I have 20 of them still unprimed, with no backpacks attached. I was just planning on attaching the backpacks after I'd applied the shoulder decals, as the backpacks sometimes get in the way. I hate cutting up decals to fit around stuff as I tend to ruin them, which doesn't make me smile. I like things that make me smile.
I'd read some nifty stuff about running 10 Assault marines in a Land Raider. LR trundles up and does it's shooting. Next turn the Assault Squad inside jumps out with their chaplain and go nuts on anyone who happens to be nearby.
DA Codex, page 34: Assault Vehicle; Models disembarking from any access point may launch an assault on the turn they do so.
See? I like things that make me smile. A friend of mine said to me "Why don't you just use Terminators?" Well, I could, but five Terminators with lightning claws, and their Interrogator-Chaplain cost 360 points. I'd get 19 attacks on the charge, and Litanies Of Hate to re-roll missed hits on the charge. An Assault Squad of 10 Marines (Sarge has Power Weapon) with their Interrogator-Chaplain would cost me 370 points, and I'd get 25 attacks on the charge. Okay, the Termies get a better armour save and an invulnerable save. Big whoop. Five extra models to spread wounds among is more gooder. Also, Lightning claws get to re-roll missed wounds. BUT you have to hit them first. There are checks and balances, but I honestly like the chance of having another round of combat to go in my favour more than losing five terminators in a really bad roll of Yahtzee...
I started looking at the ways to magnetise. I have 3mm x 1.5mm magnets from KJ Magnetics. They are a good size and fit well in this scenario. I decided to place one in the marine's back, and one in each of the backpacks. I have to be very careful in this process to ensure that all 20 marines and all 40 backpacks have their magnets oriented correctly. One magnet the wrong way round will ruin my day quickly.
3mm is just a bit smaller than 1/8", which is about the size of the holes already in the backpacks. I cut the button off the back of the marine, smoothed it down and drilled a hole into the back of the marine, about 2mm in.
Sorry about the blur, a shaky camera moment! I also had to drill down into the regular backpack to make the hole wide enough for the magnet all the way down. Then I inserted the magnets into the assault jetpack and the back of the marine, covering them with greenstuff. When the greenstuff is dry, I will sand it flat. That will help to prevent the magnets from pulling each other out. I couldn't drill down far enough for the regular backpack magnet to be greenstuffed in, so I just superglued it.
Once everything is dried I'll sand it all smooth and hopefully the results will be seamless to the naked eye of the everyday tabletop player. Definitely not worthy of a Slayer Sword or what-have-you, but it'll save you some money and give you more scope for what to do with that Fast slot on your FOC.
Links to related subjects
Space Marines Part 1, Part 2, by All Things 40k
Rare Earth magnets by Dwarf Mine
Magnetic backpack/jump packs at Heresy Online