Over-powder wad

[oldred]

Let me say from the start that I am not suggesting anything one way or the other, I am simply asking a question.


I was talking to a buddy last night about his 45/70 loads he has been shooting in his Handi rifle and he was telling me he is using 42 grains of IMR4198 and 400 JSP bullets. He then said he places a thin cardboard disc snugly onto the powder before seating the bullet, I warned him that this is not a good idea because it leaves an air space between the powder column and the bullet base but he just brushed it off and said he has been doing this for years with no problems. He shoots these in both a Handi and a T/C Encore rifle and claims it gives him more consistent loads and as far as the air space goes he argues that only matters when shooting BP and besides it would be no different than just shooting the rifles straight up which would also result in the same air space. I did not push the issue but it is my understanding this practice can be dangerous and placing even a thin cardboard wad over the powder can cause the bullet to act as a bore obstruction, or do I have this wrong? Whether or not I have the reasoning right everything I have read indicates doing this can be dangerous and that even a thin wad over the powder has a completely different effect than a lightweight filler such as dacron. Am I right or wrong about this?

[Larry Gibson]

You are correct.

Larry Gibson

[SciFiJim]

I don't use a card wad or a filler, but the results reported from those that have say that the card wad can result in a ringed chamber.
Think of it like this.

1. no wad or filler, case not filled to capacity. On ignition the the powder and gases are swirled while burning inside the case before the projectile starts to move. Pressure rises equally in all parts of the case.

2. case filled to capacity or compressed. On ignition the powder burns and creates gas without swirling until the projectile starts to move and create more space.

3. Case not filled to capacity, with a tuft of Dacron or similar. On ignition the filler does not impede the gas so pressure rises equally inside the case.

4. Case not filled, a wad on top of powder with air space between wad and base of projectile. On ignition the wad is pistoned toward the base of the projectile, compressing the air between, which creates outward pressure in all directions perpendicular to the path of the wad. It is the pressure at right angles to the path that can result in a ringed chamber.

The ringed chamber will not always result from case #4. Sometimes the pressure is not enough to result in a ringed chamber before the projectile begins moving and pressure in the case starts to drop.

If your friend has gotten away with it for years, he is still a lot closer to a ringed chamber than I am, because I don't place the cause inside of my firearms. I would guess that it is only a matter of time before your friend rings a chamber. Careful examination of his brass might show how close he is. That much pressure should start cause some thinning in the appropriate area. However, knowing a little of human nature, your friend , sure in the confident knowledge of what he is doing, would not conduct the examination.

[runfiverun]

the short way to think about it.

the air between the card and the boolit has no where to go.
you just used 40k of pressure in an inch of case to compress air in a quarter inch of space i wonder how much pressure you just created.
i'd say 2 to 4 times as much minus leakage.
even if you only have 20-k of powder pressure or a primer blast.

[nhrifle]

I'm in agreement that an over powder wad in smokeless loads is not a good idea. I remember in science class, we had an experiment of putting a piece of cotton in a glass cylinder and compressing the air above the cotton with a piston as hard and quickly as we could. The cotton ignited. It's the same basic principle of what happens in a deisel engine. Not something I want going on under ne of my boolits, and certainly not six inches from my face! That said, I do use a wad in my black powder cartridges, but that is with a case full of powder.

[BAGTIC]

I don't know as I have never used a wad like that. I do use filler wads in shotshells.

Nonetheless neither explanation makes much sense. The pressure created between the wad and the bullet is not going to be any higher than it would be otherwise. It takes resistance to build pressure and theat lightweight wad is not going to build enough resistance. If there is significant distance ahead of the wad there is a good chance the wad will cock bypassing the gas anyway.

It has long been a practice to use wads large enough to totally bridge the space between the powder charge and the bullet base in order to increase charge density and prevent powder from shifting due to cartridge orientation and they don't cause problems.

[BAGTIC]

Compression raises the temperature to the ignition point of the fine cotton fibers. Igniting cotton fiber in a hot oxygen rich environment is different that igniting a cardboard wad in an oxygen depleted environment. For many years card, fiber, and felt wads were used in shotshells with both smokeless and black powder and I never saw one of those wads burn even when exposed to very hot powder gases.

The pressure does not peak until after the bullet has begun to move forward and engages the rifling.