When officers raided the home of Geoffrey Crossland at Padside Green Farm, Harrogate, North Yorkshire, they found guns hidden underneath the property, along with ammunition.
Police had been investigating the pensioner after he was found to have amassed more than 2.2 million indecent images, described by the Crown Prosecution Service as one of the biggest known collections in England and Wales.
North Yorkshire Police said the seizure of the images was the biggest in the county, and included 6,946 in the most extreme category A.
Appearing at York Crown Court on Monday, Crossland admitted 11 charges in relation to the possession of firearms and ammunition.
He had previously pleaded guilty to three counts of making indecent images between January 2011 and October 2018.
He will be sentenced later on Monday by His Honour Judge Andrew Stubbs.
In July 2018, Padside Green Farm, which dates back to 1871, went on the market with an asking price of £645,000.