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Progressive means the powder starts burning out slowly, then burns faster as the bullet travels down the bore. Many handgun powders are degressive, meaning they start out burning faster--in order to get pressure up quickly, resulting higher muzzle velocities in shorter barrels. Some are essentially neutrail, meaning the burn at about the same rate during their trip down the bore. Thanks for the definition and the info.
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Our hobby certainly has its share of unsubstantiated lore, but I don't think that this fits in that category.
Vic in Va posted a graph from two very reputable sources, Floyd Brownell and Harold Vaughn. So I think that there is data to support the idea. I have both of their publications, and do remember seeing the graph.
It would be very interesting to compare the USMC data, and see if we can figure out why we have the discrepancy.
Be not weary in well doing.
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It would be very interesting to compare the USMC data, and see if we can figure out why we have the discrepancy.
Agreed. I don't have the data, am going only from memory. It was a time when "Everyone knew the repetitive chambering of cartridges was causing rifles to blow up".
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Mr Boone,
I'm guessing our friend GySgt G was involved in that test?
Denton and Vic in Va,
I'd like to know more about that adaptation of Brownell's paper. Lame' iirc was a thin walled, closed cylindrical vessel. I'd like to add another credible source to look up. His full name escapes me, but his last name was Watson, and his handle was OK Shooter. He self published his experiences playing with an Oehler PLB and the 30-06, changing variables and recording their effect on pressure and velocity. What I recall is that he observed a "J" shaped curve when plotting seating depth vs pressure with a significant increase in pressure occurred when you approached the lands.
Last edited by ChrisF; 05/24/21.
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OKShooter was Stan Watson, and it appears that I'm one of the few that remember him as a google search only turned up my previous posts here.
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I don't recall the source, but there is one formula for shotguns (thin walled) and a more complex one for rifles (thick walled). That may be the source of the correction. I have both formulas somewhere around here.
Brownell was using Tektronix equipment, and was trained by some friends of mine when I worked there. I don't know for sure, but I believe he was using an odd crossbreed system: A constrained rod into the chamber, like the piezoelectric and copper crusher system, with a small strain gauge on the rod.
Looking at the graph, it extends from the bullet seated into the lands to the bullet newrly 1/2" back from the lands . That's a lot.
Be not weary in well doing.
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LOL! I think in engineering terms, thick wall is considered a vessel with wall thickness greater than 1/10 of the vessel diameter. Cartridge cases (rifle, shotgun and pistol) are generally considered thin walled.
Last edited by ChrisF; 05/24/21.
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LOL! I think in engineering terms, thick wall is considered a vessel with wall thickness greater than 1/10 of the vessel diameter. Cartridge cases (rifle, shotgun and pistol) are generally considered thin walled.
Right. I should have been more clear. The formulas apply to the barrels of shotguns and rifles, rather than to the cartridge cases.
Be not weary in well doing.
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If you seat the bullet far back into the case, you get higher pressure.
The USMC ran a test, that I participated in, of seating the projectile progressively deeper in the case and actually pressure testing the round according to SAAMI procedures. This was done because of a concern that multiple chamberings of a cartridge (think unloading then re-loading) would push the bullet back and create an over pressure situation, ultimately resulting in a catastrophic destruction of the rifle. We never saw (measured) a pressure increase. Perhaps it is another case of "Unfortunately, the facts are not supportive of the fairy tale". This was a test of one type of cartridge (M855). I don't know if other cartridges/propellant types would have similar results. Straight wall case increase in pressure as the bullet is seated deeper
I got banned on another web site for a debate that happened on this site. That's a first
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Mr Boone,
I'm guessing our friend GySgt G was involved in that test? You know it! Hope you are doing well.
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Am I missing something here? Case trim length for a 7mm-08 is 2.025” and COAL for Barnes loads runs 2.735 to 2.80”
Seems like the OP length is a wee bit short, but what do I know…. Base to ogive, not tip.
Obey lawful commands. Video interactions. Hold bad cops accountable. Problem solved.
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I must say that it irks me that he has better velocity than I do. I am, after all, the source of ammunition.
Tight barrel. Been there. Normally, tight barrels are more accurate but slower. Loose barrels are faster but less accurate.
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Robert E. Lee
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I must say that it irks me that he has better velocity than I do. I am, after all, the source of ammunition.
Tight barrel. Been there. Normally, tight barrels are more accurate but slower. Loose barrels are faster but less accurate. Nope. Different OAL.
Obey lawful commands. Video interactions. Hold bad cops accountable. Problem solved.
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As a matter of practice, I have always started load development close to the lands, usually.005 off the lands and seated deeper if this doesn't produce the results I want. This way I have the highest pressure at my initial load and am reducing pressure as I back off the lands.
But with a Weatherby, it's a different process, because of the free bore. Doing load development a few years ago for a friend's 30-378 produced higher velocities as I seated deeper into the case. This follows mule deers note that pressures increase as you seat deeper if your initial load was over .250" off the lands.
Dyin' ain't much of a livin' boy - Josey Wales
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But with a Weatherby, it's a different process, ....... produced higher velocities as I seated deeper into the case. Yep, & improved accuracy.
"I never thought I'd live to see the day that a U.S. president would raise an army to invade his own country."
Robert E. Lee
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Am I missing something here? Case trim length for a 7mm-08 is 2.025” and COAL for Barnes loads runs 2.735 to 2.80”
Seems like the OP length is a wee bit short, but what do I know…. Base to ogive, not tip. Hmmm….While the term “ogive” is often used to describe the particular point on the bullet where the curve reaches full bullet diameter, in fact the “ogive” properly refers to the entire curve of the bullet from the tip to the full-diameter straight section — the shank. Understanding that the ogive is a curve, how do you measure a seating depth to it? Asking for a friend, not being a smartazz. Happy Trails
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I use a Sinclair Ogive Gauge
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I use a Sinclair Ogive Gauge Hornady comparator for me, but the same idea. https://www.hornady.com/reloading/precision-measuring/precision-tools-and-gauges/lock-n-load-bullet-comparator#!/ P
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Oops…posted pics to wrong thread.
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