Chambered Round Alignment to Bore; Neck Sized vs Full Length Sized

[woods]

IMO it is not the firing pin striking the primer that creates the most effect in the chamber it is the jetting action of the primer itself on the inside of the primer pocket. I did a test on a case that was sized to fit tightly in the chamber and an inert primer. After the firing pin impact there was no change in the headspace of the case. On an identical case tightly formed to the chamber but with a live primer the headspace was reduced .002" to .003" at the shoulder.

So the firing pin strike moves the case forward with some force but the real force is the primer pushing against the inside of the primer pocket. Some of the force of course exits through the flash hole to ignite the powder.

Easy test to do

So also IMO, full length or neck sized, the case will be forced forward and rely on the shoulder slope to chamber slope to determine final position in the chamber when firing. But full length will progressively thin the case at the pressure ring so I like as little headspace on a sized case as possible. But also like a case body that is sized so as to not interfere with the centering action of the case shoulder slope to chamber shoulder slope.

 

[Bart B]

IMO it is not the firing pin striking the primer that creates the most effect in the chamber it is the jetting action of the primer itself on the inside of the primer pocket.

I've heard of this being the cause. So I got 10 lightweight WCC58 .308 Win. match cases (only 151 grains weight) and full length sized them such that they all had headspace of 1.628 inch. Half were primed with live Fed. 210 primers and the other half primed with the same primers but water soaked so they would not fire but have virtually the same impact through the cup and anvil to the primer pocket bottom as the live ones. Then with a 26 pound firing pin spring in the rifle with 1.6305 inch headspace, loaded and pulled the trigger on all 10 cases.

All 10 cases had their shoulders set back about 3 thousandths.

All cases had their primer cup bottoms flush with the case head.

Seems to me that if the primer's explosion pushed the case forward, why didn't the primer get pushed out of its pocket an amount equal to the difference between chamber headspace and case headspace; about 4 thousandths inch or more?

I've had greatly reduced loads not produce enough pressure to push the primer back into its pocket flush with the bolt face when the round fires so I know the firing pin doesn't have enough force to push a protruding primer back into its pocket.

 

[woods]

All cases had their primer cup bottoms flush with the case head.

Seems to me that if the primer's explosion pushed the case forward, why didn't the primer get pushed out of its pocket an amount equal to the difference between chamber headspace and case headspace; about 4 thousandths inch or more?

I've had greatly reduced loads not produce enough pressure to push the primer back into its pocket flush with the bolt face when the round fires so I know the firing pin doesn't have enough force to push a protruding primer back into its pocket.

Proves you didn't do the test

A primer will back out of the case everytime to the amount of headspace you have. That's the reason you have flattened primers from too much headspace is that the primer backed out and it doesn't get reseated before the pressures mash it flat on the bolt face.

Rifle Chamber Finish & Friction Effects on Bolt Load and Case Head Thinning Calculations done with LS-DYNA

with good headspace

How is it that in one sentence you ask

"Seems to me that if the primer's explosion pushed the case forward, why didn't the primer get pushed out of its pocket an amount equal to the difference between chamber headspace and case headspace;"

and in the next you give an example of this very thing happening

"I've had greatly reduced loads not produce enough pressure to push the primer back into its pocket flush with the bolt face when the round fires"

If you did fire the case with no powder and just a primer then it would have protruded, JUST LIKE THE EXAMPLE YOU GAVE

More Bart BS

 

[Bart B]

If you did fire the case with no powder and just a primer then it would have protruded, JUST LIKE THE EXAMPLE YOU GAVE. . . . . . More Bart BS

Well then, here some more Bart BS........

Example 1: One afternoon years ago, I fired 20 rounds of reloaded M118 7.62 NATO primed match cases with Sierra 190's seated. They didn't have the 44-gr. charge of IMR4320 in them; no powder at all. Bullets stayed in the case. And all their primers' heads remained flush with the case head identical to the rounds fired with a full powder charge. 'Twasn't I who loaded those rounds for the team.

Example 2: There's a lot more peak pressure in a round loaded with a 20% reduced charge than no powder at all. Could that be why my excessively reduced loads had primers back out of the case after they were fired and empty primed cases with bullets seated had their primers still flush with the case head when they were fired? I've fired dozens of empty primed cases measuring shoulder setback from firing pin impact and none ended up with protruding primers.

