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Thread: The Components of Going Faster

  1. #81
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    I agree.

    Yes, there are a lot of factors that contribute to the heat gain, but, most are not as significant as the friction factor or the gas temp on the base of the bullet. Things like the compression of air in the bore and the air friction outside the bore would serve to keep the bullet hot after it left the barrel, maybe even increase the temp slightly.

    The interest here is why is the lead melting under the gas check and not on the sides of the bullet? Maybe a couple of reasons. 1) the gas check is copper and a good head conductor, which means the gas temp on the base of the bullet is 'felt' by the lead. 2) the friction of the gas check is higher than the lead portion of the bullet. 3) lube on the lead portion of the bullet is reducing further the coeff of friction of the lead portion of the bullet.

    Another data point. I have found when sizing bullets that the GC has a slightly larger dia (~0.0005) than the body of the bullet. The simple explanation is the copper GC has a 'spring back' and the lead has less. Higher yield limit maybe the source? Is this related to how the GC acts in the barrel or why it is heated more?

  2. #82
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    Hornady discovered that the standard plastic BT points were melting when the stated using a Doppler Radar chrono. The does give us some insight to point temperatures.

    https://www.hornady.com/support/faqs...20the%20muzzle.

    Heat Shield Technology
    At what temperature do standard tips melt?
    Every bullet manufacturer's tips begin to melt and deform depending on their specific material properties. In general, standard acetals and Delrins, currently used in bullet tips, begin to soften and deform at 150 to 200 degrees (F). At 250 to 350 degrees (F), they will begin to melt and badly deform. The longer the exposure to these types of temperatures, the more deformation will occur. This generally begins to occur from 50 to 100 yards of the bullet leaving the muzzle. Even though the effect is measurable with Doppler radar early in the bullet's flight, the effect on point of impact for ranges out to approximately 400 yards is small enough that it can't be exposed during shooting. Time of flight is not long enough up to 400 yards to expose the increase in drag that is measured by point of impact. Beyond 400 yards, however, the time of flight becomes long enough that the increase in the drag due to tip melting can be exposed during shooting and will result in vertically elongated groups and a lower point of impact than predicted.



    https://www.hornady.com/heat-shield

    https://www.hornady.com/support/faqs...tipped-bullets
    Last edited by M-Tecs; 04-14-2022 at 06:08 PM.
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  3. #83
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    Quote Originally Posted by charlie b View Post

    The interest here is why is the lead melting under the gas check and not on the sides of the bullet? Maybe a couple of reasons. 1) the gas check is copper and a good head conductor, which means the gas temp on the base of the bullet is 'felt' by the lead. 2) the friction of the gas check is higher than the lead portion of the bullet. 3) lube on the lead portion of the bullet is reducing further the coeff of friction of the lead portion of the bullet.
    I have no idea what temperature or pressures it takes to pressure or explosion weld lead but I would suspect that is part of the equation. I've observed both processes a couple of times. In one instance it was nothing more than a copper stud being fired into a steel part to form the weld.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

    "Before you argue with someone, ask yourself, is that person even mentally mature enough to grasp the concept of different perspectives? Because if not, there’s absolutely no point."
    – Amber Veal

    "The Highest form of ignorance is when your reject something you don't know anything about".
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  4. #84
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    I used to do explosive welding at NM Tech in Socorro. The process was different based on the effect desired. I was working on a method to reline cannon barrels. Much higher pressures than in a rifle chamber. My work was a compromise to finding a slow enough explosive that would allow the welding process to take place without causing a failure in the barrel. It was a very narrow window that turned out to be not feasible for field use, ie, most of the barrels burst.

    A classmate was working on cryogenic stuff and was diffusion welding, ie, polish two pieces of copper well enough and just laying one on the other will allow a weld to form over a period of time.

    Time, heat, pressure.
    Last edited by charlie b; 04-14-2022 at 08:23 PM.

