ATTENTION:  Effective Sept 1, 2020, the BBTI Project is in "Archive Status."  No further tests will be conducted, but we will maintain this site and data for the use of the firearms community.  Thank you.

Cylinder Gap Test


barrel length Cor-Bon, .38 special +P, 125 gr. JHP
.006" cylinder gap .001" cylinder gap no cylinder gap
18" 1193 1213 1253
17" 1100 1149 1236
16" 1124 1137 1183
15" 1084 1138 1231
14" 1101 1121 1226
13" 1101 1157 1200
12" 1073 1132 1192
11" 1073 1104 1174
10" 1070 1109 1180
9" 1050 1104 1161
8" 1071 1099 1148
7" 1066 1086 1123
6" 1037 1063 1094
5" 1016 1037 1075
4" 1001 1000 1039
3" 970 985 1024
2" 897 916 937

Other Resources

BBTI is not the end-all of ballistics testing, just one more component available for the common good.  In addition to extensive discussion about ballistics to be found at many gun forums, here are some other great resources pertaining to ballistics testing you should check out.  (And if you would like to recommend a site to list here, please send an email.)
  • BrassFetcher:  excellent resource, with an emphasis on bullet performance in ballistic gelatin
  • The Box O' Truth:  testing ammo penetration through various barriers
  • Terminal Ballistics Research:  Specializes in the research of cartridge & projectile performance, using hard data gathered from 20 years of hunting game.


We'd like to personally and specifically thank Pat Childs at Fin & Feather in Iowa City, as he not only helped get most of our ammunition and other supplies, he was the brilliant gunsmith who worked with us to make this insane project much more practical.  Without his help all of this would have been much more difficult and perhaps impossible.  Anyone who uses our data owes him a debt of gratitude.

And thanks to our spouses, who were not just tolerant but enthusiastically supportive of this rather nutty project.


This project, and all of its results, is only our fault.  We (well, Jim K, mostly) paid for everything ourselves, and we did not receive any kind of sponsorship or remuneration from anyone.  We did all the work.  We used products we were either familiar with, or because they were what was available, and mentioning them by name does not constitute an endorsement of any kind.  Furthermore, the data is provided purely for entertainment purposes - to better facilitate arguments over what ammo or caliber or gun is "best."  How you use the data is entirely up to you.  And if you think you could do better, feel free to spend the money and do the work and publish your own results.  Or not.  Your choice.