BIZARRE Chrono Readings... What Gives?

[Saluki91]

I tried to work up some 9mm loads this morning. My chronograph (ProChrono DLX) was throwing some really strange numbers back at me... or I was providing it with some really screwed up data. I'm sharing these results with the hopes that the collective will shed some proverbial light. Thanks in advance for any assistance you can offer.

Everything I shot was loaded on a Dillon XL750 this morning... powder in each load from the same canister.

I was shooting from a rest... perhaps some of the grouping issues are indicative of my lack of experience shooting from a rest? My first reaction (obscenities edited out) was "How hard can it be?". It must be harder than I thought!

124gr Hoosier LRN, Blazer Brass (previously fired), CCI 550, Vectan BA9, 1.128 OAL (per Vectan)

4.3gr (Vectan's published minimum for a 125gr Speer LRN)
1 - 776
2 - 217 (FTE)
3 - 236 (FTE)
4- 751
5 - 274
This has NEVER happened to me before. Even shots 1 and 4 were well below expected velocities. The "group" was all over the place, with some shots a foot low and left at 10 yards. I'm no Alvin York, but I can't make myself believe that was me. The brass from that group was at my feet or on the table - that's not good!

4.6gr
1 - 972
2 - 910
3 - 972
4 - 283
5 - 1317
Unimpressive group... lack of concentration or lack of talent.

4.9gr of powder (Vectan's published max load for a 125gr Speer LRN)
1 - 993
2 - 995
3 - 1012
4 - 1002
5 - 1011
Embarrassing group - 2 shots on target, 3 in La-la Land. But the velocities were in the ballpark, so maybe I was just fighting a Gremlin earlier... right? WRONG! Up next...

125gr Acme LRN, Blazer Brass (previously fired), CCI 550, Vectan BA9, 1.120 OAL (the limit for my barrel with this bullet)

4.3gr
1 - 885
2 - 924
3 - 929
4 - 698
5 - DNR
Group was fine, save one flier (grrrrr!)

4.6gr
1 - 1295
2 - 335
3 - 1294
4 - 953
5 - 108
This was the result I was hoping to find... 4 holes on target touching, one shot an inch left. All of the shots felt the same. Huh?!?!?

4.9gr
1 - 380
2 - 358
3 - 1287
4 - 367
5 - 389
Holy smokes! The funny thing is these shots all felt the same - just like the previous string of shots. Four of the five shots were on target.

So what gives? I've loaded hundreds of rounds from this bottle of powder with great results. Could it have somehow become contaminated? Could these numbers be indicative of weak batteries in the chrono, combined with another issue I'm not bright enough to figure out? Time to sell it all and buy a boat?

Thanks!

 

[milboltnut]

can you see if the lands stand out at the muzzle?

 

[FROGO207]

Sounds like your propellant is bridging in the drop tube and that is not good. I would take the time to actually weigh each charge when assembling the next batch. Some of it might be the crono as well. But rounds showing different on the target and FTE's sound like propellant problems to me.

 

[George P]

How far was the chrono and was it bright sun. clouds or?? I have gotten screwy readings that was (per the manual) from being in direct full sun

 

[AJC1]

You are having a major issue. As frog said I would be hand weighing everything until you get an es inside 50. If indeed your charge weight is correct you have contaminated powder or bad primers.
Fresh batteries and 5 shots to verify factory ammo is step one.

 

[Saluki91]

can you see if the lands stand out at the muzzle?

can you see if the lands stand out at the muzzle?

Not that I can see...

 

[Saluki91]

Sounds like your propellant is bridging in the drop tube and that is not good. I would take the time to actually weigh each charge when assembling the next batch. Some of it might be the crono as well. But rounds showing different on the target and FTE's sound like propellant problems to me.

Thanks! I went out and threw some powder to check on your suggestion...

Measuring with the Dillon scale that came with the press. The scale wasn't warmed up - just powered on. It was set to throw 4.9gr (per the most recent load).

