Between 52-54 Winchester built 221 7M/M rifles, (had been discontinued in 49). Probably because of their rarity, these rifles were not rechambered often. In the early 50s there was a lot of interest in 7 mm magnum calibers, but the only one available was the Weatherby 7mm mag.
Introduced in 1953, the 7x61mm Sharpe & Hart Magnum belted cartridge (A.K.A. 7mm S&H Super[1]) was developed by Philip B. Sharpe and Richard (Dick) Hart. Some articles claim it was based on the .300 H&H Magnum case,[while others claim it was based on the 7x61 MAS M1907 case. There were many wildcat 7 mm mags being touted, but when Shultz and Larson from Denmark announced their new bolt rifle chambered for the 7x61, there was a lot of interest in America in the cartridge. Factory loaded ammunition was supplied by Norma of Sweden. The belted version of the 7x61 is also sometimes referred to as the 7mm S&H Super. The 7x61's commercial popularity was limited by competition from the 7mm Weatherby Magnum, a more powerful standard length 7mm Magnum that was already on the ground. When the Remington 7 Mag came out in 62, the fate was pretty much set for the 7x61 S&H. It is a slightly shorter case with a belt. Case length is 2.394 in., COL is 3.27 in. Here is a link to Terminal Ballistics Research data.
https://www.ballisticstudies.com/Knowledgebase/7x61+Sharpe++Hart.htmlSo in the early 50s, if you have a very nice M70 in 7M/M and you want to make it shoot faster using factory ammo, rechambering to the 7x61 S&H makes sense. One of the benefits of rechambering the 7M/M is that it had a twist rate of 8.75, while the 7 MM Weatherby, and the 7 MM Rem Mag. had a 12 or 10 twist. The owner of the original rifle was probably not thinking about heavy 7 mm bullets in the mid 50s, but it would seem such a rifle rechambered would turn out to be a real neat rifle to own today. It would stabilize the new long range high BC bullets available today.
mn her eyes. 