I think mtngun has tried crimping his
lead bullets hard, but spike hardly changed.
A hard crimp on lead may not hold back as hard as one on jacketed.But he has also got them oversize to jam into freebore trying to hold them back, with no change.And most experimenters and powder people, will tell you that light for the caliber or heavier
slippery bullets jump out a little even with too slow of powders.That is why they
have over the years, used faster powders
so the burn keeps up,
but then we're limited by what that fast powder does to the initial pressure. Like if your getting 2700 with a 180 gr cast bullet in
3006 and getting spikes with medium slow
powder, and try faster powder
to get rid of spikes but initial pressure goes up say 15,000psi, then you have to say cut bullet wt back to 140 gr to get 2700 safely. Or
experiment with different slower powders.

Kind of like damned if you do and damned if you don't for Mtngun, trying to get high velocities with heavier lead bullets--Fast powder high
initial peak -- some slow powders secondary
spikes!!Ed.

quote:

Denton: you are confusing terms. Cross axis sensitivty is the gage responding to a major stress axis perpendicular to it. Poissons ratio is a physical property. A cross axis stress will have a 0.3 effect on the material itself.

I think we are actually in violent agreement. The gage itself is quite insensitive to being "stretched crossways". The steel it is attached to may do something to "stretch the gage lengthwise" when the applied force is "crossways", which is an entirely different issue.

Denton
I just briefly looked at this thread. I have blown three 338 Win mag barrels off, usually about 1 and 1/2 inches using different grain bullets. I cut the barrels back from 24 inches(starting length) to 20 inches, and the spike does go away. I dont have enough snap to debate all the technical aspects of how the system works, but I have figured out how to blow the end off a barrel and be able to reload that same piece of brass about a dozen times.
Charlie

Charley-Thanks for joining in.At least you saved the brass.Ha... Ok, have you or do you know of anyone getting the spikes in 458 and larger cases?About how heavy was the muzzles of those barrels that blew up?Ed.

Hi Charlie...

Glad you dropped in.

Your experiments show that there is definitely something going on that we need to know about. I was pulling some whoppers of secondary spikes in my Finnish milsurp. You have persuaded me to stop that!!

All the evidence points to something acting almost like a partial barrel blockage. That would have enough energy to bust or ring a barrel.

hubel458
I've not yet tested any big guns.....I hate to shoot those any more than I have to.
One muzzle was a factory stainless barrel on a brand new 70, the others were # 5 contours. One with a brake, one without.
Charlie

Just because you blow the end of the barrel doesn't automatically mean it was due to a secondary spike. Some terminal muzzle pressures can be quite high - in the 15,000 to 20,000 range, and if there is faulty construction the result could be a blown barrel tip.

Some more thoughts. We know that bullets are
like an obstruction that has to be moved out of barrel with the relatively gentle action of a propellant. IE an explosive that travels at
20-60,000 fps compared to a controlled burn
propellant at 5000 fps will not move bullet,
but blows up the gun.Bullet can't accelerate that fast.

Now we all mistate that powder expands after ignition in the burning process but it is the gases burning and being released from powder
solid that is expanding along with heat,etc.
Now the powder grains do get dispersed down the barrel some in this process that turns them to gases

So if bullet jumps out too fast--pressure drops
on the burning powder--burning slows-- bullet
acceleration slows-- pressure on powder increases--burning starts, and because there is a lot of the gaseous state at this time you have
a MINI SEE..Now this SEE explodes with much more speed, than the buring that got the process this far. Many times the speed and energy of the regular combustion phase that started at the beginning. This Mini SEE starts say when bullet is at 18 inches down barrel, but bullet can't accelerate enough to let that super high speed
exlosion from the MINI SEE out before it registers a secondary spike
and when it catches the relatively slow bullet,
if hairy enough, blowoff couple inches of
muzzle, from say 22 inches on.IE bullet went from 18 to 22 inches in the time it took the
high speed explosion from MINI SEE to register a big spike and/or blow off the muzzle, when
explosive front caught up with bullet.

Charlie cut off 4 inches on blown barrels back to 20 inches, and that gave a place
for the explosive front to release out of the gun.So he lost no muzzles on 20 inch barrels..Ed.


