The Components of Going Faster

[charlie b]

Larry, have you seen that kind of effect at a lower velocity and faster twist? I wonder if the twist rate has a function in the heating process, giving us the RPM limit? If PC does cause less friction then that might be a reason why the limit might be higher for PC bullets.

[TurnipEaterDown]

There no relative rotational motion between the bullet and rifling, so twist rate should not matter in terms of friction heating. The bullet gets spun pretty fast, but relative to the rifling twist, the bullet is static from a rotation perspective. It is however sliding the whole time down a nice dry steel bore on a jacketed bullet, w/ high normal forces from the bullet to the bore due to pressure during the time of acceleration trying to squish that nice cylinder into a flat pancake, with the bore keeping everything in shape. pretty rough trip, and I do believe it probably gets fairly toasty.

[M-Tecs]

I've never heard or seen of a jacketed bullet blowing up at the muzzle. Normally they blow at the 40 or 50 yard mark. Either it takes some time for the bore friction to penetrate or the air friction adds to the bullet heat.

[Bigslug]

Making good progress in the "Vehicle Assembly Building" and getting closer to rolling the crawler out to Pad 39A.



Innit cute?

Got a couple more questions moving forward:

1. Castings with the @19BHN alloy settled at .3115" after sitting a couple days - so a little fatter than spec. Dummy rounds made with these as cast assembled and chambered just fine in numerous .30-06's, so we opted to run them through a .312" sizer to apply the 2500+ lube and the Hornady gas checks and let the rifle do the swaging. With all the discussion of gas check separation, I'm wondering if a .310" sizing operation just to clamp the checks more tightly might be in order?

2. Any thoughts on a starting charge for H4831SC with a bog-standard .30-06 with a 1-10" twist 24" barrel? Current plan is to creep up to a point of group failure - probably with three shots of each loading on it's own aiming point. Test platform will be a CZ 550 that's been free-floated and bedded and a known shooter. Primers will likely be the military CCI 34's sunk into Lapua brass.

[TurnipEaterDown]

I don't think sizing the base to a smaller size will crimp the check tighter. The entire lead shank will just yield more under the check. The presumption is that the (properly assembled) crimp interface is being lost by the lead bullet getting getting squeezed down in the bore to where there is no more "bite".
If I remember right, the Hornady checks are made to provide the crimp by processing them in manner that leaves the material thicker at the opening edge of the cup.
Due to the difference in elasticity (spring back), I don't think the check really is in pressurized contact at the opening of the cup after sizing either, I think the opening edge of the check is just folded into the shank, and doesn't pull off easy over the remainder of the shank that is left larger because the walls of the GC cup are slightly thinner than that opening.
It's sort of like a crimp of a revolver case into the crimp groove, but the sizing die has no roll so the thickening of the check at opening is what is making the bite and forming the crimp groove in the lead shank.
I suppose someone could make some sort of tool that would (as a secondary operation) fold the opening of the check in further, but it would be a challenge as the cups are pretty short and the tool would have to have a collapsing ring that pressed the lip in. It would perhaps look something in function like a LEE factory crimp die.

(Edited my prior comment about relative motion w/ bullet in bore, as I left out a very key word. The first 10 words now read sensibly rather than being misleading.)

[Larry Gibson]

Larry, have you seen that kind of effect at a lower velocity and faster twist? I wonder if the twist rate has a function in the heating process, giving us the RPM limit? If PC does cause less friction then that might be a reason why the limit might be higher for PC bullets.

Yes, I have. With both the 311466 and the 310-165-FN when pressures push 40,000+ in 24" barrels of 10,12, 13 and 14" twists. The loss of the GCs was not to the extent that it was in the 16" twist 32" barrel of the 30x60 at 3000+ fps. Also, it appears the longer the barrel the more prevalent GC loss can be as there is more barrel time for the hot gasses to act on the GC and more friction. I also believe the ambient temperature has an effect on it as in 90 - 110 temperatures [I have that at early morning summer shooting times here in AZ] the barrel will never really "cool" between shots. The barrel can get very hot during a 10 shot test even with 2+ minutes between shots and air blown through the bore with a small battery pump.

