Jason Murray describes & demonstrates a Gauss rifle he designed & built. He posts many of the design and construction details at his Delta V Engineering site. It’s a good write-up of a nicely done piece of engineering.
My younger son and I built a very simple, capacitor-driven Gauss gun for his science fair project some years back. It was on a much more limited scale than this one. We could fire small aluminum foil "bullets" a few yards; they might have knocked a fly out of the air (if we’d been able to hit one).
No Truce With Kings 