What would cause more pressure in a 124 LRN. 9 mm. Having a bullet jammed into the rifling, or seating it 30 thou. shorter, and just barely touching the rifling. I ask this because I have loaded about 100 rounds to long. They work and function fine but they are jammed in the rifling. So I seated them deeper so they drop in and fall out if the barrel freely. The long ones where 1.169 inches long. The new ones are 1.130 inches long. Is this ok?
9 mm question seating depth
- Thread starter ReloaderRick
- Start date
My rule of thumb for minimum seating depth is 1/2 calibre diameter inside the case.
So for 9mmx19 -
Max case length is 0.754.
Random example I dredged up from my stocks is a 125g HAP projectile with an OAL of 0.566"
(9mm projectile diameter is .356, half of that is 0.177)
So 0.754 plus 0.566 minus 0.177 = 1.143 max OAL in this example.
(That leaves enough of the projectile inside the case to grip it properly thru the feeding cycle
assuming proper neck tension).
Typically you seat deeper to clear the throat with some modest margin.
In my above example, I'm using a 1.120" actual production seating depth to clear the throat
in a G17 barrel.
Ideally the cautious reloader makes up a dummy cartridge or two and tries them in the barrels
they're be using to ensure the result will fit.
I typically make up a max length dummy and keep seating the projectile deeper until it clear the throat,
and then add say 0.005 more to allow for dirt and press operation variance.
I'll then make up a fresh dummy with that press setup for a final chamber check, since a progressively reseated projectile
won't necessarily sit in a case the same way as a single-stroke seating.
Ideally you pick a seating depth first and then work up a powder charge.
If you are away from a max loading a bit of deeper seating can be safe.
Suggest checking the first fired cases after reseating for signs of excessive pressures.
So for 9mmx19 -
Max case length is 0.754.
Random example I dredged up from my stocks is a 125g HAP projectile with an OAL of 0.566"
(9mm projectile diameter is .356, half of that is 0.177)
So 0.754 plus 0.566 minus 0.177 = 1.143 max OAL in this example.
(That leaves enough of the projectile inside the case to grip it properly thru the feeding cycle
assuming proper neck tension).
Typically you seat deeper to clear the throat with some modest margin.
In my above example, I'm using a 1.120" actual production seating depth to clear the throat
in a G17 barrel.
Ideally the cautious reloader makes up a dummy cartridge or two and tries them in the barrels
they're be using to ensure the result will fit.
I typically make up a max length dummy and keep seating the projectile deeper until it clear the throat,
and then add say 0.005 more to allow for dirt and press operation variance.
I'll then make up a fresh dummy with that press setup for a final chamber check, since a progressively reseated projectile
won't necessarily sit in a case the same way as a single-stroke seating.
Ideally you pick a seating depth first and then work up a powder charge.
If you are away from a max loading a bit of deeper seating can be safe.
Suggest checking the first fired cases after reseating for signs of excessive pressures.
Last edited:
- Location
- West Quebec
Tagged
I ran into the exact same problem with my 9mm Jericho, I had to reseat the bullets .025" deeper and they shot fine, they were loaded .3 grains below max and showed no pressure signs when fired.
I'd say they are fine to shoot.