M-Tecs post #63 is correct. It takes some distance, usually the 40 - 50 yards from the muzzle mentioned for the heat to penetrate and perhaps softening the lead core for the rotational forces [centrifugal force] to overcome the structural integrity of a thin bullet jacket with it spinning apart.

[Larry Gibson]

Bigslug

"2. Any thoughts on a starting charge for H4831SC with a bog-standard .30-06 with a 1-10" twist 24" barrel? Current plan is to creep up to a point of group failure - probably with three shots of each loading on it's own aiming point. Test platform will be a CZ 550 that's been free-floated and bedded and a known shooter. Primers will likely be the military CCI 34's sunk into Lapua brass."

Suggest you start at 35 gr and use a dacron filler. "Creep up" with 1/2 gr increments.

Best to size to the throat diameter just in front of the chamber neck.

[charlie b]

Thanks again Larry. Yeah, summers out here are brutal on barrel temps. Even when I have my shade umbrella up over the rifle it can get too hot to touch after a string. I have also thought about a fan but not gone that far yet. Guess I need to search out some battery powdered ones.

Lead and steel have very low heat conduction rates, so, seeing the effects well after the bullet leaves the barrel is not surprising. Keep in mind that supersonic air flow also imparts a bit of heat to the mix as well.

I use hornady gas checks just because of the extra crimp. Most of my bullets are seated such that the GC is below the neck of the bullet, so having one come off in the case is not something I want to experience.

[popper]

It showed melted on alloy in the inside of the GC cup. Apparently, the shank alloy was melting from friction and/or the heat of gas.
Nope, PRESSURE!! Take a cast bullet, hit hard with a hammer and then pick it up - pretty HOT. About 1/50th the pressure the base of bullet sees. Simple P-V-T. Then add the friction of the GC in the barrel and you can see why GC comes off, at the muzzle. Auto oil pressure isn't very high but the oil film prevents the rod from actually contacting the metal bearing - else you get to buy a new motor.

[TurnipEaterDown]

PV=nRT is the universal gas equation. Pressure times volume = number of moles of gas times universal gas constant times absolute temperature (if I remember the factors all appropriately).
This does not work with solids.

Metals (solids) get hot when deforming because there is work being performed on them. This is not just from pressure. Work ~ displacement & force. Translational work = force times distance. No distance no work. Deformational work is analogous. (A Joke Analogy: The fellow leaning on the shovel handle but not moving dirt puts force on the shovel, but doesn't do work...)
Place a metallic block under pressure w/o work, and there will be no heating.
Take a coat hanger and bend it back and forth until it breaks and it is hot. This is work. This also causes intermetallic dislocations in something like steels, what we call work hardening. That coat hanger where it broke will have a higher hardness number after breaking than before.

The gas pressure is actually doing little work to the bullet form, though there is some distortion both temporary and permanent. Most of the energy from the combustion process and expanding gases is being expended in accelerating the bullet, with loss to thermal transfer (to barrel & case in large extent), frictional loses to bullet on bore, and high expelled gas temperature. There is energy in that waste heat.

Oil pressure in an automotive engine (feed circuit to the rod journal) is not the pressure of the hydrodynamic wedge that separates the bearing shell from the journal. There are formulas to calculate the oil wedge pressure, and the two pressures are not comparable.

The pressure in the auto engine feed circuit must be high enough only (in the case of the rod journal) to exceed the centrifugal forces in the main bearing (fed from the outer diameter of the main commonly, it must be pumped to the center of the main and overcome centrifugal force to do that, to then be forced out to the rod by the same centrifugal forces you just fought to get to the center of the main with some assistance by residual pump pressure) and create enough flow to the rod to support the hydrodynamic wedge while flowing enough remove heat from friction internal to the viscous fluid (oil) shearing and conducted heat to the journal from rod, crank, etc.
Big main diameters need big pressure to feed rods. This is why BB Chevy's need less oil pressure to run the same RPM than would a BB Oldsmobile, Pontiac or numerous others with similar oil circuits and pressure pick up points. I have trashed the rod bearings in multiple 455 Oldsmobile engines running them to 6500 rpm, so I understand it pretty well.

