Air Arms Owners Club

Does anyone know the correct twist rate for the Mpr-Ft (12ft/lb) model?
I haven't a cleaning rod to check because I use a pull-through to clean the barrel.
Plus the twist rate on the .177 S400f

I sent Air Arms an email asking the twist rates and got a reply saying the technical team advised not to disclose that information

Like rolls royce and bhp. “Its sufficient to do the job”

Lothar airgun blanks seem to be 1 in 18”

Quiz: in a 1 in 18 barrel what is the pellet rpm at the muzzle for 12 ft/lb in .22?

TenMetrePeter wrote: ↑

Mon Jul 22, 2019 3:06 pm

Like rolls royce and bhp. “Its sufficient to do the job”

Lothar airgun blanks seem to be 1 in 18”

Quiz: in a 1 in 18 barrel what is the pellet rpm at the muzzle for 12 ft/lb in .22?

Yes but turns out the Mpr Barrel is 1 in 17.7
Rpm depends on the velocity of the pellet Peter.
Just a quick guess i'd say if the pellet leaves the barrel at 800 fps then the rpm would be roughly 542 rpm

I did the maths for .177
The .22 would be roughly 400 rpm

Multiply that by 60!

800 * 60 * 12/17.7
= 32,542 rpm in .177

Roughly 24,000 rpm in .22

Bloody fast!

Its actually 1 in 450mm being bloody European, so yes 17.7inch, I was being lazy

TenMetrePeter wrote: ↑

Mon Jul 22, 2019 10:03 pm

Multiply that by 60!

800 * 60 * 12/17.7
= 32,542 rpm in .177

Roughly 24,000 rpm in .22

Bloody fast!

Its actually 1 in 450mm being bloody European, so yes 17.7inch, I was being lazy

I'm European too but still use imperial measurement and metric.
My maths was way off.
Higher velocity requires higher weight to stabilise then.
But then length of the pellet comes into the equation too, it's a minefield!
Centre fire rifles must exceed 100,000 rpm.

I was doing 12÷17.7 x 800 fps for the. 177 rpm

You needed feet per minute. Everyone gets it wrong.

Length of pellet is only a factor in that a longer pellet is heavier therefore slower at 12ftlb

I don’t have the gyro formula for mass and angular velocity but I wouldn’t mind betting the faster spin has more stability.

Discuss.

(Can’t you sleep either? )

A HMR travels at 2150 + FPS with a 17 grain bullet.
A 223 will travel 3000 FPS with a 40 grain bullet.
Just in case you was board
Centre fire twist rates vary from 1in 8 to 1 in 12

BBF