Officers today revealed they were carrying out forensic tests on the firearm following the discovery.
Police investigating the find in Chuckery Park on Monday say three bullets were also found. Youngsters discovered the items in a plastic bag in a wooded area in the park off Holtshill Lane.
Police were called to the area and recovered the gun.
A resident, who did not want to be named, saw the police arrive at the scene.
He said: "The police took the gun away after arriving very quickly on the scene and setting up a cordon.
"It was found by a group of children who were playing nearby.
"They picked it up and were playing with it. Thankfully, it didn't go off."
Councillor Rose Martin, who represents the area, said: "This is shocking news. Chuckery is a lovely community, very quiet and neighbourly, and for this to be found where children play is very worrying.
"I sincerely hope that the police find out who is responsible.
"The thought that any child would pick up a lethal weapon sends shivers down my spine.
"My fear is that anybody, especially a child as this was found in the park, might have tried out the gun.
"They might have thought it was a toy gun and tried to play with it. This could have ended terribly."
St Matthews councillor Imran Azam added: "I'm shocked to hear a gun was found. That area is well-used by children playing cricket and football. For someone to have left it somewhere where children have access is very worrying.
"It could have been very dangerous. Hopefully the police can get to the bottom of it. Hopefully there is evidence on the gun."
The gun was recovered after police were called at 4.42pm on Monday.
The bushes where the gun was found are near to five blocks of flats and between Holtshill Lane and Paddock Lane.
There is a children's play area and wooden benches at the site.
Another resident, who did not want to be named, who lives in Paddock Lane, said: "I saw a police officer standing over by the bushes.
"There are a lot of children who play around there.
"A child could have picked it up thinking it was a toy.
"Someone could have been killed. It is quite frightening to think about it." Another resident added: "We have seen people with weapons in the past, and on both occasions we reported it to the police.
"We used to get a lot of drug deals around here.
"It is a frightening prospect as there are toy guns and children shoot and play army games. They could have thought the gun was a toy."
Another resident, of Paddock Lane, added: "I didn't hear about anything but it is a bit of a shock.
"I have children myself and if they had been playing there it may have been them who found the gun."
The bushes where the gun was found are on the right hand side of the park as entered from Paddock Lane.
There was no sign of the police activity at the scene today, with no tape in place.
The park was quiet today, with just a few people passing through and no children playing at the play area.
A pathway leads through the park to Holtshill Lane to provide access for dog walkers. The park is overlooked by five blocks of flats and is within walking distance of Walsall town centre.
Police today said it was too early to say whether the firearm could be linked with any crime they are investigating.
Officers have carried out forensic inquiries and searches at the scene and are appealing for anyone who has information about how the weapon came to be be in the park to contact them on 101.
They have not confirmed the reports of sightings of people carrying firearms in the past.
Alternatively, people with information can call the free and confidential Crimestoppers number on 0800 555111.