  5. #85
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    For highest pressure accuracy you want a lube groove that is closer to groove diameter. This groove will be shallow and carry less lube but it is much stronger and doesn't pump all your lube out as soon as your powder ignites. On 358 bullets I have seen the inner lube groove shank as small as .310 and as large as 350 on tumble lube designs. If you are recovering bullets undersized from lube pressure, I would try the same mold but designed with a shallower lube groove.

    Also lube groove placement has an effect on how easily it deforms and pumps the lube. A deep lube groove close to the gas check on a 180 grain bullet might have 150 grains of bullet on top of it when the explosion hits it in the gas check. The same lube groove placed higher on the bullet might only have 120 grains of lead sitting above it and be more resistant to squishing out.

    Heavier for caliber bullets with the same alloy, same pressure, same depth of lube groove, and same lube groove placement will obturate the lube groove easier than a light for caliber bullet at the same parameters. Heavy for caliber bullets also have a harder time biting and spinning on the initial drive band. The same alloy and same .010 drive band might be spinning 200 grains up to 130000 rpm instead of the same alloy and same .010 drive band spinning 150 grains up to 130000 rpm. For this reason lighter for caliber, lower SD bullets will be easier to push the rpm threshold.

    Shorter unsupported noses will have less inertia to slump off center than a long unsupported nose.

    I have seen lube groove failure where the lube groove is too weak for the desired pressure, even with hard alloy and the bullet gets undersized from the pressurized lube. I have seen PC failure like others have mentioned from extreme obturation forces. The bullet wants to grow in diameter so badly under pressure that the PC wears off the base band. Tumble lube mostly stops this unless the obturation is so extreme that the lube grooves completely collapse. The empty lube grooves on a PC bullet seam to be like a power piston shotgun wad. If you have a weak lube groove design and high pressure, your lube grooves obturate out fully and bite the rifling, then the base band resumes its extreme obturation forces and the PC grinds off the base band. If you can get a PC bullet out of the barrel without the lube grove completely obturating into the rifling, the lube groove cushions the base band obturation and they shoot clean. Once the empty lube groove obturates out all the way the base band resumes taking the brunt of the obturation force and usually ends up with that band naked with lead in the barrel.

    My newest HV bullet idea is a powder coated gas check bullet with a single tumble lube groove up high on the bullet near the crimp groove. This should stop lube overpressure failure and PC obturation abrasive failure of the base band. The small quantity of tumble lube in the high placed groove might pump out around 40-50k psi compared to an equal weight bullet with low placed, deep lube groove that will pump out at 15k psi. The GC and the base driving band combined will be at least .20 before the TL groove where you usually see a .08-.10 high base driving band before the first lube groove. This long band will gently obturate outwards as one large unit, rather than a small .08 base band and low lube groove that has more bullet weight above it that wildly obturates outwards at 40-50kpsi leading to abrasive failure of PC
    Last edited by mnewcomb59; 04-14-2022 at 10:20 PM.

  6. #86
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    Quote Originally Posted by TurnipEaterDown View Post
    .......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.

    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.
    I can give you the time to peak pressure, the Oehler M43 m3asures that if you want to calculate?
    Larry Gibson

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  7. #87
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    "Charlie b" You had commented earlier on why did the lead melt at the GC interface, and not the lube interface (post #81 in thread).
    Again, speculation, but I would say that there are a few things at play here on the sides of the bullet that keep this from happening: (1) the area of lube exposure to combustion products and thus peak chamber temperatures is very small, basically a funny looking keyed doughnut ring w/ ID the size of the bullet base, and OD the bore/groove, (2) lubricants have a purpose of removing heat from an interface, one way the bullet lube is doing this is to have some escaping past the bullet when it does get hot (likely primarily down the bore where the bullet has already traveled) as the bullet is shedding the lube as it goes (better be doing that, or it didn't lubricate the interface).
    Since lead melts at temperatures higher than lube vaporization temp (I have thrown bullets onto my pot prior to melting and they smoke off before liquid lead fills the pot), we should have significant boundary layer vaporization if lead bullet sides were melting.
    If the lube in the interface begins to vaporize due to very high temperatures in the interface we should know about that because vaporization in a fluid interface is a mechanism of cavitation, and due to cavitation very high pressure pockets would be expected to form that would pit the bullet sides and even possibly the bore.
    We do not see this in my understanding of firearms shot to high round counts w/ cast bullets, so likely there is no cavitation and thus no vaporization of the lube while actually still in the bullet-bore interface. I suspect lots of lube is vaporized once it is exposed to the combustion products in the bullet's wake, and that is likely where any lube vapor I think we see in muzzle blast is formed.

