185-gr SWC, Chap. 4: Blue Dot? Well, Maybe

[pitted bore]

Part 1

(NOTE: My reports here are based on my bolt rifle. Do not expect similar results from any other rifle. Remember, you're finding this information on the internet, where 10-year-olds can describe how they shoot 2-inch 20-shot groups at 800 yards with terminal velocities above 3900 fps.)

The trials described in Chapters 1-3 with 185-grain SWC bullets using Lil'Gun and 296 led me to conclude that these were not ideal powders when loaded with conventional methods. I was able to get muzzle velocities up to about 2900 fps, but with unacceptable variation in velocities. Apparently initial pressures are not high enough to cause an efficient burn of those powders behind the light bullets.

Those trials did show that worry about the possible in-flight disintegration of light-weight bullets in my 1:16 twist barrel was negligible. Accuracy is not yet a concern.

Possible alternatives seemed likely to allow higher velocities: (1) Some mechanical modification that will help initial ignition of the powder, for example crimping. (2) A hotter primer, for example using a sawed-off 284 case with a LR primer, with which BD1 has been working. (3) A faster burning powder.

I decided to try option #3 first.

From a QuickLoad simulation for 200-grain bullets posted 7-18-08 on the calguns thread, a possible candidate in the powder locker was Blue Dot. Wildcatter mentioned somewhere that he'd tried Blue Dot, so I wasn't going into totally unexplored terrritory, except possibly with the use of the 185-grain bullets.

I loaded up a series of one cartridge each of 21, 22, 23, 24, and 25 grains under the 185-grain encapsulated Hornady SWC. (The sample size is small, but this was an initial what-if type of exploration.) Cases were 1x fired. The COAL to 2.000. Primers were CCI BR4.

Because I had no idea of what to expect, I sandbagged the rifle and fired it with a 20-foot string, as described in Chapter 2. As you might expect from the light charges, the rifle stayed together, and no signs of excessive pressure were observed. Sooting on the cases and zero case expansion in front of the extractor groove both indicated pressures were relatively low. Chronograph readings at 9 feet were:

21 grains . . 1549 fps
22 grains . . 1644
23 grains . . no reading (dead chrono battery)
24 grains . . 1796
25 grains . . 1868

The steady increase in velocity with increasing charge was encouraging.

[pitted bore]

Part 2

Because the initial trial with Blue Dot appeared to result in a better ignition, I loaded another exploratory series of five cartridges: 28, 29, 30, 31 and 32 grains of Blue Dot. Again, the sample size is small. The cases were 2X fired, but otherwise followed the procedures above.

I fired these without the sandbags. Velocities at 9 feet were:
28 grains . . 2127 fps
29 grains . . 2163
30 grains . . 2183
31 grains . . 2317
32 grains . . 2414

Again, there were no signs of excessive pressure. However, case sooting stopped with the 30-grain loads. Case heads showed no expansion at the extractor groove.

The trials with Blue Dot seemed to be going well, and worth further increases in powder.

[pitted bore]

Part 3

I loaded another series of increasing charges of Blue Dot using the methods of Part 1 and 2. Cases were 3X fired. The chronograph readings were:
33 grains . . 2523 fps
34 grains . . 2661
35 grains . . 2716
36 grains . . 2718
37 grains . . 2859

The bolt face on this rifle has a small burr at the inside edge of the ejector cut. With normal pressures the burr makes a slight indent on the case head. With the 37-grain load of Blue Dot, the burr made a slight smear on the case head. This indicates that the case expanded sufficiently to lock it into the chamber so that it did not rotate with the opening of the bolt. The case head did not expand into the ejector cut of the bolt face. The bolt opened easily.

Primer appearance of all cases was like that of cases pictured Chapter 1, Part 3, showing no excessive pressure.

Case head expansion after firing was:
33 grains . . 0.0000"
34 grains . . 0.0000"
35 grains . . 0.0006"
36 grains . . 0.0004"
37 grains . . 0.0007"

In my rifle with these loading methods and with me behind the butt plate, this is the end of the line for Blue Dot. It may be well worth trials for accuracy, but the current explorations are looking for higher velocities.

