Fireform/Shoulder Bump

[Dimner]

Quick question about fire forming brass, shoulder bumping and what not.

When I started fire forming new brass for my custom 7x57 mauser, the virgin brass at the shoulder started out reading 1.781. After two bouts of fireforming, the shoulders were at +0.0105 or 1.7915. So i set my forster benchrest die to set the shoulder back 0.002 ending up at 1.7895.

From there I noticed that the should does not ever bounce back to 1.7915 after full power loads. It always stays at 1.7895. I'm on my 9th time reloading this brass, and it's still at that shoulder measurement. I anneal the brass every cycle, in case that is useful information.

My load is near max pressure for modern day loads. GRT estimates I'm at 50-54k psi. Again, this is a custom barrel, so the pressure isn't an issue with this cartridge.

So my question is....what should I be bumping my shoulders back to? 1.7895 or another 0.002, meaning 1.7875?

 

[Coyotefurharvester]

What does your rifle say? My bolt doesn't want to close easily? Or my bolt closes practically by itself.
First one, bump back 0.002 and check fit(bolt closure).
2 nd one , leave your die set as is. Check bolt head clearance with spent primer to verify. 0.002 space.

 

[Dimner]

My rifle says it's as confused as I am. I did the whole bolt closing and should bump process when I first fireformed the brass. It helped me verify my decision to bump to 1.7895.

But thats not really the issue, my rifle and I are confused why my fired brass not expanding back that 0.002? Is this common?

 

[William Vogel]

If your brass isn’t growing and the bolt closes easily with your annealed and sized cases then leave it alone. The reason for the .002 bump is because generally there is a slight inconsistency and it gives the slightest amount of room for error. The ideal bump would be .0005- .0000 but then you would get a heavy bolt close on some instances. I full length resize with .002 shoulder bump. My case always grows back that little bit but it’s not always .002. My die is set and I never adjust it. I simply size a case at the beginning of the sizing session and test fit it in the rifle. I then size brass. I’d just remember to test fit a case of two before charging and seating bullets since your measurements aren’t changing much.

 

[Coyotefurharvester]

2nd question .Yes, many reloaders only neck size thru multiple firings before needing to full length/body size.
Spring back/brass memory is high on my list of reasons why there is confusion about adjusting sizing die. And brass functions differently in some chambers.

 

[mikecr]

my rifle and I are confused why my fired brass not expanding back that 0.002?

You're confused about why shoulders should be bumped.
It isn't just to say you do.

 

[6BRA]

The shoulders should not touch the front of the chamber. This allows the bullet to line with bore, without torque. Regardless of brass life. " I neck size t-shirts available"

 

[Dimner]

Thanks for the replies gents. I really appreciate it.

I think I'm not explaining the issue correctly for some.

1) I do not neck size
2) I partial full length resize (shoulder bump) with a 0.002 shoulder set back. I use forster benchrest dies.
3) I do understand why we set back the shoulder 0.002. That is why when I started with virgin brass I checked the shoulder fit with fully expanded brass and adjusted my die until I could close the bolt easily on a shoulder bumped partially fully resized case. I followed the instruction I saw in an Eric Cortina vid on the subject.

4) My only confusion.... why are my shoulders not growing back to the full size?


Thank you Mr Vogel (name sake of my high school physics teacher), I will continue with my die locked in where it is and just test on a bolt close each time I resize a batch.

 

[ShaunBrady]

4) My only confusion.... why are my shoulders not growing back to the full size?

It could be that after 2 firings the brass has work hardened enough that it springs back after firing at the pressure you're running.

Your annealing might be on the light side? I noticed that when I switched to an AMP annealer from a Benchsource my brass was a lot softer. I'd been setting up the Benchsource with the dull red in a dark room method.

 

[William Vogel]

Thanks for the replies gents. I really appreciate it.

I think I'm not explaining the issue correctly for some.

1) I do not neck size
2) I partial full length resize (shoulder bump) with a 0.002 shoulder set back. I use forster benchrest dies.
3) I do understand why we set back the shoulder 0.002. That is why when I started with virgin brass I checked the shoulder fit with fully expanded brass and adjusted my die until I could close the bolt easily on a shoulder bumped partially fully resized case. I followed the instruction I saw in an Eric Cortina vid on the subject.

4) My only confusion.... why are my shoulders not growing back to the full size?


Thank you Mr Vogel (name sake of my high school physics teacher), I will continue with my die locked in where it is and just test on a bolt close each time I resize a batch.

I think there’s a possibility that the case measurement you made initially was from an over pressure load and the case was sprung long inside the chamber. Your cases now are not being sprung but probably they are being sized down at the body and not the datum. I’d adjust the die a little tighter and push the shoulder .001-.002 from what is coming out of the gun now just for the sake of ensuring the brass isn’t causing the bullet/neck from being misaligned in the chamber.

 

[BoydAllen]

Your pressures seem to be mild, I think that the standards for that caliber are because there are a lot of weaker small ring Mausers out there. If your rifle has a modern action, you can take advantage of that, if you want to. Beyond that, we bump to create clearance, IF WE NEED IT. IF you set your die to produce the fired head to shoulder length are there any problems? If there are not, I would continue that way. With cases that have relatively small angle shoulders, particularly if the brass is kept relatively soft at the shoulder by annealing, as the case is fired, it is wedged forward in the chamber, temporarily shortening the head to shoulder measurement, until the pressure rise stretches the case. Since brass has some spring back, it will not hold the maximum datum to head measurement as the pressure subsides. The key here is to remember why we bump and not over analyze. If a thing works over a number of firings and cases do not appear to be degraded, then by my definition the procedure is correct.

 

[Dimner]

It could be that after 2 firings the brass has work hardened enough that it springs back after firing at the pressure you're running.

Your annealing might be on the light side? I noticed that when I switched to an AMP annealer from a Benchsource my brass was a lot softer. I'd been setting up the Benchsource with the dull red in a dark room method.

I let mine go for a half a second longer than dull red. Also, I am just touching the pointed tip of the blue flame to the neck/shoulder junction.

Mr Vogel (also coach of my HS soccer team) I'll give that a try. I don't think my initial loads were too high pressure, but I did use a pistol powder/cast bullet combination for the first load. Maybe it was just too fast of a pressure curve?

Mr Allen, always happy to read your suggestions. I don't think I'm under pressure. My two main loads are right around 50-54k psi per GRT. I use the software with my labradar readings to come up with the pressure estimates. I do know once I get in the 56k+ psi range I start seeing ejector flow marks on the brass.

I think springback may be the issue here. This is my first custom barrel with using reloading techniques that are well regarded on this site. I was concerned this might be a odd occurrence that could inform of some other issue going on. I'll still load up a few strings with another bump back and see what it does.

I'm a little timid right now with my reloading practices. I was able to make up a really good load earlier this spring. Everything seemed to be tuned just fine.

Then two variables changed.
1) it became a bazillion degrees outside
2) I installed my first ever 36x scope.

The powder I'm using (ramshot hunter) is know to be pretty touchy in high heat. So I tried to re-tune... but this 36x scope is just so much different that my confidence is low in my shooting. Im trying to get much more trigger time, but the weather is not allowing many successive shots before the barrel heats up.

Anyway, those are issues for another day. I'll keep plugging away. I appreciate all of your comments.