EEEU-Reek-Ah! I Found(ered) It!

[Zeek]

Dear Y'awl:
I believe that we now have the WHY of my many PPCBoo experiment failures, over the last six months or so. All but the very latest ones were patched up well over the final diameter and then sized down to final, with the result that the PPatch was a hard, dense, very thin "shell."

A couple of days ago, an interior ballistics expert friend told me that I was full of hooey about the idea that, if you PPatch to final bullet diameter and then do NOT size the patch, that the air in the patch would be expelled when the obturating CBoo core mashed the PPatch against the lands and grooves. He said that the entire shot process occurs so fast that there is no time for the gas to escape from that small-pore-matrix medium. I thought, "Mah!!!", but could take it no further until this afternoon. Meanwhile, it just festered between my ears.

Today was my last day of work prior to our leaving on vacation. After leaving work, I was standing on the sidewalk, waiting for my home-bound train and a bus stopped with its massive rear wheels just in front of me. It all hit me in a flash. "OF COURSE!!", I said.

The reason the air stays "in" the PPatch is that the air does not have time to escape (during the "life" of the shot). The reason the air is in the bus tire is that the air does not have time to escape (takes several years to do it by molecular diffusion) during the lifetime of the ride . . . then the mechanics top it up every few days.

So, the air-filled as-yet-uncrushed PPatch acts just like a pneumatic tire because the entire shot process is over before the gas has any chance to escape. Well, the air in the tire holds the bus up just fine, thank you, so it must act in the same way with the CBoo core. As the CBoo core obturates, the air-filled PPatch, which is very FLEXIBLE, RESILIANT, and THICK (all good points) compresses a bit, but the now-compressed air in it supports the CBoo core all around, just like the air-filled bus tire supports the bus (albeit only on the bottom of the well/tire assembly).

That compressed-air aspect makes it VERY difficult for any significant amount of powder gas to sneak by the boolit's pneumatic seal (this is just the way the breech of a modern cannon seals against gas leakage, by the way ~~~> the greater the gas pressure, the tighter the seal). Bus tires transmit torque from the engine very nicely, so the pneumatic PPatch will do so likewise.

So, THAT is WHY I was having such a hard time getting my PPCBoos to work ~~~~> I was patching them too big in diameter and then sizing them down to the point where they were a very hard shell by the time they reached their finished diameter. That hard shell did not have the supple pneumatic pressure/fit against the barrel and cannot accommodate the land-top-to-groove-bottom streeeetch as nicely as can the flexible, much-thicker, pneumatic PPatch. Ha! That WHY concept makes a lot of valuable sense, from my perspective.

All the buffalo-killing PPCBoos in BPCR rounds were built like that too ~~~> the undersized CBoo core was patched up to just over bore diameter and SHOT THAT WAY. Oh, they worked just fine, thank you! Lately, having tried PPCBoos that were unsized (or minimally-sized-down), after wrapping the PPatch, I found that they provide far better performance than my old size-all-the-air-out-then-shoot-it approach did. The air in the PPatch plays a VITAL role by acting as a thick, resilliant, pneumatic seal and torque-transmitting interface during the brief (typically, around 2 milliseconds) duration of the firing sequence. Better yet, the patch remains "puffy," so should disintegrate far sooner, and more reliably, after leaving the muzzle, than would a fully-precompressed hard-shell PPatch.

I know. I know. You CAN make the precompressed-patch PPCBoos shoot well. My point is that we now know WHY it is so very much more difficult to get good performance that way, as compared to just patching up to a bit over groove diameter and then shooting it that way.

I'm gone for several weeks. I'll see ya then,
Zeek

[303Guy]

Would that be why a lube saturated patch doesn't work? Apart from possibly 'gluing' the patch to the core - that does happen!

[zuke]

I'm looking for a way to water-proof my PP load's.
Any idea's out there?

[docone31]

JPW. Just wipe a little on.

[Zeek]

You can make your load water resistant by giving the exposed portion of the PPatch a light coating of paste floor wax. Just rub your index finger in the wax (just hard enough to pick up by direct smear-transfer . . . no gobs), then rub your index finger against your thumb, to spread the wax around. Now rotate your cartridge between the thumb and index finger. This puts just a bit of the wax on the outside of the paper, which will make it very water resistant.
Zeek

[Zeek]

Would that be why a lube saturated patch doesn't work? Apart from possibly 'gluing' the patch to the core - that does happen!

That makes sense, 303Guy. The air in the patch is the secret. If you displace it with an incompressible fluid (wax, oil, etc.), then it quits acting like a pneumatic tire and just sits there. My reading is that the captive air is what makes our PPCBoos work. I tried it every whichway but loose, with the hard-shell PPatches, and could not get them to work well. As soon as I switched to the non-precompressed patches, everything turned riot around, performance-wise.

