Tumbling bullets.....and keyholes on target....

[targetman]

Has anybody an idea as to why my bullets are "keyholing" on the target?

The rifle is an 1878 .43" Beaumont in excellent condition with a perfect bore. The load is a 405 grain .457" cast lead bullet over 65 grains of TPPH.

It seems to be quite accurate at 200 yards but the marker reports that the bullets are keyholing so I assume the bullet is begining to tumble.

Any ideas as to why or how to remedy would be much appreciated.

Many thanks

TM

[dodgyrog]

Possibly undersize boolit. Have you slugged your bore and checked the boolit fit.
I had cast boolits work well at 200 - 300 yards but tumbled at 600 as they went subsonic.
Boolit hardness and quality of lube will also have an effect.
What weight of boolit will work best in your rifle - look at the original boolit design for that rifle?
There's so many variables which is why cast boolit shooting is so challenging and fun.

[dromia]

Are they all tumbling or do some shoot OK?

If so where in the shot string do they tumble?

[targetman]

More research came up with a possible answer. The bullet used is fractionally too small a diameter at .457", (the rifling is very, very shallow), the bullet is also too heavy at 405grns and the charge too light at 55grns, so velocity is low.

I have found a bullet that comes out at .459" and is 350grns and when seated gives more capacity in the case, I should be able to up the charge to closer to 70 grns....which hopefully will give the required velocity.

We shall see.......

[huntervixen]

A side point chaps, does anyone know what difference it makes to a rounds ballistic performance when it goes subsonic, I ask this because i was in conversation with an Aerospace engineer at the weekend and he told me about the shift in the center of Gravity (to the rear) when an Aircraft goes supersonic.

Stands to reason the same rules of physics must apply to a bullet in flight....or not....

[IainWR]

A side point chaps, does anyone know what difference it makes to a rounds ballistic performance when it goes subsonic, I ask this because i was in conversation with an Aerospace engineer at the weekend and he told me about the shift in the center of Gravity (to the rear) when an Aircraft goes supersonic.

Stands to reason the same rules of physics must apply to a bullet in flight....or not....

The same rules do apply (which is why boat-tail bullets are a good idea - the equivalent on aircraft is called Area Ruling).

Doubt if the C of G shifts unless the aircraft has swing wings or pumps fuel around to achieve that result. Sure your friend didn't mean one of the Centre of Pressure / Lift / Drag?

In the subsonic regime, the Bernoulli equation for drag mostly applies, so drag is a function of the square of the velocity. Transonic and supersonic, the drag equations are different.

Also, by the time the bullet gets to be subsonic (talking centrefire rifle here) its got a fair bit of positive incidence to the relative airflow, which develops lift.

And the bullet has a vertical velocity which creates a transverse airflow on a rotating object, so the Magnus effect comes into play

And ...

[dodgyrog]

A side point chaps, does anyone know what difference it makes to a rounds ballistic performance when it goes subsonic, I ask this because i was in conversation with an Aerospace engineer at the weekend and he told me about the shift in the center of Gravity (to the rear) when an Aircraft goes supersonic.

Stands to reason the same rules of physics must apply to a bullet in flight....or not....

The same rules do apply (which is why boat-tail bullets are a good idea - the equivalent on aircraft is called Area Ruling).

Doubt if the C of G shifts unless the aircraft has swing wings or pumps fuel around to achieve that result. Sure your friend didn't mean one of the Centre of Pressure / Lift / Drag?

In the subsonic regime, the Bernoulli equation for drag mostly applies, so drag is a function of the square of the velocity. Transonic and supersonic, the drag equations are different.

Also, by the time the bullet gets to be subsonic (talking centrefire rifle here) its got a fair bit of positive incidence to the relative airflow, which develops lift.

And the bullet has a vertical velocity which creates a transverse airflow on a rotating object, so the Magnus effect comes into play

And ...

Clever Clogs (but not a Smart Alec)

[tackb]

A side point chaps, does anyone know what difference it makes to a rounds ballistic performance when it goes subsonic, I ask this because i was in conversation with an Aerospace engineer at the weekend and he told me about the shift in the center of Gravity (to the rear) when an Aircraft goes supersonic.

Stands to reason the same rules of physics must apply to a bullet in flight....or not....

The same rules do apply (which is why boat-tail bullets are a good idea - the equivalent on aircraft is called Area Ruling).

Doubt if the C of G shifts unless the aircraft has swing wings or pumps fuel around to achieve that result. Sure your friend didn't mean one of the Centre of Pressure / Lift / Drag?

In the subsonic regime, the Bernoulli equation for drag mostly applies, so drag is a function of the square of the velocity. Transonic and supersonic, the drag equations are different.

Also, by the time the bullet gets to be subsonic (talking centrefire rifle here) its got a fair bit of positive incidence to the relative airflow, which develops lift.

And the bullet has a vertical velocity which creates a transverse airflow on a rotating object, so the Magnus effect comes into play

And ...

if it's ok with you i'll just shoot it?

[huntervixen]

Thanks for that...... I think I'll go and sit in the corner with my dunce hat on..... so is that a yes or a no then :lol: :lol:

[huntervixen]

Has anybody an idea as to why my bullets are "keyholing" on the target?

The rifle is an 1878 .43" Beaumont in excellent condition with a perfect bore. The load is a 405 grain .457" cast lead bullet over 65 grains of TPPH.

It seems to be quite accurate at 200 yards but the marker reports that the bullets are keyholing so I assume the bullet is begining to tumble.

Any ideas as to why or how to remedy would be much appreciated.

Many thanks

TM

I fired a "slightly iffy" very old RG .303 round from my SMLE last year, the newness had most definitely worn off, but good enough for Tommy atkins, good enough for me, it went down range like a very angry wasp BBBBBBZZZZZZ and keyholed the bull at 100yds!!