Powder density

[chasw]

I stumbled across a table you all are probably already familiar with, the Lee Dipper Capacity Chart. Someone spent a great deal of time compiling this data which is useful to determine the density of a particular gun powder, including black. Column 4 of the table is the weight in grains of Lee's 1 cc powder scoop, for the 3 powders I'm currently working with to develop a CB load for my Swiss K31, 7.5X55mm. The bullet is an NEI DD (double diameter) design, 186 grains with gas check and lube, sized to .308".
SR4756 - 9.1 gr
IMR4198 - 12.6 gr
RL7 - 13.7 grains

I started the thinking process (designing experiments) by fussing once again about air space in my CB rifle loads. However, in checking Lee's numbers, I notice something interesting. All of my loads for the 7.5X55 Swiss come close to 2 cubic centimeters by volume. Each is a modest amount below what others would consider maximum for that cartridge. From this new understanding, I'm now thinking the choice of powders for CB loads should take into account two parameters:


How fast do you want to propel the bullet? The slower powders will drive em faster, no question. 4756 only got to about 1550 fps, while the others were up around 1800-1900 fps. If you go fast either the alloy has to be very hard and brittle, or leading develops as you exceed the tensile strength of the bullet material. Some people have mastered the speed challenge, but I think I'll stick to around 1800 fps or less.

The ideal powder, then, is easy to ignite and thereby fires the same regardless of position. By easy, I mean easier than other powders with the same burning rate and energy content. Such a powder, spread out along the length of the case, with open air above, should be conducive to consistency, I'm thinking.


My problem is lack of good information about the relative easy of ignition for powders typically used in CB rifle loads, the medium-fast numbers like 4227, Benchmark, BLC2, H335, 4198, RL7 and 3031. Is there a good source for this kind of info. Do any of you have any particular rifle powders you have found to be "easy to ignite"? Thanks much - CW

http://www.google.com/url?sa=t&source=web&ct=res&cd=1&ved=0CAoQFjAA&url=http%3A%2F%2Fwww.leeprecision.com%2Fcgi-data%2Finstruct%2FDippers.pdf&rct=j&q=Lee+Dipper+Capacity+Chart&ei=DCtvS8ieCYzAsgOQr-WyDQ&usg=AFQjCNEavHnTGWvOL06-EGdNDraAszRL4Q

[Doc Highwall]

chasw, welcome to the forum. LEE has in their reloading manual volumetric density per grain of all the powders and the useful volume of case capacity of the cartridges. I use AA5744 a lot for cast boolits with out fillers. As far as slow powders you can also go over the hump like in too slow and the case will be full and have a slow velocity but the cost comes in the amount of powder used read money and the unburnt/consumed left in the bore. I my self am not looking for high velocity but accuracy. In your thread you stated you sized the boolit to .308", what did the gun slug at. You will find that most people get their best accuracy .001"-.002" over groove size.

[runfiverun]

the fast powders ignite easiest. burn the quickest,and raise pressures the fastest.
the key with cast is to keep the boolit within a pressure zone.
if you can put more gas volumn behind it without stressing it the faster you can push it.
as long as you aren't slumping the nose burning up the lube or skipping the rifling.
you can obtain some pretty impressive speeds.

[chasw]

Doc asked: " In your thread you stated you sized the boolit to .308", what did the gun slug at. You will find that most people get their best accuracy .001"-.002" over groove size. "

My one and only H&I die for .30 caliber is marked .309", but when I measure the sized bullets, they come out .308". This turns out to be fortuitous for the Swiss K31 rifle, since its short throat measures .308", I'm told. Groove diameter in my rifle is also .308". Any attempt to load the K31 with boolits sized larger than the throat diameter will result in shaving and degraded accuracy, so they say.

My pet mold for .30 caliber is an NEI DD (double diameter) design. Weight is 186 gr with gas check and lube, in Lyman no 2 alloy. The driving bands are sized right at .308, the forward section is about .296" with a little ring near the nose to center the boolit as it travels down the bore. OAL is set so that little ring just barely engages the rifling. The base of the bullet extends below the case neck. Charge is about 28 grains of RL7 with a Fed 210M primer. Velocity is in the 1800-1900 fps range.

Accuracy in my rifle so far is outstanding, showing some potential for 5-shot groups in the 1" range, at 100 yds. I'm going to cast some more bullets from the same alloy and keep tweaking the charge weight to achieve optimum accuracy. When I get a nice 5-shot group to brag about, I'll post a pic here. - CW