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Load Workup for Subsonic, Heavy-for-Caliber (60+ grain) Bullets in .22 Hornet
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Old 07-17-2017, 01:27 AM
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Default Load Workup for Subsonic, Heavy-for-Caliber (60+ grain) Bullets in .22 Hornet

I've been trying to get a quiet .22 caliber round for use 'around the yard'. I have the Aguila 60-grain SSS cartridge working pretty well, but I can't get it up to it's 'factory' muzzle velocity of 950 f/s. In my attempts to achieve that MV, I have come around once again to the .22 Hornet, also known as the "reloadable rimfire". (You can read about my initial efforts in all of the above, here: http://thehunterslife.com/forums/showthread.php?t=19507 .)

Since I have now started to "get serious" about reloading heavy (60 grains and above), subsonic, or near subsonic loads, for the .22 Hornet, I have decided to start a new thread devoted to that endeavor.

At the moment, the rifle I am reloading for is a Contender with a 26" barrel with 1:9 twist. Given that twist rate, I can hover around the speed of sound (~1125 f/s) and still keep the Speer 70-grain semi-spitzer gyroscopically stabilized. I like this bullet, because at ~1125 f/s, it has about 200 ft-lbs at the muzzle, and ~175 at 50 yards, (about the max range I would use it). The Aguila 60-grain SSS, doing about 850 f/s has a ME of about 100 ft-lbs and only 80-ish at 50 yd. So you can see why I like the 70-grain bullet. Significantly, I LIKE being able to RELOAD for this application. A major negative for the SSS is being able to BUY them in Alaska!

The "bad news" with the Hornet was initially that it was difficult to keep the projectile subsonic, STABILIZED, AND keep the pressure up enough. Finally, I thought about using black powder (actually, BP substitutes), and voila'!, that shows promise! This thread will be about heading down the black powder (substitute) path in an effort to get a good, PRECISE, subsonic or near subsonic, RELOADABLE load to be used for 'plinking'. The thread cited above goes into the preliminary look down 'the black powder path'. The following is the first purpose-driven steps down that path.

I have two black powder substitutes (hereafter BPS). The first is Pyrodex's RS powder. The second is Alliant's "Black Powder Substitute" (hereafter ABPS). (I happen to LIKE that name. Straight to the point. No ambiguity.) A full-up-to-the-case-mouth charge of ABPS is 13.0 grains, and in a sample of one, gives a MV of 1325-ish f/s. A full case of RS is 10.0 grains, and gives a sample of one MV or 1127 f/s. After cleaning and prepping 20 cases, I loaded 10 of them with 10.0 grains of RS, and 10 of them with 10.0 grains of ABPS. I used CCI 450 (magnum small rifle) primers and of course the Speer 70-grain bullet. (Speer #1053.) I seat the bullet 0.49" in the case. Since 10.0 grains of RS is a full case, his compresses the RS load significantly, and the ABPS load "a little bit".

I installed the MagnetoSpeed chronograph on the rifle and set the target at 35 yd. I shot 5 rounds of ABPS first, then 5 rounds of RS, then 5 rounds of ABPS, and finally the last 4 rounds of RS. (One of the cases had a bad primer. ) Here are the targets with the shot sequence and MV for each bullet.
The first ABPS group:


The second ABPS group:


The first RS group:


And the second RS group:


Overall, I was relatively pleased with this showing. The ABPS was pretty poor, but the RS wasn't bad. Mostly.

The MVs were all over the place. Here they are in tabular form, in the order in which they were shot.

RS:
1 - 890
2 - 1051
3 - 997
4 - 817
5 - 1021
6 - 1208
7 - 1107
8 - 992
9 - 1073

The ABPS:
1 - 940
2 - 959
3 - 1224
4 - 1235
5 - 877
6 - 1020
7 - 802
8 - 943
9 - 1225
10-785

As you can see, that's some SERIOUS variability in MV! No wonder the shots were 'here and there'. So, I needed to find some reality in all of this. The first RS group looked VERY good except... for that one REALLY far flier! Dang! Could that be explained by variations in MV?

