Surprised there's no mention of this in the forum.
.....and random shitcoin chains and apps can never have enough liquidity and transactions to make something really private.
My understanding is that the Railgun contracts are open source and backed by a bug bounty. As to liquidity there's been about a quarter of a billion transacted through the various Railgun deployments on Ethereum, Polygon and BSC in the last year.
The smallest of those, Polygon, has about $500m of wBTC liquidity on Dexes, all of which is usable from within Railgun.
What prevents analysis tools from searching for wBTC, you get one wBTC for every bitcoin you locked, by tracking what is happening on the bridge block of bitcoins that are released and that are mined or burned, you can easily know which wBTC addresses belong to the owner of the bitcoin addresses. wBTC addresses are in a blockchain similar to Bitcoin and does not support privacy protocols, so it is easy to track.
The mint of wBTC is done from one bitcoin address, the burn back to bitcoin is done to a completely fresh address, from a new Polygon or Eth address.
The Railgun transaction in the middle breaks the chain, providing you have a large enough privacy set - which wouldn't be a problem for anything but truly huge transactions.
So the flow would be as an example.
Origin BTC address mints 1 wBTC worth $30,000 onto say Polygon ( which has the smallest liquidity and privacy sets currently, saying that their dexes still do billions per day ).
Then deposits by shielding into Railgun.
Privately swaps on dexes the wBTC into different amounts of USDC, USDT, Dai, Matic and Eth or whatever else has the largest privacy set.
Unshields from Railgun into fresh addresses over a period of time ensuring that sufficient volume from other users masks the activity.
Swap these amounts back to wBTC outside of Railgun.
When you now bridge back to the Bitcoin network it's from fresh addresses to a fresh bitcoin address which have no connection to the original transaction. Different amounts, different addresses and even different physical bitcoin as there'll have been other wBTC burns and mints conducted since. Meanwhile you can use the entire DEX based liquidity of those chains ( many many billions ) to enhance your privacy set. For instance simply by swapping wrapped matic for matic before swapping back to wBTC prior to bridging.
So from your $30,000 bitcoin you'd end up with about $29700 ( minus gas costs which are negligible, probably less than a dollar, and dex fees) of clean untraceable bitcoin.
Now I've no idea what native bitcoin mixers charge or how effective they are though doubt there's any more effective way of anonymising than breaking the chain through Railgun and then using the massive volumes of DeFi and Dex transactions to mask your own transactions.
Hence there is no way to track it.
