We had an unusually warm (and windy) weekend so I got to the range with my Labradar chronograph to compare a standard 6" barrel (BAR506SR) and the IMB barrel that my gun came with. The new barrel dropped right in and both functioned perfectly with full power ammo (which is all I had). The difference in felt recoil was definitely noticeable but I wouldn't say it was a huge difference. I was mainly there to get chrono data and blast some gallon jugs of water on video so I didn't compare how well I could put groups on a target with each barrel. I'll do that next time I'm at my local indoor range. I will say the standard barrel w/o the muzzle brake generates some amazing fire rings that are visible in direct sunlight.

As for the chronograph results, I foolishly left my ProChrono optical unit at home and only brought my Labradar unit and it was being temperamental. The first issue was it suddenly decided to stop recognizing my SD card once I got to the range. The built in audio trigger was very flaky so I had to switch to the ballistic trigger. And somehow the muzzle blast, even at 18" away, was enough to rattle the the AA batteries around and shut the off the Labradar without recording a shot. Very strange. Using an external battery and a USB cable I was able to keep it powered up with each shot. With all the unrecorded shots in the beginning, I was getting grumpy and stingy with ammo so some of the ammo / barrel combos comparison are based on only 5 shot strings. I'll paste in the data straight from excel and hopefully the formatting won't be completely lost.

Manufacturer Hornady XTP Hornady XTP Underwood Underwood Reloads Reloads Reloads Reloads
Bullet 300 gr. 300 gr. 300 gr. 300 gr. 300 gr. 300 gr. 325 gr. 325 gr.
Barrel 6" Std 6" IMB 6" Std 6" IMB 6" Std 6" IMB 6" Std 6" IMB
1250 1246 1297 1225 1332 1238 1315 1292
1294 1237 1401 1221 1269 1264 1310 1323
1269 1256 1361 1275 1280 1269 1373 1319
1298 1261 1337 1355 1247 1249 1348 1319
1307 1285 1383 1369 1328 1258 1336 1313
1303 1419
1278 1283
1263
1308
1305
Average FPS 1288 1257 1354 1289 1291 1256 1336 1313
IMB FPS loss 31 65 36 23

Compared to the previous readings from the ProChrono optical chronograph I'd say the 1289 fps average of the Underwood 300 gr. ammo using the IMB barrel is atypical and you wouldn't normally lose 65 fps with the IMB. So from this small test I'd sum things up by saying that when shooting full power ammo the IMB provides a noticeable reduction in felt recoil at the expense of 25-50 fps at the muzzle, which ain't bad.