SEE & pressure excursions

[358WCF]

Rather than cluttering up the temperature sensitivity thread, thought I'd start a new one. Back in the day, there was regular mention of pressure excursions *intermittently* when using small charges of powders c.4350 or slower in larger cases. Also excursions using too quick of a powder in sharp shouldered cases. Ackley warned of it. Rocky Gibbs apparently experienced it too.

I dont think it's been debunked, as Prof. Brownell had pressure data showing that it was a real thing as did Nils Kvale, a Norma ballistician in the 60s. There were various names for the phenomonon... SEE-Secondary Explosion Effect, my favorite BURP-Blow Up by Redirected Pressure, & a few others my memory cant conjure up.

Nobody talks/writes much about it anymore. With the spate of new reloaders recently it may be worth discussing. Your thoughts?

 

[jelenko]

I think it's a great reminder because it's counterintuitive.

 

[K22]

Yea, I'm old enough to remember this issue but my recollection is that it concerned too light of charges in pistol cases after a few guns were blown up. And I do remember the prevailing theory at the time was the phenomena was caused by a "secondary denotation".

My recollection is that White labs did extensive tests on this but was unable to duplicate the phenomena in the lab. There was some speculation that the guns that were blown up were due to a bullet fired into a barrel that had a bullet already lodged in it and it had nothing to do with the so called "secondary explosion" phenomena. But I think a lot of manuals warn against loading light charges of slow burning powder.

I believe that if you stay within the bounds of published reloading data in the various reputable manuals you can avoid a lot of trouble.

 

[wboggs]

I remember it as a warning not to use a reduced charge of a slow burning powder in a large case which could result in powder burning from both the front and back of the powder column. The result was very high pressures.



,

 

[mikecr]

It makes sense that powder should burn from one end of powder column, either back to front, or front to back. A reduced charge/poor case fill could allow too much to ignite at once, messing up the timing.
If you barrel is stupid short, combined with a poor case design (like 30-06), you can also get a secondary pressure spike (that exceeds primary peak) from muzzle ignition.

It always seemed that people have to go out of their way to create these conditions.
Using loads that are just obviously wrong.

 

[tommeboy]

Hodgdon told me they can make it happen on command with a 243 they have.

 

[std7mag]

I can remember when i first started reloading i hadn't heard any warnings about starting too low on powder charge.
If i recall correctly, i was loading for my 7mm-08 using 139gr SSTs and either H414 or IMR4350.
Being new i was weary of going too high on pressure, so started out below listed start charges.
Recoil was surprisingly more than some factory ammo i had bought for it.
It was only after i mentioned about it on another forum that i heard about pressure spikes using too low of a charge.
One person showed me what was happening duplicating my load then shooting with an RSI Pressure Trace.
There were two rises in pressure. One slower, curved like you would expect. And a second, sharp spike that went to about 70,000 psi.

Was a real eye opener!

 

[mikecr]

You can see examples of some of this here:

Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace

Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.

www.shootingsoftware.com