    The comments from "mnewcomb59" regarding bullet design for high speeds strike me as spot on, and a couple line up w/ what I was thinking a high speed cast bullet should be designed like, notably the bulk of the lube resevoir toward the front and if there were grooves toward the back they should be shallow. A couple comments he made I did not consider at all until reading his post, but again make great sense now that I have.

    Larry, sure, you could give me the time to peak pressure, and they type of powder you used, and I could noodle around and make a simple engineering calculation under some assumptions.
    I may not be too quick to get this done, Easter weekend and lots to do including trying to sell a restored 1969 Oldsmobile 442 that I never have time to drive, but I can look into it when I have a bit of time, for what it might be worth.

  8. #88
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    I would agree if the theories about lube behavior are correct. Same with the bullet deformation in the bore and where it occurs within the bullet. So far it is still theory with a bit of data that supports it.

    Unless all PC bullets shed the drive band at the rear I really cannot agree with the theories proposed on it. Especially since some use bullets without any lube grooves at all with PC and they seem to work well.

  9. #89
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    I would also like to add that some symptoms people see have counterintuitive solutions. For example, when people see leading near the muzzle only, they might think " I am running out of lube. I need a deeper lube groove to carry more lube for this length of barrel."

    In reality, they are experiencing a lube groove too weak for the acceleration that they want out of the bullet. The weak lube groove collapses under pressure, pumping out the lube. The lube groove reaches peak obturation near peak pressure of the gun powder. This is usually within a few inches of the throat depending on powder charge and burn speed. Ok so now your 308 bullet is riding on a lube film at the 6 inch mark in the barrel and is swaged down by the lube pressure to .303. Once your bullet is smaller than groove diameter at the top drive band, lube presssure allows the lube to flow in front of the bullet as a plasma/vapor. If you had pressurized lube, but not over pressure lube, it would not squeeze your nose driving band under size (maybe your base band would be undersized) and your lube film would not blow past the bullet. It would remain at the lube groove and on your base band only and wipe along the bore. Now at the 15 inch mark in your .308 barrel all the lube has been pumped out of your groove along the barrel behind the bullet and in front of the bullet because of your undersized nose drive band and your .303 bullet is now naked. There might be residual pressure and your bullet bumps back up to .308 but by the 20" mark it leaves a lead wash because it has been riding dry.

    You might see lead wash or leading in the last two inches of your barrel and think "Hmm it ran out of lube. I need the same bullet but with the lube groove cut deeper." Now your new mold arrives and you get leading even earlier in the barrel because the new bullet with the weaker lube groove pumps its lube sooner, makes the bullet more undersized than before as it rides on its lube gasket, and runs out of lube earlier in the bore.

    In reality if you are seeing a lack of lube star or lead wash or leading in the last few inches of the barrel you need a shallower lube groove or keep the same lube groove and move it further towards the nose of the bullet because it will pump its lube out slower at any given pressure.
    Last edited by mnewcomb59; 04-15-2022 at 07:35 PM.

  10. #90
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    Larry, or any one, does a jacketed or PC bullet lose .005 in diameter as it travels down the barrel, or is this only a phenomenon with lubed bullets?
    Don Verna


  11. #91
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    It is only a phenomenon with lubed bullets with a full lube groove. And only when those bullets are pushed at a pressure too high for a given lube groove design. There is a given pressure where everything works as intended, where the lube makes a gasket that rides with the bullet. Raise the pressure by 5k psi and all of a sudden the lube groove is pumping too hard, squeezing lube out along the front and back of the bullet and making the bullet undersized.

