I have 3 and use the rcbs cadet mold and 4.5g of Unique.ive never slugged the bores,the bullets chamber fine.The length of the chambers vary but I cut them(cases) all to 1.1"
your bore seems about right on bore diameter. Groove is about .318 IIRC.
I get 1-1.5" at 50 yards

You didn’t say if it was re-barreled or original. When you slug the bore, are there tight spots or consistent all the way, is it an original barrel that some lazy smith has run a reamer into? Best source of moulds is Cast Bullet Engineering in Australia. He also does sample packs. Original bores can be .311 to .321 which is why some 32-20 ones can shoot well and others are so-so, you need to find a projectile that fits your barrel. Also a chamber cast can ascertain if the throat is ok as some originals had long throats
Gumpy

Actually, original bores are usually a very consistent.321.  The .310-.312 measurement usually comes from people incorrectly measuring what is essentially a slug with an odd no. of grooves, there is always a land opposite a groove.

So in essence, you're shooting a bullet that's too small for the bore.  Usually best results with the converted .32-20 rifles is with the original heeled cadet bullet, which might require a specific case length though.

Mine's the original .310 cadet, and these little rifles are capable of surprising accuracy.

I'm in on the use of the RCBS bullet.

My BSA Cadet has its original chamber, and the bore looks like new.

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Here's what I am feeding it:

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And here's an actual group I shot that day at 100 yards.  Load information is shown.

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Good enough for me. 

By the way, I learned by experiment some years ago that motorcycle chain lube works great on a bullet such as this.  I feel sure the Lee Alox will also work.  I just had the m/c lube on hand.  Go outside to spray it.  Just set up a bunch of bullets on cardboard and give them a shot.  It dries in a few minutes and is ready to load.  Easy peasy!

Curly

DHB,

I'll do this in a couple of steps.  First, there is some confusion in a few of the posts above, but some have it right.  The bore is .310, and the groove is likely between .319 and .321. Because of the odd number (5) of grooves, you need to slug the bore, and use a thin strip of metal to wrap the bullet, and pliers to hold it tight, then measure.  Subtract two times the thickness of the metal strip and you have a accurate bore measurement.

The problem with the 32-20 chambering is the bullet diameter that will fit the cartridge, and allow the round to be chambered, will need to be around.312" - too small for a .319-.321 groove.  Trying to use a correct .321 bullet will expand the neck too much and the round will not chamber.  I think you have two options, both of which I have tried.   

First, you can use the chamber you have now, but you need to trim the 32-20 cartridge back to 1.14".  Then buy some 125 grain heeled bullets from Bear Creek - very reasonably priced, and coated.  Overall length should be around 1.62".  I can routinely put 5 rounds in 1 1/2" at 100 yards over the original open sights with 9.5 grains of A2400 or IMR4227.  Very sedate and gentle to shoot.

On a separate Cadet action I modified a Cadet barrel I got from one of our members, to make a hotter round (I call it a 8mm Carbine - ballistics are similar to the 30 Carbine). I rented a 8mm throater (.323) and by hand extended/enlarged the throat so I can load the same 125 grain heeled bullet in the standard 32-20 cartridge.  I made a neck expander for the 32-20 cartridges using a .312 jacketed bullet, so the heeled bullet seats easily.  After firing I don't size the cartridge - just prime, charge and seat the bullet.  Then I firmly crimp using a lee 32-20 factory crimp die.  If you 32-20 FL size every reload, you will need to anneal the cartridge neck periodically or you will get frequent neck splits. Cartridge OAL is 1.75".  The barrel is scoped.

I get 2 MOA or better at 100 yds with the following loads:
14.5g - IMR4227
15.2g - IMR4198
17.5g - Hodgden CFE BLK
13.2g - Hodgden 110
17.5g - IMR3031 (compressed)

These are pretty hot rounds (no signs of flatted primers) so proceed cautiously if you try this route, or just load milder charges.  Using the standard 32-20 cartridge makes this much easier to load, and provides enough powder capacity to allow more powder/charge options.   

The Martini Cadet is a great single shot action, and a fun rifle to shoot. Good luck.

1ISENOUGH,
I used to breech seat bullets 30-40 years ago.  I have forgotten how now.  Pretty sure it was a 32-40.  What about breech seating an 8 mm lead bullet and inserting a primed and loaded case with a business card wad?
Thanks again,
DHB

Re. Grumpy Gumpy's comment about "lazy gunsmiths" and 32-20 chambering.
In late 1950s, Klein's Sporting Goods, Chicago, IL imported 
a large quantity of the Cadets:
They sold them as Original 
AND
they were also sold after rechambering them to 32-20, 
and 32 Win Special 
Also, available were rifles that were bored and rechambered to 357 Magnum, and a very few were said to have been bored/chambered into 44 magnum.
As a kid back then, I drooled over the ads for these rifles.

I finally came into one of the 357 Mag rifles some years ago.
Fine rifle, Fine accuracy with 200 gr 35 Rem cast bullets as well as the 162 grain Keith bullet.
beltfed/arnie