First, I wanted to know if there was any way to OBJECTIVELY (honestly) remove any of the shots based on the statistical variance of the MVs. If I was a gun-writer (ptooey) like Bryce Towsley, I wouldn't let a little thing like objectivity get in the way of saying what I WANTED to say about these loads. However, I am NOT like Bryce Towsley, and I care most about not fooling MYSELF, (to say nothing of everyone else). Here are graphs of the MVs:



And


Looks like we might be able to 'reject' some of the shots based on MV. Standard statistical analysis says that we can look at the standard deviation and if - based on the SD and sample size - a given value is farther than a certain distance away from the average, it can be removed from the data set. Doing this without using a recognized standard procedure is called "cherry-picking". It is a common tactic used by charlatans, hucksters, con men, and other ne'er-do-wells like gun-writers (ptooey). (Sadly, it has become a VERY common tactic in science in general these days.)

So, in the case of the RS powder, we can legitimately remove the lowest two MVs (817 qnd 890), and the uppermost MV (1208). That leaves 6 rounds, the average of which is 1040 f/s with a SD of 45 f/s.

For the ABPS powder, we can remove the bottom two (785 and 802), and the uppermost three (1224,1225, and 1235). That leaves 5 rounds, the average of which is 948 f/s with a SD of 51 f/s.

The SDs of the two powders are similar at 45 and 51 f/s, indicating that within those MVs most central AND consistent, they have similar variance.

Still, these are very small sample sizes to start with - 9 and 10 - and to reduce them by essentially half may be statistically "allowed", but 1) it is dissatisfying to say the least, and 2) doesn't really 'help' much. If the point of impact for half of the bullets fired can't be fairly closely predicted, being statistically 'justified' is little comfort.

However, that's only half the MV analysis. I needed to see if there was a correlation between MV and point of impact elevation. Here are those graphs:

RS:

"R-Squared" value of 0.3201 (correlation coefficient)

and ABPS:

"R-Squared" value of 0.9422 (correlation coefficient)

For those not familiar with linear regression, the correlation coefficient "explains" the variability in the variable. In other words, in the RS powder, 32% of the variability in the point of impact elevation is 'explained' by the muzzle velocity. In the ABPS powder, 94% of the vertical distribution of the points of impact are due to muzzle velocity.

At first glance, one might assume something "weird" with the RS powder. However the reality is that the more precise a load is, the less the elevation is correlated to the muzzle velocity. In other words, if you have a small little group, there is very little chance that the points of impact will be associated with the muzzle velocity of each shot in the group. On the other hand, the bigger the group (bad precision), the more likely that the vertical displacement of the points of impact will be closely associated with their muzzle velocities. HOWEVER, that said, a correlation coefficient of 0.9422 is VERY high. Essentially ALL of the variation in elevation is due to MV. What that means is; if I can diminish the variability in MV, then I should be able to get more precision.

So... after taking out the "bad" MVs, what do the groups look like?
RS:


ABPS:


Eh... Nothing to write home about. Still, maybe some promise. I think the RS shows more promise, BUT, maybe if I put more of the ABPS in, it would 'straighten up and fly right". However, the BIG deal about this to me is the SERIOUSLY HIGH variability in MV. At the moment, I have only two 'explanations':
1) Crappy primers. Maybe the "magnum" primers in this small case actually result in VARIABLE ignition. I wouldn't have thought so, but I think I should try "normal" primers, and
2) Black powder (and BPS) is not particularly 'uniform' in burning characteristics. Most muzzle-loaders have low expectations when it comes to 'precision'. Maybe one of the reasons is highly variable burning characteristics of the powder. ???

In the mean time, I think I will load up some more RS, and use non-magnum primers. If that gives me more consistent MVs, I THINK I might get this idea - subsonic BP loads in a Hornet - to 'work'.

Paul

PS - I forgot to mention: Even the slowest of MVs didn't exhibit much key-holing. That IS good news!
Paul

PPS - There's something else I forgot to mention: Look at the slope and intercepts of the linear models of elevation based on MV. They are almost identical.
RS Slope = 0.0033
ABPS Slope = 0.0037
Only 0.0004 units apart! In other words, for every increase of 1 f/s in MV, the difference in elevation change between the two powders is FOUR TEN-THOUSANDTHS OF AN INCH!
RS intercept = -3.3577
ABPS intercept = -3.4811
Again, VERY close! This value reflects the relative difference in energy density between the two powders.
That means that the mechanism (in this case, burn characteristic) that causes elevation to be correlated to MV is THE SAME FOR EACH POWDER. That's a big deal. It suggests that the linear models are "good" (real) representations of the phenomenon being looked at.
Paul
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Last edited by gitano; 03-21-2019 at 05:08 PM..
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.22 caliber, .22 hornet, black powder, buffer, hornet, subsonic, w-296


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