View Full Version : RFI, soft points vs FMJ on steel, what gives?
ViniVidivici
01-11-24, 19:24
What is this madness?
So, I've loaded some 62gr soft points (unknown manufacturer, they're pulls from American Reloading), shot some at 100 yards, and they're cratering the steel!
https://i.postimg.cc/0QQryV1w/20240106-130931.jpg (https://postimg.cc/KK6m9rzG)
This is what my 62gr FMJ looks like, same 100 yards.
https://i.postimg.cc/d0FywR02/20240106-130950.jpg (https://postimg.cc/bZ6JRtkr)
Same charge of 24.4gr H335, same mixed brass. I would have thought the SPs would do LESS damage to the plate, not more!
Yes, I did check these with a magnet.
What gives? It looks like they're being hit with m855!
Maybe the lead in the soft point is harder than the lead in the FMJ?
ViniVidivici
01-12-24, 00:52
Yeah, that's all I could come up with. Just seems strange that it'd be that way.
I mean, I've shot FMJ at that thing within 40-50 yards, and not dinged it like that.
Have you run both loads over a chronological? I thought it was velocity that cratered steel. Could be that the different bullets vary enough in construction/hardness to give a velocity bump.
ViniVidivici
01-12-24, 02:10
No, no chrono available, but I can't imagine the slight difference in velocity due to a harder bullet getting slightly tighter neck tension would make enough difference to see what I'm seeing.
I would think it'd have to be 200-300 fps faster to make that kind of difference.
Damn. That looks like 55gr FMJ pocking. Interesting.
I've heard of this phenomenon before, as well as similar pitting with ballistic tip ammo. Not a clue of the physics behind it.
I've heard of this phenomenon before, as well as similar pitting with ballistic tip ammo. Not a clue of the physics behind it.
Some sort of "shape charge" effect.
Velocity = penetration
What type of steel?
ViniVidivici
01-12-24, 14:32
Allen Co., AR500, 3/8", this is a 12"x20" silhouette, bought at the LGS in town.
Adrenaline_6
01-12-24, 15:26
Velocity is key. Is that reload hot? <2850fps is usually what you want at target.
ViniVidivici
01-12-24, 17:52
It's in the upper 1/3rd of 5.56 data from Hornady's site, been using the load as a 62gr FMJ for years, 24.4gr H335. Shows 25.4 as max.
No signs of excess pressure, brass gets loaded 5 times, no issues.
Used the same charge for these 62gr SP. Different bullet type, yes, but not drastically different, as far as how it should affect velocity, I wouldn't think. Primers and brass look same, no high pressure signs.
OAL is same on both these rounds too.
FMJ tends to pancake on steel, while the SP / OTM tend to mushroom.
This mushrooming effect blasts material out of the crater.
We once shot some 6.8 SPC OTM loads through mild steel that made super caliber holes.
The holes were large enough to drop the entire case through.
Think about that for a minute.
…We once shot some 6.8 SPC OTM loads through mild steel that made super caliber holes.
The holes were large enough to drop the entire case through.
Think about that for a minute.
Sometimes I wonder if 6.8SPC2 really was a missed opportunity.
Separate from that, maybe there US should stop acting like we are abiding by international agreements to which we are not even a party.
ViniVidivici
01-13-24, 17:49
FMJ tends to pancake on steel, while the SP / OTM tend to mushroom.
This mushrooming effect blasts material out of the crater.
We once shot some 6.8 SPC OTM loads through mild steel that made super caliber holes.
The holes were large enough to drop the entire case through.
Think about that for a minute.
Thank you, this is now beginning to make sense to my brain!
Just so wierd...I mean, it's common knowledge that AP, and really high velocity stuff up close will wreck steel, but I've never heard or read that SPs or OTMs were detrimental and should be avoided.
Seems like it should be the same level of common knowledge...is it, and I've just missed hearing it?
It sucks when you beat up your steel. Velocity and bullet make or break. I tried XM193 one time right after getting some Bowling Pin targets. Thought these shoot alright but nothing that different, then I went home:
http://i.imgur.com/Y0KnTaM.jpg (https://imgur.com/Y0KnTaM)
It was brand new at the time, 5 holes through and through. This target sits on the side of the house now, but it was once special.
PB
Soft points typically have a closed base, sometimes with a thick jacket. FMJs are typically open base. Pure conjecture but maybe the structural integrity of that base section plays a role. Mill off the SP jacket from the base only and see if it still craters like that?
