Questionable chronograph readings?

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pibulloncrack

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Testing some loads on a new chronograph yesterday and I recorded some readings that I question.
In your opinion do these velocities seem possible?

I set up the chronograph about 12’ out.
Shooting a M&P Pro 5”

1304
1306
1245
1276
1248
1275
1279
1280
1304
1248

Here is the load.

115 gr X-reme rn
5.6 gr Unique
OAL 1.3
Crimp .380

I intentionally left out the make of the chronograph so the conversation did not get side tracked.

Thanks in advance!
 
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Possible yes.

Probably not.

Sure its Unique? I looked at Alliant, they have those velocities at 6.3 grains for a 115 bullet. Expected velocity is 1250 @ 6.3 grains.

David
 
What's your altitude? What was the temperature?

FWIW, I always run a known standard through my chrono (usually a string of CCI Mini-Mag through a given bolt-action rifle) before doing any serious work. If I see any serious variance from what I expect to see (and I've seen this standard a lot over the years), I check things out more before proceeding further.
 
looking at a .40 load I checked on 6/2013
I was using a 180gr bullet
5.5 Unique
a ten shot average of 970fps

so your load
115 gr
5.6 gr Unique
ten shot average of 1276
doesn't seem entirely out of reach

I always consider chronograph data more relative than absolute
There are a large number of variables that would have to be considered outside of a perfect lab situation
YMMV
 
I have 3 reloading books and many times they don't agree with each other and when I chronograph a load I get a 4th answer. When you chronograph a load it tells you what that load is doing in that gun. Change guns or brass and get a different answer. Larry
 
Since that is a "Light" load of Unique , I can see where the
numbers can be spread out. Fill that case with 5.9 or 6.0 grs
of powder and you should get better numbers.............
or you can go to a faster burning powder like Red Dot or w231
to get numbers that may have even a smaller ES in your loads.

You also need to know where the "Sweet spot" on your chrony is located.
Some start 4-5" above the unit and some 10" above the unit .....
while some might have a 140 sq inch area and the other a 380 sg area to make readings.

A shot out of the "Zone" could cause the data to be off as much as 100 fps or if bad enough toss an Err on the unit.

Good shooting.
 
pibulloncrack said:
Testing some loads on a new chronograph yesterday and I recorded some readings that I question.
In your opinion do these velocities seem possible?

I set up the chronograph about 12’ out.
Shooting a M&P Pro 5”

1304
1306
1245
1276
1248
1275
1279
1280
1304
1248

Here is the load.

115 gr X-reme rn
5.6 gr Unique
OAL 1.3
Crimp .380

I intentionally left out the make of the chronograph so the conversation did not get side tracked.

Thanks in advance!
Click to expand...

I load pretty much your identical setup but through a M&P9FS with a KKM barrel. I get about 1250fps with my load of 6.0g?( I am at work and don't have the exact number) of Unique. I will double check tonight, but I know its on the high end of the Unique scale. I also seat 1.100.
 
Last edited:
the data looks about right in terms of consistency.
YOU are using a 5" barrel, where Alliant states a 4" barrel was used
thats good for a few feet.
You are also using a different bullet. For this, you cannot expect the same results.
 
Certainly within the possible range. All guns & barrels are diff. There are "fast" barrels, tighter chamber, tighter bore + higher vel. A 5" bbl can add 30-50fps over a 4", depending on the powder.
If it's a Chrony, make sure the screens are folded out flat. Even slight deviation from flat will change the readings as the screens aren't at the precise distance from what the unit is set to measure, usually 24".
 
Last edited:
Nevada Ed said:
You also need to know where the "Sweet spot" on your chrony is located.
Some start 4-5" above the unit and some 10" above the unit .....
while some might have a 140 sq inch area and the other a 380 sg area to make readings.

A shot out of the "Zone" could cause the data to be off as much as 100 fps or if bad enough toss an Err on the unit.

Good shooting.
Click to expand...

I did not know that Ed. I was thinking that, to me, the OP's numbers look exactly like what I normaly get. Could it be that im shooting too close to the "pick-ups" ?
Last time I was out out I got an ES of 127 on one string and other high ES numbers on other strings. I was wondering "what the hell is going on"
 
Shooter Magaven said:
I did not know that Ed. I was thinking that, to me, the OP's numbers look exactly like what I normaly get. Could it be that im shooting too close to the "pick-ups" ?
Last time I was out out I got an ES of 127 on one string and other high ES numbers on other strings. I was wondering "what the hell is going on"
Click to expand...

