410 bore dia questions

[Gunnerboy]

Alright this is for all you older gentlemen with a few more years of knowledge then myself, so i just finished drilling out a mosin nagant barrel to 10.08mm and i know that a 410 bore dia is 10.4mm so will this be a big issue or not ? or will this just be a extra full choke gun ?

 

[rcmodel]

I have no idea what effect the smaller bore will have on pressure.
Or what size 10.08mm vis 10.4mm might be.
We measure in thousandths of an inch.
I have no metric measuring tools.

But if the hole is drilled straight through from end to end?
It will be a cylinder choke.

Choke only works when the shot column is squeezed down suddenly just before it exits the muzzle.

The trick to a choke is to have the shot column exit the muzzle while the shot is still being compressed toward the center of the column, but before it starts rebounding back away from the center.

Consider a water hose nozzle.
If the hose doesn't have a nozzle constriction on the end, there is no constriction to make a stream.
Doesn't matter what size hose the hose is.

If you want it choked, you could jug choke it by reaming a larger bore just behind the muzzle and leaving the muzzle what the rest of the bore is.
http://www.brimstonepistoleros.com/gazette/apr05.html

rc

 

[NCsmitty]

You have no choke, as it's essentially a cylinder bore.
I have a NEF singleshot 410 that I have cut down to eliminate the choke, but is still legal of course. The very end of the barrel measures exactly .413", and that is also a cylinder bore. I shoot .380" cast lead ball through it, and it will keep a 2.5" 410 3 ball load spread to 12" or less at 50yds. Velocity has been measured at 1180 FPS using H110 powder.

I see rcmodel explained the choke deal.


NCsmitty

 

[Gunnerboy]

no i choked it i used 3 differant bits and then polished the inside so it all flows smooth i just then realized that my micrometer wasnt zeroed when i started so the end bore dia was 10.08 instead of 10.4

 

[NCsmitty]

no i choked it

You didn't say that before. You'll just have to try it and see if it patterns properly.
Good luck with that. Take pics and post if you can.


NCsmitty

 

[Gunnerboy]

i will post pics when i can. now i just need the rest of the gun i got a barrel and a stock , just one of those boring day projects

 

[Clipper]

I'd like to know more, specifically, besides drilling the barrel, what other mods are necessary to convert the M-N to .410, chamber, bolt face, magazine etc.

 

[Gunnerboy]

i havent gotten past the barrel i just had one laying around so i decided it was gonna be my guinea pig