While I would concur with the above posters that a Mosin, modified or otherwise, is probably not going to be the path to success... it may depend on how you define success.
If you mean 'win at state/regional level or above', I'd say heck no.
If you mean 'win at club-match level', I'd say pretty unlikely, but possible.
If you mean 'get out and shoot and have fun'... then go for it.
A lot of times we get too tied up in 'winning is everything'... and thats when things stop being as much fun.