Dacron and the Honda CVCC

[JohnH]

Did some shootin' today and came away with what could be an interesting thought.....

A while back a thread on fillers had a fella who said he didn't understand how Dacron could work. His premise was that the pressure form the primer alone would compress the Dacron against the bullet base and give away any of the "holding the charge against the primer for more even ignition" Maybe.

I've no disagreement with that idea, in fact I think it is correct. Just how is Dacron going to hold the powder against the primer is beyond me, but it may instead act like a control against the resulting pressure. Let me explain...

The Honda CVCC engines operated on a quite unique concept. It was a three valve engine, the usual intake and exhaust valves, but with an added air intake in the opposite side of the cylinder head from the main intake valve. CVCC stands for "Controlled Vortex Combustion Chamber" Worked like this, the intake valve allows a gas/air mixture into the chamber, but by adding air from the opposite side of the head, a vortex is created that improves the atomization of the air/fuel mix and makes for more effiecient combustion. Proof was in the pudding. During the mid to late '70's, while everyone else was struggling with catalitic converters, air pumps, computer controlled carburation etc, the CVCC was so effiecient that Honda didn't use catalitic converters until the early to mid '80's

So here's my thought, The primer ignition pressure does in fact squish a Dacron filler against the bullet base, but the Dacron's compression "controls" the resulting cloud of powder as it ignites allowing for a more even ignition resulting in better groups.

I spent the day playing with my 375 JDJ and the Lee 379-250-RF, a plain base I ain't been able to get to shoot. I started with Lymans 379449, but no good luck there, decided I had nothing to loose, and tried 15 grains of 820 (pulldown) and a tuft of Dacron about 1/2" by 5/8". The Dacron shrunk groups that had been over 4" to right at 2". Thinking that there is still a "volume factor" at work, I cut some peices that were 1/2" by 3/4" and when put in the case, came to the bullet base. (The 1/2" X 5/8" only came up about 3/4 of the case) Bad mistake. Groups went from baseball to past softball size, worse even than no Dacron.

Overall, I'm pretty happy with I've seen today. The load lets me shoot and not grossly disturb my neighbors with excessive report, the main reason I shoot light loads.

[David R]

Fillers work for some. Sometimes for me. They always improve what my crony tells me, but usually make for bigger groups. Just my exp.

See the other thread about case size and shape. Its all about combustion chamber design.

I had a honda, it has a 3 barrel carb and the third valve is just a teeny thing in a pre combustion chamber. It works like a diesel. Ignite a richer charge in the precup and that will ignite the leaner mixture in the cylinder. Worked great, got awesome milage, but the block and crank were made out of butter and would not stay together.

[sundog]

John, your theory may have validity, but to me the primary reason for the wad is to keep the primer from spraying over the top of a powder charge that has lain down in the bottom of the [horizontal] case, thus igniting too much all at one time. If the flash hole is exposed, so is alot large surface area of powder. sundog

[StarMetal]

Sundog is right, it's merely to keep the powder against the primer till firing, then doesn't matter what it does, BUT I believe it helps seal the powder gases off from getting around bullet, more so with Kapok.

Joe

[Newtire]

Did some shootin' today and came away with what could be an interesting thought.....

A while back a thread on fillers had a fella who said he didn't understand how Dacron could work. His premise was that the pressure form the primer alone would compress the Dacron against the bullet base and give away any of the "holding the charge against the primer for more even ignition" Maybe.

I've no disagreement with that idea, in fact I think it is correct. Just how is Dacron going to hold the powder against the primer is beyond me, but it may instead act like a control against the resulting pressure. Let me explain...

The Honda CVCC engines operated on a quite unique concept. It was a three valve engine, the usual intake and exhaust valves, but with an added air intake in the opposite side of the cylinder head from the main intake valve. CVCC stands for "Controlled Vortex Combustion Chamber" Worked like this, the intake valve allows a gas/air mixture into the chamber, but by adding air from the opposite side of the head, a vortex is created that improves the atomization of the air/fuel mix and makes for more effiecient combustion. Proof was in the pudding. During the mid to late '70's, while everyone else was struggling with catalitic converters, air pumps, computer controlled carburation etc, the CVCC was so effiecient that Honda didn't use catalitic converters until the early to mid '80's

So here's my thought, The primer ignition pressure does in fact squish a Dacron filler against the bullet base, but the Dacron's compression "controls" the resulting cloud of powder as it ignites allowing for a more even ignition resulting in better groups.

