quote:

Originally posted by ALF:
Another interesting fact I came across in the 303 BT erosion saga is that to try and mitigate erosion caused by the bullet base shape they inserted a wad between the bullet base and the column of propellant and get this the cases were necked in factory only after the case was primed and charged with propellant. So the neck sizing of the basic case was done after priming and charging.

The Americans looked at trying this with the 30-06 but because it has a more defined shoulder and neck than the 303 they deemed neck sizing after charging and fitting of a wad not as safe or easily accomplished as with the 303.

Alf,
The Brits had to size the case after charging anyway. They could not get the stick cordite charge in case otherwise.
I have broken down British .303 ammo to look at the cordite strands and it contained a paper wad about .030 thick.

quote:

Originally posted by SpringTrap:

quote:

ron williams
one of us

Posted 09 March 2008 18:11 Hide Post
Buy the best you can afford.

2000.00 dollars should get you a very fine outfit.


There are no fleas on the 9.3s

Whether it is iro rifles, reloading equipment or whatever you were referring to above, it is also applicable when it comes to bullets.

Practice what you preach!

I could afford to use the GS bullets if I wanted to but refuse to use a product that is promoted in such a mean spireted manner as has been by its propenents.

If you want me to spend my money on somthing new you might want to try being a little nicer to your fellow shooting buffs.

quote:

Originally posted by ireload2:
No one here has provided any back data or theory to support the statement that boat tails cause more erosion.
If you magnify a flat base bullet you will always find there is an edge radius or chamfer. The corner of the heel is never perfectly sharp. Thus there is always some angle between the bullet base and the the bore. This angle is always huge compared to the gas molecules. I have no idea why a gas molecule would act different when pushing into the intersection of a flat base and a barrel vs the intersection of a boat tail and the barrel. After all the intersection of both is huge in comparison to the gas molecule.

The simple answer?
The simple answer that you already know?
To the gas molecules it makes no difference.

It's like arguing over the proper shape of the inboard end of a hydraulic cylinder.... or how many angels can dance on the head of a pin.

AD

Stainless steel resists heat erosion better than in chrome-moly barrels and so we see the trend that over-bore high velocity rifles like the Varminters are coming out with stainless steel barrels. Here is an extract from an article that I came across:

"The magic number seems to be that once you have about .003 of throat wear on a standard barrel or .002 on chrome-lined, the barrel is shot, and that holds true for any precision-shooting rifle. That has been my experience over decades of testing with a multitude of varmint calibers from factory offerings to wildcats." Ralph M. Lermayer

Interesting to note was how accuracy fell between 750 and 1,000 rounds; coinciding with erosion measurements between .003 and .0035 with a .223 WSSM and .22-250 Rem.

For more details, you can see the full text here ... http://www.gunhuntermag.com/features/051213Shot.htm

Warrior

A/

The shape of the bullet would be relevant if we were talking about a wider gap or a smaller pressure differential, but with a 60,000psi pressure differential across the length of the bullet that the shape is irrelevant to the gas, it's gonna leak either way.

I'm saying that the relevance of that shape difference sporting rifle owners is non-exsistant.

Does it matter if you hold your hand up to someone about to shoot at you? will your hand stop the bullet?

It's like the arguements with people over port shape and surface finish in race engines and they keep quoting xperts from the 1960's who are discussing carbureted engines and their need to keep the fuel droplets in suspension
when infact the people holding the discussion here and now in 2007 are discussing a port fuel injected engine with a turbocharger... (Keeping fuel droplets in suspension in the intake runners of an EFI engine is a moot point because the fuel is introduced to the engine further downstream...)

The Military tests were dealing with MACHINE GUN barrels

with a typical sporting rifle the bullet is firmly engaged into the rifling before the heel of the bullet is clear of the case mouth and while SOME gas leakage does ocour it is FAR less relevant than many here seem to think it is.

Frankly I think the "stick" propellant Vs "ball" propellant arguement for throad errosion is far mroe relevant.

Oh and BTW, the military was concerned with muzzle errosion and that probably is affected by boat tails as the angle between the boat tail and the slight champfer at the bitter end of the rifling lands can easily interact as the leading edge of the muzzle blast begins to escape from behind the departing bullet.

