Velocity change. Is this normal?

[old leghumper]

New barrel with 50 rounds for break in(Bartiein 5R 7.5 twist). Next fired five different five shot groups for load testing and chronographing with a clean barrel. Fired a second round with same loads and in every case the second round groups averaged 35 fps faster. Temps were no more than one degree different with a temp insensitive powder(h4350). Barrel never got warm - what am I missing. Have not had this problem in the past.

 

[savagedasher]

New barrel with 50 rounds for break in(Bartiein 5R 7.5 twist). Next fired five different five shot groups for load testing and chronographing with a clean barrel. Fired a second round with same loads and in every case the second round groups averaged 35 fps faster. Temps were no more than one degree different with a temp insensitive powder(h4350). Barrel never got warm - what am I missing. Have not had this problem in the past.

It's no different then using molly bullets .
When the barrel is cleaned it slick so you have less pressure . Larry

 

[skiutah02]

As above (my "down to metal" clean cold bore shot is typically 150 fps slower then shot #2), plus all of my Bartleins have "sped up" around after about 100-150 rounds total on them. Usually 40fps but one was almost 100fps. In all cases, had to redo load testing as a consequence. Now I never do final load testing until after 150 rounds on barrel. Drew

 

[coues52]

As above (my "down to metal" clean cold bore shot is typically 150 fps slower then shot #2), plus all of my Bartleins have "sped up" around after about 100-150 rounds total on them. Usually 40fps but one was almost 100fps. In all cases, had to redo load testing as a consequence. Now I never do final load testing until after 150 rounds on barrel. Drew

this ! 1+ ( also does not matter barrel manu,they all change as they get a few rounds them )

 

[quartermaster]

I just bought a magnetospeed chrony, because my velocity readings always change due to the change of the suns location in the sky thoughout the day. This past weekend, I said to myself, enough is enough. Been fighting it and doubting my readings for 25 years
Could hat be your problem?