Good read. Perhaps they will do a follow-up or two about jacket and core hardness, and how they affect pressure as well.

 

I have been hearing and known this for 30+ years (the length of my reloading “career” to date)... like it’s a new thing now??? LOL.

 

Hybrids are fairly new. Even the tipped match kings aren't the same as SMKs

 

It is a nice article, unless you can actually verify pressures for yourself; assume every difference matters.
I couldn't find a statistical pressure difference in the Berger hybrids, Vs. a SMK of the same weight. Also couldn't find where FlatLines with a relatively tiny driving band surface, made any more or less than a couple different bullets, one of which is positively known to have a larger bearing surface area. So perhaps the difference is in the jacket/core, more than the surface area; at least of what I've tested.

Looking forward to testing the classic SMK against the TMK this winter. Will find out what actually differences there are to be seen.

 

It is a nice article, unless you can actually verify pressures for yourself; assume every difference matters.

Kind of vague here Darkker. Each rifle isn't the same even in the same caliber and chamber theoretically .

I couldn't find a statistical pressure difference in the Berger hybrids, Vs. a SMK of the same weight. Also couldn't find where FlatLines with a relatively tiny driving band surface, made any more or less than a couple different bullets, one of which is positively known to have a larger bearing surface area. So perhaps the difference is in the jacket/core, more than the surface area; at least of what I've tested.

I have gone from 175SMK to Berger's, but my info isn't that important to you as yours would be to me. We shoot different platforms. Mine are more pressure sensitive.

Looking forward to testing the classic SMK against the TMK this winter. Will find out what actually differences there are to be seen.

Already done it with 175s, soon to be 155 Palma MK vs TMK and 168s shortly after.

 

An Observation:
Most Military projectiles over 1/2 Inch diameter Discharged from Rifled Bores seem to have a long Bore riding area before a small Driving band then another Bore riding tail zone.
Is this for Pressure consistency? Or for ease of Manufacture? Or for Reduced Bore Wear?

Chev. William

 

Year's age Herter's made a bullet called the Wasp Waisted Sonic bullet. I think the idea of it was to lessen pressure, not sure. But if you lessen the pressure don't you at the same time lessen velocity?

 

Year's age Herter's made a bullet called the Wasp Waisted Sonic bullet. I think the idea of it was to lessen pressure, not sure.

Reaching back in my residual memory, I remember reading about those when I was a kid, and going through the pages of a huge Herter's catalog making wishes over the gun/bow/rods. (The bows were actually very good).

I remember the "Wasp Waist" was contemporary with the F100 fighter that used the "area rule" concept to maintain stable flight and speeds above Mach 1, and Herter's used that feature to improve the ranging property of the bullet. My dad bought a box, and after wasting some powder and primers, found that they were not up to Speer bullet level for accuracy, but for penetration they were in a class with a FMJ.

The good 'ol days.

 

IN a Bolt Gun if pressures are different to the point of nervousness, it means the load was too close to the top to begin with. I'm sure gas guns are different but I have little experience with them.

 

...or less friction equals more velocity? That was Herter's sales pitch.

 

What ever it didn't go over to well. Old friend of mine many many years ago claimed he had invented the bullet and said the secret was RPM's! I loved the guy but just couldn't buy some of the stuff he came up with.

 

"Relief grooves" are going to lower friction. Of that there can be no doubt. There should also be a small difference in the "engraving force" needed to get the bullet fully into the rifling. Last, it does seem to help with bore fouling, in small arms, with 'sticky' jacket materials, like pure copper.

The question becomes.... how much? Is it measurable, or just in the realm of statistical noise? To claim something exists is one thing; to claim it is meaningful or measurable is another. Reloaders tend to get heads-down in the tiniest details, sometimes without the perspective of whether that detail is important! We've all been there.

I look forward to seeing the pressure traces that will yield more info as to whether "type a" or "type b" bullet really makes a difference.

Artillery.... as a practical matter, a steel or iron shell needs driving bands much softer. Since the driving bands don't have to be the full length of the shell, I'm sure there is some experimenting to find out what the minimum amount is that avoids stripping the rifling. Lesser driving bands = lower cost of materials, and most likely, somewhat reduced bore fouling/wear. Don't know where one would find such information, outside of the professional artillery folks.

