No, absolutely not... They're not even remotely close.
In terms of campaign contributions, the NRA doesn't top the top 20 of "Special Interest / SIngle Issue" category on OpenSecrets:
https://www.opensecrets.org/industries/indus.php?Ind=Q
That category is #4 overall for total contributions... WIth the entire category amounting to $180m in contributions... Compared to the top category, Finance/Insurance/RealEstate amounting to over $500m
The NRA gave about $1m in campaign contributions in 2014.
That said the NRA's campaign contributions are around a single issue, guns. And $1m in campaign contributions in an election cycle around a single issue can drive the issue... Soros Fund gives $15m but it's spread over a number of issues, some which they win on, some which they lose.
(Also, outside of direct contributions, the NRA also spends millions on lobbying and advertising, but the ratios work out the same in comparison to others)