I think it's absurd for anyone who didn't observe my tests and experiences to claim they're BS. They don't have all the facts. They may just have high scores in the DIS games.

A primer will back out of the case everytime to the amount of headspace you have.

Please explain how this can happen with a .308 Win. case and have its primer back out about 1-5/8ths inch if there's only a few thousandths inch in head clearance.

 

[woods]

You're right about 2 things

1. It is more Bart BS
2. Yes we are talking about head clearance rather than the strict definition of headspace

But here are some FACTS

http://www.btgresearch.org/High-speed measurement of rifle primer blast waves.pdf

"The measurement method is simple: a firearm loaded with a primed cartridge case without any gunpowder or projectile has all the essential elements of an explosive driven shock tube whose shock wave is emitted from the muzzle after the primer is detonated by the firing pin. The blast wave measured at the muzzle depends on the strength of the primer without the confounding factors (bore friction, neck tension, powder charge, bullet bearing surface, cartridge case variations, etc.) that affect other methods of inferring primer strength and consistency."

PRIMER / PEAK PRESSURE / SD (psi) / SD (%)

Fed210 / 421.7 / 32.4 / 7.7%
Fed215M / 552.7 / 27.8 / 5.0%
CCI200 / 371.4 / 39.2 / 10.7%
CCI250 / 520.3 / 58.6 / 11.3%
FED205M / 176.5 / 20.4 / 11.6%
FED205 / 213.0 / 15.0 / 7.1%
CCI450 / 232.3 / 15.1 / 6.5%
FED205M / 208.0 / 15.0 / 7.2%


Even measured at the muzzle after passing through the case, throat and bore, the pressure was anywhere from 8 to 25 times the force of your firing pin

And how many stories have we heard (no personal experience here) about a load fired with no powder lodging the bullet in the barrel and having to take it to a gunsmith to remove it?

 

[Bart B]

Even measured at the muzzle after passing through the case, throat and bore, the pressure was anywhere from 8 to 25 times the force of your firing pin

I disagree. With pressure ranging from 176 to 552 pounds per square iinch in the primer cup area, there's only about 4 to 13 pounds of force pushing the primer out against the firing pin.

And how many stories have we heard (no personal experience here) about a load fired with no powder lodging the bullet in the barrel and having to take it to a gunsmith to remove it?

Lots in my life; typically smallbore .22 rimfire and lighter weight lead handgun rounds with small case volumes where firing primers make higher peak pressures by themselves. Had two of them with smallbore match ammo in a rifle; the bullets stopped about 20 inches down the bore. I've also heard several folks testing such issues with centerfire rifle cartridges without powder and the bullet stays well seated in place; no evidence of moving.

Run your own tests, then you'll have some first-hand experience.

 

[Boss Hoss]

almost nobody knows that when the firing pin strikes the case moves forward a tiny little bit if the primer cannot move instead. I find this to be interesting with the concept of seating primers till they crush. But the more contact area (sq. in.) in the shoulder the harder it is to move it.
gary

Sorry guy I could not resist this one lol... Great thread---am getting a big kick reading this!

REMEMBER that when you build your rifle that the SHROUD cannot in any way drag on the firing pin! WHY------every firing pin strike is going to be different in the amount of force imparted on the primer and this is important WHY?

It causes an inconsistent condition in the ignition process. Most guns and shooters are not advanced enough in their respective shooting skills nor have the equipment, or process (eg. rest set up) to take advantage of these small things which make a difference if you and your rifle are good enough.

Ok---go ahead keep it up....

 

[Bart B]

REMEMBER that when you build your rifle that the SHROUD cannot in any way drag on the firing pin! WHY------every firing pin strike is going to be different in the amount of force imparted on the primer and this is important WHY?

It causes an inconsistent condition in the ignition process. Most guns and shooters are not advanced enough in their respective shooting skills nor have the equipment, or process (eg. rest set up) to take advantage of these small things which make a difference if you and your rifle are good enough.