Zeroed the scale with an empty case:
5.3
5.2
5.5
5.5
5.5
Hold on here!!!!

Zeroed scale with the pan:
4.8
4.8
4.8
4.8
4.9
4.8
4.8
4.9
4.8
5.0

Back to zeroed scale with an empty case:
5.1
5.1
5.0
5.0
4.9
5.0
4.9
4.8
4.7
4.9

Well... that just muddied the waters even further! Add a screwy scale to the list of variables.

 

[Saluki91]

You are having a major issue. As frog said I would be hand weighing everything until you get an es inside 50. If indeed your charge weight is correct you have contaminated powder or bad primers.
Fresh batteries and 5 shots to verify factory ammo is step one.

Thanks - That is a good suggestion - will do that first thing!

 

[AJC1]

Thanks! I went out and threw some powder to check on your suggestion...

Measuring with the Dillon scale that came with the press. The scale wasn't warmed up - just powered on. It was set to throw 4.9gr (per the most recent load).

Zeroed the scale with an empty case:
5.3
5.2
5.5
5.5
5.5
Hold on here!!!!

Zeroed scale with the pan:
4.8
4.8
4.8
4.8
4.9
4.8
4.8
4.9
4.8
5.0

Back to zeroed scale with an empty case:
5.1
5.1
5.0
5.0
4.9
5.0
4.9
4.8
4.7
4.9

Well... that just muddied the waters even further! Add a screwy scale to the list of variables.

I always warm up my scale. How long that takes is debatable but I like 30 minutes on my chargemaster

 

[Saluki91]

How far was the chrono and was it bright sun. clouds or?? I have gotten screwy readings that was (per the manual) from being in direct full sun

Beautiful sunny day... a few clouds here and there, but I don't think the chrono was ever in the shade. Chrono was about 7 feet from the muzzle (per instructions). Sounds like the sun could have been yet another bad actor in this poop show... Oy vey!

 

[FROGO207]

Does your powder measure have a baffel in it and what was the level of powder. These as well as thumping or vibrating the measure/drop tube can have an effect. I would mock up your press to load and dump the brass and weigh charges at the point you would have placed the bullet for a true test. Also try weighing a single charge(same one) multiple times with a varying pause between each reeding. That will determine how accurate your scale is at that charge weight. Personally I save my electronic scale to weight sort bullets, not for weighing propellant. If you come upon a good balance scale think about getting it. Just sayi'n.

 

[DanK3Pos]

Back to zeroed scale with an empty case:
5.1
5.1
5.0
5.0
4.9
5.0
4.9
4.8
4.7
4.9

Well... that just muddied the waters even further! Add a screwy scale to the list of variables.

Did the scale come with a check weight? If not, you can use a coin instead. Also, many digital scales are messed up by lighting. I know my FA has problems with a fluorescent light I have.

 

[milboltnut]

ya gotta beam a light at an angle to see better.

 

[Klaatu Barada Nikto]

How far was the chrono and was it bright sun. clouds or?? I have gotten screwy readings that was (per the manual) from being in direct full sun

My thoughts as well.

 

[AJC1]

Did the scale come with a check weight? If not, you can use a coin instead. Also, many digital scales are messed up by lighting. I know my FA has problems with a fluorescent light I have.

I've herd rumor that a penny is exactly a gram but I dont know I would trust that for scale verification

 

[GHinNH]

Direct overhead or angled/quartering sun, clouds, shadows, waving branches from trees and being too close all cause screwy readings. 20min is enough to cause the light reaching the eyes to change. A bright but overcast day (diffused light) is about as good as it gets for photo eye chronographs. I had a day like that this past Wed and took advantage of it.
Pistol distance for me is 12ft, rifle I put it out 21ft.

