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.
Scope of the Project
Initially we decided to test thirteen common pistol calibers/cartridges (subsequent testing expanded this to twenty-two different calibers/cartridges), each over a range of barrel lengths from 18" down to 2", and each using a variety of ammunition (most of it "premium" ammo made for self-defense purposes). In each case we fired three rounds of a given ammo at a given barrel length, recording the velocity of the bullets at 15 feet with two commercial chronographs. If we did not get two reliable readings for each of three rounds, we repeated the process until we did. Altogether we have fired about 20,000 rounds of ammunition.
In order to get consistent results, we opted to use a platform which would accommodate barrels of any caliber - a Thompson/Center Encore No. 1842. A gunsmith was commissioned to create 11 barrels (calibers tested such as .38 special/.357 magnum used only one barrel) which would each fit into a single housing, yet allow us to chop the barrels easily. This means that we could directly compare calibers regardless of mechanical issues (such as whether there was energy loss due to a cylinder gap or activating an extractor) and as such constitutes an 'ideal' performance.
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One note: in every case with the T/C Encore the length of the barrel was measured from the end of the barrel back to the breech face. This is how semi-auto pistols are measured, but revolvers are measured as the length of the barrel in front of the cylinder gap. Take this into consideration when comparing calibers using our numbers.
We have also tested a number of personal firearms (both handguns and carbines) using the same ammunition as used with the T/C Encore, in order to give some benchmark comparisons between the 'ideal' and the 'real world' performance of a given ammo at a given barrel length. The same protocols were followed, and we used the same ammo.