Good practice for offhand shooting, is shooting muzzleloaders.
We shoot mostly offhand.
Back in the 70's, the black powder section of the Squamish Rod and Gun club challenged the CF shooters to a contest.
It was held against balloons of about 5 to 6" in diameter. The range was only 25, maybe 30 yards.
The poorest muzzleloader score was higher than the highest center fire shooter.
There was a .222, couple .243's, .30/06, a .308, 7mm mag. and .300 mag., all scoped, of course.
We had 6 black powder shooters.