I'm a convert, but you can call me Zeek. Tomorrow morning, we head off to visit family and then attend the Shootists' Holiday at the NRA Whittington Center near Raton New Mexico.

[pdawg_shooter]

Dear Y'awl:
I believe that we now have the WHY of my many PPCBoo experiment failures, over the last six months or so. All but the very latest ones were patched up well over the final diameter and then sized down to final, with the result that the PPatch was a hard, dense, very thin "shell."

A couple of days ago, an interior ballistics expert friend told me that I was full of hooey about the idea that, if you PPatch to final bullet diameter and then do NOT size the patch, that the air in the patch would be expelled when the obturating CBoo core mashed the PPatch against the lands and grooves. He said that the entire shot process occurs so fast that there is no time for the gas to escape from that small-pore-matrix medium. I thought, "Mah!!!", but could take it no further until this afternoon. Meanwhile, it just festered between my ears.

Today was my last day of work prior to our leaving on vacation. After leaving work, I was standing on the sidewalk, waiting for my home-bound train and a bus stopped with its massive rear wheels just in front of me. It all hit me in a flash. "OF COURSE!!", I said.

The reason the air stays "in" the PPatch is that the air does not have time to escape (during the "life" of the shot). The reason the air is in the bus tire is that the air does not have time to escape (takes several years to do it by molecular diffusion) during the lifetime of the ride . . . then the mechanics top it up every few days.

So, the air-filled as-yet-uncrushed PPatch acts just like a pneumatic tire because the entire shot process is over before the gas has any chance to escape. Well, the air in the tire holds the bus up just fine, thank you, so it must act in the same way with the CBoo core. As the CBoo core obturates, the air-filled PPatch, which is very FLEXIBLE, RESILIANT, and THICK (all good points) compresses a bit, but the now-compressed air in it supports the CBoo core all around, just like the air-filled bus tire supports the bus (albeit only on the bottom of the well/tire assembly).

That compressed-air aspect makes it VERY difficult for any significant amount of powder gas to sneak by the boolit's pneumatic seal (this is just the way the breech of a modern cannon seals against gas leakage, by the way ~~~> the greater the gas pressure, the tighter the seal). Bus tires transmit torque from the engine very nicely, so the pneumatic PPatch will do so likewise.

So, THAT is WHY I was having such a hard time getting my PPCBoos to work ~~~~> I was patching them too big in diameter and then sizing them down to the point where they were a very hard shell by the time they reached their finished diameter. That hard shell did not have the supple pneumatic pressure/fit against the barrel and cannot accommodate the land-top-to-groove-bottom streeeetch as nicely as can the flexible, much-thicker, pneumatic PPatch. Ha! That WHY concept makes a lot of valuable sense, from my perspective.

All the buffalo-killing PPCBoos in BPCR rounds were built like that too ~~~> the undersized CBoo core was patched up to just over bore diameter and SHOT THAT WAY. Oh, they worked just fine, thank you! Lately, having tried PPCBoos that were unsized (or minimally-sized-down), after wrapping the PPatch, I found that they provide far better performance than my old size-all-the-air-out-then-shoot-it approach did. The air in the PPatch plays a VITAL role by acting as a thick, resilliant, pneumatic seal and torque-transmitting interface during the brief (typically, around 2 milliseconds) duration of the firing sequence. Better yet, the patch remains "puffy," so should disintegrate far sooner, and more reliably, after leaving the muzzle, than would a fully-precompressed hard-shell PPatch.

I know. I know. You CAN make the precompressed-patch PPCBoos shoot well. My point is that we now know WHY it is so very much more difficult to get good performance that way, as compared to just patching up to a bit over groove diameter and then shooting it that way.

I'm gone for several weeks. I'll see ya then,
Zeek

Sounds real good, for shooting bus tires out of a rifle. I just dont have any chambered that way!

[zuke]

Thank's for that little tidbit!

[303Guy]

I'm keen on exploring this 'pneumatic tyre' effect.

I test my current paper of choice and found it compresses to 75% under load and springs back to 86 % when the load is removed. (It would no doubt compress further with more load but not from my micrometer!) So it has at least 25% air-space. Then there is the compressability of the fibre itself.

Many folks are using tracing paper which is pretty tough stuff and seems to have way less air-space. So, we have a whole new set of variables. And paper patching is simple, how exactly?:veryconfu Hee hee!:mrgreen:

I'm wondering how this 'pneumatic tyre' effect affects patching over grease grooves? If one deliberately minimizes the paper taking up the groove shape, there would be a huge volume of air trapped right there, ready to blow the patch off at the muzzle!:shock:

I wonder whether this concept has ever been thought of before?

