Where's Case Head When Round Fires?

[Bart B.]

Originally Posted by RC20

Most of the time the case head is against the bolt face and then all hell breaks loose when its fired.

How does the extractor compensate for a .010" spread in case rim thickness to do that? .243 and 308 rim thickness spec is .054" -.010". My Win 70 extractor's minimum clearance to bolt face is about .080".

[hounddawg]

How does the extractor compensate for a .010" spread in case rim thickness to do that? .243 and 308 rim thickness spec is .054" -.010".

ok that made me think , thanks

on a left eject Savage the extractor sits at the 3 o'clock position and the ejector pin is at 7 o'clock. When the case is in the chamber the walls of the case and the chamber the ejector is pushing the case away from the bolt head. When the case is pulled back and there is on longer any part of the receiver keeping the case enclosed the ejector pin flicks the case up and to the right.

That would mean at firing the ejector pin would be forcing the case forward away from the bolt face until either the hook on the ejector, the case shoulder against the chamber, or the bullet contacting the throat stops the forward travel whichever comes first

edit - that would be 9 o'clock and 5 o'clock on a right extract

[jmorris]

* The primer doesn't fire until the case stops moving forward as it's shoulder stops against the chamber shoulder, then the case expands while the primer backs out then reseats at peak pressure as the case stretches back until its head stops against the bolt face.

What about Kricotronic or EtronX rifles that have no firing pin?

Or a bullet that is seated deeper into the case as the bolt is closed with enough neck tension so the firing pin can’t drive the case forward?

Or a case that has the shoulder firmly against the chamber as the bolt is closed?

[HiBC]

What about Kircotronic or EtronX rifles that have no firing pin?

I have no experience with those.I doubt I ever will,as prosperous of an idea as it seems to be.


So I will ask you your question. Please tell me all about it.


Regarding jamming the bullet into the rifling or zero head clearance to crush fit ammo....Those anomalities can be done,but are SAAMI guns and ammo designed to work that way?

Help me understand the point you are trying to make.

[jmorris]

From an email exchange with Robert Beeman, more than a decade ago.

The Blue Book GV has three errors regarding this - they will be correcting them in the next issue. 1. The Kricotronic system is not (as listed in BBGV) an electronic trigger as found on several brands of match guns but rather it is electronic ignition of conventional primers. An electronic spark instantly and without any mechanical movement ignites the primer when the trigger is pulled. (This surely would give forensic investigators fits - no firing pin mark on fired cases!). 2. Several of the Krico centerfire rifles also displayed this astonishing system- evidently ahead of its time, it was not well accepted and was not produced after 1988. 3. Beeman Precision Arms Inc. was the U.S. importer of Krico firearms about 1986-88 but was not listed as an official importer by BBGV. Also, we imported very few (ten??) of these special guns, and extremely few (50??) were made - so the values are probably well understated.”

And the manufacturer around the same time.

“Dear Morris,

there was only a small number of this rifles built in the early 80th.
As KRICO was not strong enough to penetrate the UIT-Match rifle business we stopped the project.
In the mean time we offered our know how to REMINGTON, ANSCHÜTZ, WALTHER and more companies in this business, but these are to conservative to see the advantages of this firing system.
We are still looking for a potential partner.

Best regards
Arndt G. Kriegeskorte
KRICO & falko
Kriegeskorte Handels- GmbH
Nurnberger Stra?e 6
D - 90602 Pyrbaum
Tel.: +49 ( 0 ) 9180 278 - 0
Fax: +49 ( 0 ) 9180 266 - 1
Mail: [email protected]
Home: www.krico.de
Katalog: www.falko.de
GF.: Arndt G. Kriegeskorte, Elisabeth Kriegeskorte
Reg.Nr.: Nbg HRB 12 868
USt.-Nr.: DE 132 758 038
St.-Nr. 201/130/80087
“

The Kricotronic interested me back in the 80’s but I couldn’t afford toys like that at the time, funny they offered the tech to Remington and they turned it down. Instead making their own version.

Another improvement on the EtronX is the shorter, lighter bolt throw. The bolt on a conventional rifle compresses and cocks the spring that energizes the firing pin. The EtronX firing pin does not move but serves only to transmit the 150-volt pulse to the primer. That spring is absent on the new model.

