Re: SWFA SS 1-6 vs. Burris XTR
Both are good scopes.
You kinda need to decide first what what magnification range you are looking for and whether you want the reticle in the FFP or SFP.
That is something you should more or less settle on before you look at specific scope models.
XTR is a nice scope, but I am a little confused why you would want a scope with 1x bottom end AND a Fastfire.
If you are putting a red dot on there anyway, get a slightly bigger scope, like a 1.5-6x42 or 3-9x42.
If you want the scope with 1x on the low end, then put the money into getting a nice scope, not the extraneous red dot.
Of the 1-6x24FFP scopes coming to market now, I think the SS will be the best bang for the buck. At least from what I have seen.
If you prefer SFP (and many people do), then get Leupold VX-6 1-6x24.
If you are OK with 4x on the top end, you can move a little further down the price range.
All that having been said, if you are hunting at 400 yards with a 5.56, I am guessing your targets are not going to be very big. Hence when the light gets a little low, you will appreciate a larger objective lens and a bit more magnification when there is enough light for it.
Weaver has a 2-10x36FFP coming out. Vortex has a 2.5-10x42FFP coming out. Either one of those with a red dot for when you need 1x should give you enough versatility.
If you need something available right now, take a look at SWFA SS 3-9x42 and mount a small red dot next to it (or onto it).
ILya