Standard Deviation & Extreme Spread - Idea's?


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Foto Joe
December 10, 2013, 01:57 PM
Since I started casting about six months ago I've been working up loads for the pistol/revolver calibers that I shoot. So far things have gone pretty good considering my steep learning curve at times. One of the things that has me scratching my head is "Standard Deviation" and "Extreme Spread." For instance....

Let's take 45 Colt, loading a specific charge of TrailBoss under a 226gr LRN gives me an average velocity of 803fps, a standard deviation of 12.4fps and an extreme spread of 39.2fps, not much to complain about there especially since it also includes a 1.5" group at 15 yards. Not bad for an out of the box cowboy gun really.

Now, so as to NOT throw all that extra lead downrange (the stuff can be hard to come by) just to hit a gong or a piece of paper I've attempted to put together a load for a 164gr LRNFP. Yes, I know that if I'm not throwing the lead downrange I'm throwing powder instead but the point is I'm trying to work up a decent load for each boolit that I might load the gun with. Anyway the BEST numbers I can get are posted below and both powders basically suck when compared to the heavier boolit.

TrailBoss
MV = 959
SD = 30
ES = 88

700X
MV = 1016
SD = 23
ES = 74

In actuality, the TrailBoss load grouped pretty good at 1.5" even though it had a higher SD & ES than the 700X which grouped at 3".

Keep in mind for the purposes of this thread I'm NOT looking for powder recommendations, I have what I have and until others are available that's the way it is. What I am looking for is the relevance or shall we say what is the acceptable SD & ES for shall we say 45 Colt or 45 ACP. What's considered a good Standard Deviation basically or a good Extreme Spread for large bore low pressure handgun loads such as these.

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rsrocket1
December 10, 2013, 02:30 PM
I don't think your wider groups are purely from the powder. If you load down the 700X so that it gets you 960fps, you very well might the same groups. If you are shooting from a ransom rest, then I take back that last comment.

For 15 yard offhand shooting, I seriously doubt that 10% variation is going to throw your groups off by much so long as the inconsistent recoil from the variation is affecting you. You are below that so I think you are GTG.

Foto Joe
December 10, 2013, 04:16 PM
No ransom rest I'm afraid although that's something that I might spend some fun tickets on someday in the future. All groups are 3 shots from 15 yards from a rest although the rest doesn't really do much for the groups. It's more or less used simply so I can get a little more standard groups. I used to shoot ten shot groups but there was invariably a flyer in there that skewed the results.

I'm no longer a competition shooter and even when I was I was a shotgunner not a pistol shooter. I guess I'm just anal and am looking for whatever I personally can wring out of a particular load as far as accuracy is concerned. Besides, it's fun to knock golf balls off strings at 15 yards with a SAA in 44-40 when my buddy beside me will go through two magazines just trying to get one 'em to move let alone sail over the berm.

Owen
December 10, 2013, 04:45 PM
Well your standard deviations are approximately 1/3 of your Extreme Spreads. That's good: It means that your velocities are normally distributed(ie. bell curve).

At close ranges the extreme spread of the velocity won't really mean much. The variation in group sizes will have far more to do with you, than the variations in velocity. If you were shooting groups at 50 yards and farther, it would make a much more difference.

I guess what I'm saying is that if you are getting good groups despite wide velocity variations, don't worry about the velocity variations.

LeftyTSGC
December 10, 2013, 07:00 PM
Foto Joe: Here are some of my results.

Load Data: 250gr Missouri Bullet LRNFP (Cowboy)
TulAmmo Mag Primers, Starline Brass
4.6gr TrailBoss, OAL 1.58
20rds, AVG velocity 596, STDEV 22.8, FT-Lbs 197.3
Hi- 619, Low 546, ES-75, PF Avg-88.9

Load Data: 250gr Missouri Bullet LRNFP (Cowboy)
TulAmmo Mag Primers, Starline Brass
5.0gr TrailBoss, OAL 1.58
20rds, AVG velocity 659, STDEV 8.6, FT-Lbs 241
Hi-670, Low- 641, ES-32, PF Avg-109

Pistol: ASM SA New Dakota .45LC (Cowboy) 4 in barrel
Load Data: 250gr Missouri Bullet LRNFP (Cowboy)
TulAmmo Mag Primers, Starline Brass
4.6gr TrailBoss, OAL 1.58
10rds, AVG velocity 559, STDEV 19.6, FT-Lbs 173.5
Hi-593, Low-527, ES-66, PF Avg- 78.2

Load Data: 250gr Missouri Bullet LRNFP (Cowboy)
TulAmmo Mag Primers, Starline Brass
5.0gr TrailBoss, OAL 1.58
10rds, AVG velocity 612, STDEV 10.7, Ft-Lbs 208.1
Hi-630, Low-593, ES-37, PF Avg-93.8

