2 ▁and ▁later , ▁W . ▁E . ▁Met ford ▁carried ▁out ▁an ▁exhaust ive ▁series ▁of ▁experiments ▁on ▁bul lets ▁and ▁rif ling , ▁and ▁invent ed ▁the ▁important ▁system ▁of ▁light ▁rif ling ▁with ▁increasing ▁spir al , ▁and ▁a ▁hard ened ▁bullet . ▁The ▁combined ▁result ▁was ▁that ▁in ▁December ▁ 1 8 8 8 ▁the ▁Lee – Met ford ▁small - b ore ▁( 0 . 3 0 3 ", ▁ 7 . 7 0   mm ) ▁rif le , ▁Mark ▁I , ▁was ▁finally ▁adopted ▁for ▁the ▁British ▁army . ▁The ▁Lee – Met ford ▁was ▁the ▁prede cess or ▁of ▁the ▁Lee – En field . ▁ ▁Modern ▁bul lets ▁ ▁The ▁next ▁important ▁change ▁in ▁the ▁history ▁of ▁the ▁rif le ▁bullet ▁occurred ▁in ▁ 1 8 8 2 , ▁when ▁L t . ▁Colonel ▁Edu ard ▁Rub in , ▁director ▁of ▁the ▁Swiss ▁Army ▁Labor atory ▁at ▁Th un , ▁invent ed ▁the ▁co pper - jack et ed ▁bullet ▁— ▁an ▁el ong ated ▁bullet ▁with ▁a ▁lead ▁core ▁in ▁a ▁co pper ▁jack et . ▁It ▁was ▁also ▁small ▁bore ▁( 7 . 5 mm ▁and ▁ 8 mm ) ▁and ▁it ▁is ▁the ▁prec ursor ▁of ▁the ▁ 8 mm ▁Leb el ▁bullet ▁adopted ▁for ▁the ▁sm ok eless ▁pow der ▁am mun ition ▁of ▁the ▁M le ▁ 1 8 8 6 ▁Leb el ▁rif le . ▁ ▁The ▁surface ▁of ▁lead ▁bul lets ▁fired ▁at ▁high ▁velocity ▁may ▁m