Comet tails

[holstil]

I'm guessing the orange box will be setting some records this year after people read this?
I've not had the success rate with orange box bullets as I've had with yellow.

I wonder if differences core seating setups have an effect. (Preformed boat tail cores) Not enough to make me want to stretch my jackets to a point closer to yield to try to make smoke puffs tho.

Interesting non the less. Thanks for posting those images Dave.

 

[dcali]

If I had the money and time here's what I would do. At least to start with.
Pick several problematic caliber bullet combinations which require a twist rate faster than 1-9 to achieve an Sg of 1.5 and higher.

Phase 1
1. use cut rifled barrels to maintain dimensional uniformity from barrel to barrel
2. increase bore diameter by .004" leaving land height of .002"
3. odd number of lands to reduce jacket stress. Test 3,5 and possibly 7 grooves
4. land configuration canted
5. vary total land width as percentage of the circumference. Probably three different widths would
provide data needed.
6. test test test

Phase 2 assuming some success in phase 1

1. increase twist rates to determine the point where RPM's affect bullet integrity.
2. increase case capacity to increase velocity/RPM's, find and define failure points for each combination. That's assuming you get this far.

Time and money indeed. Have you heard of anyone trying a ratchet profile rifling? like instead of a rectangular cross section, a triangle? Not sure If I'm describing that well - imagine a bore cross section that looks something like a circular saw blade.

It seems like there's plenty of strength in the rifling (I would guess) to spin the bullet up, but you'd have half of the cross sectional area (of the land). I wonder if reducing the engraving force like that would help.

 

[holstil]

Also, I'd be curious to see if differing antimony amounts have anything to do with this.

 

[dcali]

Also, I'd be curious to see if differing antimony amounts have anything to do with this.

Adding antimony in small amounts does lower the melting point of the alloy. I would not be surprised to see that bullets with higher antimony levels were more prone to blowups, but you’d still have to breach the jacket. If I’m not mistaken, the major makers tend to use a little bit more antimony in match bullets. Someone correct me if I’m wrong on that.

 

[DaveTooley]

Time and money indeed. Have you heard of anyone trying a ratchet profile rifling? like instead of a rectangular cross section, a triangle? Not sure If I'm describing that well - imagine a bore cross section that looks something like a circular saw blade.

It seems like there's plenty of strength in the rifling (I would guess) to spin the bullet up, but you'd have half of the cross sectional area (of the land). I wonder if reducing the engraving force like that would help.

Shilen does but with 4 grooves. I don't think we want opposing lands regardless of shape. I want some kind of canted land to improve the gas seal. It might not matter that much in a conventional barrel but I'd be concerned about displacing enough bullet to obturate and fill the bore with the reduced land height.

 

[Dusty Stevens]

If the source of the leak is due to a stress concentration left by the corner of the rifling, it might make sense to use more grooves and to put a radius on the corners of the lands. Or maybe vary the ratio of land area to groove area. I bet there is an optimal configuration and we may not be using it.

And this may be nitpicky, but are we really taking gas when we say offgassing or more of an aerosol of suspended liquid lead (which I would imagine would solidify almost instantly)?

You may be describing the 5r rifling. It was invented to solve those problems

 

[Canuckenstein]

So this is the low end of rl-22 loads for 6.5x55 according to 48th Lyman manual. Our store got our 6.5x55 PPU 139gr FMJs in see if I get the same thing. As well I have some 100gr Norma Jaktmatch coming in. I will have to wait for better weather to chrono these rounds. Wind gusts up to 100kmph right now. It amazes me how accurate a rifle can be even though it has a compromised bore/throat/muzzle. As well how variance of projectiles velocity and distantace can hide these issues. This is really fascinating to me.

I am gonna try to be through with my non scientific testing. So another shooter experiencing this issue can see I exhausted at least me knowledge and skill set.

