"Cylinder" is the safest choice, no question. "Improved Cylinder" is just big enough to allow the slug through, but the slight restriction might produce enough overpressure to cause cycling trouble.
Choke size varies. You will have to take it to a gunsmith.
Not recommended
BROWNING CHOKES AND THEIR CODES (ON REAR LEFT-SIDE OF BARREL)'*' designates full choke (F).'*-' designates improved modified choke (IM).'**' designates modified choke (M).'**-' designates improved cylinder choke (IC).
What gauge and grade is it?
No.None of the browning auto-5 shotguns left the factory with a adjustable choke.This was a after market add-on.
Depends on what they are. Could be choke markings, proof mark, etc..
1965 if it is an auto-5. There should be markings on barrel to indicate choke.
look under the forearm
'*' designates full choke (F). '*-' designates improved modified choke (IM). '**' designates modified choke (M). '**-' designates improved cylinder choke (IC). '**$' designates skeet (SK). '***' designates cylinder bore (CYL).
Look and see if your Browning double auto has a number ahead of the letter A or 2 numbers ahead of the letter A.This is needed to establish the year of production.No Browning double auto could be ordered with a Polychoke,this would have been a after market installation.
50-500 USD or so
In most cases "yes" Auto5's can shoot slugs, but a full choke is not recommended nor is it good if you have a poly choke. It's best to provide model and serial number and contact Browning to be sure it's safe. You can call Browning's Consumer Department directly at: 800.333.3288 or 801.876.2711