Mauser M12 308 - Loading Barnes TTSX 130 Grn Length Off Lands

[Scotty99]

As per rather complicated thread title, I’m trying to work up a load for my Mauser M12 .308 for Barnes TTSX 130 grn.

The Mauser M12 has a lot of free space in the chamber which is I think the basis of my issue.

I’ve measured the length to touch the lands with the bullet and it’s 2.305 inches to the Ogive giving a COAL of 2.935.

Barnes recommend starting seating depth of 0.050 off the lands and working back from there.

My magazine length means I can only get 0.070 off the lands which gives a COAL of 2.866.

Theory all good to this point until I load to 0.070 off the lands which gives rounds that look like these below, which to me look rather odd.

What am I missing?

 

[wytonpjs]

Post in thread '308 velocities from a 20inch barrel'

May 13, 2026

I’m currently working up a load for 130 grn TTSX for my M12, how far off the lands are you seating your bullets?

Having faffed around doing jump testing for my .243 TTSX load, I started the .308 load using the same COAL as the factory VOR-TX round - 2.079". When I first got the .308 I measured the chamber as 2.307". By my poor maths, I make that a jump of 228 thou or 5.8mm. When I acquired my Tikka T3X in .308 I tried the S20 rounds and had exactly the same results including accuracy so I didn't touch it! Fire-formed cases from the S20 fit the T3X and vice-versa - winner...

• wytonpjs

• 

 

[Milk no sugar please]

This is how Barnes load them for their factory ammunition. I copied this and surprise, they are very accurate. They need a mind bendingly massive jump. Discard this start loading at 50 thou from the lands idea; Barnes do not do this when manufacturing their own ammunition. My swede is the same, super short coal. Work up slowly, you will get the accuracy and velocity you seek.

 

[takbok]

I'd start at the length specified in Barnes load data. It will save a lot of hassle and money.

https://barnesbullets.com/content/barnes-loaddata/rifle/308/308WinchesterForWeb.pdf

 

[CWY308]

With the shape of copper bullets, I find the AOL of the cartridge much shorter, but it does not affect accuracy in my 308

69.5mm AOL with 130gn fox hunter
71.12 mm AOL with 150gn Nosler BT

Not a colossal amount in a deer stalking scenario

 

[Norfolk Deer Search]

70 tho isn’t unheard of with loading copper, but if your restricted by magazine length, your sort of buggered!

I would load a couple of 3 at the 70 tho and shoot them into the ground just to check for pressure signs, that’s what I WOULD DO and then go from there!

What you do is up to you.

 

[big ears]

Exactly this.

I'd start at the length specified in Barnes load data. It will save a lot of hassle and money.

https://barnesbullets.com/content/barnes-loaddata/rifle/308/308WinchesterForWeb.pdf

Load 3 and see what happens.
From there you can change the load and chase a node once you find it if it’s not perfect adjust the seating depth in 5thou increments until it tightens

 

[cjm1066]

308 can take 180/200g bullets, lighter shorter bullets give you this problem if you chase "ideal" loading length.

I now load to recommended length with non lead and it works.