I very recently bought a used .458 Win Mag Model 70 Super Grade at a very reasonable price. I received it a couple of days ago and ran a bore snake thru it, threw together a few rounds of ammo with 500 gr Hornady and a minimum starting load.
Drove to the range I have on my place and proceeded to shoot a group at 50 yards, iron sights. Lo and behold the first shot hit the target sideways! Never seen this before, I shot 6 times and onle one shot hit point-first! I was a bit disappointed. So, I proceeded to give the rifle a good cleaning and loaded up a few more rounds, these with almost to maximum and shot another 3 shot group, same as before. This was much more lie what I expected. Anyone else ever had such an occurance?

I am guessing that the velocity was just below stabilization, might be caused by a very dirty barrel.

I have had rifles that had so much dirt in the barrel, but never shot bullets side ways.

May be those had enough velocity to shoot straight.

I have had rifles key home with reduced velocities, others did not??

My .458Wm keyhole with reduced loads. Very accurate with full power though.

I have a 600 Overkill that keyholes 900gr woodleighs at 1100fps. I was trying to get subsonic and then suppress it but will need a faster twist to get there.

I also had a bunch of 458 win mag 500gr cast bullets loaded to about 1400 that shot well except one day at a shoot while waiting for my turn the ammo sat in the sun and the lube got melty. I didn't think much of it until I saw the target and they all keyholed. I stopped shooting them and later pulled them apart and found the lube melted and caked up a bunch of powder near the bullet base. I am guessing they were too slow too.

K Evans,

Excellent choice of firearm. Looks like you are getting it sorted out.

It is plausible that a very dirty bore and a light load might be slow enough to not stabilize.

Too slow or too fast, cast bullets of .459" diameter may keyhole from a .459"-grooved barrel.
The .458"-diameter/ 500-grain Hornady jacketed bullets that keyholed must have been mighty slow to keyhole in either a .458" or .459" groove diameter.
Or could you have gotten a lemon with over-sized groove diameter ?
.458 WinMag barrels are rarely as tight as the SAAMI minimum of 0.458" groove diameter. Most are 0.459".
SAAMI maximum jacketed bullet diameter is 0.459", minimum is 0.456".

You need to clean the barrel again, lightly lubricate the bore, and slug the barrel with a .50-cal swaged lead roundball from Hornady.
Tap it into the muzzle end with a little brass hammer, and hammer it along to breech end with a wooden dowel.
Measure the groove diameter.
Measure the bullet diameter to eliminate possibility of bullet diameter that is not in .456" to .459" SAAMI range for jacketed bullets:
.4590" - .0030".

If you do your Super Grade, I'll do my Super Grade.

Circa Y2K the Winchester Custom shop Big Five limited edition rifles had some bad barrels in .470 Capstick: Oversized.
A buddy had one that would keyhole with .474"-diameter/ 500-grain North Fork monometal copper solids at near max load.
Same load worked fine in my tighter McGowen-barreled M70 .470 Capstick, as well as a Merkel .470 NE DR.
Mike Brady made us some .475"-diameter bullets,
and that extra .001" stopped my buddy's rifle from keyholing.
.458 WINCHESTER MAGNUM PERFECTION

Non Illegitimi Carborundum

All of above of RIPs post.

If your M70 barrel is a bit overize it is not the first, I can assure you.

Glad I wasn't the only one to experience this, I've got a bunch of 405 gr bullets that I load in my .45-70. I'm going to load some of them to a low velocity just to see what happens. They shoot fine out of my .45-70.

I’m betting on a too large dimension barrel.

I slugged my M70 .458 Winchester Magnum Super Grade made circa 2011:

Groove diameter = 0.459"
6 grooves, 1:14" twist

.458 WINCHESTER MAGNUM PERFECTION

Non Illegitimi Carborundum

quote:

I am guessing that the velocity was just below stabilization,

Per Saeed and I agree.




My .357 mag rifle has a 20 inch custom made Douglas barrel that was made for high velocity .357 mag loads for which it is quite accurate.
Generally, the lighter (110 and 125 grain ) and faster, the smaller the groups. The Super VEL factory 125 grain JSP (or my equivalent hand loads) are my favorites for small game and varmints, but for hogs and deer, the 158 and 180 grain Buffalo Bore work well, shooting through most game.

Standard velocity .38 special ammo always keyholes.

I loaded a few 405 grain gas checked cast bullets, Lyman manual said around 1200 fps, I didn't chrono them since I was checking to see if they keyholed...they did. Every one of them. The same bullets shoot pretty good from my .45-70, maybe twist is a bit different? Ran a lead ball down the bore and the grooves mic'ed .459. I'm thinking long bullet and low velocity doesn't work in that particular rifle.

K Evans,
Your 45-70 likely has a slower twist than your .458 WM. It also likely has a .457 bore.
That 405 grain cast bullet is short not long and from all that, I would still vote that your stabilization problem is a combo of Bore size vs. bullet size and velocity. Put a .460 or .461 cast bullet in there, run it at 1400-1800 and I would bet it won't keyhole. Might not shoot cloverleafs as that part of cast always remains to be seen, but I'll bet it hits end on. With Jacketed bullets, your options a limited. A Remington 405 or Speer 400 smacked in the, rear let us say, by a full charge will likely bump up and work great. Let us know what you find!

I have a .458 that keyholed only with certain bullets. It wears a new barrel now.

If jacketed bullets using starting loads are key holing,that is probably because the barrel is shot out.

Curiouser and curiouser. I went to the range with another AR big-bore fan, who brought his newly rebarrelled CZ 458WM and had it keyhole at least one bullet at only 25 or 50 yards.

I don't recall the exact bullet weight but believe it was at least 450 grains and possibly 500 or more. Nor do I recall if it was a full-house load but did fire one that made me wonder if I'd detached a retina

I would try some factory ammo. If it does it with that I would call Winchester to discuss a new barrel.

quote:

that is probably because the barrel is shot out.

That would be the first 458 I've ever heard of being shot out.

quote:

Originally posted by Biebs:

quote:

that is probably because the barrel is shot out.

That would be the first 458 I've ever heard of being shot out.

???

quote:

Originally posted by Biebs:

quote:

that is probably because the barrel is shot out.

That would be the first 458 I've ever heard of being shot out.

And I won't be the one to shoot this one out.