I am aware that I'm trying to read a small number of tea leaves through a very cloudy crystal ball. Primer appearaance, case expansion, case head marks, and bolt operation are demonstrably poor predictors of pressure. Velocities measured at safe pressures from a reliable lab are better pressure predictors, but I am unable to find published velocities with 185-grain bullets for the 450B.

Comments, suggestions, and constructive criticism are all invited.

--Bob

[gunnut]

Thanks for such Great work!! We are learning a lot from your work!
I've been loading 284 case for awhile now. Because of the lack of small rifle primers in my area.
Using a modified 47-70 FCD. I worked up to 42grn. of Lil gun under a 230grn. FMJ. Seemed a little hot. But, No "tea leaf" signs of over preasure. I found a sweat spot at 40grns. So, I'm staying there untill I have the proper equipment to go further. I had problems damaging the jacket on the thin skin TMJ, TMC, Encapsulated bullets when using a heavy crimp. The winchester,sierra and zero FMJs work best for me.
The 284 cases are thicker and should last awhile. I'm sure the large primer and FCD are having a big effect on pressures. I just don't know how much. Sort of like hearing the ice crack under your feet. Any work in this area would be greatly appreciated. Thanks again for the wounderful contributions!

[wildcatter]

Way to go Doc, things have radically changed from the old 45 Pro Days and a faster powder seems to be emerging. I have used blue dot extensively for cold weather shooting, for better ignition. Blue dot diffidently needs more experimenting and how about the 2400 area powders?

Speaking of experimenting, I need to do a posting about it, look for it soon..

[BD1]

Quickload predicts - 37 grains of Bluedot under the Hornady 185 grain SWC, COAL 2.148, to produce 2499 fps @ 43,252 psi. It predicts upwards of 50,000 psi at 40 grains and rapidly increasing pressure above that.
BD

[pitted bore]

BD-
Thank you for the QuickLoad prediction of the upper load I tried. I don't think my chronograph was flakey during the firing, so the reading of 2859 fps was accurate (within the limits of the instrument). Because QL predicted about 2500 fps, perhaps their model needs tweaking, or more likely my equipment and techniques don't match their input coefficients. My barrel is 20" long, with a 1:16" twist, and almost certainly the groove and land configurations do not match SAAMI specifications for the 450B.

It is possible, maybe even probable, that with the 2850+ fps velocity, I'm well above the pressure of 43,252 psi that QL predicts for the 37 grains of Blue Dot.

I'm pretty sure several of the loads I fired were above the recommended upper pressure limits for the 450B in ARs.

--Bob

[BD1]

PB- I am sure that the Quickload model falls off of some loads pretty drastically. However, there still is no free lunch. Increased velocity generally means increased pressure. To get the model to predict 2,800 fps out of a 20" barrel I'm getting pressure predictions above 65,000 psi.
BD

[Siringo]

You should have seen some case head expansion at that point.

[pitted bore]

BD-
Thanks for checking the QL predicted pressures with that velocity.

Based on indications from reading the tea leaves (case head appearance, measurement of case expansion, etc.) I'd guess that I was not at the 65,000 psi level. However, I do not really know what the pressures were, and I'm not going to go there again, even with the bolt rifle. When I tested these loads, It was 55-degrees F, with a wind blowing to keep things cool. On a 90+ F day, and from a warm barrel, I might have popped a primer, or stiffened up the bolt lift, or seen other evidence of over-pressure with the 37-grain load. The test was designed so that I could note pressure signs and stop firing before bad things started to happen.

Powders showing up on the burn-rate charts between Blue Dot and Lil'Gun or 296 often include V-V N105, Ramshot Enforcer, 2400, V-V N110, and Accurate No.9. Of course the various charts rank them differently. I've some 2400 available, and will probably try it next.

It may be simply that very light bullets (relatively) in a straight case with a large diameter bore cannot be driven rapidly because of ignition problems with the relatively slower powders. The result of this it's possible that bullets of 200 or 230 grains may be faster from the 450B than the 185s.

--Bob