This effect is likely aggrevated by the typical rapid (fully automatic) firing rates and their ability to heat soak metal parts so as to amplify the affect of each subsequent shot.

The government's concern is multiplied by the hundred thousand plus barrels they are typically "abusing" at any given time and their subsequent cost of replacement and the effect of that cost on their budget.

For you and me that might mean that after 5-7 years of really determined use/abuse you might need to buy another barrel for your pet groundhog rifle.

For the soldier in the field he'll just hand it in to his unit armorer and say "It's fukt, gimme another one".

While if it were you or me? we might clean it up and trade it in on another rifle and let it become someone else's problem
rather than call Hart, Shilen, Lilja, etc.... for a new barrel.

EVERY SHOT YOU FIRE has SOME errosive effect on your rifle barrel and in the greater scheme of things does it really matter to you and me if that wear point occours a few rounds sooner before accuracy degrades noticably?

The average shooter will not burn out a rifle barrel regardless of what kind of bullets they choose to shoot.


AD

/

Hi
how much shorter barrel life would it result if we only use boat-tail bullets? i have seen many old M98 mausres with good bore in 8x57 after have been fired many thousend rounds with those 198 gr bt army bullets !! is it a great difference in barrel life or negligable?
regards
yes

quote:

Originally posted by Idaho Sharpshooter:
logic says that a boattail bullet traveling at 3000fps is in a 24" 30-06 barrel actually travels 20.65" inches from case mouth to muzzle. It is doing that travel in .0005736 seconds.

The government is likely using the same scientific principles that proved in 1942 that an atomic bomb was impossible to build, and in 1956 proved conclusively that a bumblebee was too un-aerodynamic to fly.

I would suggest that the velocity and type of powder have more to do with erosion than bullet base shape. As an example, the military found in the early 1960's that switching to a ball powder greatly increased accuracy and barrel life, and reduced fouling in the M-16 gas system. Prior to that discovery, the military had many detractors and few supporters of the M-16.
Stick powders erode barrels faster, and that is the most likely culprit.

Rich
DRSS
Knowledge not shared is knowledge lost...

Lots of new info (for me) in this post.

I always thought many of the spherical powders were nitroglycerine (and nitrocellulose) double-based powders (like H380), which burned hotter and dirtier than the nitrocellulose single-based 'stick' powders like IMR4064.

And I also thought the 'government' recommended powder for the M16 was IMR4198, which is a cleaner burning single-based nitrocellulose stick powder.

Could you please post your links, I/S?


Also, the travel time information for your bullet may be skewed. Your figure includes a constant velocity of 3000 fps.

Your bullet is actually accelerating from 0 fps to 3000 fps in that 20.65 inches.

/

As we have seen throat erosion manifests itself a lot quicker with some calibers (after a mere 750 rounds) than we would like to confess, and as such it is an issue when we reach the .003" mark regardless of which shape bullet we shoot. In hunting guns where we shoot a variety of bullets over time rather than shooting faithfully only flat bases or boattails, it is unlikely that we as ordinary hunters will ever resolve this issue.

The primary cause of throat erosion is the intensity/temperature of the flame right where the rifling starts. With each successive shot the barrel heats up and it becomes easier to melt steel away. (Here we have two factors under our control - firstly, the volume of the charge behind the bullet (mild or hot load), and secondly, the period of cool down between shots (rapidity of fire) and both factors are within our control.

Thirdly, A given volume of powder in a case needs to be related to a given bore size. This relates to the 'expansion ratio' being the ratio between the total volume of the bore and the volume of the case or the number of times the gas will expand by the time the bullet reaches the muzzle. A higher expansion ratio means a better barrel life. For example a .220 Swift Ackley Improved concentrates the heat on less surface area than a 308 Win with essentially the same powder capacity. This equates to more steel melting/erosion. Here we have a choice too ... to pick the efficient calibre (over-bore vs under-bore). Or if we deal with the same caliber (same surface area) then we can pick the size of the case (volume of powder) - example, 7x57 mm vs 7 mm STW. Again our deliberate choice.

These are the main variables imo in terms of throat erosion. We can manage them by intelligent choice and avoiding hot loads that yield undue high pressures. The type of powder we pick is assumed to be the most appropriate powder for the caliber and the bullet weight in question, and here in SA there is not a choice of various powders as we can only use Somchem powders, and often only two powders to choose between and in some instances no choice at all.

