Pressure Spikes Caused by Underloaded Cartridges

[weaselfire]

This is a well known and debated topic in Cowboy Action Shooting. SASS rules encourage use of low power ammunition. This is especially dangerous in large volume cartridges such as 45 Colt. I have personally seen three revolvers blow up on SASS matches. Two were clearly overcharged loads. One the cause was never determined.

This. Every one I've seen or heard about from a source I trust has been SASS and .45 Colt with a double charge of powder. The lesson is to pay attention while reloading. And shoot a Ruger Vaquero, those things don't blow up.

Jeff

 

[refuse2bafool]

Then we do not disagree

ReloaderFred

I indeed incorrectly inferred you believed it could never happen. My mistake.

Others on this string have stated so more explicitly and I wrongly believed you were supportive of that position.

This hobby/vocation/avocation is not golf. We can blow things up. I am sure a reloader of your experience level would agree that when in doubt err on the side of caution.

I gained quite a few tidbits from this string. So yes, discussing this with you did indeed help

 

[ReloaderFred]

refuse2bafool,

Apology accepted. I deal in facts and try to avoid speculation as much as I can. Yes, things can, and do, blow up in handloading, and even with factory ammunition. I know of one instance where a .44 Magnum was blown up with a factory load. The ammunition manufacturer paid for a new Model 29 for the shooter.

weaselfire,

The one .45 Colt revolver where I was present when it blew up was caused by loading two bullets in the case over the standard charge of powder. Some seating dies are more prone to building up lube than others, and if the operator doesn't check regularly, it's possible for a 200 gr. RNFP bullet to get stuck up in there. If the operator is inattentive, and places a second bullet on top of the case, thinking he forgot the first one, then two bullets will fit in that voluminous case and look like a normal loaded round. The resulting 400 grains of bullet drive the pressure beyond the design limits of the chamber and it lets loose. That's one of the reasons I use TrailBoss for my .45 Colt loadings. It fills the case, but I still use Bullseye for my .38 Special loadings, but I now use an RCBS Lockout die on my LnL press. If there's a double charge, or no charge, it locks up the press and stops everything. I wish it was possible to mount one on my Tri-Standard Loadamatic press from the 1950's, but it isn't. I just have to watch the powder drop slide and make sure it drops powder when it moves forward.

Reloading isn't one of those "start and forget" hobbies. One has to pay attention to each and every aspect of the process. The human mind is so complex, it's easy to distract it, since it's going constantly in several different directions. It takes effort to concentrate on what's going on, which is why they invented the chain mail glove for butchers to wear......... Like they say, "the only 'perfect One' was crucified".

Hope this helps.

Fred

 

[Pivot Dr]

Jlr2267,

I don't doubt he increased the powder charge after seeing pressure signs, I may have too. The one time I experienced this situation the pressure signs increased as I lowered the powder charge. I have no doubt I would have seen the pressure signs decrease had I again increased the powder charge. I didn't mostly because I didn't really want to shoot those bullets anyway. I find it interesting that I'm not the only one to see pressures increase as powder charges went down. With slow powders in large capacity cases at significant reduction in powder charges, the burn properties change drastically. It would take a lot of typing to explain that one finger at a time on my phone, so I won't just now. Like I said earlier in the thread, it's a topic for another thread at another time.

PD

 

[KB0VSO]

I ran across a reference in Kuhnhausen's shop manual for the SAA that under-loaded cartridges, (loaded to less than the minimum charge listed in a loading manual) can produce "random spikes in pressure" (pg 27; figure 17) that can result in catastrophic damage to a gun.

I can understand charges that are too low can lodge a bullet in the barrel, but I've never seen any reference to this phenomenon in any loading manual that I've read. My guess is that these pressure spikes are related to cartridges that were originally designed to hold a large volume of black powder (.45 Colt, .38-40, 44-40 for example) being filled with a relativity smaller volume of smokeless causing problems due to the distance the powder is from the primer in a largely empty case. Am I in the ballpark?

Since I still consider myself a neophyte in the world of reloading, I wonder if some of you who have more experience could explain the and physics behind these spikes?

