Funny this came up when it did, I was just reading along these lines in the riggers handbook. Anyway, you can get a pdf copy online for free. Read through Ch4. Deployment and inflation characteristics, page 4-9 there is a section on the main pilot chute. A few folks mentioned replacing your pc with a new one. That is part of what this section covers, as well as F-111 and ZP types, so all around good info. As mentioned in other post there is no firm guidance in terms of force required for the main bag pull out. However on page 4-14 there is the topic of reserve bag extraction force, which incidentally is 18lbs. So I would say that you would want your main to be close to that but you are only 7lbs from that number. Besides like also has been said wait a couple more seconds and your main will probably come right out.