 

Years ago, actually shot some of those Herter'sSonics (.224"). Kind of a neat idea, but the main problem with them is severaly linited seating options. Pretty well had to seat the bullets to the front full diameter section, so had a bit of "reloading freebore" added into the mix. Chronographs at had were the old paper screen versions,,,,,so we didn't do a lot of "wasteful" chrongraphing. Pretty much didn't bother until we found an accurate load (asting chronograph time/paper screens on an inaccurate load that you'dnever use just seemed wasteful.)
Not that they didn't have sky-screen chronographs by that time...they did. Folks with money bought them, and folks like me bought the old paper versions the rich guy's sold off in order to still be able to afford more "toys".
Any way....maybe there advertizing was almost right. The ones chronographed did shoot just a touch faster than the same weight of "normal"bullets. BUT, figuing in the extra depth they had to be seated to (And the slightly smaller volume created/slightly higher pressures?) was the more likely casue.

Noslet Zipido bullets (or was it Zippido?) also took the relief band concept, having multi- "artillery bands" aound the sold base section. For years, the old Nosler two-core bullets (and the RWS H-Mantle) had a relief band around the sold center section.

Evidently, that kind of thing isn't required....or just isn't worth the expense.

CAN PASS ON BY THESE LONG TALES IF YOU WANT TO (I just had the urge to write them down)

TALE #1: Diameter
Have some reasons to think that rifles do not care as much about bullet weight as we tend to think. Know it's common to just think in terms of weight, but there seeems to be more to it than that.

All the rifle "knows" (giving the inanimate object the pretend power of thought) is how hard it is for the expanding gas to move the bullet.

That can be simple inertia (with heavier being harder to get moving than lighter). That can be diameter (with a fat bullet being harder to get engraved and down the barrel than a normal sized bullet). That can be the harness of the material (most noticed when a lite plinking lead bullet load gets used with FMJ military bullets or the same weight).

So basically, weight is one factor (inertia)....but diameter/hardness and the resulting resistance to movement is likely as important.

Was once an indoor range here with an owner I knew for many years, with a 25 yard indoor rifle trap. Was a good place to stop after work or on rainy days to put in a little off hand practice (even at 25 yards,you can tell when you suck at off hand).

At one time was playing around with a coupld of old Winchester self loaders (.351WSL and .401WSL) which are straight blow back rifles. Worked up a nice indoor practice load for each, pretty much just ignoring velocity and looking for minimal recoil/ functioning/accuracy.

SO...to get that kind of load, I BROKE one of the rules of reloading and used bullets KNOWN to be too large for the bore. The .351WSL normally used .352" bullets of aboput 180grains, and the .401WSL used bullets of about .407-.408".

Used lead .355" 158gr. bullets in the .351 and 212gr. .410" bullets in the .401 for practice ammo. Not a lot over sized, and I did check that the case would cleanly release those bullets when fired(chambers were a touch of the large size back in the days when these two were made as fucntioinging was more important that the few odd-balls that reloaded the cases).
The same minimal loadd that functioned without a hitch with the fat bullets, would not function with the same bullets from the same molds when I finally got the right sizing dies (went with .353" for the .351wsl and .408" for the .401wsl). Took a full 10% increase in powder charge to get back to 100% functioing(still lite loads).

Difference was NOT in weight...was in reisntance to movement(friction). HAve no doubt thebreech pressure had to be higher, but not the velocity.


TALE #2: HARDNESS/BEARING AREA:

Had read of Elmer Keith "debunking" the claimes of kills by pure hyper velocity with tiny bullets that won't expand. Believe he used a .220 swift and turned copper (or maybe brass) bullets.

I used brass. At that time, was having a whole lot of fun with a .256WCF MArlin 62 as a short range varmint rifle. Did quite well with 60gr. JSP's out to about the same range as a .22 Hornet was working.

SO i decided to copy the same shape. length, diameter of the 60gr. Speer spire point (that's long gone) in brass. Basically lathed turned .2575" copy.

Well, evidently being a slow learner, used the brass bullet with the same charge as the 60gr. JAcketed lead bullet. I do not remeber the exact weight,but it was likely somthing like 46-48gr. considering the difference in materials.

SEVER HIGH PRESSURE signs (actually, I had to kind of rubber hammer the breech down (the old Marlin 62 was kind of like a savage 99 action...you could get to the top of the tilting breech).


OK...same weight...same shape...but the LIGHTER (brass) bullet generated a "CARP LOAD" more pressure.