Then we just pick the bullet that serves our purposes best, be it for target shooting or hunting as different criteria apply. Berger Bullets offer primarily boattail bullets for long-range matches in 6.5 mm, 7 mm and .300 cal, as can be seen on their website. Having a boattail design in a bullet is not an important issue for hunting under 300 yards.

Warrior

Corbin also mentions the incidence of gas-cutting of the rifling edges with boattail bullets, but he found a solution with a new design called the Rebated Boattail design. The tradional boattail design funnels the hot gas into a wedge against the bullet shank where it meets the barrel; as it exits the muzzle, the gases flow forward around the bullet, causing it to initially fly through its own turbulance. In contrast, the REBATED BOATTAIL provides a small, flat edge for the gases to press on; upon exit, the gases are deflected perpendicular to the bullets flight path, as in a flat based bullet. The turbulance problem is virtually eliminated, while retaining the benefits of the boattail design (reduced drag, higher ballistic coefficient, more retained down range velocity).


Manufacturing & Supply, Inc.
600 Industrial Circle
White City, OR 97503 USA
D.R. Corbin, President
July 5, 1986

(Refer to Dr. A.B. Bailey, "An Aerodynamic Study of the Lapua Step Boat-tail Rifle Bullet and its
Ballistics", 1981, Endrickvale, Fintry by Glasgow, Scotland, to R.H. Kent, "The Theory of the Motion of a
Bullet About Its Center of Gravity in Dense Media, with Applications to Bullet Design", January 1957,
Ballistic Research Laboratories, Aberdeen Proving Ground, Maryland, USA, and to D.L. Walters, "Crosswind
Weighting Functions for Direct-Fire Projectiles" (Report X-65), August 1975, Atmospheric Sciences
Laboratory, US Army Electronics Command, White Sands Missile Range, New Mexico, USA, for background
and mathematical support of the summary presented here.)

"When a flat base bullet flys through the air at any velocity, it displaces an equal volume of air which
then rushes in behind the passing bullet to fill the vaccuum. This happens at any velocity. But at speeds
below Mach I (speed of sound), the drag caused by this turbulence is greater than most of the other forces
slowing down the bullet. When the sound barrier is crossed, the air is compressed faster than it can move
out of the way, and it compacts into a dense wave that is dragged along by the nose of the bullet. Moving
this compressed shock wave adsorbs far more energy than the turbulent base drag. Thus, at super-sonic
speeds, the nose shape has a greater effect than the base shape on the total retardation of the bullet (as a
percentage of total drag).

If the base of the bullet were made more streamlined, then the air would be put back together more
smoothly, with less turbulence, and would fill the space left by the passing bullet more quickly. This would
eliminate much of the base drag. Putting a point on both ends of the bullet accomplishes this, but it generally
makes the bullet too long, so that it takes up too much powder space or causes other physical problems
in a practical size cartridge case or gun. There is no technical reason why a double-ended bullet should not
be used to overcome drag, except for these physical considerations.

The next best idea is to use a truncated conical shape on the base, so that the bullet has some
degree of streamlining to help reduce base turbulence. The conventional boattail does this reasonably well.
By having a base that is made of an angled portion of the shank, the size of the flat base is reduced so that
the turbulence works on a smaller area. A typical, practical size of boattail has from nine to fifteen degrees
(measured from the center-line of the bullet) and is about a caliber long. There is no great difference in the
performance of any specific angle or length within this general range.

The boattail reduces base drag at all velocities, but has the greatest percentage of effect when the
bullet is flying at sub-sonic velocity. Thus, it is more important for slow bullets, or bullets fired at long
ranges, than for bullets which will be moving at super-sonic speed over their entire path to the target.
Ideally, pistol bullets should be boattails. However, due to the length and weight limitations imposed on
most pistol bullets, this superior design is rarely used for handguns. It is often applied to rifle designs where
it will have relatively little effect, but is primarily effective for promotional purposes.


The conventional boattail bullet does have three problems associated with it.

