Date: 28 Jul 94  08:20:35
From: Ed Harris
To:   Henry Niemi
Subj: smokeless powders

In a message of <Jul 24 14:21>, Henry Niemi (1:143/220) writes: 
 HN>1.  For equal muzzle velocity, would a single base powder burn cooler
 HN>than a double based one?  I am trying to choose the coolest burning
 HN>loads in 223, 308, 30-06 to prolong the life of my barrel. The question
 HN>arose after I read an article (by WC Davis Jr. ?) in NRA book
 HN>"Handloading" which said that Winchester powders (2-base) burn cooler
 HN>than most IMR (1-base), which seems to contradict what I have read so
 HN>far.

At the same chamber pressure the double-base would be cooler.  You may be able 
to reach the same velocity at lower pressure with some double-based powders 
than with IMR, but it would probably require a somewhat heavier charge weight 
of a somewhat slower powder.  W748 works well in the .223 and .308, W760 in 
the '06 for boltguns, or for the M1 with 150 - 168gr. bullets if you do not 
load to higher than Ball M2, or Match M72 velocities. 
 HN>2. Does it matter that much if gun powders are made of cotton
 HN>linters instead of wood pulp/cellulose?

Not as far as flame temperature, but the cellulose from wood linters makes a 
nitrocellulose base material which is of somewhat less energy, due to less 
efficient nitration, so to keep up the specific energy they tend to reduce the 
amount of deterrent, which has the effect of increasing the burning rate.  
Therefore, IMR4064 you buy today burns like IMR4895 made prior to 1976, 
whereas the 4895 behaves more like old 3031.  As long as you don't use old 
data with current powder you won't get into trouble.  For instance with "old" 
4895 you could load 42 grains with an M118 bullet, but you exceed max pressure 
with about 40 grs. today.  To approximate M118 ballistics with pulled GI match 
bullets you have to use 4064 to match velocity and pressure. Similarly with 
.30-'06, 4064 is a better match to approximate the velocity and pressure of 
Ball M2 and Match M72.

 HN>3.  Can you share your knwoledge about deterrent coatings on smokeless
 HN>powders ? Why different mfg use different coatings (graphite, DNT,
 HN>Centralite, and the one used by Scot and AA whose name I forgot,
 HN>diamyl-something).  Bob Forker used to mention them in his

Graphite has no deterrent value, but is only to reduce static charges.  

Dinitrotoluene (DNT) is used on IMR-type powders, 

Dibutylphathalate (DBT) is used on Olin Ball powders

Dienthyldiphenylurea is the basis for most of the "Centralite" deterrents used 
in European practice.

Camphor used to be used in very early European powders, but is less chemically 
stable over long storage than the others, so is seldom used today, except in 
some of the Chinese powders.

The relative benefits of one coating over another are really fairly complex as 
they apply to the manufacturing process.  The DNT and Centralite coatings are 
hard and stay mostly on the surface of the base grain, which helps to give 
some mechanical strength to the grain.  DBP used in Ball powders actually 
penetrates into the base grain, and this function is important to make this 
grain form burn progressively.  The web thickness and geometry of the grain 
are controlled by rolling, and the percentage and penetration of the deterrent 
into the grain must be carefully controlled.  Davis's article talks about this 
in more detail, and he really knows a alot more about this suibject than I 
ever will.



In Home Mix We Trust, Regards, Ed

 

--- msged 2.05
 * Origin: Home of Ed's Red (1:109/120.3006)
 

