Bob Kingsbury
New member
Has anyone compared pressure traces for bullets just touching VS.
Jam seating
Jam seating
Pressure Trace
- Thread starter Bob Kingsbury
- Start date
Bob Kingsbury
New member
Varmint Al,
Does the pressure the increase again when bullets are jammed
in the lands
Does the pressure the increase again when bullets are jammed
in the lands
B
Bryce
Guest
And when pressure is up in the actual operating range of a PPC, say 60,000 plus, is there still a distinct jump or do other factors become dominant and seating depth becomes less of a factor ?
C
Cheechako
Guest
As the bullet broke it's neck tension and jumped to the lands it provides more expansion room for the gases reducing both the energy and velocity.
Al
I'm not questioniong the pressure, velocity, or energy figures. Just questioning the validity of that statement. Expansion ratio would be the same. For the deep seated bullets the expansion ratio would initially be less but would be the same as the jammed bullets once the bullet reached the lands. No??
Ray
Al
I'm not questioniong the pressure, velocity, or energy figures. Just questioning the validity of that statement. Expansion ratio would be the same. For the deep seated bullets the expansion ratio would initially be less but would be the same as the jammed bullets once the bullet reached the lands. No??
Ray
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G
GS Arizona
Guest
Ray, I agree with what you said regarding pressure vessel volume; it's the same in both cases. The primer blast is enough to move the bullet to the lands before combustion pressure builds.
In my recent pressure tests on various 30-06 loads and primers (over the past two weeks), I found an increase of 1000 to 1500 psi in pressures when seating the bullets to the lands (not jammed) versus jumping them 0.020". This was in a 55,000 to 59,000 psi operating range. I don't think jamming would have materially changed those figures. I don't normally seat right on the lands, but in this test, that was a matter of convenience since 6 bullets were being tested and soft seating them long in the cases (letting the leade finish the seating job) allowed me to load quickly without readjusting the Wilson seater constantly (burning up range time).
German Salazar
In my recent pressure tests on various 30-06 loads and primers (over the past two weeks), I found an increase of 1000 to 1500 psi in pressures when seating the bullets to the lands (not jammed) versus jumping them 0.020". This was in a 55,000 to 59,000 psi operating range. I don't think jamming would have materially changed those figures. I don't normally seat right on the lands, but in this test, that was a matter of convenience since 6 bullets were being tested and soft seating them long in the cases (letting the leade finish the seating job) allowed me to load quickly without readjusting the Wilson seater constantly (burning up range time).
German Salazar
D
Don
Guest
As the bullet broke it's neck tension and jumped to the lands it provides more expansion room for the gases reducing both the energy and velocity.
Al
I'm not questioniong the pressure, velocity, or energy figures. Just questioning the validity of that statement. Expansion ratio would be the same. For the deep seated bullets the expansion ratio would initially be less but would be the same as the jammed bullets once the bullet reached the lands. No??
Ray
Hi Ray,
There still may be a difference because the .030" seated bullets begin moving forward as the pressure overcomes the neck seating grip and the bullet may never come to a complete stop as it engages the lands and obturates due to momentum.
Where as the jammed bullet must overcome both neck grip and land obturation before the bullet begins moving forward which probably allows for a higher spike in initial pressure.............Don
C
Cheechako
Guest
Hey Don
I agree that the jammed bullet must overcome both neck grip and land obturation at the same time and the result is "X" amount of pressure. On the other hand, the deeper seated bullet allows for these two events to occur over a longer time with the result of less pressure. But the lower pressure is not because the vessel volume, or expansion ratio, is increased.
As I said, I won't disagree with the principle or the pressure figures themselves, only the sentence in Al's post that implied that the "expansion room" was increased.
But I could be wrong. I think it was Disraeli who was asked if he would die in defense of his beliefs. He said, "Hell no! I might be wrong!"
JMHO
Ray
I agree that the jammed bullet must overcome both neck grip and land obturation at the same time and the result is "X" amount of pressure. On the other hand, the deeper seated bullet allows for these two events to occur over a longer time with the result of less pressure. But the lower pressure is not because the vessel volume, or expansion ratio, is increased.
As I said, I won't disagree with the principle or the pressure figures themselves, only the sentence in Al's post that implied that the "expansion room" was increased.
But I could be wrong. I think it was Disraeli who was asked if he would die in defense of his beliefs. He said, "Hell no! I might be wrong!"
JMHO
Ray
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C
Cheechako
Guest
Charles
See, I can be wrong!
I should have said it was Ben Franklin. There's another old saying that people will accept your ideas much more readily if you tell them Benjamin Franklin said it first.
Ray
See, I can be wrong!
I should have said it was Ben Franklin. There's another old saying that people will accept your ideas much more readily if you tell them Benjamin Franklin said it first.
Ray
G
GS Arizona
Guest
Al, I have data on 6BR and 30-06, mostly in conjunction with primer testing so the load range tends to be pretty limited. However, with the 30-06 I ran a more extensive series last week that might be of interest. It was all on an Oehler 43 system.
