What are the differences? Shallow (or medium), shallow with open throat, backbore, deep with open throat and backbore?

5 feels a bit shallower, much smaller throat (most importantly).

Here's my 5GS and 5 (left and right), both small shank, both '90s large letter mouthpieces.





Rim feels are also different... maybe the same size, but the 5GS is a bit wider with a different bite.

5G will deeper still, of course.

Yeah so the Bach catalogue is sometimes a little difficult to decypher and references other portions of the document. So for small shank, which is catalogue No. 350 we have:

<TABLE>[table]
<TR>[tr]<TH>[th]Model No</TH>
<TH>[th]Depth of Cup</TH>
<TH>[th]Approximate Cup Diameter</TH>
<TH>[th]Rim Shape</TH>
<TH>[th]Description</TH>
</TR>
<TR>[tr]<TD>[td]5</TD><TD>[td]Medium</TD><TD>[td]25.50 mm</TD><TD>[td]Medium wide, semi-flat</TD><TD>[td]For players with good, natural embrouchres. Rather large cup. Produces a full, mellow, sonorous tone.</TD></TR>
<TR>[tr]<TD>[td]5G</TD><TD>[td]Deep</TD><TD>[td]25.50 mm</TD><TD>[td]Medium wide, semi-flat</TD><TD>[td]Same as No. 350-5 except for .276” throat and #429 backboresemi-flat.(same as No. 341-5G but with small shank).</TD></TR>

<TR>[tr]<TD>[td]5GB</TD><TD>[td]Deep</TD><TD>[td]25.50 mm</TD><TD>[td]Medium thin,very well rounded.</TD><TD>[td]Same as No. 350-5 except for thin rim same as No. 341-5G but with small shank). </TD></TR>

<TR>[tr]<TD>[td]5GS</TD><TD>[td]Medium</TD><TD>[td]25.50 mm</TD><TD>[td]Medium wide, semi-flat. </TD><TD>[td]Same as No. 5 but with larger “G” throat and #420 backbore.</TD></TR>
<TR>[tr]<TD>[td]6</TD><TD>[td]Medium</TD><TD>[td]25.50 mm</TD><TD>[td]Medium wide, well rounded</TD><TD>[td]Fairly large cup. For players with a strong embouchure..Full, solid, mellow tone.</TD></TR>
</TABLE>

So you'll notice that it uses say, 350-5 to be the "5" and 350-5G to be what we call the "5G" in small shank. So a 5 is the same as a 5G but with a larger, 276" throat and a #429 backbore, per the description. Similarly, a large shank 341-5G is the same as a 350-5G other than the small shank. One thing you should note is that the 6 is actually part of the 5 series as far as rim diameter. Oddly enough, for the 5GS, it indicates that it is identical to a 5 but with a larger "G" throat and #420 backbore; howver, the 6 which has a similar description of cup depth does not indicate anything other than one evidently needs a "strong embouchure" to play it.

So the short of this is that for small shanks, the ones you asked about are all a "medium wide, semi-flat", 25.5mm rim. Out of just the "5" series, the "5" itself is the smallest of those. The 5GS keeps the same cup but adds a larger throat. The "G" adds yet a bigger throat and backbore. The cup is deeper, despite the description as being "the same as No. 350-5", which would contradict the depth of cup literally in the same row.

Now the large shank, catalogue no 341 has:
<TABLE>[table]
<TR>[tr]<TH>[th]Model No</TH>
<TH>[th]Depth of Cup</TH>
<TH>[th]Approximate Cup Diameter</TH>
<TH>[th]Rim Shape</TH>
<TH>[th]Description</TH>
</TR>
<TR>[tr]<TD>[td]5G</TD><TD>[td]Deep</TD><TD>[td]25.50 mm</TD><TD>[td]Medium wide,semi-flat</TD><TD>[td]Same rim shape and diameter as No. 5 small shank tenor trombone. Similar playing characteristics to No. 4G with a slightly smaller cup diameter.</TD></TR>

<TR>[tr]<TD>[td]5GB</TD><TD>[td]Deep</TD><TD>[td]25.50 mm</TD><TD>[td]Medium thin,very well rounded.</TD><TD>[td]Same cup, throat and backbore as the No. 5G with a more rounded rim</TD></TR>

<TR>[tr]<TD>[td]5GS</TD><TD>[td]Medium</TD><TD>[td]25.50 mm</TD><TD>[td]Medium wide, semi-flat. </TD><TD>[td]Shallower “G”-style cup with smaller throat and backbore than No. 5G produces easy high register, slightly brighter sound</TD></TR>
<TR>[tr]<TD>[td]5GL</TD><TD>[td]Medium Deep</TD><TD>[td]25.50 mm</TD><TD>[td]Medium wide, semi-flat</TD><TD>[td]Old style, shallower model than No. 5G, facilitates upper range</TD></TR>
</TABLE>

So there is no official listing for a "5" in the catalogue, though I believe I've seen them (owned one?). But the differences between the large shanks in thi sseries are the same as the small shank versions.

But wait! As Aidan pointed out, there... are differences between the rims and cup depths of the 5 and 5GS. Yeah... For Bach stuff I use the catalogue as a go-to for generalities about the pieces but really not a whole lot more. There probably are instances of 5 and 5GS out there that are basically identical until the throat.

Curiously the catalogue lists the small shank 5GS as medium in depth, but as medium deep for the large shank 5GS. If they are the same mouthpiece with the exception of the shank, why would Bach label them like this? Anyone have an idea? I feel that the 5GS has the 5G cup shape but is somewhat more shallow, though not as shallow as the no letter pieces.

Large shank:

5GS Medium deep 25.50 mm Medium wide, semi-flat. .261” G 420 (modified)

Shallower “G”-style cup with smaller throat and backbore than No. 5G produces easy high register, slightly brighter sound.

Small shank:

5GS Medium 25.50 mm Medium wide, semi-flat.

Same as No. 5 but with larger “G” throat and #420 backbore.

I would just ignore everything the catalogue says and play/check them out. I think it's been proven dozens of times that the catalogue is almost 99% marketing gibberish. "Teutonic," anyone?

[quote="Burgerbob"]I would just ignore everything the catalogue says and play/check them out. I think it's been proven dozens of times that the catalogue is almost 99% marketing gibberish. "Teutonic," anyone?[/quote]

It's a typo, supposed to read "tootonic."

[quote="paulyg"]<QUOTE author="Burgerbob" post_id="105800" time="1582871512" user_id="3131">
I would just ignore everything the catalogue says and play/check them out. I think it's been proven dozens of times that the catalogue is almost 99% marketing gibberish. "Teutonic," anyone?[/quote]

It's a typo, supposed to read "tootonic."
</QUOTE>
Bravo Paul!

[quote="paulyg"]It's a typo, supposed to read "tootonic."[/quote]

If you're too tonic, does that mean you're less dominant?

I’m feeling a little sub dominant these days.

[quote="Bach5G"]I’m feeling a little sub dominant these days.[/quote]

Sort of like "Red October?"

OY, this make my head hurt. I'm going to work on diminishing my 5th.