Please give some advise on adding a second x bolt to a 458 win mag. Is a hidden x bolt ok or better than a traditional one you can see ? Is one better than the other ?

I only have one rifle crossbolted with bolts you can see (sadly they're allen head not the traditional spanner wrench style), had another one before that had blind crossbolts with wood plugs. Actually just remembered I have one more out there like that now (had split between the mag and trigger area in the stock and needed to be fixed).

A stockmaker/civil engineer by the name of chic worthing posted a good explanation on here once of how a crossbolt worked. by compressing the wood, therefore resisting the tendency to split under recoil. I would think that a traditional crossbolt might work a bit better from that regard.

Most importantly, traditional ones LOOK way way WAY better. I'm serious, I've never seen a plugged one that looked worth a darn. I also don't know how it could be done completely blind but I don't think the "compression" would work as well.

I'm sure others will have more technical or maybe results based data.

Red

Find a copy of the 1984 Gun Digest. Ther is a great article on hidden cross bolts that was written by Jack Lott.

Funny you should mention the Lott article. I just happen to have saved a picture from the article.

I have used this method of stock reinforcemnt on a number of rifles. None have failed.

+ 1 on the Lott method. I've also used it to repair/re-bed stocks that have split/cracked just like the examples in the drawing.