Soft points typically have a closed base, sometimes with a thick jacket. FMJs are typically open base. Pure conjecture but maybe the structural integrity of that base section plays a role. Mill off the SP jacket from the base only and see if it still craters like that?I was wondering the same thing.
Mill off the SP jacket from the base only and see if it still craters like that?
That's some crazy shit I might do. But you're changing the bullet weight and thus the results would still be speculation if the pocking was gone.
That's some crazy shit I might do. But you're changing the bullet weight and thus the results would still be speculation if the pocking was gone.
I suppose velocity would go up, so if cratering were simultaneously reduced that would seem even stronger evidence the closed base is a factor.
ViniVidivici
01-14-24, 20:21
I guess the "closed base theory" would explain OTMs causing more damage too, as Clint alluded to.
This experiment might be worth a try, deleting the base of the jacket on one of these.
I guess the "closed base theory" would explain OTMs causing more damage too, as Clint alluded to.
This experiment might be worth a try, deleting the base of the jacket on one of these.
Deleting the base of an OTM might run the risk of core punch-through . . .
I wonder if its the friction of the sp/otm moving in-to-out vs a fmj just collapsing.
Deleting the base of an OTM might run the risk of core punch-through . . .
Which would suck to fix. Plus as the great markm noted, you've changed the weight of the bullet and thus have two variables for the expriment.
ViniVidivici
01-15-24, 08:22
I was just gonna file the bottom of the jacket off, then weigh before seating...not sure I wanna do it now! Doesn't sound too good.
Ultimately it just sounds like, for some reason of physics, SP are a NO-GO on steel, at least at 100 yards out of an 18" barrel.
May see what they do at 200 though. Just feel like this would've been common knowledge I'd have stumbled upon at some point...
It occurs to me that one way to maintain more of the integrity of the bullet might be to use an end mill bit to remove the center of the base, rather than the whole base. That way the entire base isn't lead, similar to a standard FMJ.
ViniVidivici
01-15-24, 11:09
I think you could still have pass-through, as the other end of jacket (SP or OTM) is open.
I'm glad Lysander came in with that before I tried it.
What would be the danger of a pass through? The jacket becoming lodged in the bore?
Mill off the SP jacket from the base only and see if it still craters like that?
That's some crazy shit I might do.
It'd be an interesting experiment, but I wouldn't recommend it. The pressure will squirt the core out and leave the jacket stuck in the rifling.
What would be the danger of a pass through? The jacket becoming lodged in the bore?
Yeah, exactly.
Then next round, boom!
Yeah, exactly.
Then next round, boom!
But, if you were only firing a single round for the purpose of this experiment, this could easily be circumvented, no? And couldn't the jacket be pushed out with a cleaning rod, if it actually became necessary?
But, if you were only firing a single round for the purpose of this experiment, this could easily be circumvented, no? And couldn't the jacket be pushed out with a cleaning rod, if it actually became necessary?
But then what's the point? If only the core goes tumbling down range and you're left with an obstruction that you may or may not be able to remove easily what have you proven? Mostly what we already know...That all bullets are made with a closed end for a reason.
But then what's the point? If only the core goes tumbling down range and you're left with an obstruction that you may or may not be able to remove easily what have you proven? Mostly what we already know...That all bullets are made with a closed end for a reason.
Yes, agreed. I'm not convinced, however, that removing the base of the bullet will definitely cause a pass through though every single time. I think the risk of a pass through is increased, as lysander said, but if it happens it will be relatively rare.
I suppose if you really wanted to try it, the safest way would be to open up a minimal amount of the base so that the pressure is acting on a smaller unsupported area. Oh, and make sure the bore is clear after each shot...
But then what's the point? If only the core goes tumbling down range and you're left with an obstruction that you may or may not be able to remove easily what have you proven? Mostly what we already know...That all bullets are made with a closed end for a reason.
It can be removed.
This site has gone full fukking retard.
ViniVidivici
01-16-24, 07:54
Yeah, there's NO way I'm going to try that now, suffice it to say SP are NO-GO for my steel. I think the mushrooming effect Clint described is ultimately the culprit.
This site has gone full fukking retard.
I generally don't agree with comments like that, but in regards to seriously considering cutting up bullets and thinking having a jacket lodged in the barrel is no biggie, you're spot on.
