http://www.rangeinfo.org/ and the following may prove helpful, but for a small personal outdoor range with a "U" shaped berm of roughly 20 ft height and a minimum of 4 ft thickness should do.
RELEVANT CODES AND STANDARDS
The following agencies and organizations have developed codes and standards affecting the design of firing ranges. Note that the codes and standards are minimum requirements. Architects, engineers, and consultants should consider exceeding the applicable requirements whenever possible:
29 CFR 1910.1025, Lead Exposure (
http://www.wbdg.org/references/code_....php?i=295&r=1)
Department of Justice, Immigration and Naturalization Service/National Firearms Unit, Firing Range Design Standard (
http://www.wbdg.org/ccb/browse_doc.php?d=5086)
GSA Facilities Standards for the Public Buildings Service, P100
International Building Code (
http://www.ihserc.com/cgi-bin/ihslog...name=icc%20ibc)
Naval Environmental Health Center (NEHC) Technical Manual NEHC TM-6290.99-10, Indoor Firing Ranges Industrial Hygiene Technical Guide (
http://www-nehc.med.navy.mil/downloa....99-10Rev1.pdf)
National Park Service, Firing Range Waste Management (
http://www.nps.gov/renew/rangewastemgt.pdf)
NIOSH, Technical Information #76-130, Lead Exposure and Design Considerations for Indoor Firing Ranges. NTIS #PB266-426. (
http://www.cdc.gov/niosh/topics/ranges/pdfs/76-130.pdf)
U.S. Air Force, ETL 02-11 Small Arms Range Design and Construction (
http://www.wbdg.org/ccb/browse_doc.php?d=391)
U.S. Army, ER 210-3-2 Army Range Programs (
http://www.wbdg.org/ccb/browse_doc.php?d=3188)
U.S. Navy, MIL-HDBK-1027/3B Range Facilities and Miscellaneous Training Facilities Other Than Buildings (
http://www.wbdg.org/ccb/browse_doc.php?d=2830)