I'll start with a caveat: I have never used a Lead Sled. I think I know what it is and how it works.

Two words of caution:

FIRST: With a very heavy recoiling gun you may risk splitting the stock if the gun is jigged in a heavy object with little give. An extreme example is this - if you hold the butt of a heavy recoiling gun against the trunk of a large oak tree, essentially immovable, you are highly likely to split the stock.

SECOND: A double rifle is regulated to be shot offhand. Generally DR's will not regulate properly when shot off any setup of sand bags. They must be held in the shooter's hands to get valid results downrange. Using a lead sled is extremely counter-productive in load development for your double rifle.

Believe me, I know quite well how trying it can be to shoot a .470 from the bench. I have a Merkel 140-2 in .500NE! About 8 rounds from the bench is all I can take in a day, and then I'm not going to shoot the next couple days after that. But you bought the rifle, so you're going to have to meet the challenge.

Enjoy your DR, and welcome to the forum. You will find all kinds of helpful advice here.

My welcome also extends to you, carwi! This is the first time I have greeted two first time posters in the same thread.

Best regards,
Curl