This is an aside, but oils being used in machinery for lubrication, much like cutting fluids in machining processes, must carry heat away from the interface to avoid overheating of the interface. Many times, the heat it carries away is from some component conducting another source of heat to the interface. A great example of this in a piston engine is the piston pin. The piston is trying to heat that interface, and oil carries the heat away. Granted, a lot of that heat dissipation is carried by the oil flung and sprayed on the underside of the piston crown, but the point being that auto engine oils are also carriers of waste heat as well as lubricating compounds.

[Bigslug]

So what you guys are saying is. . .

To test this high velocity cast process to it's utmost limit, we need somebody to contour a stack of 16" twist .30-06 barrels for a water-cooled M1917 Browning. Maybe it's time we apply for a scientific grant!

All much appreciated fellas! First rounds to go downrange in about a week and a half, then probably about a month hiatus for a road trip. Back at it come June.

[Larry Gibson]

TurnupEaterDown & Popper

"Metals (solids) get hot when deforming because there is work being performed on them. This is not just from pressure. Work ~ displacement & force. Translational work = force times distance. No distance no work."

Thanks, I had not considered the heat produced by the rapid swaging down of the bullet as it transitions from case neck to bore. Since the bullet [the 30 XCB under discussion] is swaged down from .3105 to .304 - .305 very quickly we can assume there some heat added to the bullet from that also.

[dverna]

The heat generated from squeezing down the bullet is not going to amount to much IMO. We typically reduce a cast bullet by .002 when sizing and they do not get hot. We could determine the heat generated by reducing a bullet from .3105 to .304 by sizing the bullet rapidly in stages using three presses with sizing bushing....say from .3105 to .308 then to .306 then to .304. My gut tells me the bullets will not go up in temperature more than 50 degrees...and most of that will be from friction going through the dies.

[popper]

I shot 165gr GC 2400 fps 308W at a yard sign. Bullet cut the 14ga steel wire in half and the recovered GC had MELTED (re-hardened but looked like soldered into the Cu) alloy in it.
The heat generated from squeezing down the bullet is not going to amount to much IMO. So FL size a 308W case and touch it - yup, quite warm. 30% of the powder energy goes into expanding the chamber and case - that is why the case gets hot!
Per the origianal question, I did chrony my 24" 1:10 ar10 carbine 165gr GC PCd 2700 fps but didn't keep any targets to show accuracy and I only shot 100 yds.
Not going to get into a discussion, PVT works for all materials. Energy does work and created heat. Yup I got a degree too.

[Larry Gibson]

The faster the metal is worked the quicker it heats up. As was suggested, smack a cast bullet flat with a hammer, pick it up immediately and see how hot it is. then flatten the bullet in a vise the same amount and you'll find it's hardly warm. I doubt anyone here sizes a bullet anywhere near as fast as the bullet get sized going from case neck to one bearing length of travel in the bore.

[charlie b]

PVT works for everything, in some ratio or another. PV=nRT works only for ideal gases.

There are a lot of things at work here that will heat up the bullet. Temp of gases on base of bullet, pressure on the base of bullet, friction of 'swaging' down the bullet/entering the grooves, friction of bore, friction of force imparted by the twist rate, residual heat in the barrel, heat due to compression of gases ahead of the bullet. May be a couple I have missed

And they all have a time/rate component.

[TurnipEaterDown]

While I think that open source material has a large number of potential issues, here is a link that itself has internal links that might help further thought on the discussion, re: work, etc.
https://en.wikipedia.org/wiki/Deformation_(engineering)
Not meant to be a end all - definitive study, or a corrective to anyone, etc., but might help someone reading / engaged in this in some manner. More people probably read it than those commenting.

