I have an 1896 Krag that has a Lyman front sight.  I removed the Lyman sight and found that the sight dovetail had been filled in.  I bought a 1903 sight from Numrich that has a slot for a spline. 

I'm guessing that the spline fits into a slot (dovetail) in the barrel, right?  I read where another poster used a set screw to secure the 1903 sight on his Krag.  Other than cutting a slot for the spline, are there any other ways to secure the sight base?

I the dove tail was the orginal you can reinstall a Krag site depending on what it was filled with. I would go with the Krag site if I were you.

That would be my first choice, a Krag sight, but the dovetail fill is hard.  The 1903 sight slips right on, but I don't want to cut a slot for the spline.  Cutting the old dovetail out or cutting a new one for the 1903 sight is beyond my skill level.

The CMP now offers gunsmith services at both locations for all US service weapons, including Krags.  I'm sure they would be able to recut the dovetail and install an original Krag front sight.  Give em' a call. 

Battis, I used a 1903A3 sight on my Krag.  I used a short set screw to hold it firmly in place.  Did you get a 1903A3 front sight or a 1903 front sight base?
The 1903 front sight base has a horizontal hole through it.  If that base is put on the rifle and you carefully run a drill through that hole, it will cut a groove across the top of the barrel so a pin can be used to hold the base in place.
The 1903A3's horizontal hole intersects the key that would go into a slot milled in the barrel, as you suspected.  I didn't want to try to cut a slot for that key.  That's why I used a set screw instead.  I guess I could've soldered the sight in place but didn't trust my soldering skill.

It might have been your post about the set screw that I read.
This is the one that I bought. 
517470   Manufacturer: U.S. Military 
Springfield 1903, Springfield 1903A1 Front Sight Assembly (Assembly Required) 

I also bought the pin and spline.  There's a slot for the spline that does intersect with the hole in the back of the sight.  The pin they sent me is way too big for the hole.  I'll call Numrich tomorrow.
I'll call CMP to see what they offer in this area. I like the looks of the sight.  If it comes down to it, I'll try West Systems epoxy - it's holding my sailboat together.

One of my cutdown rifles has that sight, whoever put it on just drilled a hole up from the bottom and threaded it for a set screw.

Battis, I looked at the picture of that 1903A1 sight assembly.  If you slip it onto your barrel and try to look through the hole in the base, doesn't a bit of the barrel get in the way?  If so, if you had the right sized pin (Numrich 517450?) and filed a shallow groove across the barrel, that would hold the sight on, with or with out the key.
Fact is, I wished I had bought the 03/03A1 assembly instead of the 1903A3 front sight.  It probably would've been easier for me to install.

I just called Numrich and told them that the pin is too large for the hole in the rear of the sight.  They checked their stock and told me that I'm right - the pins they have listed don't fit the sight hole.  But they're not sure if the pin is too large or the hole is too small, and they want me to send both back.  I said I'll keep the sight and install it another way (set screw, epoxy, bubblegum, etc).

That's the spirit!  I used JB Weld for added security after installing my set screw.

Is the bottom of the sight base thick enough to thread a hole for a set screw?  Machinist I am not.

There's only a couple, maybe three threads in the one on my rifle.  It's now on a rifle other than the one with the hole for the set screw.  I simply swaged it down on there and it hasn't moved in a couple years and a couple hundred firings.

On my front sight I drilled and tapped a hole in the underside of the barrel because the front sight base band material is too thin.  There's a match-drilled hole in the band that is a close fit on the set screw.  So, basically, the set screw is a post attached to the barrel that the band is impaled on.
I was very careful to not drill too deep into the barrel.  Didn't want a "ported" Krag. ;)

Battis, it occured to me that you could drill down through the top of your front sight base, right in the middle of the dove-tail.  Thread that hole for a set screw.  Plenty of depth for threads there.  Then match-drill a shallow hole in the top of the barrel that the set screw can engage when it's tightened.  After the base is in place, then install the rest of the front sight into the base.  That's what I tried to do first with my 1903A3 front sight but ended up breaking my tap due to being overly eager.

There's an unthreaded hole in the filled-in dovetail for the Lyman sight set screw to bite into.  I thought of drilling down through the top of the new sight, then I reminded myself of my skill/experience with drilling metal.  I have two Vetterlis that I converted to centerfire by drilling through the bolt face - one came out perfectly, the other one had to be fixed by a machinist friend.  Maybe I'll give him a call.
I might just use the West System epoxy for now.
Another question - the butt of the stock was cut at some point.  I want to build it back out and attach a butt plate that I bought.  How long is the stock from any given point? (trigger guard, saddle ring, etc).

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I measured one of my sporters.  From the butt to the center of the rear trigger guard screw is 12.125", the distance "A" in the pic.  That's a regular military butt plate on there.

I understand what you mean about drilling.  I have a drill press and all kinds of clever ways to clamp things where I want, perfectly square, etc.  Otherwise I'd never try some of the stuff I've done.  I really wish someone would give me a milling machine.

Thanks for the measurement.  As soon as I fix the stock...
It's been one of those weeks.  The stock had a length-wise crack in it that had been repaired at some point.  It looked strong and I've been shooting the rifle with no problems.  Well, this morning I picked the gun up by the stock, and the stock split apart along that crack. Hmmm...
I was probably going to take it apart and repair it at some point - now I have no choice.  So, I cleaned it all up with Acetone, drilled holes for two pegs, mixed up some epoxy with a bonding filler, and now it's all clamped and hardening by the woodstove.  It should be much stronger than that old repair.
This is the crack before it split:
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I'm guessing that if it had come apart while shooting, it might have been painful!  I've done some stock repair with wood dowels and glue, too.  Done right it'll never cause problems again.

Hey, can you post an overall side view of your Krag?  We always like to see new specimens.

It's a work in progress.  I'll take a pic when I get it back together.
I added a repro saddle ring, I'm adding the 1903 front sight.   Madsenshooter detected what looked like the band spring slot, so I sanded down the front of the stock and found the slot and added a band spring.  I'll probably leave the rear sight as it is.  I want to build out the butt and add the butt plate once the stock is repaired.

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Why all the fuss about ways to affix a "M1903" front sight assembly on a 22" Krag barrel? Unless sight or barrel has been molested, the band is about .010" smaller than the barrel and must be opened up a tad to give a nice drive fit that won't move (even without filing a groove and installing the cross pin).

FWIW, the sight in question is the Model 1905. The actual M1903 sight, for the original rod bayonet 1903 rifle, is seldom encountered.

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The band slides on an inch or so before stopping.
Numrich calls it the US Springfield 1903 front sight. 

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The stock is repaired with epoxy and pegs - it'll never break at that point again.  I don't like to refinish old stocks but I had no choice with this one (it has been done before).
The saddle ring is a repro, the front sight is a replacement (it's still not in the right position, or permanently attached), the band spring is old but a replacement.  The rear sight will do for now.  I need a handguard at some point and a proper band ring.  The rubber butt pad is attached - I want to extend the stock and install the butt plate I bought.
This might be my favorite rifle.
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Nice stock repair!

Thanks.  I think that if I ever get another rifle with a repaired stock like this one had, I might break it to repair it properly.  They used wood glue and a biscuit of some sort in that old repair.
This is what the forestock looked like - the band spring slot was hidden under that filler.
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