Shoulder bump issues with .223

[Forensics Doc]

I've been reloading for a CZ527 Varmint in .223 for several years now using a Dillon 550B and Dillon dies. The gun is incredibly accurate, but like most of us I want to wring out every bit of accuracy it is capable of. The other day I wanted to recheck the shoulder bump so I took some fired cases and measured them from the base of the case to the shoulder using digital calipers and Sinclair Bump Gauge Inserts. The brass is twice-fired Lake City brass that has always worked well in the gun. Yeah, I know, it's not Lapua but it works well. The brass was not resized prior to measuring. The primers are seated below the base, so that's not an issue.

I expected to see the lengths within no more than about 0.002, but I was surprised to see the lengths were all over the map, varying from .002 to as much as 0.011. Given that they were all fired in the same gun and would be expected to expand to fit the chamber, I am stumped as to why they vary so much. I thought maybe the gunk on the neck and shoulder could account for the variations, so I cleaned them slightly with 000 steel wool It had no effect. And with this much variation, I can't see any way to set the sizing die to set shoulder bump back about 0.002.

Does anybody out there have any idea what's going on? I don't.

 

[mmcu]

Deprime, without sizing, and check again. You'll likely find more consistent readings.

Or, if you're shooting a very mild load, your brass may not be consistently expanding to your chamber dimensions.

 

[Forensics Doc]

Deprime, without sizing, and check again. You'll likely find more consistent readings.

Or, if you're shooting a very mild load, your brass may not be consistently expanding to your chamber dimensions.

Thanks, but if the primers are seated below the base of the case (i.e., no high primers) why will this help?

 

[mmcu]

It wouldn't be the first time that I've heard that "the primers are seated below the case head".

It's really simple, quick and easy; knock out the primers and measure again. It could be done in the amount of time it took me to type this message (admittedly, I type slow....). Either your problem is solved, or you need to look elsewhere.

Just trying to help.

 

[Milo 2.0]

It wouldn't be the first time that I've heard that "the primers are seated below the case head".

It's really simple, quick and easy; knock out the primers and measure again. It could be done in the amount of time it took me to type this message (admittedly, I type slow....). Either you're problem is solved, or you need to look elsewhere.

Just trying to help.

Take his advice.^^^

 

[JMayo]

I agree the dimple is bigger than you think. .002 is what I'm seeing on mine before and after depriming.
I'm also learning about shoulders in my new 6mm bral. Yesterday A couple out of 40 really got long. I don't know why. I had real heavy bolt lift and put them aside. Sure enough they measured .005 + longer.
Maybe they have been shot more.
New brass takes 2 Shooting to get to full length.

 

[Rsadams]

Always remove the spent primers before measuring...

 

[Forensics Doc]

Always remove the spent primers before measuring...

Thanks, guys. I'll give it a try.

 

[243winxb]

The firing pin strike sets the shoulder back.

 

[Ned Ludd]

As advised above, decap the cases, then measure the same 10 cases both before and after FL resize. If you still have the ~.009" length variance in CBTS (cartridge base to shoulder) after resizing I'd be concerned. If not, the resizing process has done exactly what it's supposed to do.

 

[243winxb]

Dillon 550B

A shell plate can do a different shoulder bump at each station.

Low pressure will not expand the brass to the chamber.

The .011" head clearance is border line case separation.

 

[C.E.Smith043]

A shell plate can do a different shoulder bump at each station.

Low pressure will not expand the brass to the chamber.

The .011" head clearance is border line case separation.

Very very very good point that I've never considered. And probably often overlooked

 

[Homerange]

Why FL size 223 ? I never have.

 

[Texas10]

+1^^^^^

I shoot an 8 twist CBI and 9 twist Savage in 223 and never FL size the brass. I get almost zero neck run out and never a stiff bolt on close.

As for your trouble with measuring base to shoulder with the spent primer intact, I have both of the Hornaday OAL and Comparator gages and set up both on one caliper if wanting to check base to shoulder after firing without removing the primer first. Works perfectly and I don't have to worry about damaging a de-capping rod by extending it to de-cap only.

 

[John Russell]

The firing pin strike sets the shoulder back.

It is not the firing pin - it hits a thin brass cup.

It is the blast from the primer, which has the force to dent a heavy steel pot.

The following are photos of a heavy duty stainless steel pot. I primed case was put in, standing on the head. The stove was lit, and the main dummy in charge, retreated to another room. Then I returned (after the bang) the case was sticking in the ceiling, and the pot had a deep dent, (and the wifie had a headache for two weeks).

 

[Milo 2.0]

It is not the firing pin - it hits a thin brass cup.

It is the blast from the primer, which has the force to dent a heavy steel pot.

The following are photos of a heavy duty stainless steel pot. I primed case was put in, standing on the head. The stove was lit, and the main dummy in charge, retreated to another room. Then I returned (after the bang) the case was sticking in the ceiling, and the pot had a deep dent, (and the wifie had a headache for two weeks).

Haha, here was my drop tray I used when I first got my Giraud annealer, I sat right in front of it watching it like a kid watching the cotton candy machine at a carnival. I had just got up to take some meat out of the freezer and bang, good thing too, by the angle of what went on, the blast would have came in the direction of my face. Right after it happened, I realized I had 3 more primed cases in the hopper.

 

[Shynloco]

Forensics Doc,
Would this be the FIRST TIME you measured your brass since firing it as NEW? The other question I have is your LC Brass all from the same lot or are they a mish mash set you acquired and started shooting it? Also, did you trim it or check it after the first first? I load both LC and Lapua brass for my son's AR and Savage .223 VLP (and my AR) and I've noticed that LC brass can have lengths all over the place (after firing) whereas Lapua is far more consistent. To be sure, I measure and check every piece of brass both shoulders (using an RCBS Precision Mic) as well as the lengths prior to resizing but after firing to see what changes (if any) has occurred during firing.

Alex

 

[243winxb]

The firing pin strike sets the shoulder back.

Like i said.

I learned this when a cci 400 primer did not fire.

 

[John Russell]

Forensics Doc,
Would this be the FIRST TIME you measured your brass since firing it as NEW? The other question I have is your LC Brass all from the same lot or are they a mish mash set you acquired and started shooting it? Also, did you trim it or check it after the first first? I load both LC and Lapua brass for my son's AR and Savage .223 VLP (and my AR) and I've noticed that LC brass can have lengths all over the place (after firing) whereas Lapua is far more consistent. To be sure, I measure and check every piece of brass both shoulders (using an RCBS Precision Mic) as well as the lengths prior to resizing but after firing to see what changes (if any) has occurred during firing.

Alex

Alex... LC brass does not have lots, it is mish-mash right out of the gate. The cases from all of the machines are put together before being loaded.

 

[onelastshot]

It is not the firing pin - it hits a thin brass cup.

It is the blast from the primer, which has the force to dent a heavy steel pot.

The following are photos of a heavy duty stainless steel pot. I primed case was put in, standing on the head. The stove was lit, and the main dummy in charge, retreated to another room. Then I returned (after the bang) the case was sticking in the ceiling, and the pot had a deep dent, (and the wifie had a headache for two weeks).

The experiment proves a primer can dent a pot, nothing more. What effect if any on setting the shoulder back isn't demonstrated simply by denting a pot.