Bizarre Chrono Results

[chp5]

I shoot a Glock 22 in Limited. I dropped my major PF load by .1 grain and chrono’ed today (180 grain Zero JHP over 4.6 grains of Titegroup).

I have 2 G22’s. One’s pretty new and the other one is old and ragged out. The old one is still great however, and still groups about 2” at 25 yards off an improvised rest.

I chrono’ed both guns with the same load today. My new G22 gave me a FPS in the range of 942-949 – 6 shots total. Right where I want it. My old G22 gave me 911 – 952 fps with six rounds of the same load. That’s a range from 163.9 PF to 171.3 PF.

WTF?! Why such a huge deviation from the old barrel? Could the old barrel just be really dirty or just shot out? The old barrel still has good accuracy. Can a barrel be shot out and still have good accuracy?

Edited October 28, 2005 by chp5

[revchuck]

Cy - Sounds like you might have light firing pin strikes. I know zilch about Glock internals, but I'd check the mainspring and also clean the chamber and firing pin enclosure really well and try it again.

[chp5]

Cy - Sounds like you might have light firing pin strikes. I know zilch about Glock internals, but I'd check the mainspring and also clean the chamber and firing pin enclosure really well and try it again.

Thanks Chuck.

I don't think that's it because I put the new barrel in the old upper (that contains the striker and striker spring) and I got good results. That seems to point to the old barrel as the culprit.

[Flexmoney]

Six rounds is not enough to draw conclusions from, I don't think.

[kevin c]

Six rounds is not enough to draw conclusions from, I don't think.

I think Flex has a good observation.

Ten, or better yet, twenty rounds through each barrel might better show how much the ammo might normally vary through each (at least on that particular day...).

[oct_97]

The smaller the sampling the larger the distortion.

Edited October 28, 2005 by oct_97

[eric nielsen]

As they said, sample at least 12 shots, 20 or 30 is better. Several things can throw chrono results into chaos. These are likely culprits:

1. Mixed brass, especially changes in case length
   
2. Primers not seated consistent
   
3. Different brands of primer
   
4. "Lead Safe" primers
   
5. Inconsistent striker hits
   

Your goal is to hit the same primer with the same resistance. Having the same case capacity and a case more than 1/2 full of powder for each shot helps, too.

[chp5]

As they said, sample at least 12 shots, 20 or 30 is better. Several things can throw chrono results into chaos. These are likely culprits:

1. Mixed brass, especially changes in case length
   
2. Primers not seated consistent
   
3. Different brands of primer
   
4. "Lead Safe" primers
   
5. Inconsistent striker hits
   

Your goal is to hit the same primer with the same resistance. Having the same case capacity and a case more than 1/2 full of powder for each shot helps, too.

Thanks Eric. The puzzeling thing is that I have completley different results (only a deviation of 7 fps) from my other G22 with the same load on the same day. That leads me to believe the vaiance is from the barrel itself.

I chrono'ed 10 shot string today out of the old barrel - with very similar results.

[George]

Brass should be all one headstamp or this test will never be valid. 10-20 rounds of the same ammo/case combo through each bbl in the same slide/frame will be needed to see if there even is a solid difference.