Quick model numbers show that 4.3gr of BA9 with a 124gr projectile is 946fps, 83.7% burned and 18,027psi. Numbers like that will easily put your ES +/- 75fps or more off from inconsistent burn rate alone. Being single base helps with environmental factors, but IDK how it meters with your equipment.

I'll agree with other statements, weigh each charge so you know it is not that. I know it's a pain and don't like to but I do when working with test loads.
Then move the chrono back, and be sure to keep an eye on the light hitting the photo-eyes.. The battery is fine until it tells you otherwise, most everything has a built in cutoff voltage that triggers the warning, not because it's dead.

I made these out of foamboard and sprayed with ultra flat black so I can keep angled sun and any shadows off the eyes.

 

[reloaded_in_pa]

Try fresh batteries for the chronograph. I had some erratic readings with mine and fresh batteries fixed that.

Check the diameter of the bullets too.

 

[Saluki91]

Direct overhead or angled/quartering sun, clouds, shadows, waving branches from trees and being too close all cause screwy readings. 20min is enough to cause the light reaching the eyes to change. A bright but overcast day (diffused light) is about as good as it gets for photo eye chronographs. I had a day like that this past Wed and took advantage of it.
Pistol distance for me is 12ft, rifle I put it out 21ft.

Quick model numbers show that 4.3gr of BA9 with a 124gr projectile is 946fps, 83.7% burned and 18,027psi. Numbers like that will easily put your ES +/- 75fps or more off from inconsistent burn rate alone. Being single base helps with environmental factors, but IDK how it meters with your equipment.

I'll agree with other statements, weigh each charge so you know it is not that. I know it's a pain and don't like to but I do when working with test loads.
Then move the chrono back, and be sure to keep an eye on the light hitting the photo-eyes.. The battery is fine until it tells you otherwise, most everything has a built in cutoff voltage that triggers the warning, not because it's dead.

I made these out of foamboard and sprayed with ultra flat black so I can keep angled sun and any shadows off the eyes.
View attachment 1002874

Those foam boards look pure genius... If creativity is >80% theft, I may get super creative tomorrow... Thanks!

 

[Saluki91]

Does your powder measure have a baffel in it and what was the level of powder. These as well as thumping or vibrating the measure/drop tube can have an effect. I would mock up your press to load and dump the brass and weigh charges at the point you would have placed the bullet for a true test. Also try weighing a single charge(same one) multiple times with a varying pause between each reeding. That will determine how accurate your scale is at that charge weight. Personally I save my electronic scale to weight sort bullets, not for weighing propellant. If you come upon a good balance scale think about getting it. Just sayi'n.

First - THANK YOU for your assistance and suggestions. This is a wonderful community, and I'm very grateful for your help!

The powder hopper was over 1/2 full, and yes - the Dillon powder system includes a baffle. There are a few after-market baffles out there, but I have never pursued it, as it seemed silly to baffle a baffle. That being said, those who have purchased them have wonderful things to say...

I started over from the beginning, and this is what I learned after revisiting the entire experience:
1 - Weighing each charge reveals my Dillon consistently drops +/-.1gr, which is adequate for plinking. I have toyed with the idea of a powder bar upgrade and micrometer fitting... and after going through the process of weighing each charge while working these loads up, I think I'll order one (cha-ching!).
2 - My Dillon scale seems to be the weakest link in the system. I'm going to be in PHX soon... may take it with me, and see if they will exchange it for a different one.
3 - The second effort took place with evening light (5:30 p.m. vs 11:30 a.m.). That seemed to make a big difference.
4 - I replaced the chrono battery... not sure if that was part of the improved results, but it couldn't have hurt.
5 - Even with much improved velocities, my groups were uncharacteristically AWFUL... then I ditched the bench rest and Bingo! Five shots touching and covering the target.

