Comet tails

[Dusty Stevens]

Looks like the tip was 170c and a soldering iron is 130c. Sure puts into perspective the heated melted tip theory degrading bc. If your tip wont hold up to a soldering iron its better to just not have a tip

 

[Ned Ludd]

Based on the images shown in the article for which Dave shared the link above, it doesn't look to me like the explanation for jacket failure is that the lead core is "melting". That would require a great deal of heat transfer in a very short time, all the way down into the interior of the bullet's lead core. If that occurred, the entire exterior surface of the bullet should be hot, not just the narrow region of the grooves cut by the rifling.

 

[STS]

Based on the images shown in the article for which Dave shared the link above, it doesn't look to me like the explanation for jacket failure is that the lead core is "melting". That would require a great deal of heat transfer in a very short time, all the way down into the interior of the bullet's lead core. If that occurred, the entire exterior surface of the bullet should be hot, not just the narrow region of the grooves cut by the rifling.

That's kinda what I was thinking also. The article is more about how they captured the images rather than data collected. Thanks Dave for posting that up. It's very interesting. They say in the beginning of the article that they are looking a atmospheric heating and to some extent heating via the acceleration process. I thought what I have observed on the occasions that I've seen this would be more consistent with atmospheric heating rather that acceleration. The bullets that I've seen do this have all started shedding lead (evidenced by the blue/grey smoke) about 30 to 40 yards down range. Seemingly enough time for heat to build up and start melting the lead. Likely it's a combo of things that cause this and there is also likely more than one pathway to these events. It is very interesting.
One additional comment. I'm not sure I agree with the notion that bullets that do this are about to completely fly apart in the next few feet of travel. In fact I've witnessed bullets travel at least 150 yards (and in some examples much further) smoke trailing every inch of the way to the target. My now dead and gone .17 barrel would smoke every shot from about 40 yards out to a p-dog colony around the 200 yard mark and connect with virtually every one of them. That's what is amazing that they can still be quite accurate with the bullet in the process of wasting away.

 

[Ned Ludd]

That's kinda what I was thinking also. The article is more about how they captured the images rather than data collected. Thanks Dave for posting that up. It's very interesting. They say in the beginning of the article that they are looking a atmospheric heating and to some extent heating via the acceleration process. I thought what I have observed on the occasions that I've seen this would be more consistent with atmospheric heating rather that acceleration. The bullets that I've seen do this have all started shedding lead (evidenced by the blue/grey smoke) about 30 to 40 yards down range. Seemingly enough time for heat to build up and start melting the lead. Likely it's a combo of things that cause this and there is also likely more than one pathway to these events. It is very interesting.
One additional comment. I'm not sure I agree with the notion that bullets that do this are about to completely fly apart in the next few feet of travel. In fact I've witnessed bullets travel at least 150 yards (and in some examples much further) smoke trailing every inch of the way to the target. My now dead and gone .17 barrel would smoke every shot from about 40 yards out to a p-dog colony around the 200 yard mark and connect with virtually every one of them. That's what is amazing that they can still be quite accurate with the bullet in the process of wasting away.

Agreed. I should have stated that it doesn't seem as though the sole cause of bullets disintegrating on the way to the target is melting of the lead core. As you noted, there may be a number of factors that contribute. I'll also add my thanks to Dave for posting that article; it was an interesting read. In my hands, jacket failure with 90 VLDs seems to be an "all or none" phenomena. I have never observed (or at least noticed) comet tails on targets at 100 yd. However, neither the jacket remnants or fragments of the core made it that far, or at least, they didn't hit the paper. Perhaps it is more likely to see comet tails with targets set up at 50 yd, possibly a little closer to where the bullet starts to come apart.

 

[DaveTooley]

I don't think the entire core melts or has to. I think that for a brief period of time there are areas that are molten. Those being the area that makes contact with the rifling. That is where there is greater pressure/stress/friction on the jacket. That brief period is where bad things can happen. The longer the bearing surface, in conjunction with thin jackets, is where we have problems. My tests, showing tails, was done at 15 yds. because the bullet didn't stay together much longer. They didn't make 50 yds.

 

[STS]

Ned and Dave may be seeing the same thing which is bullets actually flying apart at very short range. I have only seen that with guys with fast twist high velocity set-ups like 8 twist .22-243's and trying to shoot light, high velocity bullets at 300K plus RPM. My personal experience has been with bullets that bleed lead all the way to the target which as mentioned earlier can be several hundred yards away. I saw a guy shooting rock chucks with a .22-250 AI that you could see the 'smoke trail' for 350 to 400 yards. It was as cool as it was funny. Like before, I think there's more than one set of circumstances that yield this situation.

 

[Dusty Stevens]

If the core slips it does weird stuff too

 

[STS]

If the core slips it does weird stuff too

Yes it does. That's probably the understatement of the decade right there. You wanna make sure to squeeze the chit out of em when core seating.

 

[Dusty Stevens]

Yes it does. That's probably the understatement of the decade right there. You wanna make sure to squeeze the chit out of em when core seating.

And dont drop em on the floor or push on the top like for pointing either- but i digress

 

[Canuckenstein]

Wasn’t able to get on the range today freezing rain. Thanks Dave for the article very cool.

While pondering this conundrum after reading the artical. Trying to evaluate all variables at play here. I thought to call a friend and ask if he has ever seen this exploding bullet phenomena. He was a C6 (FN MAG)machine gun operator in the CAF. I asked if he had ever noticed rounds not going beyond short range. He said he had never seen it nor heard of it and he got the C6 upto near cook off temps (now that’s some heat). So I have to say it’s got to be more than just temp causing this (as others have said). Now I would suspect a rough bore would do this. But since I was at the store all day and the weather was bad I took out the old Hawkeye and that bore is exceptional condition given the rifles age. A little throat erosion but not extreme by any means.