(1.) The angled boattail base tends to focus escaping muzzle gas like the nozzle of a hose, so that the
gas flows in a laminar manner over the boattail, along the parallel shank, and partly attaches or follows the
outline of the ogive until it separates at or near the tip, and breaks up into turbulence just ahead of the
bullet. This can add as much as 15% to the total dispersion pattern of a given bullet design. The boattail
bullet literally flys through its own muzzle blast because of the focusing effect of the streamlined base during
the moment of exit from the barrel.

(2.) Since gas pressure acts normal to all surfaces (at 90-degrees), the compressive force of chamber
and barrel pressure tends to compress the boattail section of the jacketed bullet inward, peeling it away
from the bore and allowing gas to channel its way into the rifling grooves, causing gas cutting of the rifling
edges and the edges of the rifling imposed on the bullet. Micro-droplets of melted jacket material can be
observed on most boattail bullet jackets along the rifling edges, especially toward the rear of the bullet
shank, some large enough to see without a magnifying aid. The flat based bullet tends to compress in
length so that the shank is expanded into the rifling, for a superior seal.

(3.) The boattail bullet is sensitive to slight manufacturing variations in the position and concentric
alignment of the boattail angle starting point. At the moment of exit from the bore, while the rifling is just
losing contact with the shank diameter, any difference in position of the junction of the shank and the
boattail gives a tremendous leverage to the escaping gas, which allows it to push the entire bullet in the
direction of the higher starting point. That is, if the boattail is even slightly higher on one side of the bullet,
the bullet will be deflected toward that side at the moment of exit by gas pressure escaping earlier from the
opposite side.

All three of these objections are overcome by using the Rebated Boattail design.

(1.) Hyper-velocity gas escaping around the bullet base at the muzzle will impinge upon the rebate
shoulder, which acts as a "spoiler" and deflects the gas from a laminar pattern. It causes a ring of gas to be
blow off in a turbulent forward rolling expansion, but leaves a clear space directly in front of the bullet. This
eliminates the buffetting of the bullet by its own muzzle gas, a source of up to 15% of the total dispersion
factor.

(2.) Gas pressure acting normal to the surface of the Rebated Boattail will compress it inward,
causing the lead to flow forward and outward. When the gas reaches the rebated area, it acts normal to this
surface also, forcing the gas to act parallel to the bore rather than at a compressive angle, and holding the
rebated edge rather than compressing it. Internal pressure from the compressed, angled base area then
pushes the lead outward, against the inside of the jacket, which in turn seals against the bore more tightly.
The peeling-away of the base from the bore is eliminated. An examination of fired RBT bullets at the same
velocity and from the same guns as the BT design will show no micro-droplets of molten jacket along the
rifling edges.

(3.) The Corbin method of producing the RBT design, using two dies and a finalizing punch during
the point forming operation, greatly reduces or eliminates the chance of having the RBT angle start higher
on one side than the other. In addition, if this should occur, the effect on dispersion is far less because of
the vastly shorter transit time during which the gas can begin to escape around the emerging bullet base.
The sudden drop in diameter releases the gas with smaller time/resistance factor than the slow increase as
the BT angle passes the muzzle. Add to this the fact that the tooling lasts longer and is easier to produce in a
precise manner, and you have every reason to abandon the BT in favor of the RBT."

/

Mr. Warrior

If the rebated boatail is a so much better model for a bullet. Why have not our major manufactures switched over to it?

I understand that sometimes they are way behind the curve on innovation but the rebated boattail idea has been around for years if it was a practical design do you not think that at least a few would not have adopted it?

And do you think that to most readers on this forum it really matters if they use a bullet that does or does not have a bottail rebated or otherwise when it comes to harvesting game at practical hunting ranges

I admire your mind for the small details and that of Alfs and Springtraps and Gerards and others but it appears to me that you are just splitting hairs.

Is not all that matters that a piece of metal travels at a velocity high enough that when it strikes bone or flesh that it causes enough trauma to quickly and humanely dispatch your prey

Or if you are a target shooter that the bullet design is accurate and retains enough velocity to make long range shots possible

My buddies that are serious 600 and 1000yd benchrest shooters are very competitive and would jump all over the rebated boattail if it truly was the answer.

quote:

Originally posted by ALF:
AD

You cannot wish away history ! Fact is at the time of the big changes in small arms development everyone was looking at this problem, whether their deductions were right or wrong they looked at everything and their documention they left behind shows this.

