I have attempted to use a local caster's (Cheyenne cast) 45 caliber 405 grain bullet in my Ruger No1 458 win mag. I loaded them with 17-20 grains of Unique for a small game or plinking load. Every load I tried shot 12-20 inches at 50 yards out of this rifle and there was definitely sign of tumbling. Holes were totally oblong! I have never tried these bullets before but I have tried as light as 300 gr cast lasercast in my other 458’s and never had this problem. Additionally the barrel was really badly leaded! Just for the record this rifle shoots Barnes X'x 350 grains in one solid hole so it is not the rifle.
Can you give me some insight on what is going on? Thanx.

Try some of our host's Beartooth cast bullets and see if the problem doesn't go away. Ordering information is on the home page.

Heavier bullets are longer. Longer bullets have to spin faster to be stable. As with a gyroscope, it is the RPM that does it, so the faster you launch a bullet for a given rifling twist rate, the faster it spins and the higher the stability factor is. Stay with lighter, shorter bullets for low velocity and they are far less likely to be unstable. Given that 300 grain bullets from a handgun will take down pretty hefty game, I don't think a plinking or small game load would benefit from the extra weight anyway.

The leading may mean the alloy was too soft or the lube less effective. It could also be a hard alloy that is undersize and too rigid to bump up to groove diameter under light load pressure, so it suffers gas bypass and cutting. Hard alloys sometimes have lower melting points, so it is possible the bases were melted and splattered on the bore by the powder heat. This last problem can be cured with a gas check or a polyethylene (P-wad (http://www.neconos.com/shop/?shop=1&cat=16&cart=46546)) or carboard wad.

Nick

Slug it. The .458 Win Mag has a very large, tapered throat by design. It isn't the best for shooting cast bullets, but it can be done.

I'd guess that a bullet diameter around .460" is going to help, along with the longer (heavier) bullets. See if you can seat them out to just engage the rifling when the lever is closed.

You're not using a 45 caliber handgun bullet are you? For your rifle the bullet should be .458" diameter.

yUP. Them crappy bullets miked at 456..no wonder!

yUP. Them crappy bullets miked at 456..no wonder!

That will do it, all right. I looked up a list of rifling twists for different makes of .458 Win Mags, and found your #1 has a good, quick (for a big bore) 1 in 14" twist. That should stablize about any bullet length at any practical velocity, so just get the bullets sized correctly and you should be OK.

Nick