Boolit terminal performance- Can't figure this out

[45Reverse]

Looong read, might want to get yourself a cup o coffee.

Some quick background:
Been working on cast loads for 5.56 for several years now, not like most here have been tho. End goal is a Spitzer bullet, plated in thick copper, loaded to FMJ specs, accurate...all that stuff.

Finally got the bullet itself figured out. Took years to get it right. I was doing it in my garage so I give myself a pass for taking so long (first started dabbling with it in 2014).

As I keep testing these I'll post more details on how I did all of this but for now I encountered something that's puzzling me.

Here's the basic bullet and load...

Bullet- Smooth sided (no lube grooves) Spitzer undersized to .210 dia. Cast weight is ~56gr. Finished plated weight is 63 gr. It's plated with between .010-.012 inches of work-hardened copper. If you've done your math right you should realize that's way more than I should be able to get onto this diameter of a bullet...I'll explain how I did it later :)

Alloy- Ridiculously hard. Can't tell you the bnh (gotta be well north of 30) but the mix is WW/lino/pure Pb/tin/copper. Water dropped. Very difficult to scratch or dent. Can survive a 6ft fall onto concrete without a nick on it...

Case- Lake City, trimmed to 1.75", very light chamfer to inside case mouth

Primer- CCI No. 41

Powder- 22.1 gr VV N530 (just above VV factory minimum reload data for 62 gr FMJ with similar profile/weight as my bullet)

COL- 2.25" +/- .005 - Very mild crimp w/ Lee FCD

I expected about 2950 fps. I got between 2990 and 3165 on 10 test shots over a chrony. Gun functioned and fed perfectly, bolt locked open after the last round.

I wasn't testing for accuracy at all this time so I don't have anything to report on that.


Here's what happened

First test shots were this past weekend. Did a fishing trip with my son and took my DPMS 20" flattop (1:9) and 20 rds of the above cast loads with us.

First thing I wanted to test was whether the bullet (and the plating in particular) survived the trip down the barrel doing a bazillion RPMs and 3000+ fps. I was very confident it would but ya never know with stuff like this until you actually do it.

Ballistic gelatin wasn't practical so I did the next best thing I could. I took a 10x12x24 box and filled it heavy paper, note pads,old files, and basically anything else that was sheet paper. All stacked (stuffed) flat. At one end of the box I put two hardcover books, each about 1.5" thick. The full box weighed about 50lbs.

When we got to the river we set box the box in the water and fished for several hours (didn't catch anything). We took the box with us when we left.

Back at camp we set up the box behind a chrony and put 5 test shots into the end without the hardcover books from 10 ft away.

I did a quick inspection of the box- entry holes were clean, no keyholing, no halo from copper or bullet fragments, no exit holes.

The next 5 shots got fired into the end of the box with the hardcover books. Again, clean entry holes, no halo, no keyhole, no exit hole.

I sat down with the box and peeled through the wet pages one by one looking for the bullets. All I found was in the middle of the box after 7-8" of penetration, was a ton of paper and lead "powder" with some copper fleks here and there. That 'pattern' continued toward the other end of the box in a fan shape....Basically, the bullets (all of them) exploded after about 6" of penetration and produced an expanding cone of this debris for another 6 or 8 inches.

After literally sifting through every single sheet of paper (took hours but was aided by cold beer and my son) I recovered 4 bullet fragments totaling no more than 5 gr....everything else was pulverized dust.

Upon very close inspection I noticed something I wasn't expecting...That is the clean bullet holes continued through 6 full inches of paper (no fragmenting, yaw, or anything- just clean paper punches). It was as if the holes had been nicely drilled through the first 6 inches of paper, but after that bullet blows itself into dust. That same pattern occurred in all 10 bullet holes. It didn't matter if the bullets had to go through the wet hardcover books or wet paper sheets.

I half-expected these bullets to explode on contact due to how hard I cast the lead...But if they didn't, then they'd get trapped in the paper and I could fish out fragments to visually check the performance of the copper plating. Except there were no fragments :)

I never would have expected to see such clean penetration for so deep before violently shattering. I did some reading a frangible bullets, did some reading through the forum here in the alloys thread, but I can't determine if I should have expected this or not(???)

I know it's because of the super hard alloy I used, but from what I've read and experimented with on other loads of mine the bullet should have come apart on contact or immediately after impact if it was going to. Have any of you ever seen this kind of terminal performance from a boolit cast from a super hard alloy? Is this normal and I just have terrible google skills? :) Is it possible the copper plate served as some sort of (temporary) stabilizing factor? (Just taking a W.A.G. there)

I don't necessarily care that they blew apart. It's appears to be consistent behavior, so that's a good thing IMHO. I've been working on these as target shooting and plinking rounds, but maybe they'd be good varmint rounds too. I dunno.

I'm 100% certain the copper plating did it's job. The rifle's bore is squeaky clean, as is the gas tube and BCG...I don't have visual proof of that (excpt for the perfect entry holes on the box), but I will get it as soon as I can put a gelatin block together and get out to the woods again...unless of course these things explode after 6" of penetration into that medium too.

