Maximum possible volume for the Deposit

Experimented with free margin:

double volumeChecked;
  
  double cutVoluneByFreeMargin(string _symbol, double _volume, int _stopLoss, ENUM_ORDER_TYPE _type) {
    
    volumeChecked = false;
    
    double lotValue = SymbolInfoDouble(_symbol, SYMBOL_TRADE_TICK_VALUE);
    double freeMargin = AccountInfoDouble(ACCOUNT_MARGIN_FREE);
    
    double maxLot_ = (freeMargin * 0.3 / _stopLoss) / lotValue; / / only works starting from 0.3 from freeMargin
    
    double maxLot = SymbolInfoDouble(_symbol, SYMBOL_VOLUME_MAX);
    
    if(maxLot_ > maxLot)
      maxLot_ = maxLot;
    
    double lot = (_volume <= maxLot_) ? _volume : maxLot_;
    
    / / checking for sufficient funds to enter the market
    MqlTick mqltick;
    SymbolInfoTick(_symbol, mqltick);
    double price;
    switch(_type) {
    case ORDER_TYPE_BUY:
      price = mqltick.ask;
      break;
    case ORDER_TYPE_SELL:
      price = mqltick.bid;
      break;
    default:
      Print(__FUNCTION__," Error! Line:", __LINE__);
      return 0;
    }
    
    double margin;
    
    if(!OrderCalcMargin(_type, _symbol, lot, price, margin)) {
      / / - - - something went wrong
      Print("Error in ",__FUNCTION__," code: ",GetLastError());
      return 0;
    }
/ / - - - if there are not enough funds for the operation
    if(margin > freeMargin) {
      / / - - - report an error and return false
      Print("Not enough money for ",EnumToString(_type)," ", lot," ",_symbol," Error code: ",GetLastError());
      Print("margin: ", margin, " freeMargin: ", freeMargin, " lot: ", lot);
      return 0;
    }
    volumeChecked = true;
    return lot;
  }

But the function skips the volume calculated with a value of no more than 0.3 * freeMargin

double maxLot_ = (freeMargin * 0.3 / _stopLoss) / lotValue;

Why did you get exactly this pattern? Maybe
maybe I’m calculating the maximum possible lot incorrectly?

Set checkmoneyfortrade (style= ” background-color:rgb(251, 249, 245); color:rgb(0, 0, 0);”>)>,
which I do not allow the operation of the OrderSend function (if the data is not checked) gives a message about the lack of funds on the
Deposit:

2019.10.06 17:15:02.028 Core 1  2012.05.03 14:53:00   Not enough money for ORDER_TYPE_BUY 500.0 EURUSD Error code: 0
But the
Deposit, again, has grown to

47730.00, with 10000 and here the
terminal does not miss the volume of 500.0, which corresponds to SYMBOL_VOLUME_MAX.
There are no errors

– “Error
code: 0″, but there are not enough funds on the Deposit. How can this be?

I checked the code on the demo account. 

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart() {
  string symbol = Symbol();
  double maxLot = SymbolInfoDouble(symbol, SYMBOL_VOLUME_MAX);
  double margin;
  if(!OrderCalcMargin(ORDER_TYPE_BUY, symbol, maxLot, SymbolInfoDouble(symbol, SYMBOL_ASK), margin)) {
    Print("Not enough money to make a deal!");
    // Recalculation of the maximum lot for the current Deposit
    // ...
  }
}
//+------------------------------------------------------------------+

It turns out that on the demo maxLot passes the test, but in the expert
Advisor, on the tester, the message crashes ”

Not
enough money to make a deal!” and the position with the maxLot volume does not open, although the Deposit size, both on the tester
and on the demo, is 10000. On the demo, even less is a bit. How can I calculate the maximum possible lot if

OrderCalcMargin gives a fake?