Home Forums Hunting & Shooting Ask The Gunwriters The Article "How Smokeless Burns"?

Keith's tube used in the frontal ignition system was not perforated, nor was it filled with black powder. He wrote a pretty good description of it, with some commentary, about 40 years later in his Gun Notes column in Guns & Ammo:

Link: Keith - Guns & Ammo October 1982

The system in fact worked as Keith and co-workers described it, producing lower pressures, higher velocities, and lower barrel temperatures. However, it was impractical, involving too much fiddle-dee-dee.

The linked article describes a shortcoming that is rarely discussed in connection with the system: The loading requires a case-filling load of slower powder, and the cartridge case must fit the rifle's chamber very closely, to allow minimum expansion when fired. If the case expands very much when fired, that would "let the flash of the primer come back around the charge and fire it much to fast, causing a dangerous overload". One of his experimental tube cartridges in 50BMG wrecked a Frankford Arsenal pressure gun when it was fired in a loose-fitting chamber.

Hatcher at some point wrote that the flash tube concept had been used in artillery shells for some time before Keith et al. began their experiments.

--Bob

I know a few guys that played with frontal ignition in rifle cartridges a few years ago and yes it did lower barrel temps, but the chamber temp actually increased and the pain in the but of the threaded tube. It worked as Keith described according to them

Bullshooter. The case usn't expanded yet when the primer "flashes."

And shorten the war by a minimum of six months.

hawkins-
I was quoting Keith's narrative. However, I had a similar sort of reservation as yourself as I did so.

In mild support of Keith's idea about relatively loose fit of case and chamber being a problem was his apparent prediction of the over-pressure event before it happened. Of course it's possible, perhaps probable, that the event occurred for reasons other than Keith's prediction.

Related to this is a general question of the pressure developed in a case with primer ignition alone. It would be helpful to know how much pressure a primer produces in a rifle cartridge case before powder ignition. It may be enough to result in some case expansion. Are data available to answer this question?

--Bob

One can estimate the progress of the burn using a plot from Pressure Trace along with a table of the burning rate of nitrocellulose at pressure. I went through this exercise with a 7 Rem and found only about half the charge is burned at peak pressure with the rest several more inches down the bore. QuickLoad--which uses a different math model of the burn--agrees.

How does it develop peak pressure with only half of the charge burned?

At peak pressure, the volume behind the moving bullet is such that half the charge is enough to reach the pressure limit.

At this same point, the bullet is moving fast enough that the ever increasing volume behind the bullet more than accommodates the gases being created by the rest of the charge. Another way of looking at this: the second half of the charge is striving to keep the pressure near the peak level.

Denton -

I've been at the reloading, powder stuff since 1975. Read a LOT of info pertaining to ALL SORTS of related components.

I've never SEEN nor HEARD that explanation. THANKS!

I know/understand the principle from Hi performance, 2 stroke engines and race cars. You CAN get the fuel mixture TOO LEAN for reasonable length of service.

I've never heard that THEY could 'injun eer' gun powder that way.

My daughter's husband is a chemist, the son of a chemist. We got to fiddling with a black powder substitute (which showed a lot of promise). In the course of that, I mentioned that the substitute was still leaving a little carbon residue. The senior chemist allowed that it was easy to get a little more oxygen in the mix, to get rid of that. It was then that it clicked: Smokeless powder runs out of oxygen before it runs out of fuel (re-ignites when it hits air), and it leaves carbon residue, just like a "rich" engine. And that's better than running "lean".

Denton-

Very Interesting.

THANKS

AGAIN.

Spread a clean big tarp out in front of ones bench, torch off a round, and sweep up the residue.

Back when I shot pistol at an indoor range on a weekly basis, I one day had a target fall off its clips. Since there was no one else shooting, I ducked under the counter and went to retrieve it. I was amazed by the crunch beneath my feet.