The EtronX computer is powered by a common 9-volt battery that also supplies the juice to ignite the primer. A booster ignition circuit, similar in operation to an automotive ignition coil, pumps up the voltage from 9 to 150 volts. The high-voltage charge is stored in a capacitor that discharges when all the following conditions are met: The key is on, the safety is off, there's a round in the chamber and the trigger sends an input signal. The firing voltage travels along the ceramic-insulated firing pin, which is in a fixed position. When the bolt is closed, the pin protrudes from the bolt face to contact with the primer case. The voltage detonates the primer, which in turn rapidly burns the propellant, creating the pressure that sends the bullet on its way.

https://www.popularmechanics.com/tec.../a211/1277311/

But they required special primers.

https://www.midwayusa.com/product/10...0-trays-of-100

Regarding jamming the bullet into the rifling or zero head clearance to crush fit ammo....Those anomalities can be done,but are SAAMI guns and ammo designed to work that way?

Help me understand the point you are trying to make.

Only point is there isn’t just one way things happen when firing a firearm. If this was in the “general discussion” forum I wouldn’t have even brought up reloading ammunition for a specific rifle. It’s pretty common in benchrest though, then again there isn’t any ammunition for, say, a .262 neck 6mm PPC on the shelves at Walmart. However, the same techniques can be used in “regular” bolt guns too and can give longer brass life and less trimming as well.

[higgite]

First, let’s define “when rounds fire” to be when the hammer falls (or striker is released). For a typical “standard” size cartridge in a typical “standard” size chamber, the case head will be off the bolt face because the cartridge’s momentum will push it forward when the bolt stops. That is, unless the shooter points the muzzle up before he aims and fires.

Second, let’s define “when rounds fire” to be when the primer ignites. For a typical “standard” size cartridge in a typical “standard” size chamber, the case head will be off the bolt face because the firing pin will push it forward before it crushes the primer.

So, in summary, unless there are extenuating circumstances, the case head is off the bolt face when the round fires. That’s my story and I’m sticking to it.

[44 AMP]

I've been trying to wrap my head around the whole "firing pin drives the case forward" thing, and I keep coming back to a couple of points that don't seem to jibe. Speaking specifically of a rimless, non-belted bottle neck case and a push feed bolt system.

I agree that the base of the case will be a (small) distance off the bolt face when the firing pin strikes. What I don't get is where the "room" for the case to move forward comes from.

The front edge of the bolt pushes the case into the chamber as it feeds from the magazine. With many designs that front edge of the bolt is not the bolt face. When the case clears the magazine it pops up, up the slope of the feed ramp, and as it enters the chamber the base lines up with the bolt face, BUT at this point it is still the extractor and ejector that are touching the base of the case and pushing it forward. Not the bolt face itself.

This continues as the bolt closes, until something stops the case from moving forward. That "something" should be the shoulder of the chamber, but it could be the bullet jamming into the rifling. Either way, something stops the case from moving further forward, despite the continued pressure from the bolt.

So, the case is stopped, and the bolt continues to move forward a bit, until it reaches the end of its travel, at when point, the extractor has snapped over the case rim, and the spring loaded ejector is compressed.

This puts and keeps a forward pressure on the case, which is still very slightly "ahead" of the bolt face.
So, HOW does the case move back, against the tension from the ejector (and possibly the extractor) in order to create the clearance for the firing pin to drive it forward???

It's a demonstrated fact that if a chamber has been cut "too deep" for a case, (and there is no bullet jammed into the rifling) that the push feed will push the case ahead of the bolt, if the space exists to the point where the extractor does not snap over the rim and the firing pin does not reach the primer. It is the case being stopped from moving forward that makes the push feed work.

What force exists to push the case BACK against the bolt face BEFORE firing?? I can't think of any.

I do agree that the thinner case neck and shoulder seals to the chamber first when fired, and the case head gets pushed back by the pressure until the bolt face stops it, and that is why the case stretches.

But I just can't figure where this "drives the case forward comes from. Additionally, if it actually WAS happening that way, wouldn't the only available space for forward movement be the distance from the bolt face to the inner edge of the extractor claw, minus the thickness of the case rim??

A controlled round feed system doesn't need to rely on the chamber to stop the forward movement of the case during feeding, it is the rear face of the extractor that does that.

SO, if a push feed has room to drive the case forward with the firing pin strike, where does that room come from?? And if its not true, why are we talking so much about it???

[HiBC]

44AMP,you did bring up some interesting points.
The differences in extractors and ejectors do mess up a "one size fits all" story.

