Modo de Uso: var report = viewer.RptViewer.LocalReport; JonePolvora.LocalReportExtensions.ImprimeDireto(report);

LocalReportExtensions.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Printing;
using System.IO;
using Microsoft.Reporting.WinForms;

// ReSharper disable once CheckNamespace
namespace JonePolvora {
  public static class LocalReportExtensions {
    /// <summary>
    /// Recebe um array com diversos relatórios a serem impressos
    /// </summary>
    /// <param name="reports"></param>
    public static void ImprimeDireto(this LocalReport[] reports) {
      foreach (var localReport in reports) {
        ImprimeDireto(localReport);
      }
    }

    /// <summary>
    /// Imprime um relatorio direto à impressora
    /// </summary>
    /// <param name="report"></param>
    public static void ImprimeDireto(this LocalReport report) {
      var streams = Export(report);
      var mCurrentPageIndex = 0;

      var printDoc = new PrintDocument();
      if (!printDoc.PrinterSettings.IsValid) {
        throw new Exception("Error: Impressora padrão não configurada!");
      }
      printDoc.PrintPage += (o, args) => {
        var pageImage = new Metafile(streams[mCurrentPageIndex]);

        // margens
        var adjustedRect = new Rectangle(
          args.PageBounds.Left - (int)args.PageSettings.HardMarginX,
          args.PageBounds.Top - (int)args.PageSettings.HardMarginY,
          args.PageBounds.Width,
          args.PageBounds.Height);

        args.Graphics.FillRectangle(Brushes.White, adjustedRect);

        args.Graphics.DrawImage(pageImage, adjustedRect);

        mCurrentPageIndex++;
        args.HasMorePages = (mCurrentPageIndex < streams.Count);
      };
      printDoc.Print();
    }

    // Export the given report as an EMF (Enhanced Metafile) file.
    private static List<Stream> Export(LocalReport report) {
      const string deviceInfo = @"<DeviceInfo>
                <OutputFormat>EMF</OutputFormat>
                <PageWidth>8.5in</PageWidth>
                <PageHeight>11in</PageHeight>
                <MarginTop>0.25in</MarginTop>
                <MarginLeft>0.25in</MarginLeft>
                <MarginRight>0.25in</MarginRight>
                <MarginBottom>0.25in</MarginBottom>
            </DeviceInfo>";

      Warning[] warnings;
      var mStreams = new List<Stream>();

      report.Render("Image", deviceInfo, (name, extension, encoding, type, seek) => {
        Stream stream = new MemoryStream();
        mStreams.Add(stream);
        return stream;
      }, out warnings);

      foreach (var stream in mStreams)
        stream.Position = 0;

      return mStreams;
    }
  }
}