 

[RGRobinett]

Bullet failures/leaking lead can also be an issue with an individual barrel - not necessarily a jacket thickness/material issue. Via yet another long-for-caliber ordeal, involving FB bullets (in this instance, 6mm 108/104 Gr.), I purchased a pair of barrels (1:8" twist 3-groove) from a respected barrel maker, and chambered both using a 6/250 Ack/ Imp. reamer.

I had my pal, Tom, select which of the two barrels would be his, and chambered it first, then, did the second for myself: as soon as the Oehler displayed 2800 FPS, Tom's barrel destroyed every one of my FB bullets (J4 jackets), and eventually, every bullet, of every brand, except the LAPUA Scenar (I believe 105 Gr. BT). I have never been able to cause a bullet failure via my barrel - not even at deliberately excessive pressure.

As usual, I'm late to the party: spewing lead sure looks like molten/vaporized lead to me. An experiment we did was, heaven forbid, to shorten barrels, which did eliminate bullet failures - acceleration (referred to earlier, by someone) results in exponentially increasing friction/heat.
We also had some success shortening the bearing surface, via adding a BT.

Another failure reducer/eliminator: dry-film lubricant coating, which, in the case to Tom's, "bullet wrecker" barrel, reduced failures from 100%, to 10% . . . while not eliminated, a notable reduction. Dry-film lubricating is cheap insurance for a barrel which does not wreck bullets, but requires faster then 1:9" twist rate, in combination with all of the other variable attributes common to barrels, jackets and bullets. Long/heavy for caliber bullets, properly stabilized, as Dave pointed out, are very close to the edge . . .

Sadly, Tom tossed the "bullet wrecker" (checker) BBL when I wasn't looking - damn! Since then, having fallen under the influence of one George Ulrich, I have messes around with "drawing-back" (annealing) various jackets - especially J4 - and have enjoyed pretty favorable results: very good precision and greatly reduced bullet failures. Should know more by end of upcoming LR season, as pal, Tim G. will probably be shootin' some at 600 & 1K, via faster than 1:7" twist .224 Cal. BBLs, which have consistently destroyed most of the long/heavy .22 Cal offerings. RG

 

[Ned Ludd]

...Another failure reducer/eliminator: dry-film lubricant coating, which, in the case to Tom's, "bullet wrecker" barrel, reduced failures from 100%, to 10%...

Can you elaborate? Are you talking about moly? Or something else? Brand(s)?

Thanks!

 

[Bc'z]

There are some nuggets of information in Kevin's post. Thin jackets can be more accurate but they present a problem with long shot strings. Example Berger 338 300 gr. The first lot was the most accurate 338 bullet any of us had seen in 1K BR. The problem is when the LR hunting crowd pushed them to 3000 FPS they started losing bullets. Solution- thicken up the jacket. The phone stopped ring at Berger but the bullets weren't as accurate.
If you examined a bullet ogive closely it is a series of folds. Depending on the metallurgy of the base metal, hardness from drawing the cup etc. you can get fractures on the fold lines.

This explains what I've noticed in accuracy level of same weight bullet vld hunter vs target.

 

[Canuckenstein]

Can you elaborate? Are you talking about moly? Or something else? Brand(s)?

Thanks!

I would like to know too?

 

[RGRobinett]

Can you elaborate? Are you talking about moly? Or something else? Brand(s)?

Thanks!

"Take your pick" - any of the commonly used stuff works. RG

 

[Ned Ludd]

"Take your pick" - any of the commonly used stuff works. RG

OK - for those of us that know absolutely nothing about the use of "dry-film lubricant coating" on a bullet, or exactly what kind of product you're even talking about, can you give one or two specific examples? There are literally hundreds, if not thousands of products that match that description, and I'm guessing that most of them are a totally different animal from what your friend Tom used.

