Velocity by Barrel Length of Various Calibers

This page will examine barrel length to velocity differences for various calibers. We'll mostly stick to common calibers, but others will likely be added as well. But first, the concepts will be discussed below. The data will follow.

How Does Barrel Length Affect Velocity?

It is well-established fact that the length of a firearm's barrel will affect velocity (and therefore muzzle energy and even trajectory) to varying degrees. This is because the longer the propellant has had time to burn, the more of its maximum effect on the projectile can be utilized. Otherwise, energy will be wasted and propellant will likely burn off outside the barrel.

Why Does Barrel Length Affect Velocity?

This can depend on a number of factors, such as burn rate of the propellant, bore diameter, and probably others as well. The same caliber gun with the same barrel length could even show different results. For example, two revolvers of the same caliber and barrel length could differ in their amount of cylinder gap, allowing one to waste a bit more energy than the other. Likewise, semi-automatic or fully-automatic firearms will typically have lower muzzle velocity due to some of the propellant's energy being bled off into the gas system to work the action, and this can vary by individual firearm as well. Some guns, such as Heckler & Koch's integrally suppressed MP5SD are actually designed to bleed off excessive gas pressure to make sure any rounds they fire will remain subsonic! However, that is an edge case and can mostly be ignored as it pertains to the topic at hand.

We'll note various barrel lengths and load data on various calibers, from various sources.

9mm Luger

Also known as 9mm Parabellum, 9x19mm, etc. Data is from Ballistics by the Inch.

Barrel Length	Cor-Bon 90 gr JHP +P	Cor-Bon 115 gr JHP +P	Cor-Bon 125 gr JHP +P	Cor-Bon 115 gr DPX	Federal 115 gr JHP text	Federal 135 gr Hydra-Shok JHP (low recoil)	Federal 105 gr Expand'g FMJ	Federal 124 gr Hydra-Shok JHP	Federal 147 gr Hydra-Shok JHP	Speer 124 gr Gold Dot Short Barrel
18"	1754	1543	1449	1458	1297	1194	1370	1231	1038	1395
17"	1766	1550	1421	1455	1320	1207	1381	1250	1096	1400
16"	1740	1525	1430	1476	1295	1185	1358	1243	1073	1379
15"	1768	1536	1392	1416	1304	1194	1364	1244	1090	1375
14"	1767	1532	1405	1440	1295	1182	1372	1241	1090	1390
13"	1738	1517	1477	1427	1281	1183	1343	1237	1081	1378
12"	1716	1514	1385	1380	1282	1184	1273	1225	1081	1361
11"	1690	1496	1372	1391	1268	1166	1318	1212	1059	1360
10"	1647	1474	1372	1379	1253	1167	1314	1211	1067	1338
9"	1663	1476	1369	1377	1238	1161	1307	1212	1055	1345
8"	1634	1458	1366	1366	1234	1145	1278	1180	1047	1329
7"	1619	1446	1329	1350	1223	1136	1258	1161	1040	1316
6"	1566	1402	1312	1332	1188	1113	1235	1131	1030	1284
5"	1539	1372	1282	1315	1166	1085	1194	1115	1007	1259
4"	1444	1316	1226	1265	1094	1039	1140	1061	951	1203
3"	1345	1245	1170	1215	1029	976	1074	988	902	1108
2"	1215	1134	1061	1132	948	909	985	900	837	1074

Optimal Barrel Length For 9mm?

Based on the data above, it appears that almost all loads tested got their greatest percentage increase in velocity up until about a 7" barrel length. Velocity did of course increase further with longer barrels, but to a much smaller degree. For example, going from a 4" barrel to 7" (a 3 inch difference), every load got well over a 100 fps increase in velocity. However, going a full 10 inches longer up to a 17" barrel gained most of the tested loads under 100 feet per second in velocity. In fact, going from a 17 inch barrel up to 18 inches, actually LOST velocity in all but two of the loads, although the decrease was negligible.

It appears that overall, the optimal barrel length for something like an AR-15 pistol build, SBR, or similar setup, is about 7 to 8 inches for maximum efficiency and handling. If you still wanted to maintain an ultra-short setup with a suppressor, you could go even shorter with barrel length, as the additional length of the suppressor will increase velocity. Even at 7-8" barrel, the additional length of a suppressor would still allow the pistol or SBR to remain more compact than a 16" barrel. A 7" barrel with a 7" suppressor would still give an overall length of 14 inches. If you were looking for a rifle setup, there appears to be no major reason to go above the federal 16" barrel requirement, unless local laws differ, or whatever the case may be.