OK...here we have a lighter bullets, of the same length/diameter/shape as a heavier bullet...but it resists engravement a WHOLE lot more...which rasies pressure.

So I lathed bands (like the old Zippedo Noslers) along the bearing area of the bullet so that about 50% of the bearing area was gone.

They worked with about the same observed (not instrument measured) pressure. Basically, the cases lasted just as many fireing in that cheap-springy action.

BTW: Elmer was right (as he so often has been). The brass bullets pretty much made a puckered hole in critters that the expanding tradtional JSP bullets turned into hash.

Tale #3: for any 1907/1910 WSL fans:
JUST IN CASE there are any '07 or '10 WSL guys still out there (and the .351WSL hung on the longest...eventently it was a popular prison guard gun ...mine was an old Angola State Prison rifle....and the ammo stayed a factory made load into about 1980).

You can swage jacketed bullets to size, but it takes two sets of swage dies to do it right.

Just swaging .358" jacketed (or most .355") bullets to .352" won't work. The jeackets spring back from the lead cores, leaving the core a kind of rattle-fit in the jacket, and won't shoot great(and even worse results on contact with game). Same for most .41mag bullets (.410") seaged down to .408".

The way to get the best bullets is two sets of swage dies. One that swages the bullets down to UNDER the desired size (lets say .350-351" for the .351WSL and .406" for the .401WSL) and a SWAGE UP die that will bump the now too skinny bullets up to the desired sizer (and mash the core back into contact with the jacket).

Never worked with the .32WSL (but I'm not dead yet, so I may get a chance before I die) or the short .35WSL (figure it won't teach me anything the longer .351WSL didn't).

 

Another reason for pressure variations is seating depth to base of bullet. Loading density with the same powder charge plays a BIG role in pressures.

 

Yes.... Many things can matter.
I've posted several threads with traces showing how little difference some variables can actually be in certain settings; despite what people think is going on. That's why I keep asking for actual pressure data, and not bumbling anecdotes of faith.

I was told that Berger's develop different pressures, was told FlatLine develop different pressures. Once actual pressure measurements were taken, neither claim had any merit in the cartridges I tested. Now I'm told Sierra's teenage mutant Ninja turtle variant develops different pressures. Of course I'm being told that by a paid mouthpiece, which can never seem to provide any actual evidence for the claims being made...

In about a month I'll be in AZ, and will do some actual pressure testing. Maybe there will be a difference, maybe not. Either way, I'll post the actual pressure measurements.

 

I had never heard the term "obturate" before Uncle Nick mentioned it in a post, many years ago. I guess I always knew a bullet completely filled the bore of a rifle, holding the pressure back like the cork in a champagne bottle. The recoil we feel when shooting a rifle is largely a result of those gases getting "uncorked" and pushing back on the rifle, just like the champagne bottle tries to fly out of your hands when the cork shoots across the room.

So, this thread is about how bearing surface of the bullet influences the amount of chamber pressure generated by a given load combination. Darkker's preliminary testing shows not much changes from bullets known to have quite a bit of bearing surface to those with demonstrably less bearing surface. Why isn't there a corresponding increase in pressure?

Friction-generated heat turns metals into a semi-liquid state. When the bullet starts down the bore, it obturates (plugs) the bore fully, almost immediately. This is a necessity, as it allows for both peak and maximum average pressures to be reached that generate velocity as the bullet "slides" down the bore. I put that word in quotes because once the heat from the friction of being forced down the rifling increases the surface temperature of the bullet sufficiently, lubricity becomes a factor...the bullet is slippery, compared to its normal state. The nominal differences in bullets with "long" bearing surfaces and shorter bearing surfaces has minimal impact on pressures generated. While we don't all have the exact numbers, from pressure-trace readings, to show us this, we do all have access to reloading manuals, where this is made rather plain.

Look at 150gr 30-caliber bullets for something like the 30/30 or 300 Savage. The load data is the same for all bullets of that weight, despite them having disparate shapes and "huge" differences in bearing surface...except, the difference really isn't that great, which is why the load manuals make no distinction between them. Another example would be 6.5mm bullets, as listed in the Hornady reloading manual: The longest match bullets, with a relatively large surface area, use loading data from bullets weighing just a few grains (2-3%) more. What does that tell us about the relative pressures being developed? Well, it suggests to my simple mind that those really long bullets, with a lot of bearing surface, only generate a small increase in pressures. As MikeG said, a small enough amount to get lost in the other "noise" encountered when trying to quantify pressures.

