Pierced primers

B.Larson

B.Larson

New member
Tony Boyer`s book "Rifle Accuracy"...devotes a complete chapter entitled..."Pierced Primers" to this subject...very enlightening...also Nancy Tompkins in her book "Prone and Long Range Shooting" address` the so named subject in detail with possible cures....
Each very good reads and reference books....
Enjoy....
bill
 
Repeating nor publishing an error does not make it a fact.

if that was true the economy would be in great shape as would be the SS system.
 
Primer problems

DefectivePrimer.jpg
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EjectorMark_01.jpg
PiercedPrimerPressureSign.jpg
 
A little story:
Years (make that decades) back. I made a reloading mistake that made the back of a 30-06 case look like it would accept a shotgun primer. The rifle had a double heat treat '03 receiver with a NOS Remington 03A3 bolt. I had fitted the bolt with the strongest string that could be assembled to the striker assembly with strong hands. You could definitely feel a large difference in cocking effort. The firing pint tip was well made, and it was an excellent fit in the hole in the bolt face, which was well formed with a square edge. As some of you may be aware, Springfields have long pin falls and very heavy pins. The point of this is that when I examined the primer (which had fallen out of the case when the bolt was opened) it was not pierced or cratered. I believe that the inertia of the heavy firing pin at the end of a long fall, combined with the maxed out spring, and the fit of the pin tip in the bolt face were the reasons for the condition of the primer. I am not suggesting super heavy pins, extraordinarily long pin falls. or springs that are so heavy to cause rifles to move on their bags when they are cocked, but rather would suggest that if any of these variables get too far out of line that problems can ensue. I have shot hot PPC loads with a light pin in a Viper with a 19# spring. The pin fit was good, and I believe that the .062 pin tip diameter allowed me to get away with a combination that would have given me blanked primers with a larger pin tip diameter. I will say that the pin tip dents in the primers are shallower than other rifles' and I believe that this is an indication that the pin may have been backed up under firing pressure, but not enough to cause blanking. I have seen this with the stock pin as well, with no associated problems. As an aside, I am currently running the light pin with a Tubb double spring setup that has a cocked weight of 25#, takes less effort to cock than a stock Remington spring, and has reduced cross hair vibration during empty chamber dry firing to nil. The rifle shoots with this combination, and there is less disturbance in the bags as it is cocked, because of the reduced effort required at the top half of the bolt lift. Afterthought: another thing that can cause blanking, without excessive pressure is excessive cartridge "headspace" (gapspace?). This can interfere with support of the pin strike dent during firing.
 
CMaier said:
You will have to explain that one.

The 60,000 plus pressure is going to over come a 22 or a 30 lb firing pin spring.
Click to expand...

The cross section of the firing pin is not all that large.
60,000 is force per unit area.
It also has plenty of momentum for the brief peak pressure.
An oversize firing pin hole coupled with a weak firing pin spring is a well known cause of cratering.
 
brickeyee said:
The cross section of the firing pin is not all that large.
60,000 is force per unit area.
It also has plenty of momentum for the brief peak pressure.
An oversize firing pin hole coupled with a weak firing pin spring is a well known cause of cratering.
Click to expand...

CMaier


You will have to explain that one.

The 60,000 plus pressure is going to over come a 22 or a 30 lb firing pin spring.
Click to expand...

I was thinking about the .7854 rule, if there was any truth to "The 60,000 plus pressure is going to over come a 22 or a 30 lb firing pin spring" we all would be wearing hot high pressure metal cutting gas burns all the way from the bolt face back to our ears.

F. Guffey
 
There may be more going on here than simple math would reveal. Check my math.

The radius of a typical ..072 *nominal) firing pin tip/hole is .036. Squaring that gives .001296. Multiplying that by pi (3.14...)
gives an area of . .00407 square inches. Multiplying that by a conservative 50,000 PSI gives an actual pressure of 203 lbs. If my math is correct, the logical conclusion is that there is more than spring pressure involved in keeping primers from blanking. I would guess that inertia and duration of pressure are the other factors, but would like to hear from readers as to what they think.
 
Boyd Allen said:
There may be more going on here than simple math would reveal. Check my math.

The radius of a typical ..072 *nominal) firing pin tip/hole is .036. Squaring that gives .001296. Multiplying that by pi (3.14...)
gives an area of . .00407 square inches. Multiplying that by a conservative 50,000 PSI gives an actual pressure of 203 lbs. If my math is correct, the logical conclusion is that there is more than spring pressure involved in keeping primers from blanking. I would guess that inertia and duration of pressure are the other factors, but would like to hear from readers as to what they think.
Click to expand...

would like to hear from readers as to what they think
Click to expand...

Again, I would increase the pressure of the spring. Then there is 'blanking', every time I get a hole in the primer the hole appears when the pressure inside of the primer removes the primer dent. If the pressure of the spring is not strong enough to prevent the pressure from removing the dent the firing pin moves back. When the firing pin moves back a hole appears. The hole allows the hot high pressure metal cutting to gas flow back through the hole in the bolt. If the rifles is fired with a bad spring the primer will take on the appearance of a cratered primer.

F. Guffey
 
Frank,
I was not disagreeing with you. Basically we have firing pin weight and spring weight to work with, and in the case of a stock firing pin, the spring is about all we have, unless we want to have the firing pin hole and pin tip reduced in diameter.
Boyd
 
Inertia is a useful thing in cases like this.

Even the standard 'hoop pressure' calculations have been shown to not correctly account for the inertia of the material in the pressure vessel.

The very short duration of peak pressures have (luckily for us) led to significant over-design in the barrels of guns (all the way up to large guns of 16 and 18 inch size).

The huge 'secret' of the largest guns is the very large compression force produced by the shrinkage of outer bands onto the inner bands.

This pre-load' means that chamber pressure does not exert any outward forces until the 'built in' compression forces are exceeded.

There are good reasons that only government armories produced large scale barrels for many many years.

Heating and freezing large barrels is a technology nightmare.

Think of the difference between a gentle tap of a center punch and the dimple left by a decent wack.
 
A universal receiver has a floating inertial firing pin with no spring pressure. We have shot loads as high 85,000psi and not had pierced primers.
 
A universal receiver has a floating inertial firing pin with no spring pressure. We have shot loads as high 85,000psi and not had pierced primers.
Click to expand...

MilGunsmith. Gunsmith? The M1 Garand has a floating firing pin and? No pierced primers. There is a trigger group, when the bolt backs up the hammer is against the firing pin. Then there is the speed of the bolt flying back. If I was guessing I would say the floating firing pin was pinned to the front of the bolt until the ride was over and the hammer was set.

F. Guffey
 
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