CAUTION: Nerd talk ahead! Sorry fellas, sometimes I can't help myself!

I had seen data from BBTI.com before, but had not seen this one. After reading through it a bit and considering their numbers, I'm somewhat compelled to try to replicate their results!

I had a bit of free time this weekend so I did a quick plot and regression on the data from this link, and found the results rather surprising.



The charts show the different charge weights of each powder and resultant velocity for each barrel length with that charge. The trendlines show the average FPS change for each load and the regression fit - they're almost perfectly linear!

For the same barrel getting cut down one inch at a time, these 3 powders (4198, 322, and N135) for 3-6 charge weights show almost perfectly linear relationship between velocity and barrel length from 10" to 22". H322 has some funky stuff going on with the 18" for a couple charge weights, and the VV powder must have some charge density complication between 25.7 and 26.4grn but overall, the relationship for a given load is pretty linear. H4198 loses 42-49 fps, H322 loses 41-49fps per inch, and N135 loses 40-47fps per inch.

My experience with different rifles has been a trend more like the 25.0grn VV N135 load, where it's more flat at the long lengths, then progressively worsens as you shorten barrels. I only have 4 barrel lengths right now, and of course some are in DI AR's and some are in bolt guns, so it might not be relevant, but I'd love to spend time generating this type of data to explore longer than 22" barrels and other powders/loads.