Muzzle Velocity

[WATERWALKER]

Alright gents, I've got a question or y'all in regarding muzzle velocities. Earlier this year some buddies & I got a chance to stretch our legs a bit at the range. During this range trip I was using only a muzzle brake on my rifle. A few nights ago I recorded muzzle velocities while using a new can. I've got some numbers that just don't make sense to me. Each set of muzzle velocities were taken w/ a different MS-V3. The bayonet was properly secured each time & the alignment rod was about the same each time (to the naked eye). The biggest difference being that one set of numbers were taken w/ out the can & one set w/ the can. I'd fully expected to gain 20 - 25 FPS w/ the can but my MV actually decreased slightly while using the can. Just to eliminate a few more variables the chrono readings were taken w/ the same rifle using the same lot of ammunition, which is FGMM 175 gr. I used the same Kestrel both times & the gun shot lights out both trips.

*Results from range outings were taken on different ranges*

Results obtained on 01/03/2018
*Muzzle brake only
Conditions under the first set of muzzle velocities were as follows:
DA: 765 ft
Temp 29* F
Muzzle velocities for five shot group was 2,602 FPS
SD 5.6 FPS
Latitude 29.4

Results obtained 08/28/2018
*Suppressed
Conditions under the second set of muzzle velocities were as follows:
DA: 4045 ft
Temp 96* F
Muzzle velocities for group of five shot group was 2597
SD 8.3
Latitude 29.5

I was very surprised I didn't see an increase in muzzle velocity. Is this simply a question of atmospheric conditions or is there another reason that I'm missing entirely? As I mentioned above, the gun shot great both trips. I plugged the data into the Kestrel & the gun just hammered. I have absolutely zero complaints in regards to accuracy.

As always, I appreciate the help gents.

ETA: Spelling error.

 

[ZEROGUY]

I would say a difference of 5 FPS while having a SD of over 5 bettween the two tests is a statistically insignificant difference.

You need to run more tests under same environmentals with your brake AND can to get a better idea of what’s going on.

 

[WATERWALKER]

I would agree that five FPS by itself is trivial. I figured I'd gain muzzle velocity w/ the can is what has me thinking about this issue. As long as the gun continues to shoot this well it's meaningless, really. I'm just looking for some input as to how or why this might happen.

 

[damoncali]

How many shots? I sort of doubt you're getting a true 5 SD from factory ammo. This is probably just normal statistical variation.

 

[Deleted member 10043]

There is no why when the MV difference is immaterial. What is material is the difference in temperature. Statistically speaking you don't have enough data to reach an acceptable confidence level. Based on experience you will need at least seven 5 shot groups to get into the 90% ballpark for each stratum to compare and contrast. Actually, since we are only concerned with MV you don't need groups but just a total of 30 shots for each stratum fired under the same conditions.

You don't need any college level statistics course credits to understand this. But for those of us that dig this sort if shit we need at least a copy of Statistics for Dummies and a novice understanding along with it.

 

[WATERWALKER]

I figured that the DA & temp differences would be a contributing factor. Atmospheric conditions as a whole were night & day between winter & summer under the conditions described. I should've shot more groups recording muzzle velocities but I didn't. My fault there entirely.