Bullet seating too shallow here?

[Ballistix]

Hi,

I want to compare two bullets (SMK Palma 155 and Lapua Scenar 155) in my Steyr SSG 04A1 308 to see which is more accurate at 100 through 1000 yards.

Before I settle on the optimum powder charge I wanted to know what measurement each bullet was to the lands so that I could start by seating them .020 back and then experiment with loads/powders. I measured base to ogive using the hornady OAL magic wand and bullet comparator kit. The plan then, after finding my ideal load, was to tweak the seating depth to find the best accuracy between the two bullets.

Anyhow I have hit a bit of an issue already in that the Sierra Bullet is a fair bit shorter and the ogive must be closer to the base than the Lapua so when I seat the Sierra bullet 0.020 back from the lands I have very little bullet left (0.077" see pic) for the case neck to grip onto. The lapua has a good amount (0.227") Both bullets do fit into my magazine I checked.

Q1 > I'm concerned that seating so shallow is going to be detrimental for a few reasons - pressure safety, inaccuracy due to not being concentric, bullet and powder falling out in the chamber etc. Any helpful comments?

Q2 > I know that the rule of thumb is to use the calibre dimension (0.308") for the area of the bullet that is gripped by the case neck but can I ask the experienced folk out there what kind of measurement should I not go below for the Sierra bullet? Looks like the jump to the lands will need to be way in excess of 0.020".

Thanks.

[Geordie bloke]

Re Q1 - do not use that bullet as there is not enough bearing surface in the case neck and it could easily be knocked out of concentricity, or perhaps fall out whilst in your magazine.
Re Q2 - the minimum I would go for in a single feed action like a BAT is 1/2 a bullet calibre with the bullet just touching the rifling.
I would stick with the longer Lapua bullet as the Sierra is just too short a bullet for your chamber/freebore.

[phaedra1106]

COAL of 2.238" for a .308?, Min SAAMI spec is a COAL of 2.49".

My SSG04 takes 2.857" to be 40 thou" off the lands using either A-Max, Nosler CC or Lapua Scenar 168gr, I know the 155s are slightly shorter but only by about .055".

[Ballistix]

COAL of 2.238" for a .308?, Min SAAMI spec is a COAL of 2.49".

My SSG04 takes 2.857" to be 40 thou" off the lands using either A-Max, Nosler CC or Lapua Scenar 168gr, I know the 155s are slightly shorter but only by about .055".

I'm measuring to the ogive not the tip and have taken off 0.020 so the actual COAL to the lands is 2.258 for the Lapua 155.

[Ballistix]

Re Q1 - do not use that bullet as there is not enough bearing surface in the case neck and it could easily be knocked out of concentricity, or perhaps fall out whilst in your magazine.
Re Q2 - the minimum I would go for in a single feed action like a BAT is 1/2 a bullet calibre with the bullet just touching the rifling.
I would stick with the longer Lapua bullet as the Sierra is just too short a bullet for your chamber/freebore.

Q1. Thanks. It isn't a loaded cartridge just an empty/primerless case with the bullet loosely fitted to depth for reference.

Cheers

[phaedra1106]

Rough check on one of my 308's (2.857" COAL) puts the ogive at approx: 2.237" so adding the .040" I usually set back would give a base to lands on my SSG04 of 2.277"

[Ballistix]

Re Q1 - do not use that bullet as there is not enough bearing surface in the case neck and it could easily be knocked out of concentricity, or perhaps fall out whilst in your magazine.
Re Q2 - the minimum I would go for in a single feed action like a BAT is 1/2 a bullet calibre with the bullet just touching the rifling.
I would stick with the longer Lapua bullet as the Sierra is just too short a bullet for your chamber/freebore.

Half a bullet calibre thanks for the answer Geordie bloke.

I pulled an HPS 308 155g Long range bullet purchsed from Bisley that had an SMK #2155 head and that is seated about half its calibre into the neck. Incidentally I measured the OAL to the ogive on the 2155 and that is 0.010 closer to the lands of my rifle than the SMK #2156 palma.

When I do my load testing I'll just have to seat the Sierras way off the lands and my Scenars at the optimum 0.020 off.