I'm returning to a project I never finished.  I have an 1896 Krag carbine with no front sight.  I bought a 1903 (slip on) sight.  What's the best way to install it?  Does there have to be a groove in the barrel for the spline?  The splines are available at Numrich.  What about epoxy?

'Battis32' - You will need to 'step' your barrel, (reduce the diameter of the muzzle end of the barrel), for the 1903 'banded-base' to fit.

Another possibility is increasing the inside diameter of the banded-base with a 'hone' like device, until it fits. (I have done this, but, it takes forever).

I have successfully anchored a couple of 1903 sight bases on barrels by drilling a shallow hole, where the spline would be, and 'gooping' some "JB Weld" glue in the 'spline-slot' of the 'banded-base'. This cleans up easy and is invisible.

With a bit of heat, base can be removed, if necessary, at a future date.

p.s. - If you check the KCA heading "Other Firearms", there is a thread I started, ('1903 project & Khyber Pass gunsmithing'), that describes a similar install.

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I don't have a pic of it, but the front sight band slides several inches down the barrel.  And, there is a small indent in the barrel, where the sight was, as if someone had used your method.  I thought about using JB Weld.  Maybe this is easier than I thought.
I finally spent some time hand fitting the handguard, and it's looking...decent.
I'll be picking up my "new" 1896 carbine soon - the one that has the Lyman 34 sight base attached to it.  I have a new side plate and screw on the way, and I'll find a rear sight and handguard soon.

Is it possible to remove the front sight from a shot out Krag barrel and braze it onto a carbine barrel that has lost the original sight? If one had an almost original carbine it seems to me that it might be worth the effort if the original dovetail is left in the barrel. I think if you cleaned up the dovetail in the barrel first and did a good job of brazing and touch up bluing an original carbine could be restored to look good.