It spanned continents !

If you look at the British small arms history and the development of corrosion free propellants these were so important that they became issues that threatened the political viability of government at the time!

Smokless propellant was ACCUSED of being corrosive when it was infact the priming compositions that were being used at the time.

Boattail bullets got blammed for errosion of the bores of the 1903 springfield because the boattail bullet was a new innovation at the time.

Yeah, there's reams of documentation from the turn of the century.
Most of it wrong. or to be more correct the conclusions drawn from that data was wrong.

Things that have subsequently proven to be less "profound" than they were believed to
be at the time.

For the average schmuck who buys a major maker 30-06 rifle and loads boat tailed bullets the effect of them on bore errosion is something that his grandchildren MIGHT need to be concerned with... if they shoot the rifle a lot.

I'm not ignoring or deflecting history, I'm saying that regardless of the accuracy of any conclusions reached NOBODY HERE ON AR CARES!

Why don't they care? because the point is moot.

It's like explaining to a new car LEASEE that thee car they are buying will explode at 100K miles when they are buying a 2year/40k mile lease on it. you are talking about someone else's problem.

Frankly I don't give a damn that shooting my rifle with boat tail bullets is going to errode the muzzle somewhere past 10,000 rounds, because L-O-N-G before that happens the throat will become erroded accuracy will fall off and I'll either replace it or the entire rifle.

On my 223Rem bolt rifle if I don't need to intentionally "throw" one bullet slightly out
so I can SEE the single hole in the target getting bigger then that barrel is going to get replaced sooner rather than later.

I can and have (as recently as saturday) fired 20 shots into a group that I can cover with a single postage stamp


On my 30-30 winchester OTOH if my bullet holes in a target equal the number of empty cases on the bench I'm happy (This rifle has a peep sight on it)

But the simple fact is that sport shooters will keep inspecting the throat and toss it at the first serious sign of throat wear OR the slightest increase in group size.

the military tests cited didn't use scopes
they used peep sights... their definition
of "precision" and our meaning of "precision"
are so different as to defy meaningful comparison.


For most of us 8000-9000 rounds BEFORE muzzle errosion is noticable that rifle barrel will find itself being used as a prybar.

so at what point that muzzle errosion would be accelerated due to the use of boat tailed bullets is so moot a point as to defy any logical reason for you to continue to argue about it.

so in the context in which I answered the question my answer was and remains correct...


You ASSume I'm saying you are wrong.
I'm not, I'm saying your point is irrelevant.


AD

/

In trying to not be too negitive I most sincerly pray that some of the posters on this thread will marry extremely beutifull younger women that take up enough of their time so they do not have the time or energy to argue about things that matter very little.

quote:

"The magic number seems to be that once you have about .003 of throat wear on a standard barrel or .002 on chrome-lined, the barrel is shot, and that holds true for any precision-shooting rifle. That has been my experience over decades of testing with a multitude of varmint calibers from factory offerings to wildcats." Ralph M. Lermayer

Interesting to note was how accuracy fell between 750 and 1,000 rounds; coinciding with erosion measurements between .003 and .0035 with a .223 WSSM and .22-250 Rem.

For more details, you can see the full text here ... http://www.gunhuntermag.com/features/051213Shot.htm

Warrior

Allan,

As I have tried to explain, the issue of throat erosion is actually an issue with the THROAT BURNERS, and that is regardless of which bullet is being used. This is the main thrust of the problem or the emergence of the condition that is ecountered much sooner than what we like. Sure your .30-30 Win and 30-06 Spr is not in this category. I quess it is an issue if one gets about a quarter or an eight of the shots from your stated 8,000 to 9,000 shots. I can list a host of cartridges that fall under the category of 'Throat Burners'. With money nothing in the world is a problem for some.

Warrior

The Theory of the Motion of a Bullet About It's Center of Gravity in Dense Media, with Applications to Bullet Design

Never mind. Thanks anyway.
Came right up with a Google.

Report Date 14 Jan 1930
ARMY BALLISTIC RESEARCH LAB ABEDEEN PROVING GROUND MD

Old hat.