Help with identifying this mammillaria please

So I can't seem to figure out what this little guy is, I was thinking backebergiana but the spines have red tips and are slightly curved, not to mention a bit less dense than my other one. Unless they just vary a lot?

I don't think its backebergiana (described as having 10-12 radial spines and 1-3 central spines, but very short). But I don;t immediately recognise it, though it clearly is a Mammillaria.
Has it ever flowered? that might help narrow it down.

Ah thank you, and unfortunately not, it hasn't had any signs of flowering and I've had it for 2+ years at this point.

Could be karwinskiana subsp collinsii

From your photos it might suggest that your plants are being kept indoors or in a porch, rather than outside in a greenhouse. I say that, as the plant looks a tad bloated, too much water and not enough sun. However, given more sunshine, which will encourage the body to tighten up, if the watering is less often, it might still be a possible candidate for the subsp. of backebergiana, ernestii. Another contender, because of the curve spines, could be a variety of m. rhodantha. Are you sure this is one single plant and not several seedlings, that were allowed to grow on together. I ask this question because normally m. rhodantha wouldn't offset at an early age,unless it's growing head had been damaged previously. If you are successful in getting it to flower, the colour for both options will be red.