Send me an email at gasalazar@att.net and I'll try to get the data to you. It's on another computer and transfering may be tough but I'll at least try to mail printouts to you.
German Salazar
Send me an email at gasalazar@att.net and I'll try to get the data to you. It's on another computer and transfering may be tough but I'll at least try to mail printouts to you.
German Salazar
Bob Kingsbury
New member
Not quite in the days of the PPC or benchrest, but Dr. Franklin Mann
in his book, The Flight of The Bullets, was able to demonstrate that
low presure gas leaks past the bullet before it moves. I have seen
high speed photographs that show the same thing. Is it possible
that by plugging up the hole in the barrel with a tightly seated bullet
we allow less gas to sneak past, thereby causing slightly higher PSI.
It has been said that it takes 6000- 8000 psi for the bullet to
fully enter the bore. The psi/time trace does not show a difference
in that area of time. The peak is affected, and that is said to be
a few inches ito the bore.
in his book, The Flight of The Bullets, was able to demonstrate that
low presure gas leaks past the bullet before it moves. I have seen
high speed photographs that show the same thing. Is it possible
that by plugging up the hole in the barrel with a tightly seated bullet
we allow less gas to sneak past, thereby causing slightly higher PSI.
It has been said that it takes 6000- 8000 psi for the bullet to
fully enter the bore. The psi/time trace does not show a difference
in that area of time. The peak is affected, and that is said to be
a few inches ito the bore.
M
murphy
Guest
To Varmint Al and others.
Feel a little out of My depth here but for what it is worth,here is a recipe for blowing up a rifle. I know because MY face was about 5" away from the action. The recipe goes like this: Take one Marlin MR7 270WIN. One batch of Lake City 30/06 brass necked down to 270. Some 130grn Remington Corelokt projectiles. 55.5grns of Win760 and CCI250 primer. Give the cases very light neck tension and seat the bullets so that they are touching the rifeling and pushed back into the case by closing the bolt. Rifle gave brilliant accuracy and flat primers for about 20 rounds then suddenly without warning KABOOM! The action had to be belted open with a block of wood and the cartridge case belted out of the bolt face the same way.Primer pocket was 1/4" diameter and I never found the primer,the bolt face was burned and the extracter wrecked. When I hear of people jam fitting projectiles in big calibers like30/06 I just hope they know what they are playing with. Would love to have had a pressure gauge on Mine. Reguards Murphy
Feel a little out of My depth here but for what it is worth,here is a recipe for blowing up a rifle. I know because MY face was about 5" away from the action. The recipe goes like this: Take one Marlin MR7 270WIN. One batch of Lake City 30/06 brass necked down to 270. Some 130grn Remington Corelokt projectiles. 55.5grns of Win760 and CCI250 primer. Give the cases very light neck tension and seat the bullets so that they are touching the rifeling and pushed back into the case by closing the bolt. Rifle gave brilliant accuracy and flat primers for about 20 rounds then suddenly without warning KABOOM! The action had to be belted open with a block of wood and the cartridge case belted out of the bolt face the same way.Primer pocket was 1/4" diameter and I never found the primer,the bolt face was burned and the extracter wrecked. When I hear of people jam fitting projectiles in big calibers like30/06 I just hope they know what they are playing with. Would love to have had a pressure gauge on Mine. Reguards Murphy
G
GS Arizona
Guest
Murphy, I'm sure glad to hear you came through that experience with enough eyes and fingers to tell (type) us about it. That's not something I'd wish on anyone, having examined the results of more than one of those events (thankfully not my own). Seating bullets into the lands (jamming) is not, typically, by itself enough to turn a safe load into a catastrophic failure producing load, however, when enough other factors get stacked up, things can change quickly and for the worse. Your warning is a good one, and should be heeded, we take way too much for granted in reloading much of the time.
German Salazar
German Salazar
One thing that's taken for granted is that the old powder thrower will throw "within a tenth of a grain" from day to day..............
I'd like to see more folks spend some time actually CHECKING their throws with a scale and working on technique and such before blaming all sorts of esoteric "phenomena" on a blown load. Folks who run right on the edge and just arbitrarily throw their charges WILL sooner or later wreck some brass/extractors/ejectors!
IMO the difference in pressure between "jammed", "deeply jammed" and "ten thou jump" is so small as to be lost in the noise...........but the difference between 6-8 nice smooth throws, then take a swig of coffee and BS with the buddy, then turn back to the bench and resume throwing charges CAN and HAS blown many an extractor across the bench.
justanotheropinionby
al
I'd like to see more folks spend some time actually CHECKING their throws with a scale and working on technique and such before blaming all sorts of esoteric "phenomena" on a blown load. Folks who run right on the edge and just arbitrarily throw their charges WILL sooner or later wreck some brass/extractors/ejectors!
IMO the difference in pressure between "jammed", "deeply jammed" and "ten thou jump" is so small as to be lost in the noise...........but the difference between 6-8 nice smooth throws, then take a swig of coffee and BS with the buddy, then turn back to the bench and resume throwing charges CAN and HAS blown many an extractor across the bench.
justanotheropinionby
al
Bob Kingsbury
New member
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