Barrel velocity?

[Hollywood]

I don't think it has any relevance to anthing, but the question popped into my head last night. If the bullet is traveling X fps out of the barrel and decelerating immediately upon exit of the barrel. What and where in the barrel is max speed? Why do you gain more velocity in longer barrels when the bullet is in a high friction environment for longer time? I know that it is a fact you get more velocity with longer a barrel to an extent but I can't wrap my head around why. Im sure there is someone here that can answer both of my questions.

Thanks
Erick

 

[savagedasher]

Try to make the answer simple. the bullet speed will be fastest at the muzzle. with all barrel lengths we use.
The reason their is enough pressure still behind the bullet to override the friction. so the bullet is going to keep gaining. Someone will give you the figures .
Here is some QL figures on a load I pulled up 20'' 2776 30'' 3030 40''3180 50''3299 60''3382
Larry

 

[dmoran]

Bullets will continue to gain speed in-bore until the pressure has degraded to around 10,000-psi.
Donovan

 

[Hollywood]

Bullets will continue to gain speed in-bore until the pressure has degraded to around 10,000-psi.
Donovan

Does the pressure stay above 10,000 psi until the bullet exits and pressure drops or would it fall below that threshold inside the barrel somwhere?

 

[dmoran]

In-bore........ attaching a pressure trace for example (from a 105gr bullet in a 30" barrel at 3117-Mv)

 

[Hollywood]

Chart's ;D I love it! In 1.3 milsec speed begins to decrease. How long is the bullet in the barrel?

 

[dmoran]

The red + in the trace curve represents "barrel exit", and is where and when the bullet exited the barrel.

 

[Hollywood]

Full acceleration untill you run out of gas (pressure). Seems so simple now that it is written out. Thanks for the Info.

 

[normmatzen]

The rate of change of the bullet velocity does change (acceleration) as long as there is enough pressure left behind the bullet. dmoran mentioned 10,000 psi, so if the bullet is still in the barrel when pressure behind the bullet drops below 10,000, then acceleration will tend to drop to zero.

 

[XTR]

Don't quote me on this , but I seem to recall that 22LRs hit max velocity in about 12 to 18 inches, after that barrel length is wasted metal unless it's for sight radius with irons.