Complex sentence: In the 1950s he began a long career as a writer on handloading and guns, serving on the staff of various firearms publications; and contributed to publications such as "Gun Digest" and "Handloaders Digest".
Split into simpler sentences: In the 1950s, he began a long career as a writer on handloading and guns, serving on the staff of various firearms publications. He contributed to such publications as "Gun Digest" and "Handloaders Digest".