Hoosier 124gr
4.3 - 922, 951, 959, 966, 949
4.6 - 975, 1014, 1063, DNR, DNR
4.9 - 1021, 1059, 1041, 1040, DNR

Acme 125gr
4.3 - 931, 943, 951, 930, 938
4.6 - 977, 980, 988, 1006, 1000
4.9 - 1009, 1024, 1026, 1022, 1020 (wow!)

 

[FROGO207]

Sounds like you have it figured out. Thanks for sharing your findings. May help someone in the future when researching this problem.

 

[AzShooter1]

Check with Dillon. There may be an upgrade to your plate that will eliminate differences in OAL. I know I had one on my 650 but I don't know who made it.

Lighting is very important. Use the screens that came with your chronograph for better accuracy in your readings. Bright sun is not the best for the chrono. Overcast will help. I know this from shooting here in Arizona were we rarely get clouds.

 

[milboltnut]

Nice that you found out your problem

 

[lordpaxman]

Chronos with light sensors really do need a very even lighting to accurately measure velocity. The sky screens do wonders for evening out light, and make sure the sensors are not in direct sunlight. I found if it was sunny and a clear blue sky, keeping the chrono in the shade worked best. Batteries are always suspect so keep a spare with the unit always.
It might be difficult in these times, but pick some factory ammunition and record it’s velocity, then use that as a test string in the future to verify the chrono is working.

1 - Weighing each charge reveals my Dillon consistently drops +/-1gr, which is adequate for plinking. I have toyed with the idea of a powder bar upgrade and micrometer fitting... and after going through the process of weighing each charge while working these loads up, I think I'll order one (cha-ching!).

This is where digital scales really work well. Tare the sized primed case. Throw the powder. Measure the charge. Adjust charge on the scale if you want.
When I work up loads I’m really measuring how well my progressive and powder measure are capable of precision and accuracy with that powder, and I record that powder charge for each round. I may adjust the charge by adding or subtracting a few grains, but be advised on a digital scale sometimes they don’t respond to that small of a change. You may need to remove/replace the case so it will react. And of course, you can do this with a beam balance as well if you’re digitalphobic. Good luck.

 

[GHinNH]

I have to admit I failed to recognize the case fill with BA9, and despite being on the slow side for 9mm I think a large part of your success is the fill ratio you are getting.
At 4.9gr the fill ratio is 77% so chances are very good the primer will be in direct contact with the powder unless pointed straight down, and we all know that's a good thing.
So despite the burn ratio being less than ideal (87%), there is no arguing the results. 5 shot group SD/ES is 2.2/5.0 which is mind blowing. The pressure curve is gentle, and if you're getting good accuracy and don't find a problem with unburnt powder then it sounds good to me.

From my experience I have money to put down that it was just the lighting at that time messing with the numbers. Here is a quick and dirty model I put together. It is just a ballpark approximation using SAAMI and database numbers and should not be used as representative of your your combination of case, bullet, primer, firearm, conditions etc...

 

[DanK3Pos]

This is where digital scales really work well. Tare the sized primed case. Throw the powder. Measure the charge. Adjust charge on the scale if you want.
When I work up loads I’m really measuring how well my progressive and powder measure are capable of precision and accuracy with that powder, and I record that powder charge for each round. I may adjust the charge by adding or subtracting a few grains, but be advised on a digital scale sometimes they don’t respond to that small of a change. You may need to remove/replace the case so it will react. And of course, you can do this with a beam balance as well if you’re digitalphobic. Good luck.

Hmm. Doesn't really seem like a good idea, given how much variance I've seen in pistol brass weights, even same headstamp. And, when you say +/- a few grains, I think you mean granules of powder?

I find digital scales particularly annoying when trying to dial in a powder dispenser. Every time I turn around, it has turned itself off again. The new Hornady G3 allows you to disable that, per a review I saw the other day, so I may get one. My beam scale doesn't need to warm up and it doesn't wander, or care if a fluorescent light is on. I do have to remember to turn the ceiling fan off though (it will remind you, of course, because your charge weights are ridiculous).