While I don't anything close to the level of experience many here have with the AR platform, I can say from a materials science/engineering and physics point-of-view penetration is an energy-per-unit-area-in-the-least-time process (i.e. Joules per centimeter squared per second), with that kinetic energy supplied by the motion of the projectile. Simply put: dump as much kinetic energy into the smallest area in the least time for increased penetration. I've spent a good bit of time going through the publicly available .gov research reports on the topic in DTIC and elsewhere, and this is what I have learned.
My point: since the bullet's energy goes as the square of the velocity, a small increase in velocity can mean a disproportionately larger increase in energy, thus affecting penetration, possibly leading to the OP's observations. Without velocity measurements there's no way to sort it all out. If it turns out they had the more or less the same velocity, the OP's results would be a lot harder to explain.
In my view there isn't enough difference in construction between the two bullets to make a difference; lead and gilding copper alloys deform in a semi-plastic fashion at those velocities, so the penetrating spitzer cone-shaped tip is obliterated in microseconds into a metallic puddle upon hitting a AR500 steel target, not contributing to penetration much. The addition of a WC or hardened steel core in an AP round increases and maintains the energy per unit area during those critical few microseconds of contact, allowing the hardened tip to deform the target material, displacing it and facilitating penetration.
ViniVidivici
01-16-24, 23:41
Thank you for that, sir. Outstanding explanation of the physics involved, and I agree, the velocity needs to be measured and eliminated as a variable.
It's time I finally get a chrono after all these years.
You're welcome - the only other thing I can think of is if one of the bullets were bonded Speer-style so the jacket/core stays together a bit longer before disintegrating, transferring more energy and allowing for more 'plastic deformation', i.e., denting, of the AR500 plate. A higher velocity paired with a bonded bullet - the two acting together would definitely give you a bigger dent. I assume that both rounds were shot at the same AR500 target.
ViniVidivici
02-01-24, 18:13
Oh yes, same exact 12"x20" plate.
So now I have chrono data. Avg. for the 62gr FMJ load is 2,897fps, avg. for the 62gr SP load responsible for the denting is 2,913.
That's a wash. I mean, maybe the slightly higher velocity is due to the SP bullet being slightly harder therefore creating tighter case neck tension, or maybe a higher quality jacket getting a better seal as it travels down the bore, but 16fps is nowhere near enough velocity difference to account for it denting the plates.
I can only assume the mushrooming effect described previously is the cause of it.
Nothing to add, so enjoy for educational and entertainment purposes:
https://www.youtube.com/watch?v=QfDoQwIAaXg
https://www.youtube.com/watch?v=9To4vimvHYE
Since the velocities for the two loads are so close it comes down to bullet construction. So much for my earlier explanation, which is generally true - just not in this case. A FMJ will come apart on an AR500 steel plate no matter what, but if the bullet retains it's form slightly longer due to its construction that allows for greater energy transfer, which in this case means more backface deformation, i.e. a bigger dent. The videos are great for showing the actual impact. At the speed a 5.56 bullet flies the time it takes from the instant the tip hits the target until the back end meets the plate is about 20 microseconds, and you can see that the lead especially behaves like a liquid in the way it flows.
Now it's up to the metallurgists to examine the bullets to see why they're so different....
Go to about 9:30 in this video.
It shows the effect quite well.
https://www.youtube.com/watch?v=9To4vimvHYE
ViniVidivici
02-03-24, 16:49
Couple more data points:
A 55gr Hornady SP, at a leisurely 2,857fps, DOES dent the steel (same plate), @ 100yd. Not as deeply as the 62gr SP @ 2,900ish, but it is a ding.
75gr Hornady BTHP @ 2,544fps has same effect as 62gr FMJ, splat, no ding.
This is with a different gun, 16", as opposed to the original 18", but MV with these loads are very close with both guns.
I can only conclude that bullet construction rather than velocity, in this case, is what's doing the damage.
So rule of thumb for me going forward, no soft points on steel, only FMJ or frangible (the OTMs are too expensive to waste!).
Just blows me away that I haven't read that anywhere.
The video referenced two posts back reminds me of what a shaped charge does, but in this case the soft lead wad acts as the penetrator. In a shaped charge, an inverted cone made of copper backed by high explosives, when detonated on contact, sends a focused cone of molten copper into a small point on the steel. It handily forces a hole through armor that otherwise would be too thick. I think in their demo they hit a 'sweet spot' with regard to target thickness. Any thicker and the lead wad would splatter back just leaving a deeper dent, and that effect would probably not be seen. Any thinner and you might not see that effect either. I wish I cold do the experiment myself.
