Deep Seating Bullets
I don't know which bullet/shape you have, so it's hard to say exactly, but the RNFP bullets (like I posted above) usually don't need to be seated a lot deeper to reach the ogive. Other designs need more.
Recently I loaded some Rainier 250gr P-TCFP bullets in 45 Colt cases, using moderate speed powders, with a COAL of 1.600", a fairly nominal length. When I decided to try a load using a slower powder, 2400, I decided to deep seat them & crimp over the ogive to get a better burn. A change in COAL to 1.570" achieved that.
(It only needs to be seated so a caliper reading above the case mouth reads a few thosands smaller than the nominal bullet diameter & then taper crimped.)
The seating depth of the bullet went from ~.335" to ~.370" into the case. Using a simple volume calculator, created in Excel, that changed the "used case volume" from 32.1% to 35.5%, meaning there's 3.4% less case volume for the powder.
Using a chart, found in Lee's Modern Reloading Manual #1, by Vihtavuori, it indicate's the pressure would increase ~4.4% from this reduction in case capacity. If it was a 20K psi load that would raise it to ~20.9K psi.
So reducing the powder charge by ~3.5 to ~4.5% would offset the increase. (Dropping to 7grs would be a 17% reduction, way too much.)
I usually only deep seat in large capacity cases using reduced loads so the difference is of little consequence for me. Obviously deep seating in a 9mm would have greater consequences.
What barrel length are you shooting in that 8.5gr/Unique will give you 1200fps?? (More like ~925fps in a 6-1/2" bbl.)
A max. load of Unique with a 240gr JHP is over 10grs in a 44 Mag case.
.
I don't know which bullet/shape you have, so it's hard to say exactly, but the RNFP bullets (like I posted above) usually don't need to be seated a lot deeper to reach the ogive. Other designs need more.
Recently I loaded some Rainier 250gr P-TCFP bullets in 45 Colt cases, using moderate speed powders, with a COAL of 1.600", a fairly nominal length. When I decided to try a load using a slower powder, 2400, I decided to deep seat them & crimp over the ogive to get a better burn. A change in COAL to 1.570" achieved that.
(It only needs to be seated so a caliper reading above the case mouth reads a few thosands smaller than the nominal bullet diameter & then taper crimped.)
The seating depth of the bullet went from ~.335" to ~.370" into the case. Using a simple volume calculator, created in Excel, that changed the "used case volume" from 32.1% to 35.5%, meaning there's 3.4% less case volume for the powder.
Using a chart, found in Lee's Modern Reloading Manual #1, by Vihtavuori, it indicate's the pressure would increase ~4.4% from this reduction in case capacity. If it was a 20K psi load that would raise it to ~20.9K psi.
So reducing the powder charge by ~3.5 to ~4.5% would offset the increase. (Dropping to 7grs would be a 17% reduction, way too much.)
I usually only deep seat in large capacity cases using reduced loads so the difference is of little consequence for me. Obviously deep seating in a 9mm would have greater consequences.
What barrel length are you shooting in that 8.5gr/Unique will give you 1200fps?? (More like ~925fps in a 6-1/2" bbl.)
A max. load of Unique with a 240gr JHP is over 10grs in a 44 Mag case.
.
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