9mm Velocity vs OAL?

[rootacres]

Quick question, if you were to take the exact same bullet, brass, charge, and primer. Load one to an OAL of 1.120 and the other to 1.155 (for example), shoot them out of the same gun would there be a velocity difference? How much? How much would the felt recoil change?

[Sarge]

3 minutes ago, rootacres said:

Quick question, if you were to take the exact same bullet, brass, charge, and primer. Load one to an OAL of 1.120 and the other to 1.155 (for example), shoot them out of the same gun would there be a velocity difference? How much? How much would the felt recoil change?

There would be a difference BUT there are so many variables it's impossible to tell exactly how much velocity or feel would change. Very gun specific. Your grip comes into play etc.

[Ssanders224]

29 minutes ago, rootacres said:

Quick question, if you were to take the exact same bullet, brass, charge, and primer. Load one to an OAL of 1.120 and the other to 1.155 (for example), shoot them out of the same gun would there be a velocity difference? How much? How much would the felt recoil change?

 

Yes, with the constants you describe, velocity will be higher with a shorter OAL.  Smaller combustion chamber, higher pressure, more velocity.  The increase in pressure is pretty linear for all intents and purposes.

It is not impossible to determine the velocity increase, but the math is pretty lengthy.   

 

As for felt recoil it is hard to say.  Shorter OAL, or increase in powder charge?  Which is the more desirable way interns of "feel" to increase velocity?  There isn't a real definitive answer.  

[DWFAN]

My testing shows about 20fps per .010. Using titegroup in a 9mm. From 1.085 to 1.135

[Hi-Power Jack]

16 minutes ago, DWFAN said:

My testing shows about 20fps per .010. Using titegroup in a 9mm. From 1.085 to 1.135

 

But, as others have observed, it will depend on many other factors, so you cannot

say that every powder, every bullet, every caliber would increase .010 per 20 fps.

 

I've done similar testing with WW231 and seen NO increase in shortening the round,

and loading 9mm Major with WAC and a MG from 1.175" to 1.145" and seen no increase

in velocity.    

[DWFAN]

 
But, as others have observed, it will depend on many other factors, so you cannot
say that every powder, every bullet, every caliber would increase .010 per 20 fps.
 
I've done similar testing with WW231 and seen NO increase in shortening the round,
and loading 9mm Major with WAC and a MG from 1.175" to 1.145" and seen no increase
in velocity.   [emoji4] 

Yep. Agree. Exactly why i didnt state that it was 20 for .010 for everything. I gave my experience. No more, no less. [emoji1]

[Sarge]

And while pressure is linear, etc, pressure increase does not equal velocity increase. Hence the plateau effect.