From: sfaber@intgp1.att.com
Subject: [AMMO]steel vs copper jackets
Organization: AT&T

In a recent experiment I loaded 2 sets of 4 -  30-06 rounds
where the only difference was one set had 150 gr M1? ball
copper jacketed bullets and the other set had 150 gr steel
jacketed bullets of the same dimensions.  The powder was
45 grains of powder from '42 '06 rounds (loaded to 52 gr)
that looked like 4895.

These were shot from a Garand with a strain gage and showed:

steel   33K psi    2270  ft/sec
copper  36K psi    2300  ft/sec

The steel gave a significantly lower mean pressure (pressures had
about a 5% std deviation.)

The powder gave lower pressures and velocities than LC '69
Garand ammo that is loaded with 44.5 grains of presumably 4895.
These give me around 41K psi usually, but then it was a cold day.(28degF)

I was expecting the steel to give higher pressures due to
the increased engraving force, but it didn't.
Maybe the softer jacketed bullet deforms from pressure before
it hits the rifling and results in a higher engraving force,
or maybe the base pressure is better translated to a normal force
against the bore resulting in more friction for the softer bullet.

Steve

From: sfaber@intgp1.att.com
Subject: steel vs copper jacketed bullets
Organization: AT&T

Previously I posted a note about finding that old steel jacketed
150 gr 30 cal bullets gave lower pressure loads than those using
identical looking bullets with copper guilding metal jackets.
I assumed the steel jacketed bullets would be harder and had to
stretch to think of why they would not have produced higher pressures
given they would take more force to engrave into the rifling.

I happen to have come upon a hardness tester and measured the hardness
of both bullets and found that the steel jacketed ones were actually
softer which would logically account for why they gave lower pressures.
The hardness measurements sometimes varied with the penetrator
pressure used with the hardness tester since at higher pressures
the jacket gave way over the underlying soft lead.
The steel bullet had a hardness of 105 brinell at 15 kg force
and 66 at 30 kg.  The copper jacketed showed 135 at 15 kg decreasing
to 100 at 45kg.  A 1942 150 gr ball from a 30-06 military round
gave a hardness of 130 brinell that held up at 45 kg indicating
it probably had a thicker jacket or harder core.

type	15 kg	30kg	45kg

steel	105	66
Cu	135	125	100
'42 Cu	130	127	130


Steve

From: sfaber@intgp1.att.com (Steven R Faber +1 708 979 3147)
Subject: Re: Stability of Military Rifles (was: Re: Japanese World War

In article <3cj490$2hu@xring.cs.umd.edu>,
K. Karcich <kkrh@troi.cc.rochester.edu> wrote:
#In <D0op07.5q1@vcd.hp.com> johno@vcd.hp.com (John Ongtooguk) writes:
#
##K. Karcich (kkrh@troi.cc.rochester.edu) wrote:
#
#I am the last person to call Arisaka's junk. In fact I like and admire the
#action and acknowledge that they are very strong. But your original post
#offered the "proof" of swedging down of a 30 cal bullet to 6.5 as evidence
#of the strength of the arisaka. In fact, there is little evidence to support
#the fact that the resizing of a bullet, even to this extent, greatly
#affects a given pressure level. As stated, and as shown by Ackley and others,
#who have done extensive distructive testing of actions, the resizing of a
#oversize bullet occurs long before the pressure in a given load peaks. This
#means that the only thing which affects pressure is the quantity and rate of
#burn of the powder and the resistance of te bullet to being accelerated. These
#authors maintain that the same load, in the same case behind a bullet of the
#same size and weight and diameter as the resized bullet, will produce the
#same pressure. Essentially the resizing effect is a negligable contribution
#to the pressure generated by a given load. This is why I stated that the
#test as offered was meaningless as stated, without supporting pressure
#crusher data. I stand by that statement.
#
#regards, Ken Karcich
#
#BTW, just as food for thought, other actions that are in the class as the
#arisaka are surprising: the Italian Carcano and the Moisin-Nagant. Both
#of these designs will take more than the favored conventional mauser types,
#and interesting enough, both are in the maligned "junk" catagory.


