300 BO Sub-sonic

[Caseknife]

So first time loading subs for my Ruger Am GenII. The bullets are Lehigh 198 Controlled fracturing, using load data from Lehigh. Standard practice for loading subs is to start high and go down to alleviate stuck bullets in the bore. Using H110 and CFE Black, loading 4 rounds of each weight, the first round of each group was kind of what was expected for velocity, but each round fired after went down in velocity significantly to the tune of 100fps+. Weighing each load with a balance beam. Haven't changed my process at all and have been loading for 40 years. Kind of confused, any insight as to what may be going on?

 

[Sheltowee]

What does your case fill look like? Any chance the charge is getting slopped around inside the case?

 

[Caseknife]

That could be the case, because with either H110 or CFE Black, not much powder in the case, but the bullet takes up a whole lot of room. Can't feel/hear any powder slop with the bullet seated. I will keep playing with it to see if I can find a suitable accurate load.

 

[kodiakisland]

Seems strange. Don’t have much to add. Even though you are using small charges, case volume is small and shouldn’t cause that much variation. Maybe try magnum primers for more consistent ignition. I find H110 to be very inconsistent unless pressures are high enough for consistent burns. H110 is not good for reduced handgun loads and I’d guess the same applies to rifles.

I use 1680 for sub loads in the 300 and have very small variations.

 

[p_ham]

Whats your neck tension? Are you crimping your bullets? I've seen 300BO subs grow in length from being cycled. That would drop pressures and velocity.

 

[kodiakisland]

Whats your neck tension? Are you crimping your bullets? I've seen 300BO subs grow in length from being cycled. That would drop pressures and velocity.

It’s a bolt rifle so that shouldn’t be an issue

 

[p_ham]

It’s a bolt rifle so that shouldn’t be an issue

Guess I should've read that better!

The other thing that comes to mind, is that the charge ladders got mixed up. He may have been shooting each charge weight per group instead of the same charge per group.