Originally Posted by
Phreakish
1 cont: button vs hammer forged: "steel is steel" and so the expansion, all things being equal, will be about the same. That said, the cold hammer forge process creates what we call residual stress. Basically, the steel is still under pressure once it's finished. For an applied load, the actual stress of the material starts from a negative (verus zero), and therefore can take much more load prior to hitting yield. How much more is highly dependent on many variables. This is especially true for the bore, where the vast majority of the cold work, and therefore the residual stress, is retained. We effectively create a barrel that has a stronger-than-normal (even though hardness is still close to the same) liner with a considerable wall thickness. The grain of the metal will also be refined and we'd expect to see long grains (since barrel blanks start short and end long) on the surface which are tightly packed together. The impact it has on overall expansion should be minimal, and given that the residual stress state is fairly uniform from end-to-end, we wouldn't expect to see any warpage when heated versus if the profile were less than uniform. We still have the same effects from other discontinuities, but all things equal the forged barrel still has the strength advantage with the residual stresses. The tighter grain structure also gives a superior surface for applying chrome and the higher quality surface will resist corrosion better due to the tightly packed grains (similar to the corrosion inhibition seen on polished surfaces, even when untreated). These are the major benefits of the hammer forged barrels: they resist wear better due to the residual stresses and better surface finish and the hard chrome tends to lay itself down in a more uniform and dense coating which increases the benefits offered by the chrome.