Retumbo temp velocity increase in my load today i noticed.

[PA Hunter]

Came up with a load for my .300 RUM last Febuary when it was 28 degrees outside in my Fierce CT Edge 26 barrel chronographed at 3170 fps 95 GR Retumbo 200 gr Accubond Fed 215 Mag primer.

Today same box of reloaded ammo 70 degrees outside July 30th in PA chronographed 3229 average fps and my grouping went to hell.

So an increase of 42 degrees warmer gave me 59 more fps with the Retumbo at least in my rifle Just in case anyone was wondering.

 

[EE_Reloader]

I'm curious what would be the corrective action here. Would you just drop a couple grains of powder and try it again during a hot day?

 

[Bater]

Was that barrel fully broken in? Wondering if speed up is a partial issue. I shoot your same load (except 93.5gr) from well below freezing to 85° + and usually see 10-15fps spread.

 

[Firestone]

It's probably cause retumbo is garbage. Pm me and I'll give you my address so I can dispose of it for you.

 

[menhaden_man]

Was that barrel fully broken in? Wondering if speed up is a partial issue. I shoot your same load (except 93.5gr) from well below freezing to 85° + and usually see 10-15fps spread.

I noticed that on a 7RM I just bought and was using a chrono for most of the first 200 rounds. The speed jumped damn near 100 FPS with the same loads right at around 90 shots.

Retumbo is a pretty stable powder, like H4831 and H100.

 

[N.AmericanTrophyHunts]

Bump. Just loaded a bunch of 143/ Retumbo and found the load at 24 degrees.

 

[Wrench]

Humidity at the time of loading has a very measurable result on velocity as well. Dry powder is lighter than damp powder. Damp powder is harder to ignite....

There's many articles on the topic.