Barrel length questions

[Timido]

How does barrel length difference affect fps? Some of the load data I am looking at was from a Glock 19. How much different is the feet per second going to be for my full size CZ? 4" to 4.6" Barrel with different twist. The data I am looking at is from this article http://www.shootingtimes.com/reloading/reloading-heavy-bullets-in-9mm-luger/ Thanks Tim

[IDescribe]

It's different twist, and the Glock is polygonal while the CZ is land & groove. There's also a difference in the depth of the throat. At the end of the day, you're going to have to chrono because there's more going on than just barrel length.

That said, almost all my 9mm chrono data is with a full size CZ75 ShadowLine or an HK VP9. THe VP9 has a 4.1-inch polygonal barrel. If I chrono cartridges I made for the CZ in the HK, the two will typically chrono within 5-15 feet/sec of one another.

[Timido]

Thanks. I would have thought it would have more of a difference. I am going to use that data minus %10 and go up from there. That would be 2.5g N320 with the 160g Bayou at 1.15 Most of the production loads I have read on here are 2.7-3.0g

[kneelingatlas]

I've found an increase of 6% velocity per additional inch of barrel is a good place to start with your estimates (at least with pistols).

Edited July 31, 2016 by kneelingatlas

[fastluck13]

It's different twist, and the Glock is polygonal while the CZ is land & groove. There's also a difference in the depth of the throat. At the end of the day, you're going to have to chrono because there's more going on than just barrel length.

That said, almost all my 9mm chrono data is with a full size CZ75 ShadowLine or an HK VP9. THe VP9 has a 4.1-inch polygonal barrel. If I chrono cartridges I made for the CZ in the HK, the two will typically chrono within 5-15 feet/sec of one another.

This is the right answer....Different barrel, different rifling, different length, different chamber/lead. It is enough to need to start over completely.