing after initial firing on virgin brass?

[Winny94]

Got to measuring and asking some questions from more experienced guys. I always assumed in normal circumstances (ie. not fireforming a wildcat, in spec chamber, etc.) the brass filled the entire dimension after the first firing. Now im seeing some info that says that may not be true. So with that in mind, my logic is saying if im basing my shoulder bump off of the first firing measure, I may be oversizing.
Any validity to logic of waiting 2 or even 3 firings before bumping the shoulder? (assuming it still chambers obviously)

 

[Supersubes]

Yes, it’s perfectly acceptable to FL size and not push the shoulder.

Whether or not the shoulder actually pushes out to match the chamber on the first firing is simply a question of pressure. You can most certainly do that, and go beyond that if pressures are high enough. If youve ever felt sticky bolt lift, that’s a case that grew too much, beyond its own yield, and the chamber shrunk(and bolt lugs) back down onto it.

 

[Howland]

My last load workup took three firings before some - but not all - cases had expanded to the point that the shoulders needed to be sized back.

 

[Supersubes]

There’s a little hack you can use with once fired brass. Punch the primers out, and take the striker out of the bolt. Test fit the case in the chamber. On an undersized case, the only resistance you should feel is the plunger ejector thrusting the bolt backwards into the lug abutments. From here you can actually thrust the bolt forward and feel any headspace. .002 feel like quite a lot. This does not work on floating bolt head actions very well. The next thing you’d do is size the case with the die backed out slightly. The case will usually elongate in headspace slightly when you squeeze the body down. A headspace comparator tool is very handy here. Check to see if the headspace grew, and how much. Now test fit that case. If the case was previously touching or just short of the chamber, it will likely be tight to close on now. With that info, you can determine what your max headspace length should be. Adjust the die accordingly.

 

[Tokay444]

Never on the first firing.

 

[6brshooter]

I usually measure the hottest charge weight and set die of this. This thread now has me thinking I need to measure brass on a few rifles that arent so virgin anymore.

 

[spife7980]

Depends on how much they grow from virgin to fired. If its a huge growth I would expect less fully formed cases, in this case the difference between 1, 2 and 3 firings could easily just come down to how much pressure I was putting on the caliper when I measured each different session.

I find they are generally close enough post firing that Im not gonna fret over the differences and Ill bump back .001-.002"

(Different bullet in this pic, 103 eldx)

 

[cmoore806]

Depends on how much they grow from virgin to fired. If its a huge growth I would expect less fully formed cases, in this case the difference between 1, 2 and 3 firings could easily just come down to how much pressure I was putting on the caliper when I measured each different session.

I find they are generally close enough post firing that Im not gonna fret over the differences and Ill bump back .001-.002"


different bullet in this pic, 103 eldx)

From your pictures it looks like down near the case head the dimension is getting a little larger after multiple firings. Why? Is the case expanding there as well? I always imagined it getting smaller slightly as the brass thinned and moved towards the shoulder and neck.

 

[Dthomas3523]

Easy way to go about it. Take 5 cases and load them. Shoot them.

Then do a wheeler method test. Take out firing pin and ejector. Make sure brass is deprimed. Put the fired brass in and see if the bolt drops free with gravity.

If it does, load them again, fire and repeat. Do this as many times as it takes for the bolt handle not to fall free with gravity.

If either A: the first firing falls free, or B: it takes however many firings to fall free

Bump your shoulders back .001 at a time and put it back in the chamber until it falls free.

You now have the shoulder bump measurement needed for your rifle/chamber. No “I guess I’ll just bump .002“ guessing. It might be .001 or .003 for your particular rifle.

 

[Milo 2.5]

From your pictures it looks like down near the case head the dimension is getting a little larger after multipole firings. Why? Is the case expanding there as well? I always imagined it getting smaller slightly as the brass thinned and moved towards the shoulder and neck.

I think his pics illustrate what happens to brass the more it is fired, it looses the ability to hold reshaped dimensions. I stand corrected.

 

[Howland]

I think his pics illustrate what happens to brass the more it is fired, it looses the ability to spring back the way it does when newer.

Springback increases with work hardening and decreases to it's lowest when annealed. Annealing cartridge cases targets only the neck and shoulder area.

 

[Milo 2.5]

I think it is all but impossible for all your once fired brass to end up being the same dimension. I used to neck size after the first firing to try get all my brass close to chamber size. It never worked that great, and the reason being there's too many factors going in, from reamer size, to how deep did it go,, etc...
What works for me is rechambering a healthy sampling of once fired brass, like the above video, but I don't pull the firing pin. I go off bolt closure, then measure cases, I use Whidden case gauges, easier for me and I don't need to decap, and usually end up with 3 piles of brass, long unruly, medium, and short. I take 5 of each, lube, and more or less set my die where the medium length cases stay the same size, the longer ones get a bump, the shorter ones grow lengthways in the die to die settings.
One trick I use when doing this, I warm my die up with an old hair dryer of the wife's. A cold die can skew results.
And one should always measure dimensions of new brass, esp the diameter of case, that way you have an idea of where and how much it is growing and if your die is compatible with your chamber.

 

[Milo 2.5]

Springback increases with work hardening and decreases to it's lowest when annealed. Annealing cartridge cases targets only the neck and shoulder area.

You're right, it is early, I should have wrote is looses it's ability to hold a reformed dimension.

 

[spife7980]

From your pictures it looks like down near the case head the dimension is getting a little larger after multiple firings. Why? Is the case expanding there as well? I always imagined it getting smaller slightly as the brass thinned and moved towards the shoulder and neck.

In combination with the spring back as discussed before. The base will always get a bit wider, that’s why sharing brass between different rifles can sometimes cause trouble with chambering and extraction. A small base die is a couple .00x” narrower at the base to overcome that spring back and to actually set the diameter an appreciable amount smaller.