120gr ballistic tips up around the 3800fps mark out of a 26" barrel. there is a load (supposidly tested) on reloadersnest.com stating that this is achievable with 95gr of alliant reloader 25, sound reaistic to you? and is this powder similar to hodgden retumbo?
was thinking it would make a spectacular varmint load.

Like any load for a rifle that your going to build start low and work up looking for pressure signs. 3800 seems pretty optimistic for a 120 grain bullet from any published data I could find with the 7mm Ultra-mag. Most published reloading data top out the 120 grainer at 3600 fps. I'd approach that load data with some caution.

I'm loading a Nosler 180 grain Ballistic tip with RL 25 to 3300 fps for two different 300 Ultra-mags and pressure looks good on both of those. Retumbo seems to work best on heavy for the caliber bullets and the popular powders listed for the 7mm Ultra for 120 grain bullets seem to be.

Accur 8700
A-XMR-3100
H1000
H4350 and
H4831

in that order.

I'd start at least five grains under that load and work up a grain at a time looking for pressure signs. If you start seeing the ejector marks on the back of the case or cases start sticking you'd want to back off. Primer flattening and cratering is another sign that pressures are peaking.

Another thing to keep in mind is that brass life becomes much shorter when you start loading at the extremely hot end of the spectrum and Ultra-mag brass is not inexpensive.

I've found that loads that are 10 percent under published maximum loads tend to only be 2 percent slower than top published velocity and are almost always much more accurate.

Any time your looking for max or near max loads it's a good idea to use a chronograph and one of the rifle holding devices that allow you to fire it from a safe distance. When you get near those max loads that can and has dissembled guns once in a while your not want to be putting your face that near an action that cold let go. Midway and Cabela's both sell a gun holding fixture with remote firing capabilities or just put the butt inside a tire and tie the front down and use a string to pull the trigger.

Just remember that you can fire a rifle bullet at any speed you want - once.

If your plans include firing that rifle more than once, then a bit of caution is advised in the load selection.

I am supprised that the case will hold that much powder. I would be very careful.