I have a friend that struggels with his 458 Win.
It's buildt on a M98. He asked me if I knew what free bore (I know this word might be wrong, but I suppose you know what I mean.)that was suitable on this round. He tell me that if he seat a 500grs Hornady only 1mm down the troat on the case, he dosent touch the lands at all. I think this sounds like to much, but I havent played with this round before.
He have bad accuracy and have tried everything menchanicly with this rifle.
Any advices?
He uses Vv n135 so far.

Yippee, he has a Lott in disguise!

If I was building a .458 Winny I'd plan on a lot of freebore as the loss to acccracy is marginal and the gain to pressure might help me gain another 100'/sec!

I seriously doubt that the accuracy issues you're dealing with are related to throating.....more likely bedding or just using the wriong bullet for that gun!

460wby,

If you do a search on this forum for ".458 WinMag throat" you will find me repeating some of this, years ago:

The old standard .458 WinMag throat:
starts out .4690" wide
has no parallel-sided freebore
is merely a leade of 0 degrees 29' 30"
tapers down to full land height over a length of 1.137" from the case mouth
it is a long funnel throat

The .458 Lott throat:
is a tight parallel-sided free bore
freebore diameter is .4585"
freebore length is .4600"
leade angle is 2 degrees
total throat length (freebore length plus leade length) is about 0.700"

The length from base of cartridge to end of leade:

.458 WinMag = 2.500" + 1.137" = 3.637"
.458 Lott = 2.800" + 0.700" = 3.500"

The .458 Lott reamer will not clean up the throat of a .458 WinMag.

If you rechamber a .458 WinMag to .458 Lott, you will end up with a hybrid throat that is wider at the base and longer in total run, than the standard .458 Lott throat.

Finn Aagaard taught us long ago that you can easily load the .458 WinMag as long as a .458 Lott and get the same velocities with similar charges. Of course the 3.6" long COL .458 WinMag will not work through the 3.4" box. It must be single-loaded directly into the chamber.

Do not worry about the sloppy .458 WinMag throat, it works well, and keeps pressures down without sacrificing reasonable accuracy.

Every .458 WinMag that I have owned (many) has been capable of 3-shot 100-yard groups measuring 1.0" to 1.5" with my handloads ... also, these handloads would easily do 2150 fps with 500-grainers in a 24" barrel.

No flies on the standard .458 WinMag.

Thanks guys!
I just have to tell him to researce more on his loads then. He just asked me when he discovered this long throat, and was worried.
Everything else looks good on the rifle, so it has to be the loads I think.

i did .8 on all the ARs, as that allows one to put the bullets out very long, and not touch the lands


accuracy doesn't seem to be too bad with the extra leade


5 shot 470 AR MOA at 100


jimmy's 10 rounds at 50 yards, just load dev work


416 AR - 3 (yeah, really, 3) shots at 100