  12. #92
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    If someone could tell me how to capture bullets without deforming them (other than a big snow bank ) I would do it. I will be shooting some into a sand bank tomorrow. Will try to dig some out and look at the bases and under the GC's.

  13. #93
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    Quote Originally Posted by charlie b View Post
    I agree.

    Yes, there are a lot of factors that contribute to the heat gain, but, most are not as significant as the friction factor or the gas temp on the base of the bullet. Things like the compression of air in the bore and the air friction outside the bore would serve to keep the bullet hot after it left the barrel, maybe even increase the temp slightly.

    The interest here is why is the lead melting under the gas check and not on the sides of the bullet? Maybe a couple of reasons. 1) the gas check is copper and a good head conductor, which means the gas temp on the base of the bullet is 'felt' by the lead. 2) the friction of the gas check is higher than the lead portion of the bullet. 3) lube on the lead portion of the bullet is reducing further the coeff of friction of the lead portion of the bullet.

    Another data point. I have found when sizing bullets that the GC has a slightly larger dia (~0.0005) than the body of the bullet. The simple explanation is the copper GC has a 'spring back' and the lead has less. Higher yield limit maybe the source? Is this related to how the GC acts in the barrel or why it is heated more?
    An excellent post that's sparked a couple of brain waves - maybe useful; maybe not.

    As to the forces exerted upon the gas check at the base of the bullet. . . My thoughts turned immediately to my Dad's various black powder toys that use an assortment of base wads behind the bullet. These have been dry cardboard, poly-waxed juice box, poly, felt, lube-impregnated felt, and just straight lube discs. Obviously, this sort of thing is more easily applied to straight-wall cases than bottlenecks, but it seems that these kinds of things could serve to function as an ablative / consumable shield to the base of our gas-checked bullets. They would absorb the hurtin' generated by the gas buildup while pushing the bullet, without being a part of the bullet. For the application of a bottlenecked round, something easily stuffed on top of our charge (like Dacron) chosen for its ability to seal, buffer, then separate might have some benefit. To what degree Dacron serves these ends beyond being just a filler is a question for the more experienced Peanut Gallery

    Regarding the gas checks having more springback and their diameter being greater than the bullet they're sized onto. . .

    * This first got me thinking about the copper jacket fouling we see in everything from hunting rifles down to 9mm pistols. The common theme seems to be that good polished "match" barrels seem to do this less, but I'm wondering if this is due to friction against rougher surfaces as is commonly thought (at least by me anyway), or if the same forces of gas blow-by and vaporization that we see with poor sealing of lead bullets are contributing to copper deposits.

    **This also got me thinking about how the early cupro-nickel jackets were known for fouling very badly. Was this due to less resistance to friction, or not sealing as well? Point: are our current copper jackets and gas checks just a step to some better material?

    ***As mentioned, lead rapidly compressed will get hot. That heat will bleed into the conductive gas check. . .and maybe even concentrate there??? The check is getting the double-whammy from behind by the powder charge. That copper is conductive, doesn't have a lot of mass, and if the lube boundary and gas pressure are indeed negating each other at the base of the bullet, the heat getting dumped into it has nowhere to go but the vulnerable lead bullet base.

    The air quality here is horrid right now and my eyeballs and sinuses hate me tonight - - so my fuzzy brain is only seeing these dots (spots? ) and not connecting them very well. I am however thinking the base wad / filler concept would at least limit the sources of heat the gas check takes to those forces coming from the front (compressing bullet).
    WWJMBD?

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  14. #94
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    Quote Originally Posted by dverna View Post
    Larry, or any one, does a jacketed or PC bullet lose .005 in diameter as it travels down the barrel, or is this only a phenomenon with lubed bullets?
    Jacketed bullets do not. The ones I've recovered that were measurable were at groove diameter if the bullet was very close to groove diameter to begin with. If shooting a slightly undersized jacketed bullet then they would be at groove diameter IF the load was sufficient enough to obturate the bullet. For example a lot of, if not most thick or soft steel jacketed bullets won't obturate to seal the bore. They come out as the went in.

