I purchased a large quantity of Nosler #52165, .308 125 grain Accubond bullets for loading in a 308. I just purchased a 3030 Winchester 14" barrel for my Contender.
Is this bullet too "stout" to use in my new barrel for deer hunting?

If it was designed for a 308 I would think it is too tough for the 30 30 contender velocities.

I think you're right on the upper side of being to stout for the 30/30 Contender velocities. The Noslers minimum impact velocity is 1600/1800 FPS and I'm sure you could push that pill to 2100 over the top of some Benchmark or 8208 powder. I would see how they shot in your new barrel and then do some bullet construction integrity testing. A lot of people really like the plain o'le Ballistic Tips in their 30/30 T/C's. I also don't see why the Berger Bullets wouldn't do well for you. . .they expand at your T/C velocities. I haven't shot the Hornady Flex Tips from a pistol barrel, but they don't do so well on critters out of a 20" 336 Marlin rifle. They're pretty accurate, but lack the on game performance.

I reload the 30 WCF for a 14" contender and experiment with a variety of bullets.
Shooting the Barns 150gn flat nosed bullet the max velocity I could get was ~2150. Using a 110gn bullet I am getting 2500fps with RL7 (both a little more then 1500 ft*lbs of energy). playing with an energy calculator and adjusting velocity to get equivalent energy I would guess you would get around 2350 with the 125gn pill. If Offshore is correct about the minimum recommended impact velocity (I would contact Nosler to confirm) then I think they would work just fine. A ballistics calculator would give you a maximum recommended range to ensure proper expansion. My gut says you would be ok to ~200 yards, but run the calculations.

For what it's worth,,,,,,,,,Nosler told me the 125 Ballistic tips expand down to 1600 fps and Berger said 2000 fps.

MY 2 cents worth,,,,,
The bullets mentioned are great, but designed for the 308 so look at the twists recommended, as well as the velocities.
(Bergers usually require a faster twist)

I found three powders to work well with flat nosed as well as with 125 and 150 gr pointed bullets, and those are
RL 7
IMR 8208
LeverEvolution
Lever gave me the highest velocities
Phone calls can help.
Oh and yes used in 14" contender...

The ABs don't go fast enough to expand real well (but, some) in the .30-30. Also, watch your loading of them. They're bonded and cause a slight increase in pressure. JD Jones always told me to load them a few grains below BT loads in Contenders.