185-gr SWC, Chap. 6: A Brief Trial with 2400

[pitted bore]

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.

[pitted bore]

Part 2

The rifle held together, so neither calls to 911 nor blood transfusions were necessary.

The chrono readings with 2400 powder were

38 grains . . 2370 fps
39 grains . . 2488
40 grains . . 2498
41 grains . . 2576
42 grains . . 2614

There were no signs of excess pressure. Case heads showed no expansion when measured immediately in front of the extractor groove.


These results were encouraging, so I loaded up another series in the same set of five cases, starting at 43 grains. The results were these readings:

43 grains . . 2621 fps
44 grains . . 2784
45 grains . . 2763
46 grains . . 2812
47 grains . . 2851

Again, there were no suprises, and within expected and normal variation, increasing powder charge resulted in an increase in velocity.

For the last three loads, my initial indicator of higher pressures showed up. As described in Part 4 of Chapter 3, there is a slight burr on the bolt face that produces a scrape on the case head, indicating when cases expand enough to lock into the chamber and not rotate with the bolt during the initial opening. Even though the scrape appeared, the bolt opened with the usual effort, extraction was normal, and primers were not excessively flattened with any of these loads.

There was some case head expansion immediately in front of the extractor groove with this series:
43 grains . . 0.0004"
44 grains . . 0.0003"
45 grains . . 0.0008"
46 grains . . 0.0005"
47 grains . . 0.0007"

This is only about half the maximum expansion that Wildcatter tolerates, but I decided to quit here, at least for the time being. There are other powders and tricks to try before seriously tipping the powder bottle. Too, at 47 grains the case is getting pretty full, and I don't know how 2400 reacts to being compressed. I decided not to push things further with more 2400 powder.

It's sort of curious that my max loads with 2400 and Blue Dot ended at nearly identical velocities of 2851 and 2859 fps.

I think I've run through the possible fast powders. Depending on which burn-rate list you consult, there are very few powders between 2400 on the fast side and 296/H110/Lil'Gun on the slower side. Accurate No. 9 is considered by some to be slower than 2400 and by others to be faster than 2400. VVN110 is consistently listed between them, but it's scarce locally.

I've likely omitted necessary information. Please ask for it.

--Bob

[MudBug]

Good stuff.

I'm kind of at a loss here about how to save this info.

I think that as soon as I install the new knowledge base I'm gonna have to start handing out permissions for you guys that work so hard on developing this information and give you a place to put this stuff so it doesn't get lost and everyone can find it.

[wildcatter]

Part 2

The rifle held together, so neither calls to 911 nor blood transfusions were necessary.

The chrono readings with 2400 powder were

38 grains . . 2370 fps
39 grains . . 2488
40 grains . . 2498
41 grains . . 2576
42 grains . . 2614

There were no signs of excess pressure. Case heads showed no expansion when measured immediately in front of the extractor groove.


These results were encouraging, so I loaded up another series in the same set of five cases, starting at 43 grains. The results were these readings:

43 grains . . 2621 fps
44 grains . . 2784
45 grains . . 2763
46 grains . . 2812
47 grains . . 2851

Again, there were no suprises, and within expected and normal variation, increasing powder charge resulted in an increase in velocity.

For the last three loads, my initial indicator of higher pressures showed up. As described in Part 4 of Chapter 3, there is a slight burr on the bolt face that produces a scrape on the case head, indicating when cases expand enough to lock into the chamber and not rotate with the bolt during the initial opening. Even though the scrape appeared, the bolt opened with the usual effort, extraction was normal, and primers were not excessively flattened with any of these loads.

There was some case head expansion immediately in front of the extractor groove with this series:
43 grains . . 0.0004"
44 grains . . 0.0003"
45 grains . . 0.0008"
46 grains . . 0.0005"
47 grains . . 0.0007"

This is only about half the maximum expansion that Wildcatter tolerates, but I decided to quit here, at least for the time being. There are other powders and tricks to try before seriously tipping the powder bottle. Too, at 47 grains the case is getting pretty full, and I don't know how 2400 reacts to being compressed. I decided not to push things further with more 2400 powder.

It's sort of curious that my max loads with 2400 and Blue Dot ended at nearly identical velocities of 2851 and 2859 fps.

I think I've run through the possible fast powders. Depending on which burn-rate list you consult, there are very few powders between 2400 on the fast side and 296/H110/Lil'Gun on the slower side. Accurate No. 9 is considered by some to be slower than 2400 and by others to be faster than 2400. VVN110 is consistently listed between them, but it's scarce locally.

I've likely omitted necessary information. Please ask for it.

--Bob

Great Job Doc! I might suggest that you make a sacrificial case to determining the amount of compression, which can be reused . One way I do it is to drill out a primer pocket with say a 1/4" drill. Seat the bullet normally and then fill the case in through the new now unusable, but for this excercise, flash hole. I then place the case between my thumb and forefinger, facing up, so as to not spill any powder and closing off the new fill hole with my finger. I use the back of a table knife, it works better than most other tools, and begin to tap the side of the case. After say a dozen taps, I refill the case and repeat the process many times, until I can't put in any more powder into the case and the powder is slightly heaped up on the face of the base of the cartridge. Weigh this charge, for it is now the charge for a nicely compressed with your chosen OAL, but not an overly compressed load. Most compressed loads contain more powder in them than this method determines, which is why I like it on the bench... As for your case expansion, I'm looking at more expansion from factory loads, so you've got a ways to go before you get into any real problems. Keep in mind that we are dealing with a modern rifle case, at modern rifle pressures, that typically is at 63,000psi in the 6.5/284 SAMMI spec. as opposed to those other big bore AR's that are using the 50AE PISTOL case and are pushing the limits at 35,000psi. Good luck and I hope to see your work yield 3000fps+ soon..