Thread: Seating depth/ Bearing surface

Hi there.
Just watched a video where it was stated (A cardinal rule, though not always achievable. Go figure which is it!) that a projectile should be seated so that it's bearing surface is a minimum of the bore.
Just fired some reloads .243. By my reckoning the load that worked best only had a bearing surface of 5.38mm not the minimum of 6mm. This is on a bolt action rifle. So the question is how critical is this? Does it make any difference if it's bolt action vs auto? And although it may not matter in this case at what point might it become an issue?
Thoughts please.
Cheers FC

Minimum of calibre left in the neck?
Its my understanding that's mostly to do with concentricity. Insuring good concentricity. Does it matter? If the load is accurate who cares right?

It was saying that you need a minimum of projectile bearing surface on the neck of the case to ensure nothing works lose.
https://www.youtube.com/watch?v=qkzh4_hyNqc&t=5s
At 7.30 in.

It's more the point. You need some length there. I wouldn't worry about yours. (It's a general rule of thumb)
If it came loose. You would loose concentricity before it came out I would imagine.
Depends how rough you are with your rounds. Running them jammed wouldn't help. The semi if you were allowed one would be a bit harder than the bolt on rounds.

Guys that run jammed sometimes go to eject a live round and the projectile comes out as it's jammed into the rifling spilling powder into the action and maybe trigger ruining your day, until you go home and clean it all out, other than that it's not that big of a deal.

Keep it in mind when loading. If it becomes a problem you could always increase neck pressure or crimp them. But I wouldn't worry too much.
Here is some homework for you.... Load a dummy round no primer or powder.... Now try pull the projectile, see what force it takes then make up your mind if it is a problem.

Many thanks for that. I've got just such a round. Since they have discontinued my projectile (Hornady 100gn) I'm going to have to start over again. Probably opt for the Hornady BTSP. Thanks again

I loaded some 308 130gr hollow points with about 30 thou jump to the lands.
I didn’t notice there was nearly nothing in the neck until after I shot them. They shot okay, but would’ve been a risk of the projectile coming out and dumping powder everywhere.
If I can manage to hobble out to the shed I’ll work out how much was in the neck, but it really was bugger all

I called BS on that "cardinal rule" yonks ago. It's just not practical or necessary and in some cases detrimental to the performance of a cartridge. And yet you still see it recommended regularly on the net and that can't be wrong can it?

Take for example the 308. The neck is around 0.296" long (depending upon trim length). Seating the bottom of the bearing surface 1 calibre deep puts it below the case mouth to shoulder junction and puts the base of most boatail profectiles too deep into the case and restricts powder capacity. That can be aleviated by faster powders but that still may not give good performance/accuracy. For cartridges prone to bad brass flow and donut formation at the neck shoulder junction it is better to not have the bearing surface in contact with the donut. Although it is better to eliminate the donut even if you don't seat on to it.

Have just had a 308 barrel chambered up for FTR. Will probable run 20 this jump. The range of projectiles I may run (155gr to 185 gr) run from 0.113" to 0.262" bearing surface deep, as I have had it throated.

The 155 gr depth at 0.113" I wouldn't recommend in a hunting load because if you drop a round the projectile is knocked sideways badly out of true - anything dropped always lands on it least wanted point.


Also projectiles even in the same weight range but from different manufacturers have different lengths and profiles.

A better rule of thumb maybe is to have say 2/3s of the bearing surface in the neck. All also depends upon throat length and optimum jump.

And then there are theories on how the depth of the projectile into the case affects gas swirl/turbulence - my head hurts when trying to grasp these theories.

Thanks again for the replies. Even found out about donuting. Not heard that one before.