if you have never handled a small rifle primer, you are pretty much wasting your time on most of these forums. IMHO
Primer Hardness?
- Thread starter antelopedundee
- Start date
R.G. Robinett
"That'll never work."
I believe Wilbur & Kevin, have it correct - that is, presuming that the firing-pin subtends 0.00166 square inches, or, 83/50,000.
Are you talking "blown", or, "blanked" primers? Blown primers are caused by excessive pressure. Blanked primers are usually due to excessive firing-pin protrusion, and/or, sloppy firing-pin to firing-pin hole fit. Another cause [of blanking] may be thin, and/or brittle cups.
I probably got pieRsquared rounded off incorrectly - but, at 50,000 Lb. per square inch pressure, it appears that, for a 1/16th (0.0625") diameter pin, the force against the pin-nose would amount to 153 pounds.
I'm notorious for confusing radius and diameter. RG
mwezell
Mike Ezell
I believe Wilbur & Kevin, have it correct - that is, presuming that the firing-pin subtends 0.00166 square inches, or, 83/50,000.
Are you talking "blown", or, "blanked" primers? Blown primers are caused by excessive pressure. Blanked primers are usually due to excessive firing-pin protrusion, and/or, sloppy firing-pin to firing-pin hole fit. Another cause [of blanking] may be thin, and/or brittle cups.
I probably got pieRsquared rounded off incorrectly - but, at 50,000 Lb. per square inch pressure, it appears that, for a 1/16th (0.0625") diameter pin, the force against the pin-nose would amount to 153 pounds.
After asking my previous question, I stopped and thought about it for a second and came up with the same as you...152. something. I didn't follow up as I didn't get an answer to my question to begin with...so. No biggie.
antelopedundee
internet bum
I believe Wilbur & Kevin, have it correct - that is, presuming that the firing-pin subtends 0.00166 square inches, or, 83/50,000.
Are you talking "blown", or, "blanked" primers? Blown primers are caused by excessive pressure. Blanked primers are usually due to excessive firing-pin protrusion, and/or, sloppy firing-pin to firing-pin hole fit. Another cause [of blanking] may be thin, and/or brittle cups.
I probably got pieRsquared rounded off incorrectly - but, at 50,000 Lb. per square inch pressure, it appears that, for a 1/16th (0.0625") diameter pin, the force against the pin-nose would amount to 153 pounds.
Cept nobody mentioned firing pin until your post, it was firing pin hole which was said to have a diameter of .062 inches and a calculated area of .00302 square inches. In the example cited of 50,000 psi the pressure available at the flash hole would be 50,000 psi and not 152. Going back to post 3 where a pressure limit of 41,000 psi was mentioned one would expect that 50,000 psi would blow that primer in some way. Otherwise with your 152 psi thing you're saying that when I check the air pressure in my truck tires that the pressure at the valve stem is NOT equal to the pressure elsewhere in the tire. The pressure inside of a round of ammo when the bullet is ready to start moving is the same everywhere inside the case be it primer, case wall or bullet base.
If I took my truck wheel and put in a second valve stem of a different size then according to your explanation I should get a different reading at each one. I don't think that would be the case at all. How would a primer even flatten with only 152 psi pushing on it?
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antelopedundee
internet bum
I didn't say gauges. The reading [with properly working gauges] should be the same at both valve stems is my point, otherwise your pressure measurement system is no good.
By your logic a .30 cal flat base bullet with an area of .07447 sq in at 50,000 psi working pressure would have 3723 psi against it. I don't see that getting a bullet of a barrel at 2800+ fps.
R.G. Robinett
"That'll never work."
The two key issues are square inches (area) and calibration (the tire gauge): 50,000 PSI is just that - 50K pounds of force applied to each square inch: your muzzle pressure is pretty spot on.
You are overlooking the rate of expansion = speed! RGWhat exactly is PSI...
I may have it wrong....thought it meant "pounds per square inch" rather than just "pounds". My earlier point concerning the tire gauge was that they are calibrated to report a pressure in PSI rather than what is experienced at the valve stem. Further, the tire pressure gauge sees the pressure at the gauge rather than the stem pressure...which may or may not be different....just like the primer sees a bit more pressure than the flash hole.
That said, it doesn't matter which of us is right or which of us is wrong....won't change things in the slightest. If your primer doesn't look good you need to try another primer or reduce the powder charge.
