Full butt

headfirst with full force.
- Marryat.

See also: Butt

References in classic literature ?
We ain't nervous folk, as you know well; but when it comes to makin' a week-end visit and finding you've run full butt into the Day of Judgment, it wants a bit of explainin'.
The Knoxx recoil reduction system works around a cam-activated, spring that is tensioned and then relaxed back into battery as the top portion of the Copstock stock and the full butt of the Compstock move to the rear and compress under the force of recoil.
replacement of 10 full butts, consolidation of defective consoles (200unites) by the use of stainless steel