All this talk of Ruger No 1's in classic British calibres finally got me to act... over the last few months I've taken delivery of a new .303 British, and a near-new .450/400 NE 3"

I've owned a few single shots before (mainly Martini Cadets and Martini Enfields) but these are my first No 1's.

As an aside, my .303 barrel slugs out at .3125" and shoots Remington factory 180gr Corelokts into just over an inch straight out of the box.
Winchester and Highland factory ammo is another story, however...

ANYWAY... getting back to the .450/400...

Finally got down to the range with it last weekend.

Only put 5 rounds through as I hadn't got the scope I want to fit with me... solid recoil, but quite manageable... even so I'll be fitting a decent Pachmayr Decelerator pad!

Hornady 400gr DG factory loads seemed a bit lacklustre... no pressure signs, some unburnt powder in the bore, and a couple of rounds were chronied at only 1830fps and 1920fps... well below their advertised velocity of 2050fps huh

Haven't reloaded any cases yet, but trying some projectiles supplied with the rifle in the neck of a fired case led to some surprises... the Bertram 400gr at .408" fitted in fine, the Sierra 210gr .410" was a tight push fit but the Hornady 405 Win 300gr at .411" wouldn't go in at all.

Got out the Mitutoyo digital vernier for a quick check of the fired case's neck dimensions:
OD .4400, .4400, .4400, .4400, .4405"
ID .4095, .4090, .4090, .4095, .4085"

Loaded factory round neck OD .4380, .4360, .4350, .4355, .4355"

So it would seem there is only .002" to .005" total neck expansion or .001" to .0025" per side?

Seems the chamber has a very tight neck diameter, or Hornady brass is fairly thick or has a lot of springback (but seem to have been annealed OK).

I'm worried if I load the Hornady 300gr or go for cast or paper-patched bullets (which will need to be .411 to .412 to suit the .410 groove barrel) they will expand the neck of the case so much they either won't chamber or will not release the neck correctly leading to excessive pressure.

Am I missing something?
Has anyone heard anything about Ruger .450/400 chamber dimensions?
Should I do a Cerrosafe cast to establish exactly what specs Ruger has cut the chamber to?

Any info greatly appreciated... I'm interested in cast/PP bullets but don't want to order any moulds till I sort this out