We certainly have had enough discussions on headspace,but I suggest that a rim,belt,case mouth,or shoulder of the cartridge case is designed to stop against a chamber feature that controls the forward travel limit of the cartridge.

I understand we can argue off in the weeds about people using the extractor as a headspacing feature when shooting .380 in a 9mm. I understand an old P-17 with .035 headspace that would fail the field headspace gauge can still be fired by headspacing on the extractor face,but IMO,that is an abuse. A hack.I don't know of any firearm that is DESIGNED to headspace on the extractor face. The extractor was never intended to be the anvil for a firing pin strike.
Which is another way of saying when the bolt is closed,in battery,there should be clearance between the rim and the extractor when the cartridge is as deep in the chamber as it can go. On a properly set up rifle,the extractor should not absorb the firing pin energy.

Controlled round feed: If a CRF extractor is set up with the extraction hook face to bolt face dimension tight enough to hold the case head in contact with the bolt face, the gun will not feed. CRF requires pretty generous clearance under the extractor hook. Why? When the bullet starts up the feed ramp,the front of the cartridge is elevated. The cartridge is significantly tipped off square from the bolt face. In this position,it must have the clearance for the case head to travel up the bolt face under the extractor.

CRF extractors require rim to hook clearance to feed up the bolt face.
With CRF,there is typically a receiver mounted blade type ejector.There is no spring preload on the case head.The cartridge is theoretically free to move for and aft by the amount of head clearance. This is the visua model where the firing pin strike drives the cartridge forward till the shoulder stops it.


On spring loaded plunger ejectors: YES! I agree with your point that the ejector preloads the cartridge forward to stop against the shoulder or rim or other headspacing feature. That feature is the "anvil" for the cartridge case during the firing pin strike.

Because the ejector already preloads the case head off the bolt face to the limit the chamber allows,you are correct,the cartridge will not be driven forward by the firing pin.The ejector already did that.

The case head is off the bolt face typically.

[jmorris]

SO, if a push feed has room to drive the case forward with the firing pin strike, where does that room come from?? And if its not true, why are we talking so much about it???

It’s a change from “SS or turret” or “what progressive” threads.

Good points though and not being adversarial but another “non standard”, could be a push feed bolt with no ejector and ammunition where the bullet is off the lead and cases sized under chamber dimensions, could get you there.



As you point out we are talking about something that more than 90% of firearms shooters have never thought about and likely never will, because it’s inconsequential.

[higgite]

So, the case is stopped, and the bolt continues to move forward a bit, until it reaches the end of its travel, at when point, the extractor has snapped over the case rim, and the spring loaded ejector is compressed.

That's true for push feed firearms with plunger type ejectors. A couple of my rifles qualify as such, but none of my pistols do. They are all control fed with stationary ejectors. I considered a plunger type ejector to be an "extenuating circumstance" in post #31 in the context of OP's question. ymmv

[44 AMP]

.I don't know of any firearm that is DESIGNED to headspace on the extractor face. The extractor was never intended to be the anvil for a firing pin strike.
Which is another way of saying when the bolt is closed,in battery,there should be clearance between the rim and the extractor when the cartridge is as deep in the chamber as it can go. On a properly set up rifle,the extractor should not absorb the firing pin energy.

I agree, but when the stars line up, and stacking tolerances exist in just the right way, the extractor IS the final headspace "stop". Ideally, the chamber shoulder (or case mouth ledge) should stop the case's forward movement BEFORE the inner face of the extractor claw does.

But, that doesn't always happen.

Here's another point that I don't think is being looked at quite the right way. Bolt travel. The bolt, all of them, doesn't care about excess headspace, or head clearance, only insufficient clearance interfering with its travel. The bolt reaches the end of its travel, and stops. No matter WHAT the case does ahead of it. Too long a case (or too thick a rim) is an issue, but too short doesn't matter from the bolt's point of view.

CRF guns, long or short, use the case rim under the extractor the same way a revolver uses the case rim against the cylinder. It's the positive "stop" preventing forward case movement if nothing else does.

This is why semi auto pistols (CRF) work when the case is "too short".

[Jim Watson]

All this comes out of adapting military weapons as target rifles.

The Ballard single shot was once popular for target shooting because its breechblock movement eliminated head clearance. Assuming the action were well fitted and adapted to its ammunition, of course.