    I've only recovered 2 PC coated bullets that were not lubed. They were 30 calibers shot out of my Palma 14" twist rifle with a .3085 groove dimeter barrel. The muzzle velocity was 2550 fps. The bullets went in sized .311 and came out, as best as I could measure, very close to that. Since PC'd bullets do not ride a layer of lube in the barrel (unless they also have been lubed) it is my thinking that is the reason the RPM Threshold for a given cast bullet will be higher than if the bullet is conventionally lubed.
    Larry Gibson

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  15. #95
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    Quote Originally Posted by charlie b View Post
    If someone could tell me how to capture bullets without deforming them (other than a big snow bank ) I would do it. I will be shooting some into a sand bank tomorrow. Will try to dig some out and look at the bases and under the GC's.
    I save up newspapers until I have a bundle that is 30 - 36" thick. I place/line a cardboard box big enough and sturdy enough to hold the bundle while allowing for expansion with a sturdy large garbage bag. I've found the thicker large garbage bags to be best. I then fill the lined box with the papers in it and let soak 48 - 72 hours. As the paper soaks up the water more water is added until the newspapers are sopping wet and won't soak up any more water. I usually have the box sitting on a piece of 3/4" plywood (just a bit larger than the bottom of the box) already in the back of the PU. That way I and a partner don't have to initially load it as it will be very heavy. At the range the box on the plywood is set on the ground with one face toward the shooting position. With full power loads and WQ'd bullets I set the bundle at a range where the velocity will be about 1500 fps +/-. If testing for expansion I set the bundle at the intended test range.

    I can usually get 8 - 10 shots into the bundle. then when locating the bullets you can peal the papers back front to rear following the "wound channel" to the bullet looking for the GC and observing/comparing the size of the wound channels to the recovered bullet. I usually slit the box/bag along the 4 corners and lay the sides out when doing this. When done smaller sections of wet still heavy newsprint are easily put into another bag in the back of the PU for transport to a recycle dumpster.

    It's a pain which is why I don't do it all that often and then only when I really want to know.
    Larry Gibson

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  16. #96
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    Thanks for the reply Larry. It was what I expected but good to have it confirmed.

    It makes me wonder how much rifling engagement is lost with a lubed bullet at high velocity. Are the rifling marks imprinted in the first few inches of barrel travel before the lube has had a chance to squeeze the lead bullet down?

    I know liquids are not compressible, so as the lube melts it needs to fill that space between the barrel and the bullet or gas will blow by. It would seem more lube is better to insure that happens, but I know that flys against the experience that too much lube is normally not good.

    I am having problems understanding the mechanics of what is happening. Knowing the bullet is sized down as much as Larry has shown is an important factor to understand....and I cannot get there.

    BTW great thread and this is how we learn. As most of you know, I am a jacketed bullet guy when it comes to HV rifles but I still find this very interesting.
    Don Verna


  17. #97
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    Quote Originally Posted by dverna View Post

    It makes me wonder how much rifling engagement is lost with a lubed bullet at high velocity. Are the rifling marks imprinted in the first few inches of barrel travel before the lube has had a chance to squeeze the lead bullet down?
    It depends on the cartridge. Most handgun cartridges reach peak pressure in the chamber or cylinder. They are likely pumping some lube already as they engage the throat. Some overbore rifle cartridges with lots of slow powder reach peak pressure at 12" down the barrel. The area under the curve on graph of pressure vs time is acceleration. Peak acceleration occurs at peak chamber pressure. We say lube groove obturation is a function of pressure, which it kind of is, but it is really a derivative of pressure over time a.k.a acceleration. If two bullets leave the muzzle at 2600 fps, but one used 45 grains of fast powder and the other used 55 grains of slow powder, the slow powder has more gently accelerated the bullet so the bullet pumped its lube slower and reached peak lube groove deformation later in the barrel than the fast powder. Since both bullets reached the same velocity we can be absolutely sure that they received the same total amount of acceleration and therefore the same amount of lube groove deformation. Even though one bullet experienced less peak pressure, the area of below the curve on both bullets pressure graphs is the same.
    Last edited by mnewcomb59; 04-16-2022 at 10:33 AM.