Back to the gas check retention sub-thread.
If the thought is that loosing the GC is causing the loss of accuracy (unsure that this is the thought, but it is a possibility, though loosing the GC might be just a symptom of the cause), then it occurred to me that if someone wanted to cobble up a way to to crimp a gas check more than a simple sizing die does, there Might be a relatively easy way to do it.
For a 30 caliber bullet, It seems the tools required to start with would be: (1) some sort of extended shell holder that could be bored not quite through in the center for a slip fit of the bullet and cut off the lip (rim / groove engaging portion), (2) a 7 mm something LEE factory crimp die, case necks are typically ~ 0.010" and the LEE FCD is meant to crimp the necks, (3) some 7/8-14 nuts (if I remember the common die thread right), and (4) one threaded tube w/ a flat washer welded across it (a common nut would be deep enough for what this would be for).
Attach the extended shellholder to the ram and drop the bullet in nose first. Bored hole should be deep enough to let the base stick up substantially and bullet not fall through. Run the LEE FCD in the press upside down (up from the window in the press, collet fingers toward the bullet). Use normal nut to set the position of the FCD from the top. Use another nut as a lock nut, or snug down the (non o-ringed) nut good on the press to set position an lock the die to rotation. Take the threaded tube w/ flat washer welded to it and run in down on the (now) top of the die -- turning toward body will engage the collet and create constriction at the other end.
Likely / Possibly the original top of the LEE FCD would need to be trimmed to get the bullet in far enough to get the crimp ring on the GC edge.
Hopefully the slip of the bullet in the shellholder would allow crimping the GC w/o any misalignment trying to bend the bullet. Also, the die should not turn while running the threaded tube w/ washer down to squeeze the collet into the GC, and rotation angle of the tube relative to the body would have to be controlled to get a controlled crimp. The bullet shouldn't be forced down (much?) into the shellholder as the collet is driven in to crimp, as the force to close the collet would be applied by the washer on the threaded tube not by forcing the shellholder face on ram into the collet sleeve like is designed to happen w/ the FCD. The collet would move some axially during the application of the crimp however, and I don't know how much that would be to increase the crimp a couple thousandths. I think it would be related to the angle of the collet sleeve which I don't know. Concept cobble proposal, not precision tooling.

Lots of assumptions in this cobble proposal, position of a variety of parts, does the bullet slip fit through the collet during crimping, does the collet effectively crimp the GC more or does it distort / mangle it because it isn't designed to do this, etc., but if a question is how to crimp the leading edge of the GC into the bullet shank more, this might be a way to relatively inexpensively determine if just more crimp really helps it stay on. (The opposing thought / theory is the GC gets opened & forced off by hydraulic pressure.)
If it stays on better at higher velocity, and the crimp looks reasonable, maybe an accuracy comparison could be made. Maybe it is just too much cobble and some real tooling would have to be made.

A different aspect of this discussion in general: Viscous lubricants create internal heat during shearing. Shearing happens in the fluid layer due to fluid being the interface between objects w/ relative motion (bullet & bore). Higher speed of shearing, more temperature rise, higher viscosity fluid in interface, more temperature rise.

I think that common 50-50 lube gets hot enough to vaporize at least a portion of the lube in common cast bullet loads (1200-1600 fps). At least I see a cloud at the muzzle that seems to be lube "smoke" maybe it is just finely atomized lube, I just don't know and could be wrong about supposed vaporization, but if some is being vaporized, that can't really be good for it's function as a lubricant at higher speeds than commonly used in pedestrian CB loads.

I do not know if it is practical, but lowering the viscosity of the fluid will lower the temperature rise. Maybe some different carrier could be tried w/ a lower viscosity, while being used to carry a good high pressure lubricant.
One very good high pressure lubricant is colloidal copper (copper anti-seize), but I don't know how this interacts w/ lead or how to make an effective low viscosity carrier for something like this. Maybe simple colloidal copper could be smeared on a bullet, but I really doubt that thought is too original or inspired.

