Wild Velocity Variations [Archive] - Glock Talk

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BlueGuitar
10-10-2012, 07:12
I loaded up some 10mm the other day and had a chance to chrono them yesterday. The results were confusing.

155gr Berry's HBRN plated
CCI 300 primers
11.9 gr AA #7
1.250 OAL

Glock 20
KKM standard length 10mm barrel

OK, most of the rounds chrono'd in the low to mid
1300 fps range. However about 6 of the 50 rounds
I chrono'd were well over 1600 fps, with 2 over 1700 fps.
The highest velocity was 1766 fps.

I've been loading for a couple of years and am no where
near an expert....In fact I did over crimp these rounds.
On several I had a stoppage due to a "ring of copper" left
in the barrel due to over crimping and cutting into the copper plating. I can fix that next time by paying more
attention to proper crimping techniques. But 1766 fps ???

My first inclination was to blame the chrono. Well that's like a pilot blaming instruments for readings that don't make
sense. That can be a bad idea.

Any thoughts on where I biffed this one up?

I'm just another crazy New Mexican.

Zombie Steve
10-10-2012, 07:36
Mixed brass?

BlueGuitar
10-10-2012, 07:57
Mixed brass?

Yes, mixed brass

Colorado4Wheel
10-10-2012, 07:58
You need to be very careful. Your asking for trouble with numbers like that. You should not drive plated bullets that fast either.

The G20 has too weak of a spring to control heavy loads. But the spread should be downward not upward.

BlueGuitar
10-10-2012, 08:02
I really did not want to have these velocities with the plated bullets....chauk it up to inexperience. I was aiming for about 1150-1200 fps maximum but obviously miscalculated somewhere. When the first "over velocity" number popped up on the chrony F1 we were beside ourselves...automatically assumed the chrony was wrong. That was simply not the case.

PS. I do use a heavier recoil spring

F106 Fan
10-10-2012, 08:19
How far from the muzzle to the chrono screen?

Richard

BlueGuitar
10-10-2012, 08:25
How far from the muzzle to the chrono screen?

Richard

Muzzle to chrony...appox 12 feet.

Zombie Steve
10-10-2012, 08:31
You may have had some bad readings from the chrono. I had mine in direct sunlight once and it was telling me my 4" .44 mag was shooting at 1,800 fps. :supergrin:

I don't think you were getting 1,700+ from the load. Usually when you approach or go over max you'll see that you don't increase speeds, just pressure.

Using one headstamp will help even things out quite a bit, and if you want to shoot top-end loads, it's highly recommended.

Just weigh a few different types of brass and you'll see what I'm talking about.

SDGlock23
10-10-2012, 09:05
I would suspect your chronograph. It's very possible for them to at times not read right, which is why now before I chronograph anything I run some factory loads to make sure it's reading right. One time I slightly bent one of the steel arms and didn't think anything of it, but it caused my velocities to read high until I replaced it with a straight one. Make sure you're in good lighting, that it's level and you're shooting level also.

With the load, 11.9gr AA7 it would seem you should be somewhere in the 1300's maybe. Some plated bullets are only rated to 1200 fps, others higher at around 1500 fps. Like you mentioned, watch your crimp on the plated bullets.

BlueGuitar
10-10-2012, 09:14
Ok, I would agree with all these comments.

1. Chrono is wrong. We were out in direct sunlight.
2. Reduce the crimp.
3. Back off on the powder a bit...no more than 1200fps for
plated bullets. Not trying to set new land speed record.

fredj338
10-10-2012, 09:27
Cheap Chrony. A couple things. Make sure you opent he Chrony 100%, it has to be completely open & flat. Even a 1/8" diff will mess up the readings. Muzzle blast; THat much AA#7 in a 10mm is going to create a lot of blast. Set up no closer than 12ft, 15ft is better.
The 155gr HBRN is a poor bullet for speed. I have seen the skirts blow out & accuracy ruined pusing themm hard. As noted, it's a 1200fps max bullet. That will be somewhere around 11gr w/ a plated.

Colorado4Wheel
10-10-2012, 09:44
1) Overcrimping Plated bullets. They could be falling apart.
2) Overdriving them. They could be falling apart.

The denigrating bullet parts could be giving you false readings. Chrono could reading the bullet and then some part after the bullet.

BlueGuitar
10-10-2012, 10:12
Ok, good information on the chrony. I will pay more attention to the setup next time...and make sure muzzle blast is not a factor.

I still have a boatload of those 155gr Berrys bullets. I will rework the load. They are really only for general shooting and do not have to be that fast.

What a bungle. I really appreciate all the help.

ron59
10-10-2012, 12:12
I step off close to 7-8 steps (yards) from where I shoot to the chrony, as I was finding "odd" readings when closer. It does increase the chance of shooting the thing, I've hit the rods which support the screens more than once, LOL.

I also always use the diffuser screens that go over the sensors which seem to help, sunny or not.

Steve Koski
10-10-2012, 14:02
I've seen folks shoot a ring off of the outside of a berry's bullet. A cardboard target will have two round holes in it, one from the ring and one from the "core."

Maybe the chrono is picking up one of these parts (?)

BlueGuitar
10-10-2012, 15:02
I've seen folks shoot a ring off of the outside of a berry's bullet. A cardboard target will have two round holes in it, one from the ring and one from the "core."

Maybe the chrono is picking up one of these parts (?)

Well that's what happened to a couple of rounds. After a shot the next bullet would not fit in the chamber. I found a very thin 10mm ring of copper causing a stoppage in the chamber. I attributed that to over crimping. Could be the effect of too much crimp and excessive velocity.

Steve Koski
10-10-2012, 15:33
Oh, you did say that. Great reading skills Koski.

Njanear
10-10-2012, 16:48
Hopefully one of those 'secondary' projectiles doesn't stray and smack your chrony - that could suck.:whistling:

fredj338
10-10-2012, 18:03
If you are seeing two distinct holes, that is likely the side wall coming apart under the pressure. I have seen it several times w/ 40 loads going much over 1100fps. Berry's is making a newer bullet w/ thicker side walls, maybe that solves it, but for now, consider those sub 1100fps bullets for best results.

WiskyT
10-10-2012, 19:41
Normally what you describe is due to being too close to the chrony. The instructions tell people 10 feet, so you figure you're good at 12 feet. You need 20 feet with a magnum type pistol load which a large dose of a slower powder like #7 is. But, since your bullets are failing, the screwy readings could be due to that. Either way, cure the failed bullet problem first since it could really ruin your day.

I don't even bother using my chrono at less than 20 feet because it will give screwy readings with SOME loads. Keep that in mind. People shoot a 22RF over their chrono at 10 feet, get good readings, and call it good, then fire 20+ grains of W296 and a 110 grain bullet over the thing and wonder why their extreme spread is 1,500fps.