Part 1
(NOTE: I performed the following tests with my bolt rifle, which means that results may be very different if the same trials were carried out on other rifles, especially the usual semi-autos. The barrel has a 1:16" twist and .451" grooves, and I don't have to worry about port pressures or other variables that are important to semi-auto operation. Do not expect my results to occur with any other rifle. Also, don't forget that this information comes to you on the internet.)
As reported on another thread, my chronograph died after generating the data reported in Chapter 5 using BD1's LRP cases. The chrono was 18 years old, and filled with ancient electronics. The new model arrived last week, and I hope to make progress on this 185-grain series before the range gets snowed in.
Now, where were we?
In Chapters 1-3 I reported that maximum loads of powders like Lil'Gun and 296/H110 didn't work well with the 185-grain SWC bullets. It appeared that pressures don't build rapidly enough for proper burning of these powders pushing on a lightweight bullet from the 450b case.. There seemed to be 3 possible approach to making the 185's go faster: (1) Mechanical methods like crimping; (2) Hotter primers; (3) Faster powders.
With BD1's help, I tried hotter primers in Chap 5. That didn't work out as well as expected. I tried Blue Dot, a faster powder, in Chap 4. The pressure got too high before desired velocities were reached. This chapter reports a trial with Alliant's 2400 powder. On many burn rate charts, this powder is slower than Blue Dot, but faster than Lil'Gun and 296. Also, in posts on 17 and 23 July, Siringo reported that a Hornady tech suggested 2400 as a powder for light bullets.
My gunsmith happened to have a container of 2400 in his powder stash. It was pretty old, from back when Hercules was the manufacturer, but it smelled fresh and hadn't seen any high temperatures in storage, so he donated a few ounces to the cause.
I did not load up a large number of cartridges for this initial exploration. Load procedures followed those of previous chapters. I used the same Hornady encapsulated 185-grain SWC bullets and CCI BR4 primers. The cases had been fired 4X, but with lighter loads showing no measurable case-head expansion over new cases. Cases were FL resized with the Hornady sizer and flared a bit with the expander die.
Charges were weighed to the nearest 0.05 grains. The Hornady seating die was set to give a C.O.L. of 2.00 inches. The taper crimp die gave a mouth diameter of 0.476.
A the range, I set the new Pact chronograph with the midpoint of the screens at about 9 feet from the muzzle.
Some of the guys at the range gathered to watch. I made sure they had cell phones for calling 911, and compatable blood types in case bad things happened on ignition.