Standard Deviation = 1

Never heard of it, though mnaybe y’all are getting it all the time and haven’t told me.  The first time I thought is was a fluke.  20 shots from a G20 pistol with SD of one foot per second.  During the string I thought something was wrong with the chrono, because shot after shot it displayed the same number.  Then there’s the saying; if you test your velocity once, you’ll know it.  If you test it a second time, you’ll never be sure again.  Though I never got any error readings, I discarded the data.

So I went out a second time on Saturday with the same load.  The CED chrono was unwilling to get any readings from the 30-30 loads I really wanted to test.  It’s like that sometimes, even with the IR LED screens.  But it took readings from the slower, bigger 10 mm bullets just fine.  I only measured ten shots this time, so a SD is of little meaning, but the extreme spread was 6.  It might correlate to a SD of 1.  I don’t know about anyone else, and the ammo manufacturers rarely say anything about it, but I’ve thought I was doing pretty well in the past if the SD was 12 or so.

This is a light load for the ten, getting barely under 1100 fps.  More like a 40 S&W.  It’s 9.6 gr. Blue Dot (checked against a check weight) with new Starline cases, 180 XTPs and a CCI 300, just going by the dimensions in the Hornady manual.  Nothing special.  This was my starting load, but it may end up a keeper.  We’ll see.  At the moment it’s my carry load, with 43 rounds on board.

I know – handloaded ammo for self defense, blah blah.  Don’t care.  I can practice a lot more with this stuff because I can afford a lot of it, and practicing with the same load you carry makes sense.  That’s what I’ll tell the lawyers– I can shoot this load more accurately and therefore more safely, etc., because it’s exactly what I use for practice.  I tried some of the hot Double Tap 200 grain FMJ stuff.  It’s affordable for practice, and while I’m sure it’s fine ammo for some guns, my Glock did something with it that it’s never done before.  The fired case would stick in the chamber (that’s what you call a pressure sign, right there) the extractor would strip off over the case head, and a fresh round would feed into the back of the fired case.  Yikes that’s some hot stuff, but no thanks.  Two stoppages or so per magazine is more than a deal killer.  If your 10 mm can cycle it properly, it would make a good deep penetrator though.

The crimp has to be a touch under the case diameter just below the crimp though, whereas I went with “about equal”.  A couple of these XTP handloads (2 of about 150) did fail to lock up all the way – something else that’s never happened with this gun.  I’m sure it’s the crimp, and maybe that I need a new slide spring as this one is the original from the early 1990s and has been cycled umpteen thousand times.  A gentle “forward assist” on the back of the slide was all it took.  Yes; more crimp.

7 thoughts on “Standard Deviation = 1

  1. Yes, yes, yes, a thousand times yes. I carry my handloads because I know they work and I know their performance inside and out and the fact that 10mm is very expensive, I can load and shoot more at a much better cost.

    I use 6.6gr of Titegroup, Starline cases, CCI 300’s, 155 grain XTPs and I get about 1280 fps from my Glock 20. I’ve thought about Blue Dot because I use 14.something grains of it for my .357 Magnum “Sound & Fury” loads and thought it might work well for the 10mm. Might have to give that a shot (pardon the horrible pun).

  2. I usually use 10.5 of blue dot in my 180gr 10mm loads. Hot, but seem to work pretty well if I use good bullets – Rainer ballistics partially peel their jackets and keyhole at 5 yards. I don’t think they are quite reliable enough for self-defense carry (I use Hornady 180gr XTP or Hydrashock for that) but fine for practice and plinking. SDEV much higher than your 1 fps.

  3. “…and maybe that I need a new slide spring as this one is the original from the early 1990s and has been cycled umpteen thousand times”

    If ‘slide spring’ = ‘recoil spring’ then absolutely replace it. A weak recoil spring can also leave spent brass in the chamber as the slide speed overcomes extractor tension.

  4. The Hornady manual tells you which powders gave the best consistency in their tests. I like that, and Blue Dot was one of those mentioned for the 10mm, though it was tested in a Colt.

    I have a new Wolf recoil spring (20 lb.) and guide rod on the way. Being conservative here. It is my understanding that the G20 OEM recoil spring was 19 lbs. Some shooters are using 24 lb. springs. The new spring may help with both types of those never before seen stoppages I mentioned.

    I may see Rolf’s 10.5 grains of Blue Dot and call, but I’ll work up to it. Do you use the original Glock barrel? If so, do you reload the spent cases, and how many times? In my earlier days with this pistol I fired thousands of reloads, up to three or four firings from the same cases. I still have those cases, but after hearing all the warnings I haven’t used them.

    Thanks for the replies.

  5. Starline brass, 180gr XTPs and 7.5 gr of Power Pistol for carry loads, momentum at about 1100 fps is close to .45 ACP. The Hornady taper crimp die is a wonder. I’m using a Wolf 20# recoil spring and guide rod, but it’s not captive so I had to frabbercate an installation tool. Light practice loads still cycle perfectly. I did have one Winchester case that failed to fire twice, turned out to be significantly under minimum length.

  6. The only reason I’ve heard given that you shouldn’t use handloads was “It isn’t as reliable as factory-loaded”. Thus, if you are confident in the reliability of your handloads, I cannot see a problem with using them.

    I’m not familiar with the implied legal ramifications, but then, I’ve heard all sorts of things with regards to legal ramifications…things like “don’t lighten your trigger pull” and “if you use .45 rather than 9mm, you’re more likely to be considered someone out to kill someone else”. While I see an over-zealous prosecutor looking for *any* edge to get a conviction, I don’t see it being a problem, so long as everything is kept in range of “industry standard”, and you were justified in using lethal force.

  7. Lyle-In my G20 with std. barrel, I’ve recently noticed some cases that show a noticeable “belt” after resizing, just ahead of the extractor groove. These are .005 to .007″ bigger than normal looking cases after resizing. Don’t know how many firings they’ve had but suspect some of them were “upper level” loadings, not top level, but reasonable performance for the caliber. These have been retired to the scrap can. The other thing is, some cases are starting to have looser primer pockets. The new Starline brass needs quite firm pressure to seat primers but when it gets too easy I mark that case with a Sharpie and after their lase firing, send them to the “do not reload” can. Other than that my opinion is, load on. So far I have not seen a split or separated case.

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