From: sfaber@intgp1.att.com (Steven R Faber +1 708 979 3147)
Subject: Re: "HIGH-PWR" Loads, Waters method

#I do not understand why (if?) Waters' method works.
#
#A standard full-pressure .308 round in my Model 70 target rifle swells
#my chamber by .00203" in circumference (515 microstrain).  Since the breech
#diameter is 1.255", the outside diameter grows by 0.00065" (just
#over half a thou).  The inside diameter at that point is 0.464" (roughly
#the mid section of a .308 case body) - it will swell by 0.00024".
#
#In other words, maximum safe pressure in a .308 will increase the
#chamber inside diameter by 2.4 tenths of a thou - 0.00024".  This
#pressure is in the 55,000 - 60,000 psi neighborhood.
#
#A proof load is about 75,000 psi.  This is 25% more pressure than a
#safe max load.  It will result in chamber i.d. growing by 25%, from
#0.00024" to 0.0003" - half a tenth of a thou, roughly.
#
#A standard micrometer reads to a tenth of a thou.  It would be relatively
#challenging to discern a change of half a tenth - and this is the
#difference between a safe load, and a proof load!

A note from John Bercovitz suggested we compute the strain on the inner
wall of the chamber.   The inner wall will have a greater stress on it
than the outer wall.  The above calculation assumes the inside diameter
grows by .24 mils when the outside diameter grows .65 mils (proportional)
but this assumption warrants a recalculation.  Since as John says, the
volume of the steel is constant, the outside diameter growth would be less
than the inside diameter increase.

This was recalculated using Roark's formula for stress at the inner wall.
(We did use the right Roark's formula for stress at the outer wall.)
I computed it for a 50000 psi pressure in the chamber ( which would make it
about 56000 psi load inside the cartridge, given the pressure the case holds).
This gave the following results:

strain at outside         - 460 microstrain
outside diameter grows    - .58 mils
inside diameter grows     - 1.22 mils

The maximum stress on the chamber is on the inside wall and is
65,800 psi.  S = P*(a^2 +b^2)/(a^2-b^2) .
This is a design parameter for making guns.

The result shows the inside diameter grows appreciably more than the
original calculation indicated.
Next, the amount of spring back of the brass case could be figured, and
similar calcultions could indicate when the case would start to be stuck
in the chamber.  I think Waters method still suffers from a lot of potential
error, given a .1 mil resolution and the effect of the spring back of the case
and chamber.

Steve Faber

From: sfaber@intgp1.att.com (Steven R Faber +1 708 979 3147)
Subject: Re: "HIGH-PWR" Loads, Waters method

Here is an update on the Waters method calculations.
To review, the Waters method measures the "pressure ring" diameter
just behind the case head to tell when the pressure of a load becomes
excessive.   The theory was that when this diameter stops growing or reaches
a .5 mil increase over moderate loads, that it signals that the pressure
is getting too high.

Last time we calculated the inside diameter expansion due to
50,000 psi on the inner chamber wall.  Now I'll add some more pressure
points and calculate the amount of spring-back of the case.

The case will expand from its original dimensions (sized) until it
reaches the chamber wall.  The brass will stretch according to its
modulus of 16e6 psi until the yield stress is reached, after which the
pressure it supports will stay relatively constant with further elongation.
I found a chart of yield stress vs. hardness for cartridge brass in the
book "Sniper Loads".  I also measured the hardness of the mid section of
some 30-06 and .223 cases with a Rockwell N-T tester and found they were
at 160-165 brinnell.  This corresponded to a yield stress of 58K psi. (at .5%
elongation).
The case stretch at the yield point would then be 58000/16e6 = .36%.
The thin wall vessel pressure formula then predicts a 30-06 case would hold
5,400 psi given a .021 in wall thickness.
The .308 case at .464 in diameter would stretch 1.67 mils.
Given that there is at least this much clearance for the case to stretch
I claim that the pressure at the chamber wall will be lowered by an amount
similar to what was calculated for the 30-06 (even when it is at the yield
point and touching the wall, Gary ).
Then when the pressure is released it should spring back by 1.67 mils.

Here are some chamber ID expansion distances vs. pressure at the chamber wall
using a .47 in estimate for the diameter near the case head.

