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+--- Thread: COL (/showthread.php?tid=235)
COL - alwie - 03-12-2021
All,
Im new to reloading and have a lot to still learn. If everything but COL remains the same and COL decreases by 0.010” , my understanding is that the peak pressure will increase. Will velocity remain the same (since only peak pressure increased) or will muzzle velocity increase a little bit?
Thx.
Alex
RE: COL - Lemonaid - 03-12-2021
My understanding is that you may get a small increase in velocity. One test that I did with a large amount of seating depth change only resulted in 20 fps or so increase, and it wasn't a straight line change, it would go up a bit, down a bit but it trended on the increase.
It may differ for each powder/bullet/primer/firearm, so get a large opinion sample.
The extremes are a different can of worms, if the c.o.a.l. gets the bullet into the lands or if bullet seating starts powder compression it can change a lot faster.
RE: COL - grayfox - 03-12-2021
To add on to what LA says, in theory the pressure should go up a bit, although another factor is that a bit more "blow by" around the bullet happens until it fully seats into the barrel due to the somewhat higher pressure. My GRT tool says Pressure/MV increases but there's not a lot of MV change. When I compute my OBT nodes I generally assume coal changes only affect the timing of the bullet exit while MV is assumed constant. It's a simplification but seems to work ok.
The other factor as I know it, is that for a given charge of powder, there is a finite and fairly constant amount of energy to do the work of accelerating the bullet, so again, MV shouldn't vary by much.
But, as LA said, at the extremes of too short/too long-into lands, the pressure can skyrocket and do weird and dangerous things. Not a good spot to be in. Stay away from extreme Coal's.
RE: COL - CZ527 Guy - 03-12-2021
Perhaps one of the better sources of YT reloading guidance I have encountered thus far. for what it is worth Ill share the link below.
https://www.youtube.com/watch?v=rRu8NYCq9Y0