F.W. Mann said of his Neidner "Hamburg Rifle" that it had no "backleash" because its interrupted thread locking lugs "screwed the breechbolt right up to the head of the cartridge."

[stinkeypete]

Sometimes I’d say the answer has to be “b” because I have seem primers swell past flush of the rear of the cartridge and spent shells wouldn’t sit flat.

But lately I have been shooting super light cast loads in my 30-06 using the bolt to do the final seating in to the cartridge and I reckon in this case the bolt is under some pressure from the ogive’s resistance to being jammed in to the rifling. So A.

But I am willing to be educated!

[Bart B.]

Originally Posted by 44 AMP

SO, if a push feed has room to drive the case forward with the firing pin strike, where does that room come from??

That room comes from the space between the bolt face to the extractor claw being several thousandths more than case rim thickness....after the extractor snaps onto the case rim

If a 308 Win case headspace is .003" less than chamber headspace and its rim is .055" thick, the extractor claw clearance to bolt face cannot be more than .058" to prevent the case shoulder from hard contact with chamber shoulder. Then hope the case shoulder isn't set back.

Measure your stuff then figure it out.

[Bart B.]

Originally Posted by stinkeypete

But lately I have been shooting super light cast loads in my 30-06 using the bolt to do the final seating in to the cartridge and I reckon in this case the bolt is under some pressure from the ogive’s resistance to being jammed in to the rifling.

Is the case shoulder set back any amount from firing pin impact force?

[HiBC]

I cannot back this up,I never tested it.
Seat of the pants conclusion jumping.....

I'd think the answer might be influenced by the design and tolerances of the rifle...Maybe a 1903A3 with excessive firing pin protrusion could set a shoulder contact back slightly...
But generally I'd look at the force going to the path of least resistance,which,IMO would be the primer dent. I would think the greater surface area of the shoulder would be more resistant than the small area of a firing pin strike.

[Bart B.]

Originally Posted by HiBC

I'd think the answer might be influenced by the design and tolerances of the rifle...Maybe a 1903A3 with excessive firing pin protrusion could set a shoulder contact back slightly...
But generally I'd look at the force going to the path of least resistance,which,IMO would be the primer dent. I would think the greater surface area of the shoulder would be more resistant than the small area of a firing pin strike.

My tests with a Win 70's 26 pound striker spring pushing its near 3 ounce firing pin 9 fps into primed 308 cases set their shoulders back .003" to .007". Pin protusion normal at .060".

[HiBC]

Time to get the seat of my pants calibrated.

Jumping to more conclusions from your data,putting the effort and time into nailing your sizing down to .002 head clearance might still result in the case head being .009 off the bolt face at firing.

Varmint Al's pursuit of low chamber friction may have merit.

Unfortunately few understand the process of polishing.

[Bart B.]

Originally Posted by HiBC

Time to get the seat of my pants calibrated.

Jumping to more conclusions from your data,putting the effort and time into nailing your sizing down to .002 head clearance might still result in the case head being .009 off the bolt face at firing.

Varmint Al's pursuit of low chamber friction may have merit.

Unfortunately few understand the process of polishing.

One of my tests.... New Federal nickel plated 308 cases had their shoulders set back .008" with 38 grains of IMR4064 under 165 grain bullets. Primers were backed out about the same amount. New brass cases loaded the same had .004" shoulder setback.

Historical note...... Why did H&H put a belt on their first medium bore cartridge which was originally rimmed but modified by taking off the rim then putting an extractor groove so it could be used in both doubles and box magazine bolt guns?

[jmorris]

What were the components, measuring instrument(s) and techniques used in collecting your data above?

Protrusion and weight would be easy enough but striker velocity would be a bit more difficult unless simply calculated vs measured.

How much difference in set back is there between different manufacturers (cup hardness) or brass (annealed/work hardened/brand) or does the same thing vary .004 from one another?

I was assuming you were using just cases in the first example but your last post has me wondering how were you determining what happed to the fired rounds in the last post, since what happened the millisecond before pressure expanded the case to fit the chamber would be “erased”.

[HiBC]

Historical note...... Why did H&H put a belt on their first medium bore cartridge which was originally rimmed but modified by taking off the rim then putting an extractor groove so it could be used in both doubles and box magazine bolt guns?
__________________

I recall reading a "letter to the editor" response to a similar question .I think it was in Rifle or Handloader magazine.I cannot source or verify it. The response was written by an older British gentleman who apparently had knowledge of ammo making in the cordite stick era.

