Measuring the ‘Slug’ after Slugging a Barrel

[The_Saltpeter_Sapper]

Hey Gang,

I’ve finally got around to slugging the barrel of my factory sniper Nagant before I reload precision ammo for it (given the variety of Nagant bores).

I just wanted to check: I think I need to measure between two ‘lands’, i.e. the raised areas on the slug, not the groove in the slug left by the rifling?

Many thanks as ever,
Perry

 

[Heym SR20]

Very much depends. The Brits measured between the lands on the bullet. It’s the smaller bore diameter - hence .275” for the 7mm

Whereas every where else measures the major diameter, ie the diameter of the bullet - so in the above example .284 is the bore diameter for 7mm.

Also note calipres are termed guessametres by precision engineers. To be really accurate you need a micrometer which measures at a predetermined pressure.

I suspect with the calipres with a wee bit of force you could measure .308

 

[Smellydog]

Ignore that ^.
Yes, measure across where the slug ran in the grooves, not the lands.

So in your picture you want bullets of .312". Cast or metal jacket.

 

[Tim.243]

Very much depends. The Brits measured between the lands on the bullet. It’s the smaller bore diameter - hence .275” for the 7mm

Whereas every where else measures the major diameter, ie the diameter of the bullet - so in the above example .284 is the bore diameter for 7mm.

Also note calipres are termed guessametres by precision engineers. To be really accurate you need a micrometer which measures at a predetermined pressure.

I suspect with the calipres with a wee bit of force you could measure .308

If you have the "feel" for a micrometer then it will be the same for a vernier..... Those who have to rely on the the thimble of a micrometer should revert to an adjustable spanner.

 

[Bowland blades]

Cast a lead slug on the bore , micrometres and callipers can both be out so test them

 

[The_Saltpeter_Sapper]

Ignore that ^.
Yes, measure across where the slug ran in the grooves, not the lands.

So in your picture you want bullets of .312". Cast or metal jacket.

Thanks mate! I’ve been reloading pip squeak rounds using home cast 7.62x39 heads up until now, but this is only for short gallery range plinking.

 

[Smellydog]

Thanks mate! I’ve been reloading pip squeak rounds using home cast 7.62x39 heads up until now, but this is only for short gallery range plinking.

I'd just load the bullet from the 7.62x39 mate

 

[Tim.243]

I'd just load the bullet from the 7.62x39 mate

Too late he wrote head

 

[Tim.243]

Cast a lead slug on the bore , micrometres and callipers can both be out so test them

If the anvil faces are clean and the mic reads zero then a 1" mic is going to be as close as you are going to need, anything above a 1" then use a gauge slip. Besides you won't be getting a std mic in that small of a gap, you could just use the vernier and measure the internal faces