Ok, I'll switch to the coatings forum to talk about that plating work.

[Scrounge]

There are a lot of things I'm no expert on, and this is one of them, but I do have some experience documenting testing similar to this. Except for a few little things. First difference: we were slinging 2000lb bombs down a sled track at, IIRC, 1650fps. Second difference: Target was a 13' cube of steel-reinforced concrete. Third difference: We went downrange, recovered the bombs, and sectioned them, and compared them to ones that hadn't been treated that way. 2000lb bombs are a steel shell maybe 3" thick, full of explosive. IIRC, it was Amatol, and it was cast as a single grain. They had a gigantic power hacksaw with something like 12 teeth per foot, and the teeth were about an inch wide. They would slice the bomb up into sections, and check the explosive grain to see if it had cracked. Then they'd compare the photos I took to those of a bomb that hadn't been down the sled track into a big cube of concrete. You're gonna have a hard time doing that, with the result you've gotten, but you could try sectioning a few of the bullets before firing them. See if they disintegrate when they're cut. It's possible the thick plating is all that's holding them together. Maybe try thinning the coating, reducing the speed, changing the hardness, etc., but only one change at a time. See if you can figure out what's happening. Could be your muzzle velocity is too high. Or the rotational speed, or who knows what all else. And take lots of photos. Maybe make some bullets that aren't plated at all, or very thinly plated. Vary the speeds and see what happens. It's liable to take a while. I did this work in the mid-1970's. Then got to see them used early in 1991 during Desert Storm. Live on CNN. Hopefully you'll figure things out a little sooner than that. :)

Bill

[dkf]

Like 55gr fmj bullets act at high velocities. Penetrates a bit (neck) then when the bullet starts to yaw and get sideways, it usually blows apart. But in the case of the fmj bullets the cores are not anywhere near 30bhn.

[GhostHawk]

Do it again with a softer alloy. No more than say 12 bhn. I bet they stay together.

Your hard allow exploding does not surprise me, 6 inches of clean penetration first says a lot about the copper coating IMO.
You could have a good deal going there.

Try one on a deer with a good hit in the heart/lung area.

[45Reverse]

There are a lot of things I'm no expert on, and this is one of them, but I do have some experience documenting testing similar to this. Except for a few little things. First difference: we were slinging 2000lb bombs down a sled track at, IIRC, 1650fps. Second difference: Target was a 13' cube of steel-reinforced concrete. Third difference: We went downrange, recovered the bombs, and sectioned them, and compared them to ones that hadn't been treated that way. 2000lb bombs are a steel shell maybe 3" thick, full of explosive. IIRC, it was Amatol, and it was cast as a single grain. They had a gigantic power hacksaw with something like 12 teeth per foot, and the teeth were about an inch wide. They would slice the bomb up into sections, and check the explosive grain to see if it had cracked. Then they'd compare the photos I took to those of a bomb that hadn't been down the sled track into a big cube of concrete. You're gonna have a hard time doing that, with the result you've gotten, but you could try sectioning a few of the bullets before firing them. See if they disintegrate when they're cut. It's possible the thick plating is all that's holding them together. Maybe try thinning the coating, reducing the speed, changing the hardness, etc., but only one change at a time. See if you can figure out what's happening. Could be your muzzle velocity is too high. Or the rotational speed, or who knows what all else. And take lots of photos. Maybe make some bullets that aren't plated at all, or very thinly plated. Vary the speeds and see what happens. It's liable to take a while. I did this work in the mid-1970's. Then got to see them used early in 1991 during Desert Storm. Live on CNN. Hopefully you'll figure things out a little sooner than that. :)

Bill

Well, my projectiles weren't as fun as 2000lb bombs, but now that you mention it, I'd like to section these just to do some visual inspections of the plating thickness but I don't know what I'd use to cut them cleanly.

[45Reverse]

Do it again with a softer alloy. No more than say 12 bhn. I bet they stay together.

Your hard allow exploding does not surprise me, 6 inches of clean penetration first says a lot about the copper coating IMO.
You could have a good deal going there.

Try one on a deer with a good hit in the heart/lung area.

Might be the most practical way to go considering I'm doing this out of a garage. Given that pure Cu plating is not as hard as FMJ metal I went with a high bnh alloy under the assumption that it would be necessary for structural integrity of the bullet...plus I've read many posts here about soft cast boolits turning into "clouds of grey dust" when shot at very high velocities. My pistol alloy is about 15-18 bnh. Perhaps I should cast a few 5.56s out of it and see what happens.

Not a meat hunter so a shot on a deer isn't likely in my case. Ballistic gelatin is an option tho.

[Tom Myers]

This may be just a WAG, but the first thing that intuitively popped into my mind was the direction of force exerted on the lead core by the Vector of the rotational force and the forward momentum force.

Think of a sail boat crossing a river with the wind blowing at a right angle to the path of the river.

The vector or path of the boat will be at an angle somewhere between the direction of the river flow and the direction of the wind.

