Abbreviations for AM, PM (small caps) for use within \textbf

Question

I have been using \textsc for the abbreviations for AM, PM, but it does not work within \textbf{}. As you can see in the image, within a \textbf{}, it reverts to the normal lower case letter. Ulrike Fischer suggests in bold small caps with mathpazo, to switch to uppercase characters when attempting to use a bold weight font, but that does not look right as the result lablelled MyTextsc shows (I modified it slightly to apply a \tiny size change):

The results are not very good, so wondering if others have other suggestions?

Code:

\documentclass{article}
\usepackage{lmodern}%
\usepackage[T1]{fontenc}%

\usepackage{graphicx}
\usepackage{xspace}

\makeatletter
\newcommand*{\AMorPMTextModeTextsc}[1]{%
        \@ifnextchar{.}%
            {\textsc{\,{\small#1}}}%
            {\textsc{\,{\small#1}}\xspace}%
}%

% https://tex.stackexchange.com/a/24635/4301
\DeclareRobustCommand{\MyTextsc}[1]{%
 \edef\@tempa{\f@series}\edef\@tempb{\bfdefault}%
 \ifx\@tempa\@tempb%
  \uppercase{{\tiny#1}}% \small here seems to do nothing
 \else
  {\scshape\small#1}%
 \fi }

\newcommand*{\AMorPMTextModeMyTextsc}[1]{%
        \@ifnextchar{.}%
            {\MyTextsc{\,{#1}}}%
            {\MyTextsc{\,{#1}}\xspace}%
}%

\makeatother


\newcommand{\PrintText}[1]{%
\makebox[8.0em][l]{Using \textbackslash#1:} 5:00\PM to 8:00\PM.\par
\makebox[8.0em][l]{Using \textbackslash#1:} \textbf{5:00\PM to 8:00\PM.}
}%

\begin{document}
\newcommand{\AM}{\AMorPMTextModeTextsc{am}}%
\newcommand{\PM}{\AMorPMTextModeTextsc{pm}}%
\PrintText{textsc}

\bigskip
\renewcommand{\AM}{\AMorPMTextModeMyTextsc{am}}%
\renewcommand{\PM}{\AMorPMTextModeMyTextsc{pm}}%
\PrintText{MyTextsc}
\end{document}

Answer 1

A good rule of thumb for scaling uppercase to match (poorly) small caps is to use a factor 0.8 of the font size.

\documentclass{article}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage{xspace}
\makeatletter
\DeclareRobustCommand{\maybefakesc}[1]{%
  \ifnum\pdfstrcmp{\f@series}{\bfdefault}=\z@
    {\fontsize{\dimexpr0.8\dimexpr\f@size pt\relax}{0}\selectfont\uppercase{#1}}%
  \else
    \textsc{#1}%
  \fi
}
\newcommand\AM{\,\maybefakesc{am}\xspace}
\newcommand\PM{\,\maybefakesc{pm}\xspace}
\makeatother

\begin{document}

{\bfseries 5:00\AM to 8:00\AM}

5:00\AM to 8:00\AM

\textbf{\AM}\AM

\Huge\textbf{\AM}\AM

\end{document} 

Notice that your test of a following period is useless if you adopt \xspace.

It may seem too high, when compared side by side, but boldface always has some overshoot. Refine at will.

Note. If the text you pass to \maybefakesc can be more complicated than a simple string of ASCII characters, change \uppercase into \MakeUppercase.

Answer 2

My method relies on the relsize package. Please, if needed, read the package documentation.

\documentclass{article}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\usepackage{relsize}
\usepackage{xspace}
\makeatletter
\protected\def\declarescsize{\@testopt\declare@scsize{1}}
\def\declare@scsize[#1]{%
  \protected\def\makesc##1{%
    \ifnum\pdfstrcmp{\f@series}{\bfdefault}=\z@
      \uppercase{{\relsize{#1}{##1}}}%
   \else
      \textsc{##1}%
   \fi
  }%
}
\newcommand\AM{\,\makesc{am}\xspace}
\newcommand\PM{\,\makesc{pm}\xspace}
\makeatother

% You can change the scale by calling \declarescsize:
\declarescsize[-1.2]

\begin{document}
\parindent0pt
{\bfseries 5:00\AM to 8:00\AM}

5:00\AM to 8:00\AM

\textbf{\AM}\AM

\par\bigskip
{\Huge\textbf{\AM}\AM}
\end{document}