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Double Rifles, Single Shots & Combinations >> Double Rifles
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PierreCT
.224 member


Reged: 03/01/07
Posts: 4
Loc: CT, USA
Measuring bore and groove diameter in .470NE
      #70273 - 27/01/07 11:07 AM

Is this easy to do? Is there a kit that one can buy to make the measurements? If so, where?

Having read Graeme Wright's book, I understand that it is important to know these dimensions before shooting modern ammunition/reloads in old double rifles.

Thanks!

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500Nitro
.450 member


Reged: 06/01/03
Posts: 7244
Loc: Victoria, Australia
Re: Measuring bore and groove diameter in .470NE [Re: PierreCT]
      #70274 - 27/01/07 11:47 AM


PierreCT

470's were pretty much standardised and IMHO one of the least variable of all of the calibres.

However, do this.

GREASE, LUBE WITH OIL etc the inside of the barrel.
Get a 45 - 50 cal SOFT LEAD Projectile or piece of LEAD Wire about 1.5cm long.
LUBE / OIL IT UP
Get a Hammer made of Wooden or Plastic
SLOWLY and GENTLY from the MUZZLE end tap it in until
the lead is in the bore.
Then get a piece of Wooden Downling - smaller than the bore size - and tap it is from the chamber end while the muzzle is rested on a piece of wood - the objective is to exand the lead to the full size of the bore.

NOTE - Make sure the Dowling Rod does not expand too much - if it does, saw off the expanded bit and start again - don't get the piece of wood stuck in the bore !!!

Once the lead is expanded, you can either tap it in from the muzzle end so it comes out the chamber or just push it out the muzzle (won't be as accurate but will give you a good idea).

Once out, get some calipres and measure from the EDGE of one of the raised pieces to the EDGE of one of the other raised pieces. REASON for this is English gun tend not to have exactly opposite grooves and lands.

Hope this helps.

PM me if more info needed.

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Marrakai
.416 member


Reged: 09/01/03
Posts: 3591
Loc: Darwin, Top End of Australia
Re: Measuring bore and groove diameter in .470NE [Re: 500Nitro]
      #70277 - 27/01/07 01:43 PM

Agree with most of the above, but I never slug from the muzzles. I just bash a fishing sinker to approximate 10% oversize dimensions with a hammer, then drop it into the chamber throat and drive it into the oiled bore with a dowel. I like to push them right through, but with the likes of the Martini Henry with slightly tapered bore, the slug should probably be driven a few inches into the bore and then back out the same way.



Bore slugs from .360 to .577
ex-fishing sinkers all!


BTW, the new owner of a .470 in the first half of last century never slugged his bores. He just bought factory ammo or components over the counter, or through the colonial agency, and started shooting! No real reason not to do the same today.

There is a method for accurately measuring bore and groove diameter in barrels with odd-numbered rifling. It involves dropping the bore-slug into a right-angled (90-degree) 'cradle' in such a way that the lands of the slug are resting on the 'sides' of the cradle, and a land is uppermost. The distance between the 'apex' of the cradle and the top land is measured, and a formula used to convert this to barrel groove diameter. I'll try to locate the details. Meanwhile, anyone here know the formula, or an appropriate reference?

--------------------
Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

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