1956
You don't give us the model, so it is hard to answer the question. Assuming the gun does not have an obvious adjustable choke, the choke is probably not easily adjustable. A gunsmith can open the choke (from Full to Modified for example) or can install internal interchangeable choke tubes (costs around $125).
No.None of the browning auto-5 shotguns left the factory with a adjustable choke.This was a after market add-on.
It is not recommended to shoot slugs with a power pack chock on a JC Higgins model.
$400 Very Good to $500 Excellent condition.
Some bolt action shotguns had an adjustable choke, and it is generally NOT recommended that slugs be fired through those. If there is no adjustable choke at the muzzle, your shotgun should be fine. Stay with rifled slugs.
These where made from 1955-1971. If in 90% condition about $130.
1957 more likely 1961
I have a sears and robuck 20 ga. pump with adjustable choke on the end of the barrel
just bought one in like new condition for 150$
i had one it valued at $73.57 want to sell it
Measure it, or have a gunsmith measure it, with a choke gauge.
A 1953 JC Higgins shotgun 12 gauge model 20 pump is values at about $150. It was sold by Sears Roebuck.