Most folks won't belive the vertical shot stringing at long range I've observed when using weak firing pin springs. Especially when a 15 to 20 pound spring's used instead of a standard 26 pound one. I think that spring should be replaced when it's force has dropped to 90% or less below its rated value.

 

[Boss Hoss]

Most folks won't belive the vertical shot stringing at long range I've observed when using weak firing pin springs. Especially when a 15 to 20 pound spring's used instead of a standard 26 pound one. I think that spring should be replaced when it's force has dropped to 90% or less below its rated value.

Amen Brother!!!!! I compete and Hate to lose. Leave noting to chance NOTHING if you can help it!!

Love these kinds of threads---like we used to have in the old days around here! Technical rather than basic....

 

[Trickymissfit]

I've heard of this being the cause. So I got 10 lightweight WCC58 .308 Win. match cases (only 151 grains weight) and full length sized them such that they all had headspace of 1.628 inch. Half were primed with live Fed. 210 primers and the other half primed with the same primers but water soaked so they would not fire but have virtually the same impact through the cup and anvil to the primer pocket bottom as the live ones. Then with a 26 pound firing pin spring in the rifle with 1.6305 inch headspace, loaded and pulled the trigger on all 10 cases.

All 10 cases had their shoulders set back about 3 thousandths.

All cases had their primer cup bottoms flush with the case head.

Seems to me that if the primer's explosion pushed the case forward, why didn't the primer get pushed out of its pocket an amount equal to the difference between chamber headspace and case headspace; about 4 thousandths inch or more?

I've had greatly reduced loads not produce enough pressure to push the primer back into its pocket flush with the bolt face when the round fires so I know the firing pin doesn't have enough force to push a protruding primer back into its pocket.

never thought about the jet from the primer, and I can tell you that a Federal primer is very hot.
gary

 

[Trickymissfit]

Sorry guy I could not resist this one lol... Great thread---am getting a big kick reading this!

REMEMBER that when you build your rifle that the SHROUD cannot in any way drag on the firing pin! WHY------every firing pin strike is going to be different in the amount of force imparted on the primer and this is important WHY?

It causes an inconsistent condition in the ignition process. Most guns and shooters are not advanced enough in their respective shooting skills nor have the equipment, or process (eg. rest set up) to take advantage of these small things which make a difference if you and your rifle are good enough.

Ok---go ahead keep it up....

once again another good post on the subject.
gary

 

[gunner52]

These are two identical loads out of the same rifle, first group was shot well after break in.
Full length sized.

Neck sized.

 

[woods]

Here's someone else who has ACTUALLY DONE A TEST (about 1/2 way down in Shoulder Setback With Reduced Cast Bullet Loads section)

Chapter 6.7 On Headspace - Cast Bullets For Beginner And Expert

some notable excerpts

"I have twice fired one case with ~20 oiled - new dead primers in rifles with the extractor removed, and have not yet had the headspace increase. The firing pin didn't drive the case forward."

"Some claim that the primer explosion pushes the case forward, driving the shoulder back. The primer and primer pocket act as a piston and cylinder, with the primer gas acting on the forward surface of the primer pocket, around the flash hole."

"In my guns, with my tests, it's the primer driving the case forward, not the firing pin."


"It seems that substantial pressure is developed within the primer pocket, which drives the case forward and the primer backwards. The case is stopped by impacting the chamber shoulder, while the primer is stopped by impacting the breech face. Metal deformation results from both impacts: The shoulder of the case is swaged back slightly, and the primer is slightly flattened against the breech."

Of course these people may not know what they are talking about either even though they actually did a test.

I've seen many other experiences documented through the years but don't have the time to look now

 

[Bart B]

Of course these people may not know what they are talking about either even though they actually did a test.

Did it ever occur to you that there's some undisclosed elements of those tests in Chapter 6.7 On Headspace - Cast Bullets For Beginner And Expert that aren't known? I've seen much of their same results with very weak firing pin springs that won't set case shoulders back. There has to be other details different between my tests and theirs.

But lambasting me 'cause someone else gets different results than I do is rather arrogant; it won't change my results. Anytime two different sets of test details differ, so will the results. Biggest problem is folks change more than one detail at a time. You'ld be smarter learning how our tests differ than outright claiming my data is BS. But maybe your egos won't let you do that.