I've learned something though; I would not expected a SP to behave this way. Keeping in mind that a lead-tipped SP is no where as robust in construction as an AP round, but bullet construction obviously makes a difference.
The video referenced two posts back reminds me of what a shaped charge does, but in this case the soft lead wad acts as the penetrator. ... I think in their demo they hit a 'sweet spot' with regard to target thickness. Any thicker and the lead wad would splatter back just leaving a deeper dent, and that effect would probably not be seen. Any thinner and you might not see that effect either. I wish I cold do the experiment myself.
I've learned something though; I would not expected a SP to behave this way. Keeping in mind that a lead-tipped SP is no where as robust in construction as an AP round, but bullet construction obviously makes a difference.
Okay, that spark reminded me of something lodged way back in the dinosaur-part of the brain reference the effect of high explosive squash head.
A projo hitting steel, boosted by an explosion, causes steel on the back-side of the impact point to scab off and ricochet around inside a tank turret. In the example of the target plate in the video the scab flies off followed by the lead core and the little copper base.
https://en.wikipedia.org/wiki/High-explosive_squash_head
... the soft lead wad acts as the penetrator. I think in their demo they hit a 'sweet spot' with regard to target thickness.
I would not expected a SP to behave this way. Keeping in mind that a lead-tipped SP is no where as robust in construction as an AP round, but bullet construction obviously makes a difference.
OK, that sparked a part of my dinosaur brain about how high explosive squash head works through impulsive loading.
A projo hitting the front face of an armor plate fast enough in a small area sends a shock wave through the target armor strong enough for steel to scab or spall off the back side to hurtle around the inside of a turret fast enough to kill the occupants and perhaps set off ammunition. In the case of the soft-point rifle ammo on a plate the lead core and the tiny copper base are just fast enough to penetrate as well as scab.
One of the reasons tankers wear their low-profile Combat Vehicle Crewman body armor.
https://www.gear-illustration.com/wp-content/uploads/2018/10/DSC_8052-e1538535292391.jpg
https://en.wikipedia.org/wiki/High-explosive_squash_head
https://upload.wikimedia.org/wikipedia/commons/6/64/HESH_function.png
Front:
https://upload.wikimedia.org/wikipedia/commons/f/f9/HESH_round_%2Cimpact_from_front_and_back_side_of_an_armour_block_and.jpg
https://upload.wikimedia.org/wikipedia/commons/1/1e/HESH_round_spall_damage.png
Not quite.
A penetrator fails because the stress on the penetrator exceeds the maximum strength of the material, and the penetrator breaks up before sufficient mass impacts the target .
When a FMJ hits a steel plate, the stress is highly concentrated on the small amount of material at the nose at overloads it, causing it to fail. As the rest of the projectile feeds itself into the impact area, the failed jacket will no longer support the softer lead so it will just mushroom and spread the projectile's force on an ever growing area, and as it does so, it slows down.
With an OTM, two things happen: First the unsupported jacket in front of the lead slug collapses inward, instead of being forced outward by the lead core in the FMJ, and slows the projectile slightly and delays rose-pedalling. The second thing is the area of the lead core supporting the impact is larger and can deliver more energy to the target before it is overwhelmed and breaks up.
Typical OTM construction:
https://i.imgur.com/EJlEDxm.png
ViniVidivici
02-09-24, 13:00
Yeah, it was interesting that my OTMs didn't damage the plate, but they're 75gr, and going around 2,530 or so from the 18" gun, and my plate was at 100 yards.
So rule of thumb for me going forward, no soft points on steel, only FMJ or frangible (the OTMs are too expensive to waste!).
XM193 is the only problem round that has really messed up steel for us. Minor pocking doesn't even get noticed. Most soft points don't match what we'd use for any other type of shooting, so we don't run many of them on steel.
It should be noted that impacts on soft armor (cloth) is going to be very different. The point of an FMJ will have a better chance of getting in between the fibers and spreading them apart before slowing. The OTM will be more likely to catch a fiber (or fibers).
ViniVidivici
02-09-24, 21:09
Well, I shot the same load today with same rifle, basically just "proofing" this load. I like it alot.
Same plate, at 300 yards (off a wobbly tripod on soft mud). It STILL makes ever so slight dings. Amazing.