  18. #98
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    The current theory of copper fouling as I understand it is the gases of combustion form a plasma with the copper and that is deposited in the barrel. The rougher the barrel, the more blow by and more copper deposited. Undersized copper bullets will severely foul due to the excess blow by. Which is also why match/hand lapped/ barrels exhibit little to no copper fouling?

    Plain based lead bullets would follow that same rule, IF, they are not 'bumped up' to fill the throat and grooves on firing. Again, my understanding of current theory is this is the primary cause of lead fouling in firearms, ie, the bullet not filling the throat/grooves. Gas checks are an added factor and I really don't know how they work so well. I've had gas checked lead bullets 'clean' the copper fouling from a barrel. Maybe the pressure on the base forces the edges of the GC outward? Maybe this force comes from the upset of the lead bullet around the base? Does this function act that much better than a copper jacketed bullet that 'probably' has no upset to force the copper against the grooves?

    My experience with the few 'undisturbed' copper bullets I have recovered is the same as Larry's, no change in dia from the bore.

    I have to admit I failed at the range today. Fired 45 XCB's at 2200and 2400fps and didn't find any of them in the backstop. Normally I just dig back about 12" and they will all be in a 'tunnel' of less compact dirt/sand, fairly easy to find. Today, nothing. I'll just hang my head here and will try again next time.

    Larry, father-in-law and I used to do the wet paper thing when testing expansion of lead bullets. We only did a few rifle bullets back then so don't remember if the bases got upset terribly or not. Lots of fun trying to find bullets in that stuff We ended up using the small moving boxes so we could at least tell which box the bullets were in. I can't handle that much weight these days, and, I'd like a non-destructive recovery if I could. One reason is I want to see what the bore riding noses look like.

    The good news is the 2200fps powder coated XCB's out of a 1/10 twist barrel grouped less than 3" at 200yd.

    I will try them again next outing.
    Last edited by charlie b; 04-16-2022 at 03:51 PM.

  19. #99
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    PS I suspect the PC acts quite a bit differently than the lube. Like discussed, the lube forms a layer around the bullet, distorting the bullet as it does so. The PC is already in place so the 'lube layer' of PC doesn't change during firing.

    Need more data!! Motto of the test engineer

  20. #100
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    Some good early preliminary results. . .

    My Retired Old Man Of Leisure got out to the 100 yard line to zero a new peep on his recently-acquired '95 Winchester in .30-40 Krag, and he loaded up some cast-long-ago .30 XCB's cast of air cooled WW+2%, as well as some 2/1 Lino/#2 Accurate 31-170EN's (his design that has been showing promise for an HV .30-30 practice bullet) - - both with H4895.

    Seems like a pretty good test bed for a lot of this: the .30-40 has a hella-long neck for packing on the series of skinny lube grooves; the rifle has a 28" barrel which is close to Larry's operational concept; and it's rocking a 1-10" twist.

    The 13BHN XCB's are undoubtedly a little too soft for this kind of thing, but they still grouped 8" high x 3" wide in a workup string in not great conditions with a number of variables still to sort out (new sight, unfired brass, and awaiting a replacement sprue plate for cleaner cuts). 37.4 to 37.6 grains seems to throw it at 2525 fps

    The harder 31-170EN's workup dropped 8 out of 10 into a 3" circle with some weird velocity fluctuations in the 36.5 to 38 grain charge range, but 2500 seems to be very do-able here. He's already got a tweaked-for-the-Krag version of this mold on order.

    Clean barrel for both bullets with 2500+ lube spooge at the muzzle. We seem to be off and running!

    Friday, we test the XCB's with the hard alloy and 4831SC in the .30-06. Bullets hand sorted for the cleanest sprue cuts from the warped plate. Stay tuned!
    WWJMBD?

    In the Land of Oz, we cast with wheel weight and 2% Tin, Man.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check