A 2/10gr variation with a fast powder can cause that large a swing, especially if matched with a case slightly larger in volume & with less neck tension. There are a lot of variables affecting vel deviation.
 
fredj338 said:
A 2/10gr variation with a fast powder can cause that large a swing, especially if matched with a case slightly larger in volume & with less neck tension. There are a lot of variables affecting vel deviation.
Click to expand...

These were hand weighted 357 loads of 4227, trimmed cases and using a Lee FCD. So I was a little suprised at this variations in volocity.
But these were loads using very well used mixed brass, so there may be something in the neck tension :o
However, I noticed on this outing that I was shooting closer to the chrono than I usually do

Sorry OP, didnt mean to hijack you. I'm done.
 
No worries Shooter. Anyone else have any experience with Unique and plated 115 gr bullets?
 
Would not be worrying about the "ES", as that ain't bad for a pistol load. Does seem a little fast for 5.6 grains unique at that col.

Would wonder why a 115 rn is seated out to 1.3 in, which is considerably longer than the listed max for 9mm of 1.169. There can't be much of that bullet in the case, and minimal interference fit?

Did you check for setback, using a seated bullet but no primer or powder from full lock back of the slide? What cases and primer are ya using? How was the accuracy?
 
I'm still trying to understand the question. Forgive me for being slow ;) Not trying to be a wise cracker either! I'm starting here because you said it was a new chronograph!!!

Are you questioning the spread in the data? or the max velocity? or the min? or the value(s)?

Like other discussions on scales and weighing powder, we need to be clear on Accuracy (for a known value of X, how close the reading is to X) and Precision (how frequently does the reading for a known value of X repeatedly come up Y).


The link below gives some great pictures for how minor changes can impact readings. These devices compute V (velocity) based on measured T (time) across a fixed D (distance) as measured parallel to the sensors and perpendicular to the front and rear planes. In other words, straight dead center through the middle of the box above the sensors.

If you think of the geometry of the actual bullet path through this "box" created by the sensors, changing the trajectory up or down OR left or right changes (increases) the distance (D) the bullet is actually traveling between the sensors. The manifestation is actually a higher value for T reported by the sensors for this shot than if the bullet traveled that nirvana path of "straight through the middle" of the box. NOTE - this is how shadows from multiple light sources can also impact measurements

This then changes the accuracy of each measurement as the device computes V (velocity) = D (distance)/T (time) assuming D to be a fixed value less than the actual distance traveled.

Now to confuse things more, if you really did have a repeatable round (true velocity) but each shot traveled a different path through the "magic box" past the sensors, you might incorrectly conclude the device is not precise :)

pibulloncrack said:
Testing some loads on a new chronograph yesterday and I recorded some readings that I question.
In your opinion do these velocities seem possible?

I set up the chronograph about 12’ out.
Shooting a M&P Pro 5”

1304
1306
1245
1276
1248
1275
1279
1280
1304
1248

Here is the load.

115 gr X-reme rn
5.6 gr Unique
OAL 1.3
Crimp .380

I intentionally left out the make of the chronograph so the conversation did not get side tracked.

Thanks in advance!
Click to expand...
 
Last edited:
I am afraid I am in the camp that doesn't understand the question! While the average velocity of the noted load is a bit faster (maybe 100 FPS) than I would expect it isn't beyond the realm of possibility. The extreme spread of 61 FPS is certainly not out of line for any handgun cartridge.

What is it that you think is so odd about the readings you are getting?????
 
Last edited:
It is nice to have a chrony and see what your loads are doing
in the fps department but I still go with the loads that are the
MOST accurate ..........or at POA, depending on my needs.

Now if I had some factory SD ammo that had a 60 to 80 fps
ED I might get upset with the difference in energy for the loads.

No big thing with maximum loads in the 9mm or higher calibers
but the little 38 snub nose needs every drop of energy it can get !!
For a 125gr that could be a ME of 177 or 205 with just a 60 ES
plus the chance of the bullet not expanding if it is the one out
of the box with a low fps !!

Don't you just love numbers.....................
 
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