Thanks for your input....DocNote: According to Dennis Olsen, a very experienced gunsmith in Plains Montana with an excellent reputation, the model 70 conversion from 458 win mag to 458 lott does not require a magnum action like the 375 h&h, which I also have, i.e. it only requires the 3.5 inch action on a standard model 70 in 458 win mag. Dennis has performed many conversions on Winchester model 70 458 win mag to 458 lott. He told me as long as the model 70 is a standard 458 win mag chambering, there is sufficient room in the magazine box to accommodate the lott cartridge. I am having Dennis do the conversion for me on a used model 70 458 win mag I purchased.
SAAMI length for the 458 Lott is 3.6", same as the 375 H&H, so it won't fit in a 3.5 magazine if loaded with the longer bullets.
natman; good clarification, I agree, my post was specific to the Winchester Model 70 Chambered in 458 win mag used as a basis for conversion to 458 lott. These posts go a long way toward specifically clarifying the conversion from 458 win to 458 lott. Excluding these posts, my review of the internet on this subject resulted in equivocal data at best.SAAMI length for the 458 Lott is 3.6", same as the 375 H&H, so it won't fit in a 3.5 magazine if loaded with the longer bullets.
As you can see the cartridge is considerably longer than the 458 Win Mag and is the same length as the 375 H&H:
458 Lott..............375 H&H.............458 WM
Some rifles chambered in 458 Mag come with magazines long enough to handle a 375 / 458 Lott, but many don't. You have to check carefully.
HankB; What you say is a very good reason why it is worth the $100 dollars or so to contract with a gunsmith that has a successful record of doing the conversion on your specific rifle. This is a dangerous game rifle and unless someone just wants a thumper for the range, there is no margin for chambering difficulties when hunting for any dangerous game. I also agree with your thoughts on erosion of the chamber. Following the conversion to 458 lott, the 458 win mag should only be used in a 458 lott converted rifle as backup if you unexpectedly loose access to 458 lott ammunition on safari.
When converting the 458 win mag model 70 to 458 lott the block at the rear of the magazine box (close to the bolt face when the bolt is retracted, i.e. it is a small piece of metal squared on one side that keeps the 458 win mag rounds from moving in the magazine box of the 458 win mag model 70) must be removed. Once the block is removed, the chamber reamed and possible adjustment of the rails, the Winchester model 70 458 win mag conversion works. Due to the heavier recoil, the rifle action bedding should be checked for play and corrected since play may result in rifle damage.
Good post. Feasibility of the conversion from 458 win mag to 458 lott aside, the entire rifle needs to be viewed as a system and how that system will respond in the short and long term to firing the 458 lott. As an example on the classic super express model 70 rifles there was a flip up leaf rear sight (which folded forward) instead of a fixed express sight. Using the 458 lott the chances of that rear leaf sight not folding itself down under recoil is low, i.e. replace it with a rear express sight from NECG for example: http://www.newenglandcustomgun.com/ (the single blade adjustable fixed sight not the multiple blade classic express sight). Also in converting to the lott consider replacing the original hard rubber orange recoil pad on the classic super express model 70s (has Winchester written on it) to help manage the lotts recoil.