Thanks

If you need a hammer to open the Bolt - now you will know why

What is the best powder
Rifle Cartridge Powder / Load Density
Modern smokeless powder once ignited produce expanding gases that push the bullet down the rifles bore giving us a certain amount of velocity to our bullet.
Modern smokeless rifle powders have varying burn rates and come in two types, single base nitrocellulous and double base nitrocellulous with the addition of nitroglycerine.
Modern smokeless rifle powders have various shapes and they are, extruded or tubular, ball or spherical, round flat flake and diamond flat flake.
Rifle Cartridge Powder Reloading:
There are many rifle cartridge powders to choose from for the avid reloader today each of which vary in their burn rate. With all the powders that are available how does anyone know which powder to select for their particular rifle cartridge reloading.
Load Density:
Load density is one factor to consider in selecting powder for a particular rifle cartridge with 86% density just about ideal in most cases. Load density is the ratio between case capacity and actual powder charge. Most factory ammunition is loaded with a density of 80% - 90% of the cartridge case capacity.
1. You should do not to exceed 90% load density.
A. Primers need room to flame through the powder charge which gives uniform velocity and pressure.
B. Cases that are full or compressed charges of powder will accelerate barrel wear in the rifle barrels throat area and then over time will destroy the accuracy of the rifle.
2. You should never drop below 80% load density.
A known condition named detonation (excess pressure spike) can occur with cases that are not significantly filled with powder. Some years ago the U.S. Ordnance and DuPont ballistics laboratories were able to duplicate the strange phenomenon called detonation and they had determined that excess air space in the cartridge case to be the trigger for detonation.
How to figure load density:
Powder charge weight divided by case capacity equals load density. Example: Powder charge 40 grains (divided by) Case capacity 50 grains = .8 or 80% load density.
Case Capacity:
Case capacity is the amount of volume inside a cartridge case that is available for the rifle powder or propellant to fill.
How To Measure Case Capacity:
Measuring case capacity is actually quite simple. Once you have established your bullet seating depth in the bullet section of this guide.
1. Weigh one case with bullet seated to proper depth without powder or primer.
2. Now fill the case with water through the primer hole using a hyperdermic needle and weigh again.
3. Now subtract dry weight from the water weight and this will give you your case capacity.
Example:
470 grains = water weight with bullet.
- 420 grains = empty weight with bullet.
50 grain = case capacity.
Once you have your case capacity using your reloading manual select powders that fall into your load density range.
In the above example of a 50 grain capacity your range would be.
1. 50 grain capacity x 80% load density = 40 grains of powder.
2. 50 grain capacity x 90% load density = 45 grains of powder

Larry
Northern Minnesota

 

[.452]

"Measuring case capacity is actually quite simple. Once you have established your bullet seating depth in the bullet section of this guide.
1. Weigh one case with bullet seated to proper depth without powder or primer.
2. Now fill the case with water through the primer hole using a hyperdermic needle and weigh again.
3. Now subtract dry weight from the water weight and this will give you your case capacity.
Example:
470 grains = water weight with bullet.
- 420 grains = empty weight with bullet.
50 grain = case capacity.
Once you have your case capacity using your reloading manual select powders that fall into your load density range.
In the above example of a 50 grain capacity your range would be.
1. 50 grain capacity x 80% load density = 40 grains of powder.
2. 50 grain capacity x 90% load density = 45 grains of powder

Larry
"

Larry you've overlooked the last step in this calculation, that is converting the water weight to volume in cc. , then changing the bulk density (basically the specific gravity) of the particular propellant into weight in grains.
Propellant does not weight the same as water. Your method would be off by about 60% on double based propellant, even more on some single based.

K0FF

 

[Jlr2267]

Some years ago the U.S. Ordnance and DuPont ballistics laboratories were able to duplicate the strange phenomenon called detonation and they had determined that excess air space in the cartridge case to be the trigger for detonation.

yea, this exact statement is found all over the internet...no one can seem to produce actual credible documentation of this duplication, or of the conditions under which it occurs

 

[refuse2bafool]

Much that is not understood...

I looked around a bit could not find the subject study either. However, I did find some interesting books on Detonation Theory on Amazon.

Most were geared to those that have a "background in thermodynamics and fluid mechanics" which I do, but its been loooooong time, and they were fairly pricey. But I did find one that is about $16 that seems like it might be more digestible.

Detonation: Theory and Experiment by Wildon Fickett and William C. Davis.


Here is quote from the add...

"Detonation, as the authors point out, differs from other forms of combustion "in that all the important energy transfer is by mass flow in strong compression waves, with negligible contributions from other processes like heat conduction." Experiments have shown that these waves have a complex transverse structure, and have puzzled scientists by yielding some results that are at odds with the theoretical predictions."

So no one really understands it. And if the eggheads don't then I think we are all a little out of our depth. Still, for a few bucks I am going to order it just to see how much of it might apply to cartridge ammunition.