More questions about brass sizing and shoulder bump.

[Joshboyfutre]

So I got the proper device to measure relative headspace (hornady comparator is why I say relative). I had some brass around that had been shot with just neck sizing way to long, some I can barely close the bolt. The measurement I got for that was 3.636, Then I measured some Fed. M80 7.62×51 and got 3.630. Heres where my confusion sets in. I went and shot some reloads I had already loaded by just setting my FL sizer up as instructed by lee. Those are measuring 3.631. Should I go with the old overused brass measurement, or the stuff I fired today? 3.636 or 3.631? I'm probably just gonna go buy new brass and start from scratch till I find the numbers I need unless someone has a better idea of what measurement I should use. Thanks

Continued from here.

 

[243winxb]

308 Winchester- SAAMI has Head to datum at 1.634" - 007" for a cartridge. Not sure about your measurement. Have not used a Hornady tool.

I can barely close the bolt. The measurement I got for that was 3.636,

Bump the shoulder back 2 or 3 thousandths.

I had already loaded by just setting my FL sizer up as instructed by lee. Those are measuring 3.631.

This is not to much, or dangerous, ok to use.

Do a test. Take your neck sized 3.636" empty case that chambers hard. Double check the measurement , head to datum. Place a used primer in empty case. Place empty case in the rifle. Pull trigger so the firing pin hits the primer. Now measure the head to datum again. Has it gotten shorter from the firing pin strike??

 

[Joshboyfutre]

The Hornady tool doesn't give me a specific measurement per se, as in I cant measure the exact shoulder from datum point to head or any of that. It provides a fitting that is for a number of cardridges. It's basically only good for measuring how far the shoulder has been moved relative to the original measurement.

As far as putting a piece of brass in the rifle and striking the primer I'm afraid I don't understand wjat you mean. I went ahead and put a empty from today in and dry fired it and everything measured the same. Primer kinda dented in more and took on a concave shape but other than that no change.

 

[Walkalong]

I had some brass around that had been shot with just neck sizing way to long, some I can barely close the bolt. The measurement I got for that was 3.636

Set up the sizer to move the shoulder to .003 less than that. Shoot a couple and take an average of where the shoulder is. Set up sizer to move the shoulder .002, which may end up being the same thing. Then again, the cases might be hard to chamber from being fat, and not necessarily from the shoulder holding it back. That is why I say to move the shoulder .003, shoot, & check again.

 

[Joshboyfutre]

Ok I'll give it a run and let u know.

I'm also wondering this. If I set my fl size die for a certain setting for shoulder bump, and I run 3 cartridges of different headspace through, will each one get moved back x amount or will they all get sized to x headspace? Hope I was clear there lol.

 

[243winxb]

As far as putting a piece of brass in the rifle and striking the primer I'm afraid I don't understand wjat you mean. I went ahead and put a empty from today in and dry fired it and everything measured the same. Primer kinda dented in more and took on a concave shape but other than that no change.

In some rifles, the firing pin strike will set the shoulder back about .006" Different types of rifle extractors, act differently.


Shoulder bump is best controled, when the shell holder contacts the bottom of the FL die.

 

[Orcon]

So I got the proper device to measure relative headspace (hornady comparator is why I say relative). I had some brass around that had been shot with just neck sizing way to long, some I can barely close the bolt. The measurement I got for that was 3.636, Then I measured some Fed. M80 7.62×51 and got 3.630. Heres where my confusion sets in. I went and shot some reloads I had already loaded by just setting my FL sizer up as instructed by lee. Those are measuring 3.631.

For what it's worth, maybe zero your caliper to the size of the comparator. Mine measures 2.0040 inches.

 

[Walkalong]

Ok I'll give it a run and let u know.

I'm also wondering this. If I set my fl size die for a certain setting for shoulder bump, and I run 3 cartridges of different headspace through, will each one get moved back x amount or will they all get sized to x headspace? Hope I was clear there lol.

Other than differences in brass spring back, they'll get moved to the same spot. How much head clearance you have will depend on how much the shoulder is set back compared to your chamber. That is why you start with brass fired in the gun you are loading for.

 

[MEHavey]

Gradually size a "too long" case until it juuuuuust closes w/o resistance.
Measure that case (or couple of cases/average) ** That is your baseline.
Size your cases ~2 thou less than that baseline number.

** (BTW, zero your calipers after you put the Hornady adapter on.
That way you'll get the 1.634" (or so) SAAMI-like figure.

 

[Bart B.]

In some rifles, the firing pin strike will set the shoulder back about .006" Different types of rifle extractors, act differently.

The extractor has nothing to do with shoulder setback. Do you think extractors hold case heads against bolt faces? I'm not aware of any that do.

Shoulder bump is best controlled when the shell holder contacts the bottom of the FL die.

That typically bumps shoulders back too far. Unless Redding Competition shell holders the right height are used.

 

[243winxb]

The extractor has nothing to do with shoulder setback. Do you think extractors hold case heads against bolt faces? I'm not aware of any that do.

Some do a better job (Rem 700) then a Savage Axis. Less slop.

Head Clearance
No Shoulder, & it still Fired -

Shoulder not needed to fire a primer. Savage Axis 223- TEST- Cut case off behind the shoulder. Install new primer in fired case. Load into rifle using a cleaning rod to keep case head in bolt face & under the extractor. REMOVE CLEANING ROD BEFORE FIRING. Did this 2 times. Both primers fired when the trigger was pulled. 1 case ejected normal, the other did not. Some firearms will need the shoulder, some dont. The extractor must keep the case head from moving forward to far. Firing pin protrusion can be as much as .055" Its going to reach the primer. If you bulge the neck or shoulder by over crimping, 2 things may happen. 1.A Misfire from a bulge in the neck/shoulder junction. This will cause the firing pin strike to be absorbed, as it pushes the neck deeper into the chamber,but only if the cartridge head clearance is large/loose. 2. If the shoulder is bulged from over crimping, the bolt will not close correctly & extraction may be very difficult. http://www.thehighroad.org/showthread.php?t=689597

 

[Bart B.]

Some do a better job (Rem 700) then a Savage Axis. Less slop.

That stuff happens when thing are dimensioned wrong when the rifle fires. Won't happen when stuff is correct.

A Misfire from a bulge in the neck. This will cause the firing pin strike to be absorbed, as it pushes the neck deeper into the chamber,but only if the cartridge head clearance is large/loose.

That also happens when head clearance is zero with a good case. What prevents such a case from being driven deeper into the chamber setting shoulder back making the neck longer?