Another factor to keep in mind is that once a bullet has traveled just a few short inches down the bore, peak pressure has already occurred and is dropping rapidly, even with bullets having a relatively large bearing surface. Expansion ratio clearly has a mitigating effect on peak and MAP that far exceeds any increase caused by the amount of bullet shank in contact with the rifling.

 

I recall an article in an old NRA publication that mentioned a military experiment using bullets of the same design and dimensions except one used soft lead and the other used hardened lead. Surprisingly the soft lead core generated more pressure with the same load.


I believe it was because after initial engraving the hard core did not transfer pressure to the bore as much as the soft lead which expanded under gas pressure and tended to maintain that radial pressure longer.

 

Bagtic,

That explanation you remembered is correct. The bullet undergoes a lot of g's when it is fired. The effect is the same as setting it on a platform close enough to a neutron star that its weight equals that number of g's. The result is the base widens under the weight of the column of bullet mass above it, but the nose isn't changed much because it doesn't have a big column of mass above it, so there is less weight trying to squash it. Where the sides of the bullet are most bulged is where that weight squeeze is greatest and where the bullet will push outward hardest against the bore, creating the most friction. So if you simply extend a bearing surface forward, having less weight squashing it closer to the nose will not produce a proportional degree of added friction. This is why the measurements show less effect than anticipated.

F. W. Mann, in his 1909 book, The Bullet's Flight From Powder To Target, shows the result of numerous experiments with very short barrels cut down, IIRC, to as little as 1/4" inch and leaving much of the bullet outside the barrel and unsupported. The high acceleration at the base turned lead bullets into sort of Christmas tree profiles. Others were mangled.

Since the copyrights of anything published before 1926 are gone, I can put in an image from the book here. The jacketed 30 cal RN bullet shown has LOTS of bearing surface, but the first three bullets show what firing them from a 4" barrel produces. They are exiting the barrel while still under the influence of very high pressure and a lot of g's. The one that didn't tip and get distorting by gas pressure playing on it is #3. The bulge shows exactly where the friction is maximum while it is still inside the bore with the bore is constraining it from expanding like that. 4 and 5 were fired from an 8" barrel and that extra distance dropped the pressure enough that acceleration fell off and ant obvious distortion is gone. The fact the distortion goes away further down the barrel is why friction there is much less. The also explains why metal fouling is worst closer to the throat. It happens where the base of the bullet is at the moment pressure peaks.

The bottom row of pictures are pieces of bullets fired from a 1-inch barrel, and the muzzle blast clearly opened up the exposed bases and blew jackets off and caused all manner of destruction, so you can't see how localized bore friction is, as you can with #3 above it.

 

"F100 fighter that used the "area rule""

I think you mean the F-105 and/or F-5?


I have wondered from time to time on this subject, in moderately blissful ignorance. My thoughts related to the copper allow solid bullets which are longer for weight than lead and jacketed bullets. I was concerned about (my perceived) the extra surface friction on the longer bullets. Not such a big deal it would seem.

 

The wasp waist is no more applicable to bullets than the 11° angle for minimum drag on the tail of a car is applicable to bullet boattails. Nor does an 11° angle have any special benefit for the crown of a muzzle. Achieving perfect symmetry with a muzzle crown at about any angle produces the same precision on target.

Those misapplied ideas come from a fundamental misunderstanding of aerodynamics. Both the wasp waist bullet and the 11° muzzle crown are prime examples of the willingness of most industry and shops to indulge people's misconceptions as long as they will spend money on them.

The reason for the wasp waist on supersonic aircraft is to subtract from the fusilage the same amount of cross-sectional area the wing adds to it at that location. I'm not versed in aircraft aerodynamics, but I saw this covered on an episode of Nova (IIRC) about the development of supersonic flight. I believe it was the British who figured out constant net cross-section down the length of a fusilage behind the nose helped prevent air flow separation that killed the effectiveness of the flight control surfaces (rudder, elevator, ailerons…we can leave out the flaps; nobody in their right mind would deploy flaps at supersonic speeds). A bullet has no wings and no flight control surfaces and has constant cross-section down its bearing surface just by being a straight cylinder. So that's what's best for it. The waspwaist will just add to shockwave creation.

 

Herter's just needed to add wings to that bullet to achieve ballistic perfection... ;p