Yes, I'll probably stop torturing this plate with this load now. HA!
https://i.postimg.cc/cJmJS5Xw/20240209-174748.jpg (https://postimg.cc/WDdVmSR1)
https://i.postimg.cc/W3xzWq5H/20240209-175332.jpg (https://postimg.cc/njYnMrb4)
Quit makin a fuss and go tear up that target!:cool:
https://i.imgur.com/xTo6nOw.jpg
Quit makin a fuss and go tear up that target!:cool:
https://i.imgur.com/xTo6nOw.jpg
What could possibly be more fun than that? An M4Carbine art form.
ViniVidivici
02-16-24, 18:27
Yeah I consider that pic to be a classic around here!
This post has been interesting. At our range we keep ending up with some steel damage during our comps.
We check for M855/SS109. Never would have thought a SP would do damage.
So we have decided run our own test with fresh AR500 steel, and various 55 and 62 gr loads.
Just to see if we need to get more restricted with ammo.
Sent from my SM-G991U1 using Tapatalk
This post has been interesting. At our range we keep ending up with some steel damage during our comps.
We check for M855/SS109. Never would have thought a SP would do damage.
So we have decided run our own test with fresh AR500 steel, and various 55 and 62 gr loads.
Just to see if we need to get more restricted with ammo.
Sent from my SM-G991U1 using Tapatalk
Perhaps this is in the offing??
https://www.polyfrang.com/5-56-mm-frangible-ammunition-safer-made-in-the-usa-lead-free-ar500-steel-safe-linkable-suppressor-safe/
ViniVidivici
02-18-24, 20:48
This post has been interesting. At our range we keep ending up with some steel damage during our comps.
We check for M855/SS109. Never would have thought a SP would do damage.
So we have decided run our own test with fresh AR500 steel, and various 55 and 62 gr loads.
Just to see if we need to get more restricted with ammo.
Sent from my SM-G991U1 using Tapatalk
Outstanding, please do, I eagerly await the results. Yeah this really has been surprising.
I definitely want to see more SPs hitting other plates, to eliminate the possibility of MY plate just being inferior quality.
The only other one I have is a 10" round, it gets used for rifle and pistol, but exact same brand as the other, and bought at the same time.
And no, I personally wouldn't want any of that "polyfrang" stuff.
That's some crazy shit I might do. But you're changing the bullet weight and thus the results would still be speculation if the pocking was gone.
And the lead core could blow out of the jacket.
Leaving the jacket stuck in the bore.
And the lead core could blow out of the jacket.
Leaving the jacket stuck in the bore.
That was covered up-thread. Sorry for proposing it.
Piston Driven
05-08-24, 21:22
[QUOTE=kerplode;3141604] Deleted
This post has been interesting. At our range we keep ending up with some steel damage during our comps.
We check for M855/SS109. Never would have thought a SP would do damage.
So we have decided run our own test with fresh AR500 steel, and various 55 and 62 gr loads.
Just to see if we need to get more restricted with ammo.
Sent from my SM-G991U1 using Tapatalk
M855/SS109 is unlikely to do any more damage/probably less than M193 spec 55gr ball. Copper plated steel stuff is loaded to a low velocity and will do less damage than anything.
There is a decent chance something like a 45gr jhp may surprise you all on target damage.
I know I'm extremely late to the party on this thread and admittedly I haven't read every post, but seeing as it was recently bumped anyway I'm going to throw in my 2˘ on the matter...
I presume that the soft point bullets in question may have been designed with medium-sized game in mind, ergo a harder lead was used in order to prevent the bullets from fragmenting or deforming too easily for the purpose of yielding maximum penetration.
FMJ bullet is made by swaging a lead core into a copper cup. Depending on the pointiness of the bullet tip, it is possible that there is a void right under the tip. It wouldn't help energy transfer on hard target.
SP bullet, however, eliminates such possibility.
-TL
Sent from my SM-N960U using Tapatalk
ViniVidivici
05-23-24, 10:21
Yep, that all makes sense.
Somewhat related, I've inadvertently discovered that m856 tracer at 100 yards makes a nice little flash on the steel! HA!
Perhaps this is in the offing??
https://www.polyfrang.com/5-56-mm-frangible-ammunition-safer-made-in-the-usa-lead-free-ar500-steel-safe-linkable-suppressor-safe/
Is LeMas Blended metal going by another name? Seems….familiar….
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