Can a load be too compressed? Have a new barrel, and am finding that to get 10 'off' on this chambering, both the 109 and 115s (6mm) are seated past shoulder-depth. Is this a concern? In general, are there drawbacks to compressed loads? Thx.
- Thread starter Dunraven
- Start date
Are you actually compressed or are you just past the shoulder?
Yes. Absolutely.
Compressed loads depend on seating depth, yes, but also powder volume (directly related to charge weight).
How much is “too compressed” depends on many factors, but the biggest one tends to be powder type: ball/spherical vs stick/extruded. Ball powders do not like compression; stick powders actually prefer it sometimes, up to about 5-10% compressed.
Basically, when I’m loading up a charge ladder, I know I’m compressing the load when it crunches, and I know it’s time to stop when the seating die can’t maintain my target CBTO without having to adjust the die to seat deeper. What’s happening is that the pressure required to compress the powder at that point is overcoming the seating die.
Going back to your original question: the bullet base below the neck/shoulder junction does not inherently cause a compressed load, and a compressed load (with stick powder) is not inherently bad. Bullet base below the junction does mean you can’t fit as much powder in there before getting compression, though.
How much is “too compressed” depends on many factors, but the biggest one tends to be powder type: ball/spherical vs stick/extruded. Ball powders do not like compression; stick powders actually prefer it sometimes, up to about 5-10% compressed.
Basically, when I’m loading up a charge ladder, I know I’m compressing the load when it crunches, and I know it’s time to stop when the seating die can’t maintain my target CBTO without having to adjust the die to seat deeper. What’s happening is that the pressure required to compress the powder at that point is overcoming the seating die.
Going back to your original question: the bullet base below the neck/shoulder junction does not inherently cause a compressed load, and a compressed load (with stick powder) is not inherently bad. Bullet base below the junction does mean you can’t fit as much powder in there before getting compression, though.
I spoke someone once and they said up to 8% of compressed load, so 108% as max. Not sure if that's true... but I've stayed near that and not over
It’s not hard, or particularly dangerous, to find your own pressure limits in your own system. You don’t need to (and maybe should not depend on) some random rule of thumb when you have the tools to do your own testing.
If you see any pressure signs, it’s too far (cratered or totally flattened or pierced primers, ejector marks on case heads, stiff bolt lift, significant web diameter growth, incipient head separation, etc.). Cratered or pierced primers is a bit complex, because an oversized firing pin hole can cause that too, but stiff bolt lift or case head marks are pretty darn reliable.
Work your charge up slowly, watch carefully for signs, and stop when you see them. No rules of thumb required, really; I offered the 10% as a general range, but I always load my ladders well above what the book says, then end up not firing some of the max loads because I see signs before getting to them. It’s much easier for me to break down overloaded rounds than it is to go home and load higher charges because I stopped too soon on my ladder work up.
If you see any pressure signs, it’s too far (cratered or totally flattened or pierced primers, ejector marks on case heads, stiff bolt lift, significant web diameter growth, incipient head separation, etc.). Cratered or pierced primers is a bit complex, because an oversized firing pin hole can cause that too, but stiff bolt lift or case head marks are pretty darn reliable.
Work your charge up slowly, watch carefully for signs, and stop when you see them. No rules of thumb required, really; I offered the 10% as a general range, but I always load my ladders well above what the book says, then end up not firing some of the max loads because I see signs before getting to them. It’s much easier for me to break down overloaded rounds than it is to go home and load higher charges because I stopped too soon on my ladder work up.
