TMK175

stu47 · February 5, 2017

Hi,

I have had a new barrel on my Tikka M55 - work completed by Big Al on this forum and can thoroughly recommend both him and his work, extremely knowledgeable and top bloke to boot.

Barrel is a Sassen .308, 28", 1 in 10, cut for TMK175.

I managed to fire it for the first time today - only at 100m to find the load it prefers.

Virgin Lapua brass (not Palma), BR2, N150, TMK175, ogive 2.235 giving a 15 thou jump. Brass prep included neck turn to 15 thou (just to remove high spots).

I took my Magneto Sporter but didnt to fit it as I didn't want to influence anything once I had started.

My questions are:

1. Now brass is fire formed to my chamber will pressures change considerably on the next firing - comparing pre and post firing dimensions shows the brass gained 2 thou headspace and diameter grew 3 Thou?

2. I "think" mv will be in the region of 2760-2790fps with the 44gr load - could someone confirm this with quickly load or similar please? I want to retain 1250fps at 1000.

3. I understand the 45gr load is smaller but bolt lift required very slightly more pressure to unlock so, using OCW, I think it best to stay around the 43-44gr area - would you agree?

4. Once I have established a powder weight (N150) I will experiment with jump - is this the right way forward?

Any observations, input or recommendations are gratefully received!

Thanks in advance gents