50,000 psi 1.25 mil
60,000	   1.50
65,000     1.62
68,000     1.70
69,000     1.72
70,000     1.74
75,000     1.87

This shows about a .25 mil increase per 10,000 psi.
The point where the expansion equals the spring-back of the brass is
at 68,000 psi or so.   At this point or beyond the case would be stuck
and the bolt lift would be hard.  I don't know how much bolt lift resistance
one would get as you approach the zero clearance point due to dirty chamber
effects, but you might notice a sticky bolt before that point.
A quick look at Daniel's tests show that he experienced signs of bolt
sticking around 63,000 psi with heavier bolt lift at higher pressures.

In summary, the results are consistent with Water's observations of a
.5 mil increase if you go from say 45,000 psi to 65,000 psi.
The increase should also stop when you reach the 68,000 psi point.
(For chambers of these dimensions).

The sticky bolt lift probably makes a better high pressure indicator, since
it seems to be noticable somewhat gradually before the stuck case point,
where this is probably not the case with the Water's method.
It would also be inconclusive to judge what pressure you are at by some
absolute amount of pressure ring expansion, since it would be relative to
the starting pressure, which you probably don't know.


Steve Faber

From: sfaber@intgp1.att.com (Steven R Faber +1 708 979 3147)
Subject: re: "HIGH-PWR" Loads, Waters method

#
#(.. written by Daniel Chisholm)
#
#Steve, it's been a while since I read Waters' method; my recollection
#of his method was to take a box of new factory ammo, and pull the bullets
..

Thanks for clarifying the Water's method.  I just caught the tail end
of some of the posts on it.


#>The point where the expansion equals the spring-back of the brass is
#>at 68,000 psi or so.   At this point or beyond the case would be stuck
#>and the bolt lift would be hard.  I don't know how much bolt lift resistance
#
#Bolt lift may become hard before this point.  Brass flowing into the
#extractor, for instance, will cause a stiff bolt lift.  But when the
#pressure finally reaches a level such that the chamber spings back more
#than the brass, there will start to be sticky _extraction_ problems.  This
#may manifest itself as stiff bolt lift, because most bolt actions have
#some camming action to assist extraction.

Good point, so the brass will start flowing at its yield point of around
58K psi causing stiff bolt lift due to that.

...
#
#In the case of a bolt face that did not have an ejector, or perhaps an
#action with a smaller diameter ejector, this pressure sign would be
#absent.  It would be interesting to ask Toby Bradshaw about pressure
#signs in a benchrest action (which uses no ejector).  Is there any
#stickiness in bolt lift, or difficulty in extraction, or does everything
#remain easy to operate up until the point of blowing primers?
#I know that in my .223 bolt gun, I'll blow a Federal primer before any
#bolt-lift stickiness is observed.


I noticed the flow into the ejector hole of an AR-15 occured above
45K or so on our scale.  It seems our pressure estimates are low on
our .223 guns, also considering the pressure where your primer blew.
I wonder if the chrome plating on the chamber affects this? :)
The chambers are relatively thicker on these guns, so the stuck case
point will be quite high - I'll have to calculate that.
I finally did some pretty hot loads in the AR - up to 550 microstrain
that caused a fair amount of flow into the ejector hole.  One even
jammed probably due to the difficult bolt twist similar to what you
related above.

Steve

From: sfaber@ihlpb.att.com (Steven R Faber)
Subject: Re: Pressure Signs, Favorite Loads
Organization: AT&T

#From article <54304@mimsy.umd.edu>, by vanetten@unix.cie.rpi.edu (John S. Van Etten):
# Eric E. Snyder writes:
#
# [stuff deleted]
#
# #Am I missing something important and perhaps things are really hotter
# #than they appear? If not, is it unreasonable to exceed the maximum loads
# #if one does it in small increments and continues to look for excess pressure
# #signs?

I tend to agree that the  .223 factory ammo seems to be hotter than any
maximum load I've seen in a few reloading books.
The WW cartridges I've taken apart exeed the Win. reloading guide load
by about 1.7gr if I remember right.  Of course it could be the
factory load powder is different than WW748 which it resembles.

The PMC ammo I've used is even hotter, and is filled with an even
greater charge of a similar ball powder.

#
# with the XP-100 guru ;-).  I'm posting instead of replying directly to
# you as I feel it is of general interest and is a safety issue.
#      UNDER *NO* CIRCUMSTANCES SHOULD THE MAXIMUM PUBLISHED LOADS BE
# EXCEEDED!

