Reduced Load Pressure Spikes, Detonation: Best Explanation Yet

[dbooksta]

For all the discussion of the perils of reduced loads, and speculation on the ability of smokeless powder to detonate in a cartridge, I think we can finally settle this issue: I got an excellent dissertation on the subject when I recently called Hodgdon and talked to one of their technicians about subsonic rifle loads.

Note that Hodgdon publishes a subsonic load for 55gr .223 Remington using just 3 grains of their TiteGroup powder. This is barely enough to cover the bottom of the case -- if anything qualifies as a reduced load, this does -- yet it is considered perfectly safe.

So why does everyone warn about reduced loads blowing up guns? Nobody has found a way to get powder to detonate in a reduced load, but apparently it's quite easy to create a reduced load that will produce a pressure spike sufficient to damage a gun: Take a slow-burning or ignition-resistant powder, then reduce the load enough that when the case is on its side the primer can fire over it. The pressure of the primer firing can push the bullet into the barrel, like a squib load, before the powder begins to burn. If the bullet comes to a complete stop in the rifling it will take a lot more pressure to get it started than it does from the cartridge, where it essentially has a running start before contacting the rifling. That pressure to restart the bullet on its way shows up as a spike in the lab, and it can exceed the pressure limits of the gun.

Therefore:

1. Nobody can get smokeless powder to detonate in any conditions you will produce reloading.

2. Reduced loads can produce dangerous pressure spikes, and we know the precise mechanism whereby it happens. Note that this is more of a problem with slow powders.

 

[ophidia]

Interesting info.

 

[Shoney]

Since it has never been demonstrated in the lab, detonation theories are all "dust in the wind", or maybe like doing other things into the wind.

I was first introduced to detonation in an article in the "American Rifleman" well over 20 years ago, maybe longer. The article was entitles S.E.E. something???? The article made the point that SEE (Secondary Explosive Effect) is more commonly referred to as detonation, but that in reality it was not a detonation, rather it is a unique pattern of burning of the powder.

The phenomenon is theorized to occur in reduce rifle loads that are well below the minimum load. The greater the reduction, the greater the chance of catastrophic problems. Loading a good deal below minimum load has always been promoted as a dangerous and unwise practice since I started loading 50 years ago.


The article theorized when a small amount of powder lays flat in the horizontal case; that the primer ignition hits the rear portion of the powder igniting it, and the flash ricocheted or skips over the middle section of powder, igniting the front portion of the powder, and both ends burn rapidly toward the middle. The result is theorized to be an uneven but rapid burning of the powder, causing a very high pressure spike.

 

[Magnum Wheel Man]

Interesting topic, since there are several cartridges or guns that I like lighter loads in...

my buddy ( local builder, retired machinist, gun builder, life long reloader & bullet caster ) warned me that double based powders would be more likely to show a "detonation" with overly reduced loads, than with single based powders...

... but I can also understand the reverse burning, & related powder burning properties previously listed with larger cases & very small powder charges... a good reason why I like to, if I'm expirimenting, to use powders that better fill the case, than ones that put only a few grains of powder in a case, if I'm trying anything unpublished ( which I seem to be doing alot of lately )

 

[dbooksta]

Two other points the Hodgdon tech emphasized to me:

1. "Secondary Explosive Effect" (S.E.E.) is a term that has been misappropriated from large-bore naval guns and howitzers, where I think he said it refers to reignition of unburned propellants outside of the bore. Unfortunately it has been used so widely to describe pressure spikes in reduced small-arm loads I can't verify that original usage....

2. Hodgdon makes a specialty powder called Trailboss that is extremely light for its volume: So light that you can safely fill any case to capacity and it will still produce lower pressures and velocities than the starting load of any conventional powder. So if you're interested in building safe, reduced loads you should give that a try.

Finally, one other common and reproducible scenario for pressure spikes on reduced loads: One round produces a true "squib" firing that lodges a bullet in the barrel. The operator fails to verify that the bullet left the barrel and then fires another round into it. Even a reduced load can destroy a firearm when firing into a plugged barrel!

 

[Doodlebugger45]

I've noticed Hodgdon publishes Trail Boss loads for nearly every cartridge, even magnum rifle cartridges. I haven't tried it yet but I think it would be a hoot to try shooting a 7 mm mag at 1500 fps.

 

[bfoosh006]

Funny, I just quoted this same article in another post.....

From the Sept. '09 "Shooting Times" ( the author started work at CCI in 1987)

Quote'..."You can have to much primer. When the output gas volume of the primer approaches that of the cartridge case, sometimes special handling is required. I remember when CCI was working with some experimental primers for 9mm Luger, and we started seeing odd time-pressure curves on the computer. Instead of the normal single peak, we saw two. One QA tech commented that it looked like the dual humps of a Bactrian camel.
It was a classic case of high gas volume but too little temperature. The primers extra gas unseated the bullet while still trying to light off the main charge, producing one peak. Then the bullet retarded as it engaged the rifling, creating the second peak. Although a shooter would never notice this in a production firearm, that double hump was worrisome, and we abandoned that mix. ....Un-Quote

Kinda makes me wonder....

 

[Master Blaster]

The phenomenon is theorized to occur in reduce rifle loads that are well below the minimum load. The greater the reduction, the greater the chance of catastrophic problems. Loading a good deal below minimum load has always been promoted as a dangerous and unwise practice since I started loading 50 years ago.

Yes, the real problem is that folks underload (most rounds underloaded work fine) and hit a round that has just slightly less powder, and stick a bullet in the barrel. Then when they fire the next one, kaboomm, they then blame it on detonation, or they way overcharge what they thought was a light load.

 

[Dave P]

So... if making reduced loads, we should

A) use a low energy primer, and

B) put extra crimp on the bullet.

C) and maybe seat the bullet to the lands, so the primer does not send it further.

What do we think?

 

[dbooksta]

Interesting ideas: If this hypothesis is correct, then if you crimp/prime/seat the bullet in such a way that the primer cannot dislodge it then you would avoid the problem.

I wonder if that is actually possible? You could build a set of test loads using primer only and see if you can crimp or seat in such a way that the bullet doesn't move when fired.

 

[sundog]

All old news.

 

[F. Guffey]

I see nothing new, it has not been that long ago a hand loader rendered his rifle scrap, (300 Win Mag I think) right up to the last shot it handled like a doll buggy and then all at once the rifle swarmed, he would not consider his recoil-free loads had sudden shock from the beginning.

Norma published test results many years ago and then quit talking about it, but then Norma never was much on talking it to death and the 03 was feed reduced loads for a short time, something about meets and or then exceeds, depending on how far the shooter had to walk to pick up all the parts.

F. Guffey

 

[F. Guffey]

Dbooksta, possible, yes, will it happen? No, R. Lee in his book did the test to determine the value of a crimp in pounds per square inch, or the amount of effort that is required to dislodge the bullet, Lee is a big fan of the crimp, in these matters position of the powder is most important according to Norma. I do not use reduced loads, if I want less recoil I use a smaller gun.

F. Guffey

 

[Blue]

Loads ?

Everything load I need is found in one of my many reloading manuals. I stick to the published loads and have had very favorable, safe, and enjoyable results.

I trust my manuals! I hope the rifleman in the next station isn't experimenting too far out there and follows safe and proven procedures. Someone tries to blow me up at the range -- it wouldn't be pretty!

I don't rely on phone conversations with employees at Powder Companies - might be speaking to the janitor - but then he could be a proficient reloader, too.