AR-10 work up questions

[186thFCo]

Today I took my new 16" barrel AR-10 to the range with my Magnetospeed V3 to do some MV readings. I was using factory ammo, 175gr FGM, as a basis on what to expect when I load my own.

At the range I shot a 5 shot string. Between each shot I waited at least 1 min to try and keep the barrel at an even temp. This is what my readings were.
Shot #1, 2441fps
Shot #2, 2429fps
Shot #3, 2426fps
Shot #4, 2418fps
Shot #5, 2406fps

Why would factory FGM have the MV drop after each shot, the last shot from that string being 35fps slower than the first. Is this normal to see? I'm still learning when it comes to reloading so should I expect the same kinda of results from my own loads?

 

[bruddah]

Not sure. Gas block working loose?

 

[186thFCo]

Thats something I could check

 

[JimmyT]

First 5 shots, or is barrel broken in?

 

[Hawk in WY]

Interesting thing about statistics: If the standard deviation is 10, all those nimbers are not statistically different from one another.

Shoot it some more more and you may see other random patterns.

Throw 100 pennies in the air. What should you conclude if five are all heads in one corner?

 

[186thFCo]

First 5 shots, or is barrel broken in?

rifle has 112 rounds through it, the damn thing shoots great, 1/2 moa all day with 175gr FGM, but this was the first time I measured MV so I was surprised to see different speeds