It is far easier to hit that '7' than it is to hit that '11', even though there are more opportunities to do so, and far harder to reach a '2' or '20' with 2D10 than it is for a 2D6 to get a '2' or a '12', the maximum amount. All those additional numbers reduces the chances of a certain number coming up as other numbers come in to play.

Getting exactly 7 on 2d6 is a lot more likely than getting exactly 11 on 2d10 (16.67% vs 10%), but in BattleTech you usually want to roll

*at least* a 7 on 2d6 or

*at least* an 11 on 2d10. Those chances are reasonably similar (58.33% on 2d6 vs. 55% on 2d10).

Hitting extreme values on 2d10 is indeed harder than on a 2d6, so either you leave, say, the HVAC/UAC failures as 2 on 2d10 and find certain weapons are a little more reliable (1% chance of failure vs. 2.78%) or you adjust it so that they fail on a 2 or 3 (a 3% chance of failure vs. 2.78%).

If you scale carefully, you should be able to get similar (but not identical) results. For example, there's about an 8.33% chance of rolling 11+ on 2d6. Your options for 2d10 are either 18+ (6%) or 17+ (10%). Likewise, there's about a 41.67% chance of rolling 8+ on d2d6. Your options for 2d10 are either 13+ (36%) or 12+ (45%).

Scaling the to-hit modifiers helps, but now you're scaling things by roughly 1.68, so there's going to be a lot of rounding. At least, I assume you'd use 1.68, since that's the ratio of the standard deviations. There may be a better option, but it's probably still going to involve a lot of rounding. Do you round each modifier? In this case, +1 on a 2d6 turns into +1.68 on a 2d10 and then gets rounded to +2, which means that two +1s get converted to +4. Or do you round total modifiers? In this case, two +1s on 2d6 turn into 3.36 on 2d10 and then get rounded down to 3?

You aren't going to replicate the 2d6 system on 2d10. You can get pretty close in most cases, but it won't match up completely. On the other hand, if you look at BattleTech's to-hit modifiers and think "We need a bunch more of these," then it's easy to reduce the importance of some modifiers to fit new ones in. It won't match up with BattleTech's 2d6 system, but that's the point.