How much to lower powder charge?

[MHWASH]

Sig Cross 6.5 CM
The load in question is 43.2gr H4350,
New Peterson brass
135 Berger CH
First outing the load shot fine firing 4 shots. Temp was around freezing. A week later I had loaded up 20 more to do final sight in. First shot was fine, next two had hard bolt lift. I did not fire any more. Temp around 50.

Should I back off a half grain or a couple tenths? Bear season starts in April and I’d like to settle in a load soon so I can get to practicing.

 

[Justin Crossley]

I would back off by at least half a grain.

42.3-42.5 grains of H4350 is usually a good max load for that class of bullet in the 6.5 CM.

 

[Chris in TN]

In this exact case I’d back off to at least 42.5. Without knowing seating depth, throat, etc, anything else I said here would be a guess, but I strongly prefer settling in loads in half-grain intervals just to make remembering data easier if I ever need to go from memory. Also, Peterson brass is notoriously ‘small’. Also, you’ll likely see more velocity with 1x fired brass if you’re resizing it less than maximum. So you might drop to 42.8-43 before you see any speed loss at all.

Personally I’d likely go down to 42. Leave room for lot variations in new components. It’ll cost you ~50’mv to do that. It’s usually worth it.

 

[HuntHarder]

Virgin brass and hard bolt lift, I would back off a full grain.

 

[mtnbound]

Sig Cross 6.5 CM
The load in question is 43.2gr H4350,
New Peterson brass
135 Berger CH
First outing the load shot fine firing 4 shots. Temp was around freezing. A week later I had loaded up 20 more to do final sight in. First shot was fine, next two had hard bolt lift. I did not fire any more. Temp around 50.

Should I back off a half grain or a couple tenths? Bear season starts in April and I’d like to settle in a load soon so I can get to practicing.

Any other signs of pressure other than hard bolt lift with this firing?

Did you see any signs of pressure when you were developing this load?

 

[Wrench]

What's the chronograph telling you? Could be anything from tight brass to a carbon ring. If you have obvious signs of pressure with 4350 you're already well over pressure now.

 

[MHWASH]

The only other sign is a shiny spot from the extractor. Other loads did not have an issue. Velocity is 2735 from the 18” barrel.

 

[streamerfish]

The only other sign is a shiny spot from the extractor. Other loads did not have an issue. Velocity is 2735 from the 18” barrel.

What's your C.O.A.L????

Peterson brass is also pretty well know to be on the low end for volume. Especially new. So it builds pressure earlier then say hornady brass.

My guess would be that your probably hitting max pressure around 42gr of H4350. I would back it off to at least 42 grains and do some testing. Maybe even a handful at 41, 41.5, 42 and see how it goes.

 

[MHWASH]

COAL is whatever fits in the magazine, it hasn't been an issue with other loads.

Shot 42.5 grs of H4350 today, no stiff bolt lift or extractor marks. Velocity was 2684, SD 9.2.
Velocity difference of 50 fps between 43.2 and 42.5.

 

[Telford29]

If 42.5 shot good I’d stay down there. How did it do?

 

[MHWASH]

If 42.5 shot good I’d stay down there. How did it do?

It did ok, these are 1” dots. All are 4 shot groups.