The 870 3" barrel is rated for shotshells with a Maximum Average Pressure of 11,500 psi. A 3.5" barrel is rated for a 14,000 psi MAP. By removing material from the barrel walls you can only weaken them.
Just curious whether the 3.5" barrel is wider than the 3" about 5" from the mouth of the breech. The problem is whether the walls of your rechambered barrel will be thinner than a factory 3.5" barrel.
Last edited by TheKlawMan; August 30, 2012 at 01:06 PM.