Semi-auto science

Benelli Test 005Question

Dear Sirs,

My name is Gerhard Zeilinger from Austria. We, my wife Elisabeth and me, are both reader and subscribers to your famous shooting magazine. Please, allow me to ask a technical question:

When shooting Sporting, I use a Benelli SuperSport, which is absolutely failsafe. This semi auto works by recoil. Recently, a gunsmith made me an additional weight under the barrel for steadier handling.

The problem is, I personally feel that the repeating process is slower than when I use it without the additional weights. Please could you tell me why this is? I thought the opposite would be the case – more weight, faster repeating.

Many thanks in advance for your answer.

Greetings from Austria,

Gerhard Zeilinger, MBA



Hi there!

Thanks for your question – one, which I must confess, is not easy to answer. As you say, Benelli semi-automatic shotguns are inertia operated (they do not rely on vented gases to re-cycle), which cuts down on cleaning gas ports and other parts. Their drawback is that they tend not to cycle, or to cycle slower, on low recoil cartridges. Adding weight to the gun should not affect the lock time (the time it takes the bolt to move back and forward) in any way, but it can affect the perceived lock time as it will make the operation feel smoother with less perceived movement and recoil.

How to tell if the lock time has really been slowed down is to fire a few cartridges both with and then without the barrel weight and check if all the ejected cartridges are dropping near each other on the ground. A slower lock time will produce a group of cartridges nearer the gun, a faster lock time will be further away.

Different cartridges and weather conditions can also affect the lock time, so check that all conditions are the same when carrying out this test. Also, ensure the gun is in the same state of cleanliness when testing with and without the barrel weight.

Please let me know what you find out from these simple tests, and I hope this helps.

Tim Greenwood


Reader’s response

Hi Tim,

Last weekend, I carried out the suggested test, but had some strange results.

I measured the distance of the ejected cases, with and without the additional barrel weight. The cases were ejected twice as far without the additional barrel weight. As I said, very strange.

Best wishes,



Expert’s response

Hi Gerhard,

Your findings make perfect sense to me. As previously stated, the gun you shoot has an inertia operated recoil bolt to eject then reload the next cartridge. Inertia can be dissipated not only by the bolt cycling but the whole gun moving backwards (what we know as recoil). We all know that heavier guns, everything else being equal, recoil less than lighter guns. Therefore, by adding more weight to the gun, less inertia is transferred through the gun as recoil, so more of the inertia can be used by the bolt to cycle the gun quicker. This causes the cartridge cases to eject further. Because the cycle rate is quicker and less inertia is being lost as recoil, the gun will feel smoother.

Tim Greenwood

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15 comments on “Semi-auto science
  1. Phil Simon says:


    You missed Gerhards point entirely.

    He said that the empty cases went further without the extra weight, not with it.

    Perhaps you should re answer his question?

  2. Martin D says:

    Hi Tim & Gerhard,

    As an semi-auto shooter of the gas cycling variety (Remington). it appears that the extra weight fitted is absorbing some of the recoil which in turn is slowing the cycling down. I know the Benelli SS has to have at least 28g shot to cycle, less and it stalls which would be the effect with more weight to the gun, no?

  3. Jon S says:

    Benellis absolutely rely on rearward motion of the gun during recoil, to “charge” the spring responsible for opening the bolt.

    Anything that reduces actual recoil on these guns, reduces the amount of energy transferred to this spring, and will be detrimental to the cycling of the bolt.

    This is surely the reason why the empty shells are ejected further without the weight.

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