Low powder load/high pressure spike

[floydster]

One of my favorite loads in my 7.65 and 8mm. Mausers is 12 gr. Unique pushing a 168 gr. cast bullet. I also was thinking of using this load as a starting load in one of my 06 Mausers.
Every so ofter one hears about a high pressure spike and secondary explosion happening in reduced loads, causing devisation to the gun and shooter.
Can anyone shed more light on this subject?
Thanks, Floyd

 

[rcmodel]

SEE or Secondary Explosion Effect is a know phenomenon in over-bore Magnum calibers using very slow burning powder & jacketed bullets.

Two theorys exist.

The first is that powder just "detonates" and blows the gun apart.
This is very hard to believe, as smokeless powder sold for reloading simply can't detonate in small quantities due to the fact a detonation shock wave cannot propagate in such small volumes of powder as handgun & rifle cartridges, 1 pound powder cans, and 8 pound drums as sold & shipped all over the country.
Classed as a Flamable, not a high explosive, which it would be if it could detonate in such small containers.

The only documented cases of actual powder detonations happened many years ago in bulk rail car powder shipments or factory warehouse fires containing many thousands of pounds of powder in one container.

The second theory, and the one I believe to be true is this.
With very slow powder, in over-bore cases, the primer pops and starts to light the reduced charge of powder.
Moving the bullet out of the case and into the rifling.
Where it sticks tightly before pressure has risen enough to keep it moving.

But just about then, the whole charge finally gets going and pressure builds so fast the bullet can't get unstuck and moving fast enough to get out of the way.
So the case fails and the rifle blows up.
It was not a detonation. It was a bore obstruction right in front of the chamber.

It is not a factor with your Unique loads using fast pistol powder & lead bullets.
It is not a factor in any handgun caliber using fast to medium speed powder.
It may be a factor with reduced loads of ball magnum handgun powder like H110 or WW296. That is why they recommend not reducing the listed loads more then 3% or so.

For the other sixgun folks who blow up cowboy guns with mouse-fart charges of fast powder?
Not detonation!
2.5 grains of Bullseye or something doesn't contain enough energy to distroy a six-gun if it did detonate. Which it can't.
Much more likely a double charge or a squib load stuck a bullet in the barrel beforehand.

rc

 

[Kernel]

Get a super bright LED flashlight. Add a step to your reloading process: before seating the bullet, visually check 100% of your cases for a double charge.

24 gr of Unique would not cause an overflow in an '06 case, but it would be easy to see - if you look for it.

 

[howlnmad]

rc,

I have to says thanks for that indepth explanation. After reading the OP's question, I was thinking total detonation but your second theory seems more realistic.

 

[sansone]

thanks RC for explaining it so well.. I finally understand the low powder problem as more of a "bore obstruction" situation.. helped me greatly

 

[floydster]

Thanks rc for your insight and knowledge, I am not so worried now as I really like shooting my rifles with reduced loads, as I am getting older and can't take the recoil like I used to.
Thanks again
Floydster

 

[shenck]

That is by far the best and simplest explanation for that phenomenon I have ever read. When I have tried to explain it to someone I would over explain it. I have saved a copy of that and the next time someone asks me I will give them a copy of it. Thank you

 

[TriTone]

Sounds like some legit hypotheses there, thanks very much. I have just begun to prepare to start loading for cowboy action shooting and after hearing a few of those stories was wondering as well. I plan to use 6gr of titegroup pushing a 250gr lasercast to start with.

That should be safe, yes? It's supposed to hit around 700fps.

 

[rcmodel]

Yes, it is perfectly safe.
As long as you don't double-charge a .45 Colt case with Titegroup.

Hodgdon says:
7 1/4" barrel
250 grain LRNFP bullet
Titegroup powder

5.0 Start load = 716 FPS.
6.2 MAX load = 881 FPS.

rc

 

[Jim Watson]

There was the case of the demolished CAS gun in which the owner/loader/shooter/kaBoomer said "There is absolutely positively no way in the world that I could have remotely gotten close to double charging a round."

So a couple of guys figured that was overconfidence and said "Let us watch you at work and see." And they watched him load ammo for a while. One finally said "You are right, you have very good technique on powder handling and no risk of double charging a case with powder. HOWEVER, you just put two bullets in that last one." Seems that bullet lube had stuck a bullet up in the seating die and the case had come out with no bullet in place, so he just assumed he had skipped picking up a bullet and put in another. And the big old .45 Colt case is big enough with thin straight walls to hold two bullets, seated without enough increase in effort to notice.

 

[Clark]

In an internet world of global warming, big foot, 9-11 truthers, Kennedy conspiracy, UFOs, Bermuda triangle, Birthers, water well dowsing, Keynesian economics, and haunted houses, I expect that lite load detonation will be with us for the rest of our lifetimes.

 

[Archie]

No mistake, SEE is a real phenomenon. There are several theories about why it happens. Along with the one related by rcmodel, one researcher thought it could be caused by a harmonic wave function in a nearly empty case. The shock wave travels back and forth in the case and generates excessive pressure.

Typically, it's more common in rifles than handguns. Always when using a very slow powder - usually 4350 or slower - in a severely reduced load.

The problem is, no one has been able to duplicate the effect on demand. No one can - so far - load a single round and 'make it' blow up; within the characteristics of the Secondary Explosion Effect parameters. So, 'we' don't know exactly what causes it.

The best advice is to follow published guidelines for reduced loads. The fairly low dose of Unique is normally one such guideline. However, understand the actual load is fairly high pressure at its peak.

Also remember, one can blow up a gun with too much fast powder a lot easier than too little slow powder.

 

[Jim Watson]

As a PhD of my acquaintance says, it seems like that would be a great project for a grad student. Cheap labor to just load and fire a zillion rounds of some load considered the scariest.

 

[jerkface11]

Light load detonation? No. Goofing and double charging? Yes. They make trailboss for a reason.