7mm Rem Mag confusion..........advice please

[Laurie]

Can anyone provide a link or reference explaining the supposed role of bullet stability in this? [GAZ]

Good question, because as you imply the Enfield action's well known 'positive compensation' has nothing to do with bullet stability. It purely compensated for very variable military 303 ball ammunition MVs (likewise that of not quite so bad 7.62mm Black Spot 144-146gn NATO cartridges in the 1st gen TR rifles using a heavy-barrel Enfield conversion) that allied to modest MVs and BCs would be expected to produce very large vertical spreads at long range. In practical terms, I can't see how it would do anything for precision in terms of group size in anything other than the vertical plane either, and that only where such dispersion is caused by different MVs and hence trajectories. If the rifle and ammo cannot better say 3-MOA dispersion for mechanical reasons at short range, it has to be a fallacy that it'll shoot what becomes a smaller group in MOA terms at long range.

If it's a twist rate / bullet stability issue, group dispersion is increased before the degree of under-stabilisation is such that oval holes appear on the target, so round holes are not an infallible guide here especially at short ranges. At long range when the bullet is travelling slowly, hitting the target can cause it to tumble.

So far as the short barrel / muzzle blast dispersion issue goes, it's generally reckoned that muzzle pressure under 10,000 psi is desirable to avoid random deflection effects on the bullet base. But I can't see how that would produce better groups at longer ranges than at short. If deflected at the muzzle, the actual amount of defelection should increase with distance, not decrease. I suppose it could create some sort of temporary instability that is ironed out with distance, but that sounds too good to be true!

Incidentally running your loads through QuickLOAD shows all three exceed 10,000 psi muzzle pressure running from just over 12,000 psi to the worst (N560) at 13,740 psi. BUT, all three are mild, the N560 and Hunter loads far too mild with estimated PMAX running at 54,236 psi for Magnum, 51,727 psi for Hunter, and only 39,687 psi for N560.

I once knew a guy who tried very hard to download 7mm Rem Mag as it did too much damage to Roe - he brought it to the range Sunday after Sunday and results were poor. One day, he turned up with a short barrel Ruger that made a nasty crack and had a bit of muzzle flash - he'd given up and bought a .243 keeping the seven for Scottish reds!

In my own experience of Ramshot ball powders and even more so Viht N560, lowish pressures produce very poor results, inconsistent MVs and in N560's case horrendous muzzle flash. Allied to the short barrel, high but also very inconsistent muzzle pressures might affect bullets badly.

Nosler recommends Viht N165 as its most accurate powder for its 140gn bullets, the max charge weight being 66.0gn. N160's maximum is only slightly lower at 65.5gn for a higher MV - 3,137 fps from a 24 inch barrel. I know Ramshot says 64.0gn Hunter is max for 60,000 psi, but QuickLOAD says that only produces 54,000 odd psi.

I'm also intrigued (and pleased) that you've got Hunter from somewhere. A few weeks ago, Henry Krank staff told me they couldn't import Hunter as it's not legal for use here - presumably not CE certified. I noticed just today that Hunter had reappeared in their latest GunMart advert and wondered if this was a mistake. There are several 6.5s that should be ideally suited to this powder.

[Scotsgun]

Laurie,

Thankyou for the advice and info. i think i followed most of it. Essentially i should try Vhit N165 or even 160?

I started using Ramshot powdes a few years back due to probs sourcing my fav Vhit powders nearby. A small local dealer had invested in ramshot, i tried it, loved its ease of reloading and now have stocks of magnum, hunter, big game and blue trail.

I popped out this morning to try the rubber band idea. A mate lent me a small rubber doghnut thing which he bought from the US a while back. I tried it on all my existing loads and along the barrel in quarter lengths. It certainly altered the results but there wasn't a noticeable improvement. I also checked the barrel twist when cleaning. It was a smidge under 10, so i approximate 1:9.5

Although I will use it for some paper punching, I will primarily use it for reds and sika at extended ranges. I also have a wee project planned for Scandanavia this year which i'll share once ive done it and have the pics

[Scotsgun]

Almost forgot. A few folks have responded using Quickload as evidence for their suggestions. Is this program truly so informative or just the simple powder/bullet calculator i assumed it to be?