Beretta Gas System Changes

Dear Bruce,

I have found a Beretta Mod AL2 -20ga. I am thinking about buying it, but I have a question first. I have a Silver Mallard 12-ga. When I remove the forend on the 20, there is no spring there like the A390. Is there supposed to be a spring there like the A390? I guess I could call Rich Cole and get one sent. The gun is in beautiful shape and I hate to pass it up. Your response is appreciated, as always.

Thanks again.

Dear Brune,

The AL1/2 and 300/1/2/3 series Berettas did NOT have exhaust valves at the front of the gas chamber the way the 390 does. The AL you are looking at is perfectly normal and doesn’t need any additional parts.

The original Beretta gas gun design (which also includes the current 304 Lark, advertised, but seldom seen) had only one set of primary gas ports leading from the barrel to the gas chamber. The new 390 model has two sets of ports, a primary set like the original Berettas, and a secondary set of ports at the front of the gas chamber. The idea is that this will enable the gun to function with a wide variety of 3″ and 2-3/4″ loads. It works very well.

When using a large shell in the 390, gas comes through the primary ports into the gas chamber and starts to push on the piston. It also pushes on the secondary valve held in place by a spring in the front of the gas chamber. If the shell has generated excess gas (as in a magnum), the heavy gas pressure opens the secondary valve, bleeds the gas pressure down to normal, snaps shut and then gets along with its business. With gas “normalized”, the piston moves rearward at its ideal speed (in theory). When the load is light, there isn’t enough pressure to open the secondary valve and all the gas goes to operate the system.

With the old Berettas, 100% of the gas operated the system. If a magnum shell was used, the system just operated real fast and hard. The gun is strong enough to take some of this. With this old system, 3″ chambered guns were given small gas ports so that the gun would not hammer itself to death. Unfortunately, this meant that when using light loads there wasn’t enough gas to function the action reliably. You had to compromise and make sure that the shell fit the gun’s intended use.

That is a potential problem with your AL2/20. If your gun has 3″ chambers, it may not handle light target or light field loads properly because the gas ports will not be big enough. You may wish to have the gas ports opened up slightly. Use the same dimensions as Beretta uses in its 2-3/4″ 20 gauge barrels. Get a skilled gunsmith to do the work and check the barrel out to make sure that everything is safe. I suggest Beretta guru Rich Cole at Cole Gunsmithing, Rt. 123, Harpswell, ME 04079, Tel: 207-833-5027 if you don’t have a favorite gunsmith in your area. If your AL2/20 has 2-3/4″ chambers, it may work with target loads, it may not. Depends. Many of the Beretta 20s had trouble with light loads regardless of chamber length. Opening the ports a bit can solve it, but – again- get a good gunsmith to do it.

Best regards,

Bruce Buck
The Technoid at <>
(Often in error, never in doubt.)

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