The bullet engraving resistance can have a substantial effect on peak
pressure from looking at internal ballistic calculations, but as you
increase the engrave force or shot start pressure level, the velocity
increase tends to level off.  I don't have a 6.5mm Arisaka, but do have
a 7.7mm, so I used the dimensions and case volume for the 7.7mm to
do a simulation of the effect of engrave force.
The load was 42gr of imr3031 with a 150 gr bullet.
A constant 50lb bore resistance was used.
The burn rate was assumed to be linear with pressure.
The engrave force was assumed to start immediately and continue for
the length of the cylindrical portion of the bullet (.47 in.).
The resultant pressures and velocities are a bit higher than actual
partly because the engrave force doesn't start until after freeboring
a ways and leaking some gas, but this will give an idea of the effect.

engrave force 	Pressure (Kpsi)	  velocity

50  lbs		41.1		2578
300		55.7		2707
700		72.9		2797
1000		84.4		2836
1300		95.2		2860


Steve

From: sfaber@intgp1.att.com (Steven R Faber +1 708 979 3147)
Subject: Re: Stability of Military Rifles (was: Re: Japanese World War

In article <3cr5tl$nuk@xring.cs.umd.edu>,
K. Karcich <kkrh@troi.cc.rochester.edu> wrote:
#In <9412141650.AA14122@ig1.att.att.com> sfaber@intgp1.att.com (Steven R Faber +1 708 979 3147) writes:
#
#
##The bullet engraving resistance can have a substantial effect on peak
##pressure from looking at internal ballistic calculations, ....
#
#Its not clear to me that the engrave force is linear for the movement ( re
#sizing ) of the bullet or that the burn rate is linear. However, pressure
#gun tests reported by Ackley, Vol II, page 76 are as follows:
#
#"another .30 cal pressure barrel was fitted to the test gun, but the neck
#and throat were enlarged to accept the 8mm bullet, with the bore remaining
#the standard .30 caliber. A Remington factory 30-06 cartridge with the 150
#grain bullet had been previously tested and gave 57,300psi for a velocity
#of 3030fps. Then the bullets were pulled from two more Remington 150 grain
#, 30-06 factory cartridges and were replaced with 8mm, 150 grain bullets. To
#everyones surprise, although the velocity was rather erratic, these loads
#averaged 2901 fps with a pressure of 40,700psi."
#
#If you chose to dispute these results, you will have to explain to me why the
#germans could modify 8mm .318 barrels to fire a .323 bullet in some guns,
#merely by enlarging the throat, but not the bore....or how ruger, in this
#age of liability could put on the market a gun like the mini-30, which
#could be expected to be used with milsurplus eastern block ammo with .310-
#.311 diameter bullets and provided that gun with a .308 bore? Surely you
#are not going to suggest that their lawyers would have let them do this,
#unless their pressure data had not backed up that position rather conclusively?

Won't disagree with that :).  Interesting examples.

I think it would still be dangerous to conclude that engraving forces
are not important in determining peak pressure.  There are other factors
entering in here, particularly the nature of the throat.  When the throat
is enlarged or lengthened - it can have a big effect both due to the
extra distance the bullet moves before encountering the large resistance
and the extra time for gas to blow by before being sealed while engraving.

Here is a simulation of a 30-06 with 150gr bullet and 49gr of imr4064:
The bullet pull force was set at 20lbs.  Engrave length is .48 in.

Freebore	Engrave Force	Pressure	Vel
.14 in.		350 lbs		52.0 Kpsi	2752
.14		700 		60.5		2797
.14		1000		69.6		2830
.3		700 		53.3		2740

This shows that increasing the throat length a little has quite
an effect on pressure and it doesn't even include the effect of
gas leakage, which would reduce it more.
These effects could then explain your above examples.

Steve Faber