 

[RGRobinett]

OK - for those of us that know absolutely nothing about the use of "dry-film lubricant coating" on a bullet, or exactly what kind of product you're even talking about, can you give one or two specific examples? There are literally hundreds, if not thousands of products that match that description, and I'm guessing that most of them are a totally different animal from what your friend Tom used.

I'm guilty of presuming that all of these products [used for bullet plating/coating] had been beaten like the proverbial, "dead horse".

I don't want to hijack this thread, but two very good options: 1) hBN (Hexagonal Boron Nitride); 2) MoS2, or, "moly" (Molybdenum disulfide).

Tom allowed me - after much frustration, and skepticism - to "moly" plate some bullets, of several brands, all of which went from 100% failure to 10%, or less failure rate. @ a 100% failure rate, what could the plating hurt? I have used MoS2 extensively, and without a negative issue since the mid-1990s: I plate over 95% of the bullets I shoot, using only the "moly", without the carnuba (Sp?) wax.

Again, bullet failures are a multi faceted, somewhat unpredictable phenomena. RG

 

[Ned Ludd]

I'm guilty of presuming that all of these products [used for bullet plating/coating] had been beaten like the proverbial, "dead horse".

I don't want to hijack this thread, but two very good options: 1) hBN (Hexagonal Boron Nitride); 2) MoS2, or, "moly" (Molybdenum disulfide).

Tom allowed me - after much frustration, and skepticism - to "moly" plate some bullets, of several brands, all of which went from 100% failure to 10%, or less failure rate. @ a 100% failure rate, what could the plating hurt? I have used MoS2 extensively, and without a negative issue since the mid-1990s: I plate over 95% of the bullets I shoot, using only the "moly", without the carnuba (Sp?) wax.

Again, bullet failures are a multi faceted, somewhat unpredictable phenomena. RG

Thanks for the clarification! From reading your original reference, I was thinking you may have been referring to some type of aerosol dry lube, of which there many types available. I have tried a few things such as running a couple patches of Kroil after firing a string, followed by dry patches in between relays. Other than removing carbon fouling, those types of barrel treatment probably don't have an effect more than a shot or two. Obviously, direct treatment of the bullets would be a different story. Again, thanks for the clarification.

 

[Canuckenstein]

Factory ammo no comet tails. Still gotta do some loads with 4350 chrono these others then I am done to the extent I want to work on this. All targets shot at 50yards.

Norma 100gr jaktmatch
S&B 140gr FMJ
PPU 140gr FMJ BT

 

[fyrewall]

My thoughts are:

The bullet does not spend enough time in the bore to cause the core to melt.
Fast twists and bullets having long ogives are most likely to fail.
Air resistance heats up bullets but due to the time of flight at short ranges like feet or 100 yards is not enough to melt cores.
Lead is weak material and has a low tensile strength.
Odd number of lands and groove barrels do not subject bullets to squashing effects of even land/groove barrels - like opposing lands at 180 degrees apart.
Bullets are spun at huge rpms causing large centrifugal forces.
A force applied to a spinning bullet will cause it to move at 90 degrees from the direction of the force.
Many materials being subjected to compression exhibit fractures at right angles to the direction of the applied force.
Upon forming ogives jacket material is work hardened and grain size reduced.

So in my simple mind I see a bullet spinning like crazy that is filled with soft weak squishy lead emerging from a rifle barrel. The nose (ogive) of this bullet has been squashed into shape forming a long tapered surface ending in a point. During the forming process the grain size has been altered by work hardening and expansion fractures have developed that run longitudinally along the ogive. Upon emerging from the barrel any force directed at the bullet at right angles causes it to momentarily be deflected 90 degrees from the direction of the force but as the bullet is spinning like crazy it resumes its nose forward flight but in decreasing amplitude wobbles (going to sleep). This rough stuff combined with spinning like crazy and the tiny but jacket strength compromising expansion fractures begin the jacket failure process and bits of lead escape from jacket failures.

