P-Max versus GRT data

[Husky]

From the Vihtavouri website regarding N140 in a 308.
150 grn Sierra SPBT, COL 2.765 inch, max load 45.7 grains gives a velocity of 2857 fps.

Put the data into P-max ballistics it give a velocity of 2801fps and a pressure of 56583 psi.

GRT gives a velocity of 2828 fps a pressure of 60238psi and the dire warning "Attention Overpressure This charge is dangerous do not use "

I wasn't going to load to the max load, but who do I believe ?

 

[User00040]

I wasn't going to load to the max load, but who do I believe ?

Neither!

What barrel lengths are these supposed to be from?

 

[308tikka]

VV data is more consistent with my findings.

You cant fit enough VV140 powder in to the 308 case to make a 150-155gn projectile over pressurise.

Ive had significantly more N140 in a case over that with nil issues.

But none of it is needed... a nice steady 44.5 will do fine.

 

[Husky]

24 inch barrel, I was curious to see the results as I had downloaded GRT to try it out.
Interestingly there was no difference between a 24 and 20 inch barrel regarding pressure.

 

[Apthorpe]

24 inch barrel, I was curious to see the results as I had downloaded GRT to try it out.
Interestingly there was no difference between a 24 and 20 inch barrel regarding pressure.

Why would one expect maximum pressure to vary with different length barrels? Surely the peak pressures are reached before the bullet has travelled far down the barrel? By the time it's even 15 inches down the barrel the pressure must be relatively low.

 

[Husky]

Why would one expect maximum pressure to vary with different length barrels? Surely the peak pressures are reached before the bullet has travelled far down the barrel? By the time it's even 15 inches down the barrel the pressure must be relatively low.

I wasn't expecting there to be any difference between barrel lengths and pressure.
My second sentence was down to a long day and being tired, once I had realised my mistake it was too late to edit it.