Unexpected Chrono Results

[ScottQ]

I'm quite new to reloading, but so far I've loaded up 500 rounds or so of 9mm and they seem to be quite accurate and I've had no issues shooting them. So far so good. I'm using a single stage Lee press to begin with, and I'm quite careful and meticulous when I load my rounds.

Thus far I've used 125gr Sierra Tournament Master FMJ bullets and two different loads with Titegroup. The first load is 4.0 grains of Titegroup loaded at 1.09 OAL. With the understanding that those were probably a bit higher power factor than they needed to be, I loaded a second batch with 3.9 grains of Titegroup, and an OAL of 1.12 which from what I understand should place the bullet closer to the lands and improve accuracy a bit.

My ultimate goal is a nice soft shooting and accurate round for Production class matches using either my Springfield XD or Glock 34. Figuring I didn't want to leave anything to chance, I went out to the range today and broke out my new chronograph, a Chrony F1. This is where the unexpected results come.

I was expecting something around 1075-1100 FPS out of the first load, and somewhere around 1050-1075 FPS from the second load, with the second one giving me around a 131-132 power factor, which is around what I was shooting for.

It was a nice, cool, cloudy day and seemed like a good day to test my loads and my new chronograph, so off I went. Set the chronograph up exactly 10 feet from the muzzle, with a target dot set up behind it so my rounds should be a nice consistent 4" or so above the chrony.

All went well, and I didn't even shoot the chronograph!

Except the velocities I measured were much higher than I was expecting, and I was hoping some more experienced shooters and reloaders could give me some insight. Here's the data:

Load #1:

Sierra 125gr FMJ

4.0 gr Titegroup

1.09 OAL

Each string was 5 shots:

Glock 34 (5.3" barrel): Average Velocity 1205.2 FPS, Standard Deviation 11.30

Springfield XD Tactical (5.25" barrel): Average Velocity 1238 FPS, Standard Deviation 10.93

Load #2:

Sierra 125gr FMJ

3.9 gr Titegroup

1.12 OAL

Each string 5 shots:

Glock 34: Average Velocity 1255.6 FPS, Standard Deviation 16.0

Springfield XD Tactical: Average Velocity 1267.2 FPS, Standard Deviation 8.17

So I'm confused. I'm getting much higher velocities than I expected, especially from Load #2. I suppose it's possible that my scale is completely messed up and I'm putting more powder in than I think I am, but it's a Lee balance type scale and those are pretty hard to screw up.

Any other ideas or insights?

Safe shooting,

Scott

[Hi-Power Jack]

Scott, it's really not difficult to "screw up" a Lee balance scale. Why not

throw five charges and weigh them - see if they're 20 grains.

2nd, five shots is a good start, but really not enough to determine velocity.

I'd load up 20 of the 3.7 grains (lower the charge a bit) and see what that averages.

Someone should be along in a few minutes with a good load for you to start at:))

Edited August 17, 2013 by Hi-Power Jack

[atbarr]

2nd, five shots is a good start, but really not enough to determine velocity.

I was checking a load for my Open pistol this morning and I had a thought. Why find the average of 10 or 20 rds., when at a level II or higher, they only Chrono 3 rds. What I think would be better is, only use the lower reading as the Power Factor. What am I missing?

[Youngeyes]

With that logic why not just shoot one round and save time and bullets. Standard deviation and average velocity mean nothing without a good sampling. Once you've worked up a load then a spot check here and there is fine. That's what they do at a match. OP: Check your crimp and definately check your powder weight. Also check the calibration on that chrono. If you have a 22LR with a known FPS, use it for a check.

[ScottQ]

Well, as it turns out after I posted I started thinking more about it (sometimes the process of writing up the problem spurs the thought process) and considering Occam's Razer (the simplest solution is usually the correct one), and the problem was nothing complicated or obscure at all.

As careful as I was with weighing charges and checking OAL and so on, as it turns out I overlooked a very simple and important step. The Lee Balance Scale was not properly calibrated to zero. Given that all of my velocities were rather higher than I expected, it's likely been off by a bit less than a grain for all of my reloading. So what I thought was 4.3 grains of Bullseye was actually about 5.2 grains. Completely explains my results.

As it turns out, I'd already ordered a digital scale to use for double checking myself, and it's a good thing I started out with fairly light charges so my overcharging didn't really create any problems.

Lesson learned,

Scott

[blind bat]

Wow, 155pf+ with Titegroup! That's got to be some crazy pressure. What did your primers look like? Pull the bullets from those batches before your guns decide to disassemble themselves.

[Dacsoft]

Was this Titegroup or bullseye? You mentioned both.

Sent from my SPH-D710 using Tapatalk 4

[ScottQ]

Sorry, these were all done with Titegroup. Bullseye came in with my .45 Auto loads which I also ran across the chrono with similar results. All of the 9mm were loaded with Titegroup.

As far as crazy pressure, I didn't fire that many rounds but they don't show any excess pressure signs to me (not that I'm any kind of expert). At the end of the day the ammo ended up in the general range of most +P ammo, which both guns can handle fine, so I don't think any damage was done really. Other than to my pride. And a good lesson was learned.

[mjohn]

I understand that you did not zero your scale. However, no matter what the scale is set at the relationship between the load #1 and load #2 should stay the same.

So.......................the real question is why did fewer powder grains and longer OAL produce a faster FPS?

Hmmmmmmmm...........

[acpie360]

I understand that you did not zero your scale. However, no matter what the scale is set at the relationship between the load #1 and load #2 should stay the same.

So.......................the real question is why did fewer powder grains and longer OAL produce a faster FPS?

Hmmmmmmmm...........

I think the OP meant to say the scale's calibration changed, hence load #1 and load #2 did not start at the same zero.

[blind bat]

Probably too small of a difference in load (.1gr and .003" OAL) and too small of a sample size to draw any conclusions. Most of the consumer grade scales we buy are only accurate to ±.1gr and an OAL variance of ±.003" is very reasonable with bulk bullets and progressive presses. Temp could also be a factor. If the scale is suspect all bets are off.

As for +P pressures, you don't want to be messing with super over pressure loads and fast primers because pressure isn't linear. I'm certain your gun is fine now, but a little extra powder can cause a pressure spike. Most high pressure loads will use a slower powder like HS-6 (great powder for 9mm major or replicating carry loads for practice). Maybe I'm wrong and Titegroup is slower than I remembered but still be careful. The money you "save" reloading goes right out the window if you blow up a gun or end up with medical bills.

[CZ85Combat]

Hodgdon loading data for Titegroup list 125gn fmj start at 4.1gn & go to a max of 4.4gn with an OAL of 1.090" You were way past +P+ pressure in the chamber! You should not be going over 1136fps with Titegroup. As you can see from your test Velocity you were way over loaded. 1 thing to remember is as you add powder velocity goes up, until it hits a wall, then as you add more powder your velocity starts to go down but the pressure still goes up. So that is why your second test velocity went up with less powder!