The question was about "How do you load the charge of cordite sticks through the neck of a smaller bore,such as 300 H+H?"

The answer was they used cylindrical basic brass.They loaded the charge of cordite sticks,then ran the brass through a forming die.This is why these cartridges had the long,shallow slope to the shoulder.


This shallow slope shoulder made for a mushy and unreliable stop for primer ignition.

The belt addressed that issue and would still feed from a box mag.

[Jim Watson]

The first Holland's belted was the 1905 .400/.375 for primary use in Mannlichers.
But the 1912 .375 Magnum in Magnum Mauser made their day.
While the belted cartridges can be accommodated in doubles, they have the same trick extractors as plain rimless. Serious users can still get .375 Flanged in the superior rimmed case.

[44 AMP]

The answer was they used cylindrical basic brass.They loaded the charge of cordite sticks,then ran the brass through a forming die.This is why these cartridges had the long,shallow slope to the shoulder.

There is also the fact that those African "Express" cartridges were made knowing they were to be used in great heat, and in double rifles without the powerful camming extraction of a bolt action rifle. The long shallow slope, while giving headspace issues (requiring a belt or rim) also tend to be less "sticky" in the chamber. AND, those rounds were also not loaded to 50Kpsi +, but a more sedate 40K+psi, again, to function acceptably in the high temps expected in Africa.

I saw a series of pictures, of British women loading .303 rounds "during the war" (WWII I think, but might have been WWI). Interesting process with the cordite charge. (for those unaware, Cordite "powder" is sticks, rather like graphite coated angel hair pasta, long thin "sticks" or "cords")

They would take a bundle of cordite sticks, place them in the case (sadly, I can no longer remember if the cases were straight or not) cut off the sticks flush with the case mouth, using a knife, and repeat the process until the bundle was used up, then get a new bundle, until the tray of cases was finished, then the charged tray was moved to another station where the bullets were seated.

the smell of Cordite is unique, it doesn't smell quite like the powder we use today, but "the smell of coridite" has become a phrase used by undereducated writers describing ALL gunsmoke.

The next time you read something written about modern times, but the writer uses "the smell of cordite" or a "whiff of cordite" or "cordite fumes", you need to know its FICTION.

[Jim Watson]

They would take a bundle of cordite sticks, place them in the case (sadly, I can no longer remember if the cases were straight or not) cut off the sticks flush with the case mouth, using a knife,

Then where did the bullet go?
Picture at
https://www.milsurps.com/showthread.php?t=59543
shows Cordite strands clearly shorter than the case and a post further down that thread says the usual load was 44 strands 1.55-1.60" long.
Which agrees with Greener who said that Cordite was loaded in "ropes" with the bundle cut to length specified to the 20th of an inch.

There is a story that PWHs became dissatisfied with .458 Winchester Magnum because backing down the load of compressed Ball powder for tropical use and shortening the barrel to 22" brought the velocity below 2000 fps. So they pulled down the ammo and reloaded it with Cordite from surplus .303. That got the velocity back up in line with the .450 N.E. without "pressure signs."

[Metal god]

Well would you looky there , BART B ! How the hell are you old internet friend ?

The case head will be forward of the bolt face the same distance of head clearance if there is any . This has been debated a few times on here with the most recent that I remember being a thread Jeephammer was in . His thought/theory was even though the firing pin drives the case forward . The pressures created at combustion was not enough to stick the case to the walls of the chamber resulting in the case quickly moving back against the bolt face .

I tried explaining with others that there is more then enough pressure to hold the case in the position the firing pin left it . I not only post a pic of a extracted case from a poorly cut chamber that clearly shows the tool marks in the chamber imprinted on on/into the fired case . I then went back into my notes and showed how at least 2 light loads I tested did just as you say here

New Federal nickel plated 308 cases had their shoulders set back .008" with 38 grains of IMR4064 under 165 grain bullets. Primers were backed out about the same amount.

I never measured how far they were sticking out but they were noticeably protruding from the primer pocket . This was all I've ever needed to see to confirm not only does the firing pin drive the case forward creating any allowable head clearance . It also showed that the case does indeed stick to the chamber walls and if there is not enough pressure to stretch the case head back to the bolt face . Your primers will protrude from the primer pocket the same amount as your head clearance or pretty close to the same amount .

Nice seeing you again
Metal