But whose published loads?  The books can vary considerably and many
like to err on the side of a more conservative load.
On the other hand you can dig up some old manuals that show pet loads
that that can definitely be dangerous.
Some books use test barrels which are tighter than many actual rifle
barrels, and some don't always give the bullet seating depth.
Seating depth variations can cause a 25% variation at least and
the barrel differnces could easily be a 20% factor.
Differences in the chamber throat dimensions can cause more variation
than the barrel.
If you change bullet brands or especially if you go from a boat tail
to a flat base, even if it is the same weight it can increase the
pressure a lot because of reduced gas leakage.

You need to compare and weight the  published loads closest to your
own conditions most heavily, but even so, my point is there are a lot
variables that can affect your own results.

#  Visual checks for flattened primers and other methods of
# case inspection are poor indicators that pressures are too high.
# Trust the men with the copper-crusher gauges that have done the
# research and published the numbers.  They have no reason to lie (they
# get to sell more powder if you use more ;-).

I agree that primer flattening is not a reliable indication of any
absolute level of pressure.  Primers differ a lot in stiffness,
so to compare you would have to have the same primer.
It makes you wonder, though, when Win. factory ammo has a lot more
flattened primers than your hottest reloads do using Win. primers,
and the factory loads also use more powder and get higher speeds, that
maybe you can safely increase the power of your reloads.

Also the crusher method is quite error prone which could account
for discrepancies between some published loads.

Steve

From: Norm Johnson <njohnson@nosc.mil>
Newsgroups: rec.guns
Subject: Re: Pressure for .45-70
Date: 15 Apr 1997 22:53:54 -0400

C.H.,

At 07:08 PM 4/14/97 -0400, you wrote:

#> Please give us the details of the above.  The nature of the physics of
#>the beast would seem to preclude such possibility.

# I kind of agree with you it don't sound right does it. That is what JD
#says in his loading data, they don't exceed 31,200 psi. He also says not to
#use SSK load data for factory bbls (T/C), his load data runs about 10%
#higher than the load data for the older guns which factory loads are for.
#They are about 10-12% lower than the 35,000 CUP loads for strong bolt
#actions and >the Ruger #1.

#I do know that his chamber is a lot longer than the SAMMI spec. I
#shoot 500 gr bullets in my bbl now and they would not work in the factory
#bbl.

The above statement gives a good clue to what is going on.  When a sizeble
freebore is employed, greater powder charges can be used because the bullet
gets a good running start before it hits the rifling lands.  This results in
the cartridge generating less pressure than it would if there were little or
no freebore.  At the same time, because more powder is burned, its total
energy output is greater, so higher velocities result.  Roy Weatherby
recognized this, and a good part of his success with the (then) ultra-high
velocity Weatherby cartridges was due to very ample chamber freebore.

#and that is 1340 ft/sec with 405gr bullet. JD's loads do around 1625 ft/sec
#with his loads on the 400gr speer which is max. I don't go past the max as
#the recoil is stiff to say the least. This data, I think is base on the
#case expansion technique and measurement.

Knowing the above, this increased velocity is understandable.

# What I implied by "not showing typical preasure signs" by the time a
#primer starts to flatten or the case head exspands to show high preasure
#the 45/70
#case head is so large that you have over preasured the Contender frame. I
#have one that was stretched a little, and I never saw a sticky case flat
#primer and was only getting about .0008-.0009" expansion on the cases. I
#can see the wavey look at the standing breech and frame juction. I still
#shoot it but with lesser loads.

WHEEEEEEE!!!  I have taken my Contender .45-70 to .002" over the fired
factory pressure ring using maximum loads taken from the Contender Loadbook.

However, there is expansion -- and there is expansion -- and there is
expansion!  If you are speaking of CASE HEAD expansion, that is one thing.
If you are referring to PRESSURE RING expansion, it is another.  And if you
are speaking of expansion of the (fired) pressure ring over that of the
factory loaded round or reload, as opposed to that over the FIRED factory
load, it is still another.

                ***********************************

There are two approaches to practical pressure measurements
(really comparisons, since most of us have no real measurement
facilities) that have been used by the ordinary reloader.

The first is to measure the case in the web area (or the belt, in
the case of belted magnums) before and after firing.  Maximum
pressure allowed is generally agreed to have been reached when
the web area measures .001" greater than that measured after
first firing of the factory loaded ammo.  This is the method that
I used in the years before I became familiar with the writings of
Ken Waters.

