Thoughts on a long lead in a barrel

[Geocodyrgia]

All, as I know there are a number of gunsmiths on the forum here, I would like to kindly ask for your input. I'm looking at project for reducing the wear in the throat of a barrel, but one of the limiting factors will be the requirement for not having rifling for the first 2-4". Essentially a long, non-tapered lead. I'm still investigating machining tolerances, obviously less is better, but if you have particular expectations you look for that input would be greatly appreciated as well.

So my question is: do you believe a bore diameter lead that is long enough to cover the area that becomes fire-cracked from hot/high pressure rounds would be detrimental to accuracy?

If accuracy in affected by a long lead and the lands/grooves really need to start in very close proximity to the ogive of the bullet as it's seated in the case, I will need to re-work my plans or at least make some changes to how it would be implemented.

Thank you all for any input!

 

[Alex Wheeler]

A 2-4" throat gives a long time for blow by to occur. I would expect terrible coppering from gas cutting and poor accuracy, not to mention possible jacket failures from hitting the rifling at higher speed.

 

[tobnpr]

^^^
My first reaction was, is he seriously thinking about slamming a bullet into square-edged rifling?

Sounds to me like a bad idea. Combustion gases aside, seems a bit like slamming into a bit of brick wall.

Any misalignment between the precise centerline of the cartridge and the center of the bore, uneven release of the bullet from the neck, will make the bullet impact the bore off-center.

Purpose of the tapered rifling /leade is to mitigate those issues, to guide the bullet into dead center as it is released. You have the base of the bullet still in the case and the front of the bullet fully in the rifling simultaneously.

Essentially, you're shooting a bullet through space, trying to hit the center of the bore. I'm not sure about blowby in that short a distance, but I do think this would a significant (perhaps dangerous) pressure spike when the bullet slams into the rifling. I haven't studied chamber pressure science much so others can comfirm or shoot down that theory...

 

[Liven The Dream]

Sounds like you may need to up your Insurance ?

My Wife would say ask " Why three times " .