I have heard that stainless Steel barrels gets less velocity than other barrels, it is a Shillen barrel, is there big differences between stainless Steel and other.

anytime i have choice i chose Stainless Steel
Shilen SS barrels are some of the best to be had
i have 6 rifles with Shilen SS barrels and all shoot vary good
i also have 2 rifles with Shilen DGA actions

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Death Before Dishonor

I don't think there is any difference in MV between blued and stainless.

Look in the Blue Book of Gun Values. Prices are given on blued guns down to 60-80% condition. Stainless only go down to about 95%... apparently stainless doesn't degrade nearly as much as blued in condition.