I wouldn't allow it (but I'd be tempted). Let's say you did break a caliber V into 2 IIIs. You buy one piece of gear and then reserve the other. When you're in the field, you use the reserve pick and buy a caliber V pick (since as stated, reserve picks have no caliber). Now you've gotten your original cal V AND a bonus III. That's breaking the system.
Can't do that. You can only acquire calibers up to 4 in the field.
That said, I never realized that as-is, there wasn't a cap on the reserve pick to the caliber you put in. Easy enough to house rule.