BIZARRE Chrono Readings... What Gives?

[Nature Boy]

I have the same chrono as the OP and I’ll sometimes get impossible readings like over 4K FPS for .308 win loads. Since I still have fingers and can type this reply, these are obviously not the result of loading bench errors.

I’ve not correlated these to light conditions but I’ve always assumed that was the culprit

 

[Saluki91]

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...

View attachment 1002967

Thanks for sharing that... it's quite interesting!

 

[lordpaxman]

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?

Just to clarify, placing a sized primed case on a digital scale and pressing the TARE button results in the scale zeroing at that weight. Charging that case with powder and placing it on the scale then displays the weight of ONLY the powder. You must do this for every case, as case weights vary considerably especially in mixed HS. Personally I find this much easier and faster than using a beam, but to each his own.
Regarding +/- a few grains, yes, I meant the other definition of “grain” : “A small hard particle or crystal”. Isn’t English a wonderful language?

 

[lordpaxman]

I have the same chrono as the OP and I’ll sometimes get impossible readings like over 4K FPS for .308 win loads.

You may be surprised to learn my Labradar showed over 5K for .243 loads once. It was an RPR with a muzzle break, not sure if this interfered in some way or it was the terrain or the unit. I have a wooden shield I use between the chrono and the rifle, I set up on a different firing point, verified the chrono with a pistol and factory ammo and re-did the .243 and it seemed more reasonable.

 

[DanK3Pos]

Just to clarify, placing a sized primed case on a digital scale and pressing the TARE button results in the scale zeroing at that weight. Charging that case with powder and placing it on the scale then displays the weight of ONLY the powder. You must do this for every case, as case weights vary considerably especially in mixed HS. Personally I find this much easier and faster than using a beam, but to each his own.
Regarding +/- a few grains, yes, I meant the other definition of “grain” : “A small hard particle or crystal”. Isn’t English a wonderful language?

That makes sense. I'll have to tuck that one away for future use. In fact, that probably would work better than what I've been doing. I still have trouble trusting a digital scale, when I can weigh a given charge and get one reading, pick it up and set it back down and get a slightly different one.

 

[DanK3Pos]

You may be surprised to learn my Labradar showed over 5K for .243 loads once. It was an RPR with a muzzle break, not sure if this interfered in some way or it was the terrain or the unit. I have a wooden shield I use between the chrono and the rifle, I set up on a different firing point, verified the chrono with a pistol and factory ammo and re-did the .243 and it seemed more reasonable.

https://www.snipershide.com/shooting/threads/muzzle-brake-gas-dispersion-and-labradar.6887738/

 

[Mostly Lead]

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

According to this random website, a penny is 2.5 or 3.11 grams depending on which penny you have. https://cointrackers.com/blog/43/how-much-does-a-penny-weigh/

I weighed a coin multiple times, under different conditions over time and arrived at a reasonable consistent number. Then wrote that value on the coin with a Sharpie. If I got to wondering about my scale settings, I could weigh that same coin and reassure myself that it hadn't chained significantly. Finally realized that the beam scale never changed and promptly lost the coin.

Trick is that we measure in 1/70000 of a pound. (7000 grains to a pound, we measure to a 1/10th of a grain) Not much else out there gets weighed with that type of precision and coins may not be consistent due to wear, damage, etc... makes grams seem pretty course at 1/454 of a pound...

 

[GeoDudeFlorida]

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!

Chronos with light sensors really do need a very even lighting to accurately measure velocity.

Time for a new chronograph.

 

[drband]

Just to clarify, placing a sized primed case on a digital scale and pressing the TARE button results in the scale zeroing at that weight. Charging that case with powder and placing it on the scale then displays the weight of ONLY the powder. You must do this for every case, as case weights vary considerably especially in mixed HS. Personally I find this much easier and faster than using a beam, but to each his own.
Regarding +/- a few grains, yes, I meant the other definition of “grain” : “A small hard particle or crystal”. Isn’t English a wonderful language?

This is key— zero EVERY case if measuring drops in primed cases. You will never get a true idea of drop consistency unlesstvypu do this. As stated, different case weights are just not consistent.