Speer is my go-to for varmint bullets. I have used a ton of their 52 gr hollow points and their 55 gr soft points in my 223 because they are so accurate and reliable. While I haven't personally used their 50 gr or 55 gr tnt bullets yet, my friends who have sing nothing but praise of their performance.
Which cartridge are you loading for? Here is a description of the tnt construction from their website...
From Speer Website:
EXPLOSIVE AND ACCURATE. TNT® gives you what you want most-superior on-game performance. Starting with TNT's thin precision jacket, we add internal fluting and a dead-soft lead core to ensure complete bullet disruption. We finish the forming with a long ogive and a small hollow point. This gives us the ballistic coefficients needed for long shots. In fact, TNT's coefficients rival those of similar boat tail bullets. In a little over ten years, TNT has become one of our best sellers. Why? Great accuracy and impressive terminal performance.