Some fluids experience a greater change in viscosity relative to velocity than others. Viscoelastic fluids get "firm" if impacted quickly, and flow more easily if force is applied slowly.
Also, in general, most fluids get less viscous as temperature of the fluid goes up.
This really isn't my "bucket", but maybe someone reading this understands this viscosity/carrier part better than I and can comment on the possibility of some fluid having properties that could be exploited as a higher speed lube, or carrier for another lube, to reduce frictional heating and fluid boundary thickness/ pressure.

The fluid pressure of the lube seems to do some very undesirable things here (reducing bullet size radially), so trying to offer something on that. Even if just prompt a comment from someone who knows much more on topic.

[TurnipEaterDown]

To anyone interested in a better understanding of metal forming, and the various effects, "Metal Forming, Mechanics and Metallurgy" 3rd edition, by William F. Hosford, in pdf form, can be downloaded online for free. A person can find this text by a search for "metal forming mechanics and metallurgy pdf"

There are sections in the text on strain rate and temperature dependence, and many others, and notably for this discussion, heating from work done on the metallic body during forming.

The equation for temperature increase during work is given in section 5.9, and it is stated to be dependent on strain in a direct manner. It uses an adiabatic assumption: no heat loss. So, this would be conservative: providing a high estimate.
Very small strains, low temperature rise.
I have not calculated the value for the lead bullet discussion here, but with small strains described, but it would appear to be low. Certainly if strains were very low (in the elastic region entirely), then the temperature rise, by work of gas pressure creating deformation of the bullet, would be low.

Most likely, at least in the case of jacketed bullets which are described by Larry as having been found on the ground hot after firing, the temperature rise is due to frictional effects, by the air as the bullet passes through, or perhaps also there is a significant contribution from friction in the barrel. I well recognize that there is significant friction effects on the bullet during barrel residence, but w/o calculating its a guess as to what matters most: frictional heating of the bullet in the air during flight, or barrel.

Again, my intention is not to "correct" anyone by providing this link to Hosford, just to provide what I believe is sound information relevant to the discussion.

[Larry Gibson]

"Most likely, at least in the case of jacketed bullets which are described by Larry as having been found on the ground hot after firing, the temperature rise is due to frictional effects, by the air as the bullet passes through, or perhaps also there is a significant contribution from friction in the barrel."

Here's the problem I have with the theory in is the air resistance on the that is the cause of the alloy melting inside the GC. Since the air resistance is greater on the nose/ogive of the bullet the heat generated should be the greatest there, correct? Yet none of the recovered bullets which lost the GC showed any melting of the bullet nose, ogive or anywhere else EXCEPT on the shank inside the GC. Are you saying the heat generated is somehow transferred to jus the base of the bullet?

I believe it is the friction of the GC on the barrel that heats it to the point it melts a layer of alloy along the inside of the side of the GC. This allows the crimped GC to then slide off.

[TurnipEaterDown]

Larry, Yes, my comment you returned post on was more about the bullets you stated as finding lying on the ground that were still hot (think you said something about a possible "teaching moment" for someone and fingers getting burned) and not the GC w/ lead observation you noted.

I believe that the lead on the GC you are seeing is from the combustion gas temperature of the nitro components.
I seem to remember combustion temperature of gun powders in the thousands of degrees Kelvin range. The common GC is copper alloyed, and transfers heat well. Very high temperature flame, thin conducting disk: I think you get boundary layer melting on the lead bullet base. The time exposure to the very high combustion temperatures is low, but the temperature differential across the disk is high. Very high. The energy transfer is probably significant and likely high enough to melt the lead.

Lead melts much lower than steel, and we now about flame cutting of top straps and throat erosion from high temperature gases. So, I would lean toward very plausible.
Also, consider the pictures from another earlier poster on the bullet appearance w/ & w/o the filler. Sure looked like the filler (not a good heat transfer media) cut down on bullet base localized melting / pitting.

This heat transfer isn't a difficult calculation if it's important. An assumption could be made on time exposure by simply plugging the load into GRT, getting time to pressure peak, looking up flame temperature of gunpowder in 50Ksi combustion environment, and use a simple heat transfer equation. Perfect answer: No. Good answer to determine plausible dominating contributor: Yes.