I have a bunch of once fired 30-06 miitary surlus cases with a capitol U on the head stamp .These came from a manufacturer in Utah .I did all the prepping and finally cleaned them before i anneal them and noticed the flash hole sizes are all over the place . From .080 to .100 thousands . I was going to fire them in my 03A3 but am afraid the pressure might be high on those larger flash holes .Any one have experience with this large of a flash hole ? Arnie
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Re: Flash hole size
As an engineer, I've considered this concept on a number of occassions.
I'd love to hear what some of the "old timers", and highly experienced fellas have to say about this, but here's my take - which is an opinion only!
This is a basic fact:
An orifice/throttle can ONLY create a pressure differential from one side to the other if there is ample flow, such that a restriction is created.
Example: The throttle on an engine...
When the engine isn't running, and hence no flow, the pressure inside the intake manifold (downstream of the throttle plate), will be equal to atmospheric pressure.
If you were to hook up a small vacuum cleaner (capable of very low flow) to the exhaust pipe, you would create airflow across the throttle, but again, you'd see that regardless of throttleplate position, pressure inside the manifold would be equal to atmospheric - or DAMN near exactly equal, because there is so little flow, the throttle poses no significant amount of restriction, wheter open or closed.
Here's where my opinion comes into play:
It seems to me that the ignition/pressure rise event inside a rifle cartridge case would create almost zero FLOW from one side of the "throttle" (in this case an orifice - the flash hole) to the other. The only "flow" would be the required gas needed to be stuffed into that tiny crevice volume to raise pressure from 15psi to 50,000psi.
I don't know how to calculate that volume, because it is FAR from being an ideal gas. If it were "ideal gas", it could be calculated according to P*V=n*R*T.
Regardless, I **suspect** that gas volume (and thus, required flow from one side of the orifice to the other) would be tremendously small, effecitively making it a moot point - which would mean that flash hole size would have little to no effect on the pressure on inside the primer pocket.
<span style="font-weight: bold">The above is a long-winded way of saying I think that pressure inside the cartridge case = pressure inside the primer pocket.</span>
As an engineer, I've considered this concept on a number of occassions.
I'd love to hear what some of the "old timers", and highly experienced fellas have to say about this, but here's my take - which is an opinion only!
This is a basic fact:
An orifice/throttle can ONLY create a pressure differential from one side to the other if there is ample flow, such that a restriction is created.
Example: The throttle on an engine...
When the engine isn't running, and hence no flow, the pressure inside the intake manifold (downstream of the throttle plate), will be equal to atmospheric pressure.
If you were to hook up a small vacuum cleaner (capable of very low flow) to the exhaust pipe, you would create airflow across the throttle, but again, you'd see that regardless of throttleplate position, pressure inside the manifold would be equal to atmospheric - or DAMN near exactly equal, because there is so little flow, the throttle poses no significant amount of restriction, wheter open or closed.
Here's where my opinion comes into play:
It seems to me that the ignition/pressure rise event inside a rifle cartridge case would create almost zero FLOW from one side of the "throttle" (in this case an orifice - the flash hole) to the other. The only "flow" would be the required gas needed to be stuffed into that tiny crevice volume to raise pressure from 15psi to 50,000psi.
I don't know how to calculate that volume, because it is FAR from being an ideal gas. If it were "ideal gas", it could be calculated according to P*V=n*R*T.
Regardless, I **suspect** that gas volume (and thus, required flow from one side of the orifice to the other) would be tremendously small, effecitively making it a moot point - which would mean that flash hole size would have little to no effect on the pressure on inside the primer pocket.
<span style="font-weight: bold">The above is a long-winded way of saying I think that pressure inside the cartridge case = pressure inside the primer pocket.</span>
Re: Flash hole size
Flintlock probably has the right idea, I don't know how you would prove anything, otherwise, without some ridiculously expensive lab equipment.
My take on the subject is that if you have different sized flash holes, you have inconsistent flame fronts issuing from the flash hole. Powder will be ignited in a different manner from shot to shot with resultant differences in pressure, velocity and trajectory.
Sort by flash hole diameter ? Seems like a PITA - load 'em up with moderate loads and don't expect bug-hole groups.
Paul
Flintlock probably has the right idea, I don't know how you would prove anything, otherwise, without some ridiculously expensive lab equipment.
My take on the subject is that if you have different sized flash holes, you have inconsistent flame fronts issuing from the flash hole. Powder will be ignited in a different manner from shot to shot with resultant differences in pressure, velocity and trajectory.
Sort by flash hole diameter ? Seems like a PITA - load 'em up with moderate loads and don't expect bug-hole groups.
Paul