Zeek, thanks for the thought provoking concept and do have a good trip!:drinks:

[Zeek]

I'm keen on exploring this 'pneumatic tyre' effect.

I test my current paper of choice and found it compresses to 75% under load and springs back to 86 % when the load is removed. (It would no doubt compress further with more load but not from my micrometer!) So it has at least 25% air-space.
Yes, that is how much gas you can get ride of (~30% to 40% of the thickness the PPatch ads) before the PPatch becomes harder than the lead alloy. However, the in-the-barrel response cannot be modeled with a vice, given that the entire bullet travel is complete in less than two milliseconds. The gas simply cannot escape the paper anywhere near that fast, so the patch acts like a pneumatic tire.


Then there is the compressability of the fibre itself.
The fiber is harder to compress than any lead alloy, so the only compressible portion of the PPatch is the included gas.


Many folks are using tracing paper which is pretty tough stuff and seems to have way less air-space. So, we have a whole new set of variables. And paper patching is simple, how exactly?:veryconfu Hee hee!:mrgreen:
Tracing paper compresses around 30% before becomming "harder than lead alloy". So, there is no real difference between it and regular paper, in that regard.


I'm wondering how this 'pneumatic tyre' effect affects patching over grease grooves? If one deliberately minimizes the paper taking up the groove shape, there would be a huge volume of air trapped right there, ready to blow the patch off at the muzzle!:shock:
The two millisecond time period makes the gas stay trapped in the paper covering even a very short drive band. The CBoo's adjacent empty lube groove exerts no compression on the PPatch, so is completely "out of the picture" ~~~> all that counts is those portions of the PPatch that are pressed outward against the rifling.


I wonder whether this concept has ever been thought of before?
That's a hard one to answer, but I have never heard anything like it. My impression is that folks have tended to just use what worked, without going into the WHY of it much. At this point, the pneumatic effect is a theory, but PPCBoos made and shot that way work, and PPCBoos wrapped large and then sized way down to final diameter tend to work poorly, by comparison. Therefore, the theory works and should be rejected only if there is another theory that explains the gas-in-paper's beneficial effect better than this one.


Zeek, thanks for the thought provoking concept and do have a good trip!:drinks:
You bet! It was a great trip and we are back all safe and sound.

[redneckdan]

In the paper jacket Mr. Matthews states that he dips the bullet nose/jacket of a loaded round into molten wax to 'weather proof' the round for hunting purposes. I did up a batch of these that I hope to test in the next couple weeks.

[Zeek]

That sounds like it should work, so long as most of the patch is protected in the caseneck. I find that a light coating of paste wax causes no problem to the in-the-neck part and renders the exposed portion of the patch virtually proof against being wetted under any but dunking conditions. A lightly-lubed PPatch seems to make the PPCBoo easier to seat, compared to one with no light-wax coat.

In order to keep the lube coat light, I smear my thumb across the surface of the paste wax, then smear my index and waxed thumb, then roll the PPCBoo between them. The result is that the PPatch shows almost no visual evidence of having been waxed, yet it is very water resistant. This provides the benefits of the lubed patch (seats easier and resists wetting) without displacing a significant portion of the vital gases trapped in the patch.

It seems like the dip-the-exposed-nose-in-molten-wax approach would work better, though, in any instance in which one expected to be hunting in the rain.
Zeek

[DIRT Farmer]

After spending 10 hours driving back and forth at 4 miles per hour planting beans, I should have had this to think about. I wounder, The 03-A3 load I tried worked on the first attempt with a .309 core, wraped to .320, waxed and sized to 309 again. The 303 load is working, not great, with no sizing. Is there no constants? Or is it just magic?

[303Guy]

It's just magic!:bigsmyl2:

There are constants, we just don't know what they are.

What's the variable when it takes a hundred or so shots before a paper patch starts shooting accurately? Something is changing! It can only be the condition of the bore. Can't be a big difference.:roll:

[rhbrink]

It's just magic!:bigsmyl2:
Yep black magic better get friendly with your local witch.

There are constants, we just don't know what they are.
Oh yes and they are different for each rifle.

What's the variable when it takes a hundred or so shots before a paper patch starts shooting accurately? Something is changing! It can only be the condition of the bore. Can't be a big difference.:roll:
100 rounds about right and firelapping don't hurt either. Took me about a 100 boolits just to learn how to wrap them little suckers.

All in fun have a G'day :bigsmyl2:

[DIRT Farmer]

Dang and I could have married her to.

[Zeek]

Sounds real good, for shooting bus tires out of a rifle. I just dont have any chambered that way!
Oh, I wouldn't do that. It would be far to tiring.
Zeek

[robroy]

Just goes to show: Fools rush in where angles fear to TREAD:mrgreen:

[Zeek]

Yup. Triggernometry strikes again!