What does the following mean? "originally made for Purdeys as manufacturers mule"? I won this 10 bore rifle at Holt's yesterday. The Mule part wasn't in the description when I bid on it. Just wondering if it was used to test loads or something?

UNSIGNED IN THE WHITE 10-BORE (2 7/8IN.) FALLING BLOCK RIFLE, serial no. 10010, 27in. very heavy nitro proofed (in 2013) barrel, fixed rifled choke with knurled cap, 2 7/8in. chamber, fitted with a Schmidt & Bender 6x42 telescopic sight, serial no. 236386 on a picatinny rail, plain action, believed to be built by G. Whittome, 15in. figured pistolgrip stock including ventilated rubber recoil pad, no fore-end, weight 19lb. 9oz., in a slip, originally made for Purdeys as manufacturers mule