Bullet Velocity Variation (2)

[Brillo]

I thought it best to start a new post on this subject rather than highjack the original, which was a query about accuracy of reloading scales.

I read with interest the German Salazar article about .308 1000 yard load development because I'm finding 1000 yd shooting particularly challenging (and enjoyable).

My rifle is a .308 Sako TRG-22 with a 26" barrel and up to now I have used, exclusively, the 155 grain SMK #2155 bullet. With this head and various load combinations I have had good results up to 900 yards, but it fails at 1000 yards.

My favourite load has a MV of 2850 and by the time it gets to 1000 yards its velocity is only 1100 fps. I have developed a load that gives me 2920 fps but even this will not get me near to the magic Mach 1.2 number mentioned in the article.

I have been advised to go to a heavier bullet and I'm in the process of developing loads for the 175 grain SMK, coincidentally the same bullet referred to in the article and used in the mentioned ballistics test.

So far I have reached 2730 fps without pressure signs, with the aim of reaching 2750 fps and so replicating an established accuracy load I found on the 6mmBR website. But even this will only get me to Mach 1.147 (1280 fps) at 1000 yards at a range height of 220 feet (this is the height of Stickledown at Bisley).

To reach Mach 1.2 at this height I need to have a MV of 2860 fps. I would have thought that this MV with a 175 grain bullet would produce very high pressures and I'm reluctant to even progress towards it especially when the maximum loads on the Vihtavouri data tables for the 175 SMK is 2631 fps.

Comments?

[Eagernoskill]

Double post

[Eagernoskill]

"exlusively, the 155 grain SMK #2155 bullet"

 

Changed to the 2156 and you will get noticeable improvement in down range velocity

 

2155 = G1 BC of 0.417

 

2156 = G1 BC of 0.447

 

That is almost the equivalent of driving your 2155 +- 150 fps more.