If you want to accommodate a heavier cartridge on your Dual 505 turntable, a supplementary balance weight is available as an accessory.
This is a 21.5 gram brass weight that you can screw on to the standard balance weight to increase the total mass by 30% to around 93 grams.
I recently fitted a Goldring E3, with weighs nearly 7 grams. Originally the 505 was fitted with an OEM Ortofon cartridge similar to the OM-20, which weighs about 5 grams. My new cart is about 38% heavier. There is enough adjustment on the arm to move the weight out far enough to achieve balance, but only just.
It all seemed a bit precarious, so when i spotted the additional weight available on eBay I thought i would give it a try.
Comparing the position of the balance weight before and after fitting is quite revealing.
When balanced it makes a difference in position of about 2 cm. The weight seems a lot more secure on the arm, rather than tottering on the edge. There is now a couple of cm of clearance between the back of the weight and the turntable lid. Previously it was only a couple of mm.
I doubt it will make much difference to the sound, but the whole thing seems a lot more secure and correct, so I think it was a worthwhile upgrade.