Think I got a Handle on It

[ET]

There seems to some confusion of the relationship of vent orifice size and PFC size. Vent orifice size dictates the level/amount of thermal energy transfer to the powder.
The PFC size dictates the resulting pressure feed from the primer and how much back pressure from the bore it can handle before pressure reaches a point it can be detrimental to the 209 primer.

Again one has to understand what transpires through ignition.
When the primer ignites it fills the PFC with thermal energy and pressure. The larger the volumetric size of the PFC the less the pressure buildup from the primer.
The vent orifice which acts like a regulator allows a specific rate of flow from the reservoir of thermal energy in the PFC into the bore. The larger the vent orifice more thermal energy and pressure is allowed to pass through to the powder.

Once the powder ignites it begins building pressure where a point of equal pressure exists between the PFC and bore stopping any flow in either direction. Eventually as the pressure in the bore exceeds the remaining pressure in the PFC a backward flow begins.

Knowing what is transpiring kind of allows some reasoning as to why there is less primer bulging occurring with the larger PFC and larger vent orifice. To keep it simply if that’s possible by reducing the remaining pressure in the PFC and having a larger volumetric area for housing return pressure we are reducing the reachable/attainable level of return pressure from the bore.

This is what I see happening and plausible explanation for the why. If you see anything wrong with this explanation or have any other thoughts to add feel free to chime in.

Ed

[jims]

Thanks again for your well thought out inputs.

[Deleted]

I'm picturing the directional flow from the primer to the orifice to be less restricted with the .040...The PFC volume once pressurized ...boost the remaining thermal energy through the orifice and creates more penetration of energy into the powder column...BUT if the pfc volume is too big then theres not enough pressure for optimum penetration....
After ignition pressure builds but we still have high preesure coming from the pfc creating a backflow buffer...when the pfc and chamber equalize and after the  pfc gets backflow from longer dwell time, then it is able and will take more pressure to exceed  the primer bulging threshold.....

My question is...Is it just volume of the pfc or length and volume.??...A short and fat pfc compared to a longer but not as big in diameter pfc....I believe there exist a

"perfect" combination of the two for a 209 primer....

[ET]

SML

In answer to your question I don’t believe length of the PFC on its own would be a governing factor as length combined with diameter in a formula gives the result of volumetric space available.

As for the feed from the PFC for a good ignition there is a balance point for optimum heat and pressure but varies with the powder burn rate and temp. By going from a regular primer to a magnum primer we can also alter the heat and pressure feed in a given size PFC if necessary.
Again it comes down to a balancing act for best response. The testing results from our pioneers will shed more light on this as they progress forward.


Ed