I see a reason or a few.
1. Removing that 1/4" of metal doesn't make the gun stronger and better able to shoot 2-3/4" ammo, it makes it weaker.
2. If you're not sending it back to England for reproof you're molesting a gun and making it illegal for sale in most of Europe. That will make the gun less valuable even in the USA.
3. 2.5" chambers shoot 2-3/4" loads just as safely/unsafely as their equally loaded and pressured 2.5" load counterparts.
4. You remove a safety. By keeping it 2.5" there is a modicum of warning to any future operator that this gun is special and needs soft loads. By lengthening the chambers, the next owner may feel entitled to feed the gun any 2-3/4" load leading to potentially dangerous results.
