Extrapolation

[konkapot]

I have access to a lot of factory .40 ammunition. Manufacturer claims 1300 fps out of a 4.5 in barrel.

 

Any thoughts as to what the velocity might be out of a 6 inch gun?

 

Won't be able to chrono until next week sometime. Just looking for some collective wisdom.......

[Hi-Power Jack]

Depends on the powder, and your individual barrel.

 

You might get 1200 fps, or 1450.

 

Your chrono is your friend ....    

[lefty o]

hard to say, as even two separate barrels made one after the other can have quite the variance in speed. ballpark estimate, 25-50fps.

[jwhittin]

I would also say about 30 to 60fps higher just based on some of my own measurements.  

[Part_time_redneck]

I have a little spreadsheet I downloaded. It is actually surprisingly accurate changing charge weights in my open gun. Naturally I don't trust it and chrono, but it does give a rough idea what to expect.  It says 4.5 > 6.0 inch will be 1300 > 1333. 

[Hi-Power Jack]

If you have a load at a known velocity (1,300 fps) out of YOUR gun, and you

cut 1.5" off the same barrel, you can expect a 25 - 60 fps difference.

 

BUT, in the case you mentioned,

 

1.  you don't know what the load Advertised as 1,300 fps would do in your 4.5" barrel,

 

2.  if it did 1,300 fps out of another 4.5" barrel, you would have no idea what it would do

     in Your 4.5" or 6" barrel.

 

Got to chrono it ...   

[MemphisMechanic]

It also heavily depends on the burn rate of the powder that was used.