Now the very high rotation of the rapidly spinning bullet will exert a force at a right angle to the bullet axis and any change of the foreword momentum (deceleration) will exert a rearward force along the axis of the bullet resulting a total vector of force at an angle to the axis of the bullet.

More of the vector force is directed along the axis where the bullet is strongest and less of the vector force is directed outward toward the diameter where the bullet is weakest.

Now, the instant the bullet leaves the muzzle, the air resistance creates a strong deceleration force along the bullet axis, resulting in a decrease in the 90 degree rotational force of the bullet, allowing the bullet to stay together.

The rotation of the bullet decreases slowly along the bullet path and the deceleration of the bullet also decreases, keeping the vector of the two forces at some angle less than 90 degrees to the bullet axis.

Even after the bullet penetrates into the wet paper medium it is still spinning rapidly with little loss in rpm, but is decelerating rapidly until until the velocity decreases to the point where is more easily penetrates the wet paper, the deceleration vector has decreased to the point where the total vector or force is directed almost at 90 degrees along the bullet axis.

Think about slapping your hand on the surface of water The resistance of the water to your hand is quite strong until the velocity of your hand slows down. Your hand decelerates and the force against your hand decreases.

In short - The vector of the rotational force and deceleration force has now moved toward the diameter of the bullet and is now great enough to overcome the strength of the brittle lead and plating and the bullet disintegrates.

Like I said, it's a WAG and I am no physicist and may be completely wrong on my interpretation of the rotational and deceleration vector forces on the bullet.

[45Reverse]

This may be just a WAG, but the first thing that intuitively popped into my mind was the direction of force exerted on the lead core by the Vector of the rotational force and the forward momentum force.

Think of a sail boat crossing a river with the wind blowing at a right angle to the path of the river.

The vector or path of the boat will be at an angle somewhere between the direction of the river flow and the direction of the wind.

Now the very high rotation of the rapidly spinning bullet will exert a force at a right angle to the bullet axis and any change of the foreword momentum (deceleration) will exert a rearward force along the axis of the bullet resulting a total vector of force at an angle to the axis of the bullet.

More of the vector force is directed along the axis where the bullet is strongest and less of the vector force is directed outward toward the diameter where the bullet is weakest.

Now, the instant the bullet leaves the muzzle, the air resistance creates a strong deceleration force along the bullet axis, resulting in a decrease in the 90 degree rotational force of the bullet, allowing the bullet to stay together.

The rotation of the bullet decreases slowly along the bullet path and the deceleration of the bullet also decreases, keeping the vector of the two forces at some angle less than 90 degrees to the bullet axis.

Even after the bullet penetrates into the wet paper medium it is still spinning rapidly with little loss in rpm, but is decelerating rapidly until until the velocity decreases to the point where is more easily penetrates the wet paper, the deceleration vector has decreased to the point where the total vector or force is directed almost at 90 degrees along the bullet axis.

Think about slapping your hand on the surface of water The resistance of the water to your hand is quite strong until the velocity of your hand slows down. Your hand decelerates and the force against your hand decreases.

In short - The vector of the rotational force and deceleration force has now moved toward the diameter of the bullet and is now great enough to overcome the strength of the brittle lead and plating and the bullet disintegrates.

Like I said, it's a WAG and I am no physicist and may be completely wrong on my interpretation of the rotational and deceleration vector forces on the bullet.

I'm surprised I actually understood that. Good stuff. No idea if that's what's happening or not, but I get what you're explaining and it makes sense.

A working thought of mine was that ~6" of travel through wet paper slowed the bullet's forward movement to the point that it's rotation caused a sudden yaw and stressed the bullet along it's long axis, causing it to explode b/c it's so brittle. Isn't 6" a roughly typical amount of penetration that a standard 5.56 M193 round experiences before it yaws and continues an arced path (along the vector of the yaw) through the target medium?

...IOW- M193 yaws (possibly breaks) but the fragments travel more or less along the same axis as the yaw that was induced (typical arced 5.56 wound channel). Whereas mine hit that same 'yaw point' in penetration but shatter violently b/c they lack the malleability needed to endure the sudden change in direction like a soft-cored M193 would...make sense?

Kinda like what you're saying...I think :) ...but I'm no physicist or ballistics expert either.

[Scrounge]

Well, my projectiles weren't as fun as 2000lb bombs, but now that you mention it, I'd like to section these just to do some visual inspections of the plating thickness but I don't know what I'd use to cut them cleanly.

32 TPI hacksaw should work. Get Starrett blades, and treat them right, and they should last a long time, too. https://www.amazon.com/Starrett-KBS1232-2-Bi-Metal-Safe-Flex-Hacksaw/dp/B000FCINVQ/ref=sr_1_1?dchild=1&keywords=starrett+32+tpi+hacksaw+blade&qid=1592870594&sr=8-1

Nicholson is probably easier to find, and may be cheaper.

[Wayne Smith]

Or use a grinding wheel to grind off half of the boolit.