How about a 5.7 carbine?

Give the Ruger 57 a big brother. Same frame with longer barrel and buttstock.

Do you have the Ruger 57 pistol?

No, I do not. Just noticed a GLOCK adaptation and wondered 'what if'.

My son has a 5.7 he got for $800. Saw one going for $1100 now.
A carbine in 5.7...interesting. Still would be a 0.224409 but with a little more punch.