It's simply a 7MM STW necked to .25 with no other changes. The first one I heard of was done by Lex Webernick of Rifles Inc. for Layne Simpson. A friend of mine had a 25-06 Sendero blueprinted and rechambered by Webernick. This rifle shoots 0.4 with 100 gr. Bal Tips & 0.6 with 100gr. Partitions, loaded to 3800 +. Now the downside, cases are only good for 4-5 loadings with a lot of RL22, and Webernick dosen't do these conversions anymore so he can devote his time to building his own rifles.