Shoulder bump issues with .223

[BoydAllen]

If you think about it, the dent in the primer is always a lot less than the firing pin protrusion, which means that when a round is fired that some of the energy of the firing pin is transferred to the case, because it is the primer that stops the pin's fall, not the dry fire shoulder on the pin. Of course the question then becomes what percentage of the force that drives the case forward in the chamber comes from the primer going off and how much is because of the firing pin strike. For practical purposes I am not sure that this matters. The short answer is I don't know.

 

[John Russell]

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.

Actually, it proves a lot.

If you remember your tenth grade science (I know it's been a long time, but give it a try.)

There is that boring thing about, "For every action, there is an opposite and equal reaction."

So, the force it took to dent the pot was ~ = to the launching force (the force that drove the case forward/up to the ceiling)

The fact that the case was sticking out of the ceiling, indicates the level of force (acceleration) of the case... ergo, how much force was applied to the rear of the case, pushing it forward...
...and that force is only applied for ~1/10". In a rifle, the primer and case are held together, so ALL of the primer's force was against the case, pushing it forward.

I was at the range a month ago, testing loads. There was a guy there who was doing the same, and then he couldn't open his bolt.
The RO asked me to help, cuz I keep a large box of gun tools in the car.
I went over and pounded the bolt handle up with the palm of my hand... and sure enough, the bolt would not open.

It was a Rem .220 Swift, so I asked him how hot was the load. He said the round didn't shoot at all. He just heard a click and couldn't open the bolt.
I tried the open the bolt with my palm, and it didn't budge. I really leaned on it, and no dice, it wouldn't move!

So I got a rubber mallet from my kit and with 20+ taps, the bolt opened.

The primer was fired, and was protruding from the case about 4 thou. The bullet was still in the throat... but there was no powder.

The force of the primer alone was enough to force the case forward, and the primer cup back, and lock up the action. Primer was a BR4 and the case was a .220 Swift. Rifle was a Rem 700 VSSF-II, and judging from the fired cases, it has a beautiful chamber.

Now, I have had primers that didn't lite, and there was no stuck anything - they didn't not set the shoulder back at all.

So.. that is what it proves.

 

[John Russell]

If you think about it, the dent in the primer is always a lot less than the firing pin protrusion, which means that when a round is fired that some of the energy of the firing pin is transferred to the case, because it is the primer that stops the pin's fall, not the dry fire shoulder on the pin. Of course the question then becomes what percentage of the force that drives the case forward in the chamber comes from the primer going off and how much is because of the firing pin strike. For practical purposes I am not sure that this matters. The short answer is I don't know.

Take a case which has been fired several times - don't size it. Measure the "headspace" (with apologies to Frank Guffey) with what ever tool you have. Write it down.

Now prime it, but leave the primer up high about 8 or 10 thou.

Chamber the case and fire the primer, then extract the case.

Then push out the primer.

Measure the case " headspace", Write it down.

Now, remove the bolt and let the firing pin down.

Now, set the fired primer on the firing pin which is protruding from the bolt face.


I get full primer dent and no change in headspace.

Lemme know how that workie for you.

 

[BoydAllen]

It may workie differently depending on several factors. The cases that I had the most noticeable shoulder to head shortening in from light loads were .30-06 fired in a Springfield that had had its stock spring replaced with the heaviest one that could be assembled onto the pin. The firing pin fall for that action is very long, and the weight of the whole firing pin is very much more than my more modern actions. On the other hand, with thicker shouldered brass, a larger shoulder angle, and the relatively light peck of a modern benchrest action I would expect a different outcome. Your proposed test is a good one. I could also fire a primed case for comparison. Another variable that comes to mind would be annealing. If the shoulders were softer than they came from the factory then that would tend to exaggerate the effect...I think.

 

[Shynloco]

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.

John,
Now that's a new one I'd never heard before. If true, how do you explain date stamps on the heads (or on the packaging) that indicate the same date of manufacturing, especially on their Match Brass? That's different than brass made years apart and then mixed together from a batch that had more run than another and then mixed. Please explain. Thx!

Alex

 

[John Russell]

John,
Now that's a new one I'd never heard before. If true, how do you explain date stamps on the heads (or on the packaging) that indicate the same date of manufacturing, especially on their Match Brass? That's different than brass made years apart and then mixed together from a batch that had more run than another and then mixed. Please explain. Thx!

Alex

The year on the headstamp is the year it was made. That is to insure that ammunition does not sit and sit and sit...

Civilian manufacturers use lot numbers to isolate any changes, no matter how small. They start a new roll of copper to make jackets, the lot number changes. They change a die and the lot number changes. Some companies change operator and the lot number changes. It helps them find minor changes - much too small to be of interest to the military.

In the military, they do it differently. All the case making machines get the same year stamp, even though there might be 40 stamp mills making 223 cases. They can change dies every week, and the year number never changes. On new years day (give or take) all the case machines change date for the next year, and then never change. So, why would you sort cases by year - it has no bearing on anything.

LC Match is made from hand selected cases - with no concern to "lot number", cuz there is none, until it is fully assembled... which is for different purposes.
Sort it by neck thickness and weight and then get on with loading.

 

[243winxb]

LC 5.56
Some US GI cartridge cases are run on SCAMP (Small Caliber Ammunition Modernization Program) lines. This is HIGH speed cartridge case making equipment. Several lines of SCAMP machinery may be used to run cases througout the year, or on the same lot/year of ammo. Those dots identify which SCAMP line the case was made on.

Any problem with an individual case could then be traced back to the actual production equip used to make that run.