KB! In New G20. Ideas? What Next?

Discussion in 'Reloading' started by pasky2112, Aug 29, 2012.

  1. pasky2112

    pasky2112 Senior Member

    Well, I had my first KB! yesterday. Fortunately the G20 held strong and just the mag well vented most of the discharge. Also, some came out of the slide/frame gap and made it's mark on my thumb. I THINK pieces of the follower or the top plastic part of the mag that blew off is what hit me in the face...right cheek (I'm a lefty). After I came to my senses and counted to ten on each hand, I started trying to piece together what happened. I was working up a load from the Hornady 7th guide... trying to get 180g MG JHP's to 1200fps with:


    • NEW Stock G20/stk bbl with NEW 22# SS RSA

    • NEW Starline brass

    • 180g JHP (montana golds)

    • AA#7 @ 12g w/ CCI#300 LPP

    • seated COAL 1.255" and crimped with Lee FCD
    Location in FL - ~80-85* and VERY humid; breezy; ~60' ASL (near coast). I have NEVER shot lead rounds in ANY Glock.

    With 10 rnds in mag, I fired the first rnd @ 1253 fps. Brass case-head was .433" w/ flattened primer BUT didn't hit target (paper plate @ 15y)...I'm not THAT bad.
    Case had usual Glock bulge for hot rnd out of stk bbl...no smiles or other chamber lines noted.
    Fired rnd 2. Same results but 1220 fps... no rnd on target, either. The ejected case was in same condition as first. At this point, what was on my mind is why the heck was I not hitting a freakin' 8" target @ 15yds!
    Fired 3rd rnd which was the KB. It crossed my chrono at 1135 fps. The pistol blew out of my hand fwd about 3-5' and the mag exploded down dumping the remaining 7 rnds around me. The mag is completely 'self disassembled'.

    After I checked out all the G20 frame/slide/bbl/RSA parts for anomalies, I (maybe foolishly), fired a factory HDY 155g XTP that was in my 'carry mag'. I hit target @ POA at the expected speed of around 1300 fps. I collected everything, packed up and went home to my family, thank God.

    I think that's all the facts. Any ideas on how i could have gone from a guppied case to a full rupture?

    Double charges ruled out; no room for powder and/or bullet. No bbl obstruction; previous rnds crossed chrony and cases were recovered and assessed. This IS a max load according to the HDY book I used but it's not the first time I loaded to max...even in .40 in my G23. I'd expect the brass would have shown symptoms of over-spec pressure in previous rnds of that load b4 blowing on me? Any ideas? :dunno:

    I attached pics of failed case and factory rnd in chamber.
    You can see them below on 10mm-firearms.com below if they don't show up here.


    - Dave

    Wanna kill these ads? We can help!
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  3. When I look at the Accurate load data (Edition 3.5) for a 180 gr Hornady XTP it shows:

    It seems to me that 12.0 gr might be a little hot but you're using a different data source. I think I would use Accurate's data - they actually make the powder!

    Could it be that the bullets got set back from recoil? Have you measured any of the rounds that hit the ground?



  4. SPIN2010

    SPIN2010 Searching ...

    Crimped and 1.255 OAL with a max charge of AA#7 ... I would say you are very lucky.

    Advice (IMHO): Get an aftermarket barrel to do load testing on the 10mm platform with your G20. Check several load data sources before you shoot a work up.
    #3 SPIN2010, Aug 29, 2012
    Last edited: Aug 29, 2012
  5. I don't have a Hornady guide, but Accurate Arms thinks 10.7 gr AA#7 is maximum with a 180 gr Hornady bullet. I think Montana Golds are pretty much a clone of the XTP but their brass jackets are going to increase resistance by some amount, maybe not enough to matter.

    How did your lighter loads do?

    I think failure of the bullets to hit a target at 15 yards has to mean something, but I don't know what.
    #4 Jim Watson, Aug 29, 2012
    Last edited: Aug 29, 2012
  6. Boxerglocker

    Boxerglocker Jacks #1 Fan

    You loaded and fired max loads right off the bat in a new gun? You didn't work up prior? (every batch can be different) Did you size your new brass?
  7. dkf


    Does that mean you started at say 10 grains and tryed different powder charges in between or did you just load a bunch up with 12gr and try them out?
  8. pasky2112

    pasky2112 Senior Member

    Yep. In hindsight, That's the first thing that came to my mind. But I've done the same thing in .40 reloads using HDY tables for 1000's of hot rounds. With all of the mixed data out there, I thought I was using a consistent resource. But yeah...default to powder data when there's a conflict. But Damn! 10.7g vs. 12.0g! I started at 11.0g and got ~1050f/s. 11.5...11.7 all fine. Then 12.0 seemed fine velocity-wise and case symptom-wise and I got 2 shots off with no case deformity (chamber lines, etc.) Then boom... hit by pitch.
    [edit] I just measured the remaining 7 and there's no change. 2 are 1.256, 1.257. Rest are 1.255...
    #7 pasky2112, Aug 30, 2012
    Last edited: Aug 30, 2012
  9. PCJim

    PCJim Senior Member

    Per Accurate's reload data, you are at least a full grain of powder over max loading for a 180gr HP bullet. Owning a chronograph, there is no reason in the world you should have experienced a KB had you properly developed your loads. The reason for the lower FPS reading on your third shot is that a lot of pressure, read as velocity, was dumped thru the mag well.

