Grain in render/grainy shadows

I am using cycles to render an internal scene, i always get grain when rendering internal scenes, so i turned
clamp up to 40 or so and set to 1000 samples, when it was done after 30 mins it still had grain.
is there something im doing wrong? I have an hdr set up for the render but i dont think that
really matters.

Hard to say without any relevant information about the scene. Please ALWAYS supply an example .blend file with any support question.

That’s not how clamping works. Clamping gets stronger the smaller the clamping value is (read: “clamp to the entered value”, not “clamp by the entered value”). The only exception to that rule is a value of 0, which means clamping is off.

Also: 1000 samples still is a quite low value for an interior render.

If you only have a low amount of grain left, you can make use of the new denoising feature and get a squeaky clean image.