Terry, I must be missing something. Are you talking about rechambering the gun, since you state the current chamber length is shorter than that? If so, why would you rechamber at 3 1/4", since 10ga shells are either longer or shorter than that? It's interesting to note that the SAAMI service pressure standard for both the 3 1/2" and 2 7/8" 10ga shells is 11,000 psi.