Made calls to the Massachusetts State Police and Connecticut State Police. Here is what their firearms enforcement department told me:
Massachusetts
1) As a non-resident you cannot stay overnight in the State of Mass with a handgun without a Temporary Permit. A Temporary Permit takes multiple days and must be applied-for in person. So, you can't have the handgun in your car, drive to the permit office, get the permit and be good.
2) In Mass, Mags over ten rounds are not allowed, even if you are just driving in to shoot the match and not staying overnight.
3) Mag Blocks ARE legal, and may be used to restrict the number of rounds that can be loaded into the magazine. (I pressed the point about being readily converted, and she said mag blocks are good.)
4) It would be fine to fly-in and out of a Mass airport with handguns as long as you don't stay overnight and have 10 round mags or mag-blocked mags.
Connecticut
1) As long as your mags and handgun are legal in your State of Residence, and you are legally entitled to possess it there, they are legal in Connecticut if you are staying overnight and you are "passing through" CT to and from the shooting match. You are required to keep it locked with ammo separate, per the US Title 18 requirements, since that is what is allowing the rule. Remember you are just "in transit" to or from the match, even if you stay overnight.
2) Your hotel room is considered your private residence in CT. And, there is no license required just to possess a handgun in your private residence.
3) You are allowed to possess high cap mags while you are "in transit" which means staying overnight as well. If I was shooting a match in another state where the high cap mags were allowed, that would be fine. But since my destination is Mass, and they have a hard rule against any mags over 10 rounds, so Title 18 wouldn't protect you in that case. (However the Detective I talked to said he has a hard enough time keeping up with CT laws).
So, planning on ordering mag blocks, putting them in before I leave Virginia, flying to Hartford, staying overnight in CT, driving to Springfield MA to shoot the match, returning to stay overnight in CT and then flying home from Hartford. I will keep the mag blocks in the entire time.
Finally a solution to this mess. If only Mass would just make a sporting exception....would make things a lot easier.
This is not legal advice. USe of this information is at your own risk. That being said, I am repeating what they told me.
Cody