[ahpd1992]

I have a Glock 35 which I have dropped in a KKM barrel in 357 Sig. The barrel on this gun is 5.5" and all of the ballistic date I can find is for a 4" barrel, my question is can I estimate what kind of ballistics Im getting as I do not have a Chronometer to test the performance I am getting?

BTW I am using Winchester Ranger SXT 125gr. Their listed ballistics are 1330FPS 506ME in a 4" barrel. Now if I were to take those figures and simply divide by 4 (for the 4 inch barrel) then I would the FPS and ME per inch of the barrel, but I know that is overly simplistic because doing the math that way gives me 695ME and 1828FPS out of my 5.5" barrel. Impressive, but I know thats not accurate. So is there any mathmatecal formula, or do I have to try and find someone w/ a Chrono?

[SaxonPig]

The high intensity calibers gain and lose velocity more dramatically with changes in barrel length than do more sedate calibers. In 38 Special I see a 40-50 FPS drop going from 6" to 4" barrel lengths, more like 90-100 with a 357 Magnum.

Your gun is likely closer to the 357 in effect of barrel length.

[GRIZ22]

BTW I am using Winchester Ranger SXT 125gr. Their listed ballistics are 1330FPS 506ME in a 4" barrel. Now if I were to take those figures and simply divide by 4 (for the 4 inch barrel) then I would the FPS and ME per inch of the barrel, but I know that is overly simplistic because doing the math that way gives me 695ME and 1828FPS out of my 5.5" barrel. Impressive, but I know thats not accurate.

You cannot figure velocity using your method. It just doesn't work that way. You may be getting 50 fps more or even less than that advertised velocity. Even out of a 16" carbine barrel you only gain 100-150fps with just about any load.

I chrongraphed loads out of a G17 and a G19 one time. factory ammo from not only the same lot even the same box. G17 shot the ammo 60 fps average slower.

You need to get a chrongraph. A basic one is only about $100.

[Claude Clay]

find a crono

having tested to find the best powder for IDPA night shoots i use bullseye with a 3" defender and power pistol for 4" 9mm or 357 SIG. bbl length allows for complete powder burn: thus no muzzle flash. clean enough that the smoke from the shot does not 'fog blind' my flash lite.

to answer your question --without a crono-- one may think that the factory round is designed to burn in 4" as that is what most 357SIG bbls are tested with. my 239 and a friends 229 in 40 S&W with the same load of bullseye both had a velocity close enough to not really matter. let us know when you have cronoed them.

[Mello]

Depending on the pressure in the barrel behind the bullet, you can get a situation where the pressure drops below that level needed to keep accelerating the bullet. In that case where a barrel is longer than the length where the pressure in accelerating the bullet, the bullet will begin to decelerate.

This is why there are powders with different burning rates. Ammo manufacturers can design their load for a specific case capacity, bullet weight, barrel length and SAAMI pressure limits.

As others have said, get a chronograph and have fun learning more about your ammo and guns.

Found this website which address some aspects of barrel length and velocity.
http://www.ballisticsbytheinch.com/
For the 357sig with the Federal Premium 125 gr. Silvertip JHP, they measured:
6" 1531
5" 1501
4" 1426
3" 1319
2" 1145