Why would brass shoulders stop moving forward?

[Falfan2017]

Using a dasher with lapua brass in a custom f class chamber. I always measured the shoulders before and after resizing to make sure I was getting the right sizing. After about 8 firings the shoulder quit moving forward. It used to grow to 1.602 or 1.603 using the Harrels shoulder measure tool and I’d bump it back to 1.600. Now the last couple firings it’s stayed at 1.600 and when I resize it stays at 1.600.

What could cause this? I’m not having any problems chambering the ammo but I’m curious as I haven’t seen that in any of my other chambers. Also I don’t anneal

 

[Stickler]

Sounds like a case of "work hardening". Have you annealed the cases recently?

 

[Bc'z]

Last statement says it all.
I just went through this.
Your gonna have to start annealing.
I use the poor boy method.
Dark room with a butane torch and a socket on my cordless drill.
Get case in to point of flame where it meets neck shoulder junction.
I'm finding spinning them faster 6-7 count in flame, spinning slower 9 to 10 count.
This should help with consistency in set back and sizing of neck.
Reloading sure was easier when I only neck sized.

Edit... You want to remove brass from flame just as it starts to glow, dont get it RED hot you'll ruin your brass for sure.
I drop my HOT brass into a pie pan and keep moving. I also let them air cool no water.

 

[Falfan2017]

I’ve annealed with the blow torch drill method before it just didn’t seem to affect the groups at all so I quit. Also was never confident I was getting the right temperature and for consistent heating between pieces.

 

[Bc'z]

I’ve annealed with the blow torch drill method before it just didn’t seem to affect the groups at all so I quit. Also was never confident I was getting the right temperature and for consistent heating between pieces.

I feel it's better'n nuthin.
Let me e'splain.
I have some hornady 6fove brass with undocumented firings some maybe 6 some maybe 10.
I wasnt getting consistent set back or bullet hold before poor boy annealing.
After annealing I had consistant .002 set back, cept the 1st piece I pushed back .008.
Inside necks all measured .262-.2625.
Measurements dont lie.

You'll have to be mindful of putting brass in flame at same angle and contact point of flame, spinning at same speed.
Start with a charged battery on drill.

Yes an annealing machine would be better, but a fella has to work with what hes got.

 

[rwj]

Is overall case length increasing or also remaining constant?

 

[Falfan2017]

Is overall case length increasing or also remaining constant?

That’s staying constant

 

[rwj]

That’s staying constant

Verify that the end of the case neck is not contacting the end of the chamber counterbore as it would resist the forward motion of the entire case when the round is fired.

 

[Falfan2017]

Verify that the end of the case neck is not contacting the end of the chamber counterbore as it would resist the forward motion of the entire case when the round is fired.

I don’t think it is. The cases are measuring 1.540 to 1.543 which is well below the trim length

 

[rwj]

I don’t think it is. The cases are measuring 1.540 to 1.543 which is well below the trim length

Ok... but easy to check by cleaning a neck end face, coloring it with a Sharpie, chambering, ejecting, then examining the neck face for smearing/loss of color...

 

[Cecil S.]

Annealing is like an art form and I still work at it. But I found Tempilaq useful to help me learn the techique of temp flow through the brass as color changes. Oh and I have a Bench Source still an art form. Lol

 

[rardoin]

If it is still shooting groups that are where you need them to be.....don't change a thing IMO. No absolute need to anneal if you are not splitting necks.

 

[Falfan2017]

If it is still shooting groups that are where you need them to be.....don't change a thing IMO. No absolute need to anneal if you are not splitting necks.

No split necks and groups haven’t changed yet. I would like to get 10 more firings on this brass though to get through the barrel so it might not be a bad idea to anneal

 

[varget204]

I’ve annealed with the blow torch drill method before it just didn’t seem to affect the groups at all so I quit. Also was never confident I was getting the right temperature and for consistent heating between pieces.

Get a bottle of 750 degree tempilaq,when put on inside neck it turns color when proper tempature is reached

 

[Ledd Slinger]

This is not really a 'problem' as some might think.

As to the why?...its because of work hardening. If you have custom dies to match your chamber and headspacing is under .003" and neck clearance is the same or less, you shouldn't have anything to worry about. Not enough flexing there to cause cracking on work hardened brass. And as long as the brass still chambers smoothly and neck tension is remaining consistent, I wouldnt even worry about annealing. The 40 deg shoulder with large surface area is what keeps the brass from growing.

If brass was growing AND work hardening, you may want to be concerned as the neck walls would be getting thinner and could eventually crack. But you stated case length is staying consistent so you should be good to go. Keep loading and sending rounds down range

 

[Falfan2017]

This is not really a 'problem' as some might think.

As to the why?...its because of work hardening. If you have custom dies to match your chamber and headspacing is under .003" and neck clearance is the same or less, you shouldn't have anything to worry about. Not enough flexing there to cause cracking on work hardened brass. And as long as the brass still chambers smoothly and neck tension is remaining consistent, I wouldnt even worry about annealing. The 40 deg shoulder with large surface area is what keeps the brass from growing.

If brass was growing AND work hardening, you may want to be concerned as the neck walls would be getting thinner and could eventually crack. But you stated case length is staying consistent so you should be good to go. Keep loading and sending rounds down range

Using the Harrels sizer fit to the chamber so in theory it’s pretty tight tolerances.

 

[Sheldon N]

Never thought I'd say this, but it looks like guffey was right.

The shoulder does not move!

 

[Jarhead6870]

Never thought I'd say this, but it looks like guffey was right.

The shoulder does not move!

My immediate thought; Ohhh...Right in fguffey's wheelhouse.

 

[BoydAllen]

When a round is fired, the case is forced forward in the chamber just a bit, then its body grabs the chamber walls and if the pressure gets high enough (which it usually does) it stretches back to the bolt face. With a forty degree shoulder and the case being work hardened, with a small primer and a relatively light pin fall the case may not be knocked forward in the chamber, and if the load is mild, the shoulder to head dimension may not change. With rimless cases using reduced loads you can have the shoulder to head dimension decrease progressively as a number of firings accumulate on a case. Work hardened cases have more spring back. You come up against this in short range group competition where a small number of cases are reloaded between matches. After a while the same die setting will no longer bump the shoulder, and you have to make a very slight adjustment.

 

[Falfan2017]

When a round is fired, the case is forced forward in the chamber just a bit, then its body grabs the chamber walls and if the pressure gets high enough (which it usually does) it stretches back to the bolt face. With a forty degree shoulder and the case being work hardened, with a small primer and a relatively light pin fall the case may not be knocked forward in the chamber, and if the load is mild, the shoulder to head dimension may not change. With rimless cases using reduced loads you can have the shoulder to head dimension decrease progressively as a number of firings accumulate on a case. Work hardened cases have more spring back. You come up against this in short range group competition where a small number of cases are reloaded between matches. After a while the same die setting will no longer bump the shoulder, and you have to make a very slight adjustment.

It’s not a very stout charge. 30.4 of h4895. I’d tested up to 32 grains with no pressure signs but this had the speed where I wanted it and most consistent grouping and velocity spreads. So it sounds like it’s a combo of light load, work hardened brass and good die to chamber fit. Grouping hasn’t suffered so I’m not worried about it just curious.