131,xxx = 1917
If your revolver accepts 45 Colt ammo , it has been physically altered . The .455 chamber length will not accept the longer 45 Colt ammo . If any of you have a .455 New Service , you will be able to visually inspect the chambers and see that they are too short to accept the Colt round .
If you will open the cylinder on your New Service and carefully inspect the rear cylinder face and ejector , you will see that it has a different appearance . Not a factory "look" . This is because the gunsmith had to face off this area to accept the thicker rim of the .45 Colt brass as mentioned earlier by other members . Some of these conversions are pretty well done , but most I've seen were fairly crudely machined and then cold blued or not blued at all .
But , more importantly there will be no proof marks on the rear of a modified/converted cylinder . I happen to have a British military purchased New Service revolver in the 90,xxx range . There are 2 proof marks visible on the rear of the cylinder. A Colt number applied by the workman at Colt as well as a Common Wealth proof mark .
As for being safe , as mentioned earlier , an inspection by a professional is recommended .