Where this stuff really needs more analysis is the presence of these expansion fractures in bullet jacket metal - yes or no - possibly Xray analysis might show something.

Just some quick thoughts. Never used PPU bullets - good photos. I have never had a bullet blow up and I shoot many 75 grain .224 at 3150 with a 7.7 twist and other long for caliber bullets at velocities of 2900-3100 fps. Never had a 87 Vmax .243 @ 3300 from a 8 twist blow. I have fired many FMJ bullets having exposed lead at the base at high velocities and have never seen any evidence of melted lead. A certain high grade barrel maker promotes 3 groove barrels and he would be mortified to have one of his barrels responsible for destroying bullets and if notified would subject that barrel to all and every test possible.

 

[dcali]

That doesn’t explain the puff when a bullet comes apart completely, or the fine mist nature of the lead that breaks through the jacket.

I’m also not totally convinced that an odd number of grooves matters. I could be wrong, but intuitively, it seems like bullets are big enough in diameter to keep the stress on one land from interacting with that on another. The stress concentration due to the corner of the rifling is there either way, and that seems to be the spot that cracks open first.

 

[Rtheurer]

Ned Ludd Wrote:
In my hands and those of quite a few other F-TR shooters here at Accurate Shooter, the issue with jacket failures has been observed predominantly in .223 Rem F-TR rifles loading heavy .224" bullets such as Berger's 90 VLD, and Sierra's 90 SMK. In talking to a number of other people that have experienced this issue, it does appear to be exacerbated by using a twist rate faster than 7.0, but that is not the sole cause as people using 7.0-twist barrels have also experienced blow ups. All my .224" barrels are 5R, 0.218"/0.224" land/groove configurations. So my question is, could I get away with using a 0.219"/0.224" barrel, or even a 0.220"/0.224 or 0.221"/0.224" configuration? I'm just curious as to whether a modest decrease in land height might be enough to help minimize the potential for jacket failure without sacrificing precision, if the failure is caused in part due to the relative "thinness" of the jacket itself with a particular bullet.[/QUOTE]

Interesting tidbit of History I had the fortune to be involved in. The US Army Reserve Service Rifle shooting team was trying desperately to get the 90gr Bullets from Berger JLK and Sierra to work in the short 20" Service rifle's in the early 2000's. At the time Joe Carlos of PA was building our rifles for the team. This was about the same time frame that Eric and Walt where looking for the reason for bullet Failure. I had taken over the Ammo portion of the teams job in 2007. Mr Carlos had been working desperately to get these bullets to not come apart and for the life of the barrel.
One experiment was working with Kreiger to make a barrel with less Land height. It was called the GEN II design in 6.5 Twist.
If you want more info I suggest you reach out to Joe or even Kreiger to see how that shook out.
One of Joe's experiments was to use a PAC NOR Polygonal barrel. And also 5R's. 5C. and all types of methods to prevent bullets from coming apart to include Moly. This was all done back in 2006 to 2010. A decade ago now.

Hope this finds you all well.

 

[fyrewall]

Catastrophic jacket failure, like essentially no jacket - logically it would appear that molten lead is being sprayed off.

Would exposing the lead core, a soft weak metal spinning at enormous revolutions, having great velocity, and removing a protective jacket and a compounding effect of much increased air resistance tear the tiny lead, low melting point, core into tiny pieces. Is the lead actually melted? Possibly, yes but only after the jacket has been destroyed. I don't think the jacket contained lead soup on its way to the target. Bad stuff happens fast at high speeds.

Upon jamming a bullet into a sharp edge, the upper corner of a land, and subjecting the bullet to hard and quick acceleration & torque - it would also logically appear if failure were to occur it would be at that point. This would get into jacket composition and work hardening. Lining up that point with any (in theory) expansion fractures might do jacket failure.

I just ran out of thinking. About the odd - even land groove stuff. It would seem that smaller diameter bullets would have more of an opposing land squashing effect than larger diameter bullets.