Rifle: Uberti .45LC Model 1873 19 Carbine LeverAction
Load Data: 250gr Missouri Bullet LRNFP (Cowboy)
TulAmmo Mag Primers, Starline Brass
4.6gr TrailBoss, OAL 1.58
10rds, AVG velocity 724, STDEV-12.1, Ft-Lbs-290.7
Hi-741, Low-703, ES-38, PF Avg- 131

Load Data: 250gr Missouri Bullet LRNFP (Cowboy)
TulAmmo Mag Primers, Starline Brass
5.0gr TrailBoss, OAL 1.58
20rds, AVG velocity 786, STDEV-10, Ft-Lbs-347.8
Hi-804, Low-770, ES-29, PF Avg-154


Basically I used an increased powder load that provided both smaller SD and ES and also accuracy. Make a few more rounds to test. My results showed improvement when i increased to powder load to mid-range loads.

Just my 2cents worth.

LeftyTSGC

Jim Watson
December 11, 2013, 12:06 AM
A 164 gr .45 is pretty far outside the normal operating range. I think you are lucky to get as uniform velocities as you show.
How's your zero?
I would be surprised if a 164 shot to the same point of impact as a 226.

ArchAngelCD
December 11, 2013, 03:52 AM
Like said above, if you're getting good groups don't worry about the ES.

I have seen some very high ES numbers from commercial match ammo yet the groups were very tight. Many reloaders think only small ES numbers will produce accurate ammo but nothing I've seen prove that out.

Foto Joe
December 11, 2013, 09:00 AM
A 164 gr .45 is pretty far outside the normal operating range. I think you are lucky to get as uniform velocities as you show.
How's your zero?
I would be surprised if a 164 shot to the same point of impact as a 226.

Yeah I know, 164's are definitely not the norm. A few years ago I was picking up some El Paso Pete's Ultra Gamers that were .454-150's from Dash Caliber and loading them for Black Powder Gallery Loads and I loved those things, they were nail drivers. Anyway, I can't get those anymore and I don't load very much BP cartridge either anymore so I figured I'd play with a Lee 160LRNFP mold and see if I could replicate the performance with smokeless that I was getting out of those BP boolits. Not so much I'm afraid.

As far as the point of impact, the 164's do print in the same area but in a much larger group than the 226's. So far not real good as a "golfing" gun. I just got a 200gr SWC mold yesterday so I'll start working up some loads for that one and let the 164's rest for a while.

Owen
December 11, 2013, 09:27 AM
How much do round balls weigh in .45 cal? It might be fun to try those too.

Foto Joe
December 11, 2013, 09:38 AM
I loaded a LOT of round balls before I found those EPP Ultra Gamers. A .454 RB is approximately 140gr. I'm not sure that using them for smokeless would be a really good idea though. TrailBoss might let you get away with it but those little buggers are pure lead and soft, you'd probably get to break out the ChoreBoy to scrub the lead out of your barrel.

Assuming that you are referring to loading them above smokeless, keep in mind that with a round ball you have to crimp right on the equator of the ball. With Black Powder it's no big deal simply because I use 20-25gr of powder then fill the rest of the brass up with cornmeal. The RB sits right on top of the compressed cornmeal and can't get set back into the brass from recoil. With smokeless you'd have to consider the possibility of setback due to recoil.

fecmech
December 11, 2013, 05:11 PM
With smokeless you'd have to consider the possibility of setback due to recoil.
Bullets do not set back in revolvers they go forward if there is insufficient case tension or crimp. Bullets are set back in autos by the trip up the feed ramp.

ArchAngelCD
December 11, 2013, 06:19 PM
How much do round balls weigh in .45 cal? It might be fun to try those too.
The ones I used in my 45 Colt were 142gr. I found load data in one of the older Lyman load manuals.

Foto Joe
December 12, 2013, 10:07 AM
Bullets do not set back in revolvers they go forward if there is insufficient case tension or crimp.

True enough and I have never loaded RB's with smokeless. The point that I was trying to make is that there is VERY little load bearing area on the equator of an round ball. It would be inconvenient at the very least to fire the gun and then have a ball roll out of one of the chambers that isn't in battery.

Jim Watson
December 12, 2013, 02:20 PM
I once loaded some round ball .45 ACP. It took some tweaking to get them to stay in place up the feed ramp, but they really shot quite well.
I did not care to go to the expense of the next step, a smoothbore barrel to test a theory of mine.

PPS43
December 12, 2013, 04:14 PM
Extreme spread is a very noisy metric. It is also affected by number of shots, so it's hard to say whether your numbers are good. Even more so because those are best numbers from unknown number of trials ("best" metric is noisy, average is much better).

Unless you have enough observations and patience to do normality tests, measure kurtosis or otherwise determine how heavy-tailed velocity distribution is, I would just look at standard deviation (average of standard deviation if you have many trials).

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