The above method, while satisfactory in some aspects, is not ideal for
the reloader who uses his cases for a number of reloads.  Meas-
urement of the web most often requires a micrometer with a blade
anvil since the web on most cases is narrow enough that the
barrel anvil of standard micrometers is too wide to make that
measurement - the rim and the enlarged pressure ring get in the
way.  I spent over a hundred dollars on one of these micrometers
that I used in my pre-Waters years.

Since dies do not size the web back to spec, once the .0001" maximum web
expansion is reached, these cases may not be used for further pressure
comparison testing.  In addition, cases (webs) tend to grow gradually over a
number of firings with loads that are at or near maximum so false indica-
tions may be encountered.

The above method also suffers from the possibility that when
pressures are great enough to expand the web, some old firearms
may be damaged or destroyed.  I used this method only for modern,
high pressure equipment.

The second method is that advanced by Ken Waters and that which I
have touted here too many times to count.  It uses the pressure
ring, that area immediately ahead of the web.  This pressure ring
is swaged back to near its factory specs each time it is resized;
and that is true even for those of us who only partially (say
90%) resize as long as a full length die (as opposed to a neck
sizer) is used.  It is also less dependent on brass hardness
because the brass is so thin in the pressure ring area.

This method is usable for any firearm with which I am familiar.
Allowed (maximum) expansion of the pressure ring depends on the
cartridge and the gun in which it is fired.  Ken Waters gives his
guidelines for this judgment in his excellent pressure article
"Developing Pet Loads, Ken Waters' Methods for Judging Pressure",
a reprint from the September 1982 issue of Handloader magazine,
available from Wolfe Publishing, 6471 Airpark Drive Prescott, AZ
86301 (602) 445-7810.  It is also reproduced in his collected
series, "Pet Loads".

His article is a thorough dissertation on pressure comparison and
control.  It is invaluable for developing loads in that it covers
the signs to watch for in order to stay out of trouble and dis-
pels some old wives tales that seem to persist.

Wolfe Publishing
6471 Airpark Drive
Prescott, AZ 86301
(602) 445-7810

Same address for Handloader and Rifle Magazines

I have not gone to the range in more than 20 years without my
micrometer.

            ********************************************

#As far as Ken Waters I am not upon who he is. Did he design the 7-30 >Waters?

Yes, that is his design.

I have used his pressure comparison method to develop loads for otherwise
unused powder combinations while getting the most out of the bullet/powder
combination without blowing my head off.

God Bless!

Norm

From: Norm Johnson <njohnson@nosc.mil>
Newsgroups: rec.guns
Subject: Re: Pressure for .45-70
Date: 15 Apr 1997 22:55:54 -0400

At 05:15 PM 4/14/97 PDT, you wrote:
# the tc comes in 30-30 has more pressure than the 45-70 but has about >the
same size head.  i think the big head spreads the pressure out over a
#larger area than the 223.
#all my barrels that were rechamber by Bower uses 356 or 307 or 444marlin
#brass has a head of about .500 and working pressure around 40,000 to 44,000.

Alan,

Back thrust on the Contender has little to do with the "case head" diameter,
if, by that you mean rim diameter.  Rim diameter of the .30-30 is .506"
while that of the .45-70 is .608".

It is, however, the internal diameter of the respective cases that dictates
their pressure limits when used in the Contender.  This is because the
pressure (psi) generated in the case exerts a force (pounds) against the
inside of the case head.  This force, at a given pressure, is dependent only
on the internal diameter of the particular case and is not in any way
influenced by the rim diameter.

For example, let's assume that the peak pressure of a safe .45-70 load is
28,000 psi.  The inside diameter of the .45-70 case at the base is .460".
This calculates to an area of .166 square inch.  At 28,000 psi, a force of
4,653.33 pounds is generated against the case base which must be withstood
by the Contender frame.  There is some reduction of that force due to the
case gripping the chamber wall but it is small compared to the numbers that
we are talking about here.

Now, we can gain some insite into what the peak allowable pressure would be
for your .30-30 cartridge when held to that 4653 pound back thrust limit.

The .30-30 case has an internal diameter of about .375" and an area of .110
square inch.  In this case it would take 42,303 psi to generate that 4,653
pound thrust,  This is consistent with normal safe .30-30 loadings which are
in the 38,000-40,000 psi range.

We can further extend that to the .223 to see that, with an internal
diameter of .330" and an .086 square inch area, it would take 54,104 psi to
apply 4653 pounds back thrust; right on for .223 loadings.

GREAT design, that Contender!!!

God Bless!

Norm