So extreme heat not an issue for my case nor is a rough bore or a dinged crown. I am also uncertain if as mentioned above if heats from acceleration would cause the lead to melt. If you go by the analogy of the soldering iron made above. Yes a soldering and those temps will melt lead. However you have to hold the soldering iron for a few seconds. Much longer than a bullet traveling down a barrel. Not to mention it is a way smaller amount of lead. So I can imagine the surface is the temps shown in the pics to be real. However, I would believe it would be superficial and mostly on the surface. I am not saying the artical or other theory's are wrong. Just a little devils advocate. Now you could say what about the burning powder (ignition). Yes that is true but it is very very brief. A good example is I can dip my finger in water and swipe it through (quickly)a propane torch flame and not be burned. Again not trying to disprove earlier posts just looking for more data on the molten lead theory.

Just trying to make sense of it all...

 

[grovey]

I can't find the target pic, but I bought a shot out swift some yrs back that put lead spray on the target at about 30 yds as I was first getting it on paper. It still shot MOA @ 100 yds, but a fairly well known smith borescoped it and said it was literally the worst bbl he's ever looked at.

 

[Intheshop]

I have really enjoyed this thread,as a cast bullet rifle shooter. I try not to get too wound up in theory,choosing to keep my head down(cheek weld,ha) and working through problems on my own. But am having a hard time accepting lead cores melting,seeing as it's pretty routine to be @3000 fps with non coated( powder coat) gas checked bullets.... out of factory barrels. Yes it takes a whole bunch of effort and experience....

My gut says the jackets are getting a bad start at launch,then it just gets worse. And yes,heat and barrel roughness is part of the equation but think there's something more going on.....

One thing to try,and not as a fix,but to see what happens..... roll a canelure on the bullet,see if that makes it better or worse?

 

[DaveTooley]

I have really enjoyed this thread,as a cast bullet rifle shooter. I try not to get too wound up in theory,choosing to keep my head down(cheek weld,ha) and working through problems on my own. But am having a hard time accepting lead cores melting,seeing as it's pretty routine to be @3000 fps with non coated( powder coat) gas checked bullets.... out of factory barrels. Yes it takes a whole bunch of effort and experience....

My gut says the jackets are getting a bad start at launch,then it just gets worse. And yes,heat and barrel roughness is part of the equation but think there's something more going on.....

One thing to try,and not as a fix,but to see what happens..... roll a canelure on the bullet,see if that makes it better or worse?

Our problems were in 3 different 1k yd. BR rifles. Nothing half assed in any of them. First lot of bullets worked well. New lot of jackets and things went to hell. I'll get some pics up of the targets later.

 

[KevinThomas]

Dave Tooley pretty well nailed this one. Interestingly enough, the worst example I’ve ever seen of this phenomenon was with this exact same combination of gun and components; a 142 SMK, in conjunction with an M96 Swedish Mauser in 6.5x55. A fellow sent the targets and load info into us on the Sierra Tech Line, asking about this. His were similar, but far worse. On his targets, there was enough lead out gassing that the particulate matter was actually cutting the paper, not just marking it. Clean through it, leaving a little comet tail opening in the heavy target paper. From his load data, he wasn’t using a hot load by any means, just a common old rifle 6.5x55 Swede load, perfectly suited to his rifle.

The causes of this plagued Berger some years back, and to their everlasting credit, Walt Berger and Eric Stecker spent the time and money to find out what was happening. This involved thermal images of bullets in flight, so as to learn the real-time temps of the bullet in flight. Based on these thermal images, they learned some very interesting facts about bullet heating. One, the base of the bullet that gets subjected to all those hot gases . . . doesn’t warm up much at all. Stays relatively cool, in fact. One of the hottest points on the bullet in flight, is the meplat. Pure atmospheric friction of pushing through the air. The rest of the bullet stays relatively cool, with the exception of those areas of the jacket that are physically engraved by the rifling during its transit through the bore. This area becomes extremely hot. Based on the thermal image, they learned that the temps were high enough, and the jackets thin enough, that it was literally melting a thin boundary layer of th core inside. And defect in the jacket, such as that presumably caused by sharp rifling edges or a rough throat, provided a minute weak spot through which the now molten lead could outgas as a near lead vapor. Enough worse and the particulate matter becomes heavy enough to cut paper, as the customer I mentioned was seeing. Anything beyond that, and you get a nice little mid-air FLAK burst somewhere between you and the target, with no impact whatsoever down range. Berger solved their issues with this problem by slightly vamping the jacket thickness of some bullets, which then became th “Target” line. The original more thinly jacketed bullets were retained in the line, but now designated as their “Hunting” bullets.

The M96 Swedish Mausers were originally manufactured with cut rifled barrels, which must have generally produced some very sharp rifling, at least at the leading edges of the land/groove transition. In any case, I’ve seen the same phenomenon any number of times, and brand new barrels, or very tired older barrels are usually involved somewhere in the mix. A little judicious cleaning may help, bumping the velocity back may too. But that’s the cause, and that knowledge may help you correct the problem one way or another.

 

[Intheshop]

Mr Tooley,this is a little self serving but..... what are you running for leade angles?

 

[DaveTooley]

Mr Tooley,this is a little self serving but..... what are you running for leade angles?

I worked at solving this for the better part of year. I started with 1'30" then designed a double tapered throat that I thought would lesson the stress on rifling engagement. That didn't change the end result.

 

[DaveTooley]

These are pics of some of my targets. On one I believe I identified individual land involvement. I had several with double tails.

 

[DaveTooley]

Pic

 

[DaveTooley]

Pic

 

[Bojo]

If you rotate the OP's pic 90° clockwise , it resembles a face with bushy eyebrows and a mustache.