    Had you properly developed your load, I am quite sure you would have hit a velocity wall well before your 12.0gr AA#7. IF you are an experienced reloader, you should well know that we aren't always able to duplicate velocities that the factory says is obtainable. There are too many variables in components and testing apparatus.

    While I'm glad that the experience has been nothing but a hopeful eye opener, how about letting me know in advance if you plan to drive south to do any shooting.
  10. OP- You say in the thread on the other site that you haven't calibrated your digital scale in a year. Is that true?
  11. pasky2112

    pasky2112 Senior Member

    Ironically, I have a KKM on order. They've served me well in my .40 G22/23's.

    No. I worked up from warm loads and didn't just start at max published. I haven't been doing this for decades but I usually start pretty light with a new caliber and pistol/bbl. My first loads with the G20 were the same 180's JHP MG's around 1000 fps w/ BD. I just wanted to work up to 1200fps with the 180's which seemed reasonable to me.
  12. pasky2112

    pasky2112 Senior Member

    I have a 100gram check weight I've popped on it once in a while but it has never regged anything off. So I stopped doing it, honestly. In hindsight, yeah. But at the time, what was the point? It never changed.
  13. Boxerglocker

    Boxerglocker Jacks #1 Fan

    Remember, check and cross check your data. Start low and work up slowly. Most importantly "Powder charges are not linear" even working up with a chrono, there is a point of diminishing returns.
    I don't think a KKM barrel would have changed anything given your particular chain of events. Be careful, glad to hear you walk away unscathed.
  14. Boxerglocker

    Boxerglocker Jacks #1 Fan

    You should calibrate your scale frequently and use check weights, and zero often even during a loading session. Load cells can go out of spec at any given time. Digital scales are great, my personal preference but they are not fool proof.
  15. pasky2112

    pasky2112 Senior Member

    sure. I'll pick you up... funny guy.
    Other than showing my my velocities were going up, I'm not sure how you mean having a chrono should have prevented a KB. I was checking my cases for pressure signs. And I know why the last round was slower.
    It HAS been an eye opening experience. That's why I'm HUMBLY sharing the experience with everyone. So myself and other new reloaders can get experienced and helpful ideas on how to prevent and avoid these issues from reoccurring. We all start somewhere. Thanks.
  16. pasky2112

    pasky2112 Senior Member

    I think you pretty much summed it up, Boxerglocker. Frankly, I likely worked the load up too fast and was complacent with the data that i had was safe if I stayed 'in the book'.
    And that 'a book' is not enough. I should have been more patient and reviewed other resources rather than turn the page and start again. Thanks. I didn't realize the digital scales had those issues, either. I will research a higher quality scale and best practices to keep it accurate often. Much appreciated. I'm glad I walked away unscathed as well ;)
  17. pasky2112

    pasky2112 Senior Member

    Thanks Jim. My lighter loads went great. I was seeing what I expected on the chrono for ea. load (vel, ES, SD, Avg), I was shooting my usual grps on target and my cases were normal in terms of no unusual pressure deformities. I was quite pleased. The load that KB'd was my 5th for the session. I maybe shot a total of 100 rnds max.

    Not hitting the target did give me pause, like i said, but nothing that would have indicated what was to happen. I knew i didn't have a squib. I slow fire and go hunt down the case and measure it when I get into max load territory.
    I use MG 99% of the time. I've never had any probs with them. I treated them like the XTP's as far as load workups go for 1000's of rnds. They perform great.
  18. sellersm

    sellersm disciplinare

    Is there any chance you weren't actually using AA #7 as your powder, but had BD instead? 12.0gr of BD in a 180gr JHP sounds like it could be trouble...
  19. shotgunred

    shotgunred reloading nut

    On another note. Try to seat a mag in your gun. Normally when a glock KB's they blow a chunk off the mag release. It no big deal and you can get a new one from lonewolf for a couple of bucks.

    Point two. Let me introduce you to the shotgunred philosophy of reloading. Start low. Check for accuracy. when you find a load that is accurate stop. There is nothing to be gained from going higher at that point. You just put more strain on your arm joints and your gun. You are not going to find a good medium burner out there that will not be accurate load at a lot less than max load. If you want more bark and to feel more recoil switch to power pistol.
  20. Your velocity will increase as you increase your powder charge. Let's say 100 fps per .1 grain. If you notice that all of a sudden, you get 25 fps, you know you are near/at max load.

    Keep in mind, I haven't been loading very long and just recently got a chrono, so my understanding may not be totally accurate.
  21. You need check weights for your digital scale. A calibration weight of 100 grams (1543 grains) just doesn't mean much when you're splitting hairs at 10 to 12 grains. Here's a selection:

    Just for info, which scale are you using? Digital scales come in various quality levels and only the Dillon D-Terminator or similarly priced units are good enough. Fred has stated before that there are no good digital scales less than $100 and I think inflation has probably bumped that up a bit.

    As to checking for 'pressure signs': Read starting at page 59 of Speer #14. Their point of view is that by the time you can see evidence of overpressure, you are at least 20% above max. And if they can't read pressure signs, I certainly can't!

    The flattened primer thing might be important if Federal primers didn't flatten in a wind storm and others have to be mashed with a freight train. Then too, primers are extruded into the striker slot on Glocks whether the loads are hot or not. I don't think measuring the height of the extrusion will be a standard test anytime soon!

    I'm real curious about the scale. A little booboo in the reading and a charge that exceeds the powder manufacturer's recommendataion could very well be the cause of the KB.

    #20 F106 Fan, Aug 30, 2012
    Last edited: Aug 30, 2012

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