I spent the day playing with my 375 JDJ and the Lee 379-250-RF, a plain base I ain't been able to get to shoot. I started with Lymans 379449, but no good luck there, decided I had nothing to loose, and tried 15 grains of 820 (pulldown) and a tuft of Dacron about 1/2" by 5/8". The Dacron shrunk groups that had been over 4" to right at 2". Thinking that there is still a "volume factor" at work, I cut some peices that were 1/2" by 3/4" and when put in the case, came to the bullet base. (The 1/2" X 5/8" only came up about 3/4 of the case) Bad mistake. Groups went from baseball to past softball size, worse even than no Dacron.

Overall, I'm pretty happy with I've seen today. The load lets me shoot and not grossly disturb my neighbors with excessive report, the main reason I shoot light loads.
Ha ha, just thought I'd be a S**t disturber. The engine that did the swirl effect was the Mitsubishi. the Honda actually utilized a small separate chamber with a mixture rich enough to be lit off that set off the main charge which ordinarily would not be burnable. That's why they got such great emission results. A stratified charge like a duplex load. Burns clean. So there....Just felt the need to be aknow it all. Have cabin fever. Wish it would quit raining!

[JohnH]

Well, I've been corrected twice today, guess it serves me right for coming out of my room :) :)

[Buckshot]

Well, I've been corrected twice today, guess it serves me right for coming out of my room :) :)

...............HA! That's okay John. You got'em thinking and I'd have never known different anyway. It's the theory and question that count.

................Buckshot

[Leftoverdj]

I'd be inclined to think that the dacron is moved against the base of the bullet by unburned powder, not the gases. Within the case, pressure is going to be uniform very quickly, and that loose web of dacron is not a significant barrier to the gases.

[StarMetal]

leftoverdj,

It's not so much that the dacron or kapok is a gas barrier, it's that the fine fibers (especially in kapok) that plug what irregularities there may be in the bullet that gas is trying to slip by (as in gas cutting). Much like stopleak in radiators. Dan from Mountain Moulds and I talked about this and he feels the same. He also told me his belief on lubes are that they serves a sealing effect as much as they may lube even.

Joe

[Flash]

Doesn't fast burning cast bullet powder produce all it's energy upon ignition and not while traveling up the barrel? With this in mind, the filler and bullet hasn't moved until the pressure peaks enough to get it moving and should travel at the same speed. If there was a gas seal between the filler and the bullet, the filler would certainly compress against the bullet during ignition. If the density of the filler is less than the case or the bullet(which it is), it should become a smaller mass but not against the bullet. The filler should just collapse on itself but still will have done it's job to keep the powder against the primer. I suspect that the point where the filler takes a real beating is when the bullet leaves the barrel and all that pressure escapes through the filler. PoooooF!

[fourarmed]

I have read that even the slowest smokeless rifle powders are completely consumed by the time the bullet has moved 4 inches.

[felix]

Fourarmed, that author of that what you read is wrong. Of course, you know that by simple observation! Especially at night. The answer is between 15-18 inches, and is the location where the 1st derivitive of the boolit's acceleration changes direction. You can visuallize this by looking at the land-groove junction. The fouling switches from one side to the other. ... felix

[felix]

The very best filler is the powder itself. Mainly because the internals of the case changes shape enough, and quickly enough, to keep busting up any possible conditions for a dangerous wave development. ... felix

[waksupi]

I have read that even the slowest smokeless rifle powders are completely consumed by the time the bullet has moved 4 inches.

That one was proved false to me, when I started shoting WC 860, and WC 872. Shooting over snow, I had unburnt powder strung out at least fifteen feet in front of the shooting bench. And in such rifles as Swedes, you have lotsa unburnt powder left in the bore and chamber.

[fourarmed]

I presume the author meant "at SAAMI pressures." When we load that stuff behind cast boolits at low pressure, naturally it doesn't all burn up.

[Leftoverdj]

leftoverdj,

It's not so much that the dacron or kapok is a gas barrier, it's that the fine fibers (especially in kapok) that plug what irregularities there may be in the bullet that gas is trying to slip by (as in gas cutting). Much like stopleak in radiators. Dan from Mountain Moulds and I talked about this and he feels the same. He also told me his belief on lubes are that they serves a sealing effect as much as they may lube even.

Joe

Sure, after the dacron has been forced against the base. I was addressing the behavior of a gas in a sealed chamber.