@ 06:20 pm (GMT)
Nathan FosterYes, unfortunately, the .25-06 derives its good killing performance from high velocity. It fires a very light bullet and is reliant on dsiprortionate to caliber wounding via velocity. A good number of .25-06 users end up with .257 Weatherby rifles as a way to enhance this further, whether they understand or have the words to describe these things or not. They simply see what they see and want more.
The .25-06 loses 35fps per inch so you stand to lose around 100fps. This may or may not be a big deal depending on how fast your loads are currently going. Some rifles are quite slow to begin with. Have a read of the .257 Roberts article to gain an understanding of mild velocity .25 performance.
Take note of what what Thomas said about meat in the barrel versus threading. This could be the reason why the smith wants to cut it back.
A major problem is that the .25 bore uses slow burning powder. Cutting the barrel back will cause high gas cutting at the suppressor. Will pay to throw the suppressor away after 1200 rounds. The DPT design would be good because you can take this apart, inspect it and discard any unburned powder. However, a more serious problem for the .25-06 is carbon build up in the barrel and chamber, lifting pressures. This can be quite dangerous if left unchecked. A shooter might think- hey this suppressor gives me really high velocities, not knowing that the carbon is making chamber dimensions smaller each shot. Again, this is can be quite dramatic in short barreled .25-06 rifles. Summer temps can make this even worse, locking up the bolt.
Your smith will quite possibly disagree. I really don't give a shit. These are things I have seen with my own eyes.