@ 03:50 pm (GMT)
Nathan FosterAs I understand it- Nosler brass is Norma Brass. Both are very soft in my experience. I tend to use Rem Brass in the Ultra mags.
Do not go fiddling powders in either the 7mm or .300 RUM. Use only what the manufacturers recommend. The case design is over bore and if the wrong powder is selected and downloaded, uneven burning can alter the burn rate of the powder (all powder ignited at once), resulting in pressures over 70,000psi.
Yes, low PSI equals lower pressure but the differences are very small.
I have done many tests with bullet deflection. One test was with FMJ military ball .308 ammo, studying deflection in Manuka scrub. I used Tracer ammunition and did the tests at night. Conclusion- the bullets could go anywhere. Through other tests I found that a high SD bullet would sometimes do better than a shorter bullet. In the .30 cal, this means bullets 180 grains and heavier. But even SD has its limits. If the bullet glances the side of a twig rather than hitting it dead on, it will yaw and tumble the same as anything else. I saw the tests you are talking about and yes, the TSX performed quite well, but it still has the same limitations if it glances twigs, rather than hitting dead on.
Your project is an intersting one. On the one hand, you are wanting the power of the .300 RUM but on the other hand, recoil is an issue that is already worrying you. One could easily say- why buy a .300 RUM if you are worried about the recoil? But on closer inspection, what we are talking about is a very light rifle for the power generated. So a better question is- how do you utilize this power without being beaten into next week with a resultant loss of accuracy. Ideally, a heavier barrel would be better, but the SPS does not have a heavy barrel so thats moot. Also, you are wanting to use the rifle for bush work which calls for relatively light barrel weights. If you were after a dedicated long range rifle, I would have recommended that you do not adopt the SPS and instead save for a Sendero type rifle.
Ultimately, the challenge will be how recoil effects accuracy by jolting the rifle of its point of aim during ignition. This will naturally become your primary focus as opposed to felt recoil. You will probably either have to replace the stock with a Laminate or use my sniper tape and paint method (blog) to increase grip area or texture. A muzzle brake can help but a spiral ported brake will make the rifle worse to shoot. If the brake thread is cut to M12, the muzzle will most likely swell after a while and the barrel will have to be docked. I don't know if you can go M14 thread on an SPS RUM barrel, I can't recall right now and am not about to go to the scrap bin on Christmas eve to find out. I think half inch is what the barrel will need to be cut to- awfully close to 12mm/M12.
I still think there is room for the creation of front pistol grips for bolt action rifles. An SPS stock could be worth experimenting on seeing as it is a cheap (who cares) stock design.
For now, focus on the rifle accuracy factors of bedding, stabilizing, stock replacement or tape and paint, trigger work or replacement, running the bore in, load work, shooting technique, trigger control- long eye relief optics, hunting methods, drop charts etc etc etc.
Down loading is fine as long as you are not trying to go overboard and causing problems. You have basically 600 rounds or so to decide whether you like the .300 RUM before its time to rebarrel. When you rebarrel, you will have the option of adopting the same contour barrel, going for a heavier contour barrel or perhaps adopting the .300 Win Mag for lighter recoil.
I can understand where you are coming from. You will need to be patient and put a lot of attention into quiet observation and careful planning as you move forwards.