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The Good Fight

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391 Gas Valve Spring Modification


I own a Beretta 391 which I’m very happy with, but I also like to reload my shells. The 391 seems to toss my empty hulls a mile which isn’t too much of a problem on a skeet or 5 stand lay out which is very open. In a woodsy sporting clays situation however the hulls disappear into the brush and retrieving them isn’t that practical cause it takes too much time to hunt em up.

I presume the reason for this is that the 391 is designed to, and does in fact, cycle everything. I use the gun primarily for target shooting and use target loads, although I do use it for ducks as well and feed it 3 inch 1 3/8 oz steel shells for that. I don’t reload the steel so I don’t care about those hulls.

Is there a different spring set I can use for target loads that will keep the target hulls from flying into the next county? I’ve also heard of but never seen “hull deflectors” that are supposed to knock the hulls down as they are ejected. I’ve used a hull catcher which is fine for singles but not doubles. Any Technoidal insight would be appreciated.


Dear John,

You have a number of choices of ways to change hull ejection on the 391.

One of the easiest was is just to order a T&S shell clip from Brownells, http://www.brownells.com. It costs around $10. It instantly snaps onto the side of the gun and retains the fired hull for easy extraction. It snaps off just as easily. The downside is that it only functions as a single shot. If you are going to shoot doubles, you can’t use it. All the trap shooters use them. In addition to the T&S, there are and were any number of other gizmos to catch hulls. All of them, except the Morton modification, made your gun into a single shot. Unsuitable for sporting, of course.

You might also consider a shell deflector stud. You’ll need to be handy with tools or get a gunsmith for this. An ejector stud is simply adding a small “bump” in the barrel extension on the ejection port side so that the shell is deflected down towards the ground. If look carefully at the barrel extension on a Remington 1100/11-87 Trap barrel (not on any of their other barrels, just trap) you will see what I am talking about. The ejecting hull hits the little bump on the way out and gets angled down towards the ground.

The third way is to order a set of Rich Cole’s 391 valve springs. Here’s how they work: When the 390/391 fires, a small porting of the gas goes through the gas ports in the barrel and into the gas chamber under the barrel. Obviously, gas pushes equally in all directions. Inside the gas chamber there are two ways for the gas to go.

1) pushing the piston rearward and thus operating the action, and

2) pushing forward against the gas valve.

In operation, the gas valve’s function is to open first to bleed off excess gas so as to regulate the amount of gas used to push the piston. This in turn regulates speed and vigor with which the action operates, which governs how far the empty is tossed.

This gas valve is regulated by a valve spring. By changing the strength of the gas spring, you can regulate whether that valve opens early or late and by how much. If the valve spring is strong, the valve won’t open at all and all the gas goes to operated the action. This is perfect for a very light load that needs all the gas it can get to work things. When a heavier load is used with a heavy spring, the action cycles very quickly and tosses the empty a mile. When a lighter gas valve spring is selected, the gas valve opens earlier and bleeds off more gas, thus causing the action to cycle slower and not heaving the empty as far.

So, by getting a set of Rich Cole’s gas valves (quite inexpensive) and tinkering a bit, you should be able to regulate the bolt speed of your 391 and thus it’s ejection distance as to a specific shell. If you always use the same shell in the gun, then use a gas valve spring that will pitch the empty about six feet or so. That assures adequate bolt speed for proper functioning, but avoids the excessive bolt speed that increases wear and tear on the gun.

Most people find that the 391 works just fine as it comes, but if you like to tinker for not too much money, swapping gas valve springs is fun to do. You can always stick the original back in. The valves for the 390 came color coded and perhaps the ones for the 391 do also. You can confuse the enemy by asking an opponent whether he’s maximized his 391’s performance with the special light blue spring or does he prefer the red. It’s always worth a bird or two.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)

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Big Sky

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Chrome Barrel Work And Cones

Dear Bruce,

Thanks for your worthwhile advice in the past. My question today is;

I have an Ithaca/SKB model 500 o/u mfg in Dunville Ontario. I believe Chromed bores. I love this outfit beyond words, and have been shooting skeet using the current full/mod barrel config. with remarkably good results. Sure smokes the birds!!!!

Rather than investing in a new outfit, I am wondering if it is possible to have the chokes cut to skeet or I/C, and the forcing cones done without ruining the barrels.

Thanks for the advice in advance, and keep up the good work. I enjoy your site immensely.


Dear Don,

Chrome bores? No problemo. The chrome coating does make the first cut somewhat harder, but the gunsmith will just use a specially hardened tool. If he says, “Gee, this job requires a carbide reamer and I don’t have one.” then skip him and go on to someone who does this for a living. All the “majors” will do the work for you- Briley, Seminole, Rhino, Ballistics, etc.

Be careful when lengthening the cones. How long are your cones now? Did you measure them? It doesn’t cost a manufacturer one cent more to make the barrels at the start with long cones compared to short cones. Why do you think that so many pick short cones? There’s a reason. The shorter the cone, the quicker the transition from chamber to bore. This ensures a better gas seal if there is a possible problem with the wad due to wad design or cold weather. Long cones provide a smoother transition from chamber to bore and thus might possibly damage less shot, but at the expense of possible gas blowby under certain conditions. Stan Baker has done a great deal of research on long cones and feels that cones over 2″ simply don’t add any advantage. He also mentions that the 2″ cones really only help with larger hunting-size pellets. The effect on target pellets is minimal because their small size helps them flow better to begin with.

With modern plastic wads, it probably doesn’t hurt to have cones of 1-1/2″ to 2″, but you can go overboard. I once sold a Superposed to a friend who had the cones run out to 5″. When I shot the gun later that winter, I got off-sounding shells. It never did that before. Also, if someone says that lengthening cones reduces recoil by a noticeable amount, but suspicious of gas blow-by and reduced velocity.

I’m not totally against lengthening cones, but I’m suspicious. For example, people are always lengthening the cones on Berettas and most of them already come with 1-1/2″ long cones. That’s plenty long enough. They are wasting their money. Don’t just “lengthen” cones out of reflex. Know what you have, what you want and why you want it. If your cones are lengthened and the job isn’t done right, you’ve got a real mess- literally. That chrome is gone in the throat area and you will lead up and scrape plastic like you can’t believe if the coning job isn’t done carefully.

I have one FN Superposed that I had the cones run out on. I also have several absolutely identical FNs with factory short cones. I can’t tell the slightest difference in recoil. I’m sure that long cones do change the width of the pressure curve very slightly, but I’m just not sensitive enough to pick it up.

It’s usually very difficult to discern what longer cones do to the pattern because cones are almost never the only work that is done to the barrel. Usually there is also backboring, porting or screw chokes involved in the work done at the same time. This makes it harder to figure out what does what. It might make a lot more sense for you to get your chokes cut first and then do some pattern tests. If your patterns are good, stop there. If they aren’t what you want, then consider working on the back end of the gun.

Remember, these aftermarket barrel borers make their money by putting metal shavings on the floor. The more stuff they that they can cut out of your barrels, the more they can charge you. I’m not saying that it’s all useless. It isn’t in some cases. It’s just that “more” isn’t always better and sometimes it’s worse. It’s interesting to note that Miroku (Browning