I may have it wrong....thought it meant "pounds per square inch" rather than just "pounds". My earlier point concerning the tire gauge was that they are calibrated to report a pressure in PSI rather than what is experienced at the valve stem. Further, the tire pressure gauge sees the pressure at the gauge rather than the stem pressure...which may or may not be different....just like the primer sees a bit more pressure than the flash hole.
That said, it doesn't matter which of us is right or which of us is wrong....won't change things in the slightest. If your primer doesn't look good you need to try another primer or reduce the powder charge.
antelopedundee
internet bum
I gathered/interpreted from your comment that you would say that 2 valve stems of differing diameter would give 2 different pressure readings for the pressure inside the tire.
As for this comment..............
"If the pressure is 50,000 psi then the pressure within a .062 primer hole would be 83 psi."
While the corrected value was 152 since it is acting on a small area then the pressure available at the flash hole and then to the primer on the other side is in effect 50,000 psi when normalized to 1 sq in. A better answer IMO to the question preceding it would have been the equivalent of 50,000 psi as it is everywhere inside the case.
So in your opinion is primer hardness a useful indicator of whether or not a primer will give more consistent shot to shot velocity variation? It seems that ones that are GRAB Generally Recognized As Best are the ones that RG told me long ago are the softest.
Kevin Gullette
New member
A little something......
.....I wrote on the small caliber board, a few years ago.
A little Jerry Stiller math.....
A 0.082" firing pin probably has an 0.084" boltface hole. The hole is 0.005412 square inches. At 50,000psi, this results in a total shearing force of 277.1 pounds.
Now use a 0.060" firing pin, with a 0.062" boltface hole. The hole is 0.003019 square inches. At 50,000psi, this gives a total shearing force of 151.0 pounds.
So.....for a 0.022" reduction in the boltface hole diameter, there is a 45.5 percent reduction in the shearing force.
As a reference, and a good read, refer to Precision Shooting magazine, May 2001, page 31, "The Real Reason Primers Pierce" by Jerry Stiller.
As would be expected, a stronger firing pin spring has little effect.........been there, tried that.
Why these things only seem to happen with small rifle primers AND small calibers????.....I do not know, or can prove........but I strongly suspect that as the sectional density is lowered, a more "focused" pressure spike through the flash hole is created.....and the firing pin is pushed rearward. BUT.......that's just me.
BTW.....my old 20BR had about the same situation as above. Quite an eye-opening experience. Greg Tannel reduced the firing pin diameter, and bushed the boltface to a smaller firing pin hole size. The result.........with 40gr bullets blanking at 3400fps.........to NO cratering whatsoever at 4150fps.
Hope this helps.
Kevin
.....I wrote on the small caliber board, a few years ago.
A little Jerry Stiller math.....
A 0.082" firing pin probably has an 0.084" boltface hole. The hole is 0.005412 square inches. At 50,000psi, this results in a total shearing force of 277.1 pounds.
Now use a 0.060" firing pin, with a 0.062" boltface hole. The hole is 0.003019 square inches. At 50,000psi, this gives a total shearing force of 151.0 pounds.
So.....for a 0.022" reduction in the boltface hole diameter, there is a 45.5 percent reduction in the shearing force.
As a reference, and a good read, refer to Precision Shooting magazine, May 2001, page 31, "The Real Reason Primers Pierce" by Jerry Stiller.
As would be expected, a stronger firing pin spring has little effect.........been there, tried that.
Why these things only seem to happen with small rifle primers AND small calibers????.....I do not know, or can prove........but I strongly suspect that as the sectional density is lowered, a more "focused" pressure spike through the flash hole is created.....and the firing pin is pushed rearward. BUT.......that's just me.
BTW.....my old 20BR had about the same situation as above. Quite an eye-opening experience. Greg Tannel reduced the firing pin diameter, and bushed the boltface to a smaller firing pin hole size. The result.........with 40gr bullets blanking at 3400fps.........to NO cratering whatsoever at 4150fps.
Hope this helps.
Kevin
antelopedundee
internet bum
I thought the advantage of a stronger firing pin spring was in reduced lock time resulting in the FP hitting the primer sooner as opposed to harder which means that the bullet should hit the target a scosch quicker. Wasn't fast lock time one of the extolled virtues of the Rem 788 action?