AIU- these were all newer guns with barrels
having yield strength in excess of 125,000
psi!!!And his barrel thickness's weren't the featherweight styles..Ed.

Charlie,
When you blew the barrels on the three rifles you stated it was with various bullet weights. Did the spikes you saw doing this suddenly appear, start out high, or did they increase with the powder charge in a progressive fashion?
You say the case life of these cartridges was ~11 loads so I take it you did work up to the loads that destroyed the barrels and the spikes were present dureing all if not most of the load development?
Did all wgts of bullets behave in a similar way in reguard to the growth of the spike?

hubel458
One trend I am seeing, I am using much faster powders than in the past. Seems several calibers will get to a certain pressure(say 60000 psi) and shoot a certain speed(say 3000 fps) with a powder that uses 50 grains and another that uses 65. What happens with that extra powder ? I thin it gets blown out the end of the barrel.
Charlie

Ol Joe
The spikes are extremely predictable. As the load went up, so did the spikes. As the load(powder charge) goes up, the spike comes back toward the chamber ever so slightly but regularly.
Charlie

Yes it and gases it generates do get blown out into the air. Causes a little more muzzle
blast.Now that same powder may get a heavier bullet to your speed, thus using more of the
energy wasted on trying to get a lighter bullet to go faster.

And another thought just occured to me. A lot of wildcaters like the STA cartridges take the slow powders to 75-80k-- thus being able to keep a constant pressure and bullet acceleration
goin--All of the devellopers of those cases
say they are safe loads in good guns.I know
now that if you took same bullets and lesser amounts of same powder to say hold loads at 55k, you'd have spikes and have to use faster powder.Ed.

quote:

The spikes are extremely predictable. As the load went up, so did the spikes. As the load(powder charge) goes up, the spike comes back toward the chamber ever so slightly but regularly.

Plus, the secondary spike grows exponentially, and predictably, with powder charge, until it hits the upper limit of the PT system.

Denton, if you're shooting a string of "identical" loads, do you see the secondary spikes with every shot fired?

So far.

Denton, what do you have to adjust to make them go away?

PS. Also, in the Medium Bore forun section under "180/200 gr 30-06 loads - question" you'll find some additional QL predictions with correlating piezo-electric transducer PSIs, the latter provided by M98. You might be interested. I hope to post much data later, after I get M98's permission.

Adjust the powder charge... at moderate loads, the secondaries are mild or non-existent. As you increase charge, they grow very quickly.

Thanks for the info about the other thread.

In years past (many) there was work done on Front Ignition. Where the powder column is ignited from the front rather than the rear. Wonder if anyone has duplicated those loads and done some measurements.

I've done some but years ago before all this instrumentation we have today.

Denton et. all, can you think of any other way to check for a resonating pressure wave than the multiple sensor system I have discussed previously? In reading mtngun's tests, he tickled my brain and got me to wondering if maybe the pressure wave was in the gas...I had been thinking of a resonating wave of barrel expansion/contraction...how would one differentiate between the 2 possibilities, and would we care?

Resonance is a funny thing...and could easily explain why this issue is so tricky.

Denton, do you notice differences in velocity in those rounds with secondary spikes vs. those without such spikes?

CDH-- I myself also feel that any pressure waves
is in the gases. A MINI-SEE with bullet moving that say starts over the length of the gases
when bullet is about 18 inches down barrel,
acts like a wave, as SEE(detonation like
a high explosive) is much faster than
regular powder burning rates, and catches
bullet a couple inches before muzzle, thus making the rings seen there, or if high enough
blowing couple inches off.

I have thought about a Mini SEE that I
think is happening over the length the gases and whatever ungasified powder is there at the time; and I think that it starts at chamber and moves forward instantly,(accounts for chamber sensor seeing it even though bullet is about 18 inches away)....May do it so extremely fast,it can't be easily measured.
The reason I think a Mini-SEE starts in chamber area is when bullet out run powder burn
and powder burn slowed, the area of most heat I think is in chamber area yet, and when it starts
Mini SEE and does the catch up process it
restarts in area where I feel there is most
heat...Ed.