TromboneChat

I have a contra (and an EEb Tuba) that take bass bone shank mouthpieces, but... finding a 'piece that allows the low register so speak properly is not simple.
I started with a Marcinkiewicz 107, and it gets most of the way there, but not all the way. Went to a JK Exclusive KBP 1C and it's better but still a touch narrow to get the pedal register solid.
What would those of you who play this kind of thing recommend?

Practise. I use smaller stuff than that. Nothing comes without effort.

107 is just a Schilke 61 copy. They are not that big.

1C should be pretty good on contra, though I do think there are better contra pieces.

I like the Ferguson 2A, which I believe is a heavier copy of the JK 2A. Not sure they're made anymore...

You can also do something really good with Doug Elliott. A CB118/N/N10 is very similar to that 2A.

The Laskey 105C that comes with the Shires Q contra is very nice. Not sure if you can buy it separately though.

All of my contra and tuba mouthpieces are avaliable with bass trombone shank.
If you're looking for something for both contra and your Eb tuba, smaller mouthpieces can work but so can big mouthpieces. The choice just depends on what sound you're looking for, and whether your contra needs more focus. I'd want to know more about what you have been using on the Eb and how it's working.

From my experience (played a lot of contra many years ago and got my own 1,5 years ago), mouthpieces for contra are tricky.

If you are spending considerable time on it (and typically also play lots of bass trombone or maybe tuba), a "real" contra mouthpiece like the models mentioned here certainly make most sense. BTW I am pretty sure JK/Klier can also make them in more or less any shank you require.

If you are playing contra only occasionally, a smaller mouthpiece will probably help with control, response etc. But of course may have some limitations as well. However honestly: Using "only" a large bass mouthpiece is not really an excuse for issues with the pedal range on contra, as Chris probably also intended to say.

E.g. I had a large trombone ensemble project last year with some demanding contra parts (excerpts from the Ring...) and used a Klier contra mouthpiece for that.
This year I subbed on short notice on contra to replace a tuba player in a small orchestral work. Had not practiced much contra the weeks/months before, used a large bass mouthpiece and it worked just fine. Much easier to adjust to (for me).

2nded on the smaller sizes working well. The Jim Nova / Greg Black series is only a slightly larger rim than the 3G (and actually a smaller throat than his bass trombone series), for example, and he sounds amazing on his contra stuff.

Model: B1 Bass Trombone
Rim: 3G Cup Depth: 1 1/2G Depth Bore: .284"

Model: C1 Contra Bass Trombone
Rim: 27.25mm, 1.063" w/3G Contour Cup Depth: Deep Bore: .281"

https://gregblackmouthpieces.com/produc ... 7247937790

Also fwiw, I have one of Doug's shanks for an Eb tuba I had for a while that played great. Was specifically made for a Conn Eb, and I used an LB L cup for it. I think I was using an LB110 rim on it at the time.

Trombone/bass bone/tuba gigs are about 1/3 of my work the last few years. I'm mostly a trumpet player. I got a 25 tuba 'piece that had been cut for a bass bone shank, and it was way out of balance, and just doesn't work.
The 107 is on the small side for a contra or tuba, but like I said, when I get below a C, it is just too small to get a decent sound.
My tuba is a 1912 Holton - nice horn, heavier than some people I know. Contra is a Chinese knockoff of the Thein - it plays well, but the 'piece it came with is not great, so I went back to Marcinkiewicz (they do all of my mouthpieces and trumpets), but ... too small.
Yeah - trumpet player, mostly. Raised with Mic Gillette, so I have always thought playing everything was normal. It usually works, but sometimes issues like this come up.
Thanks for all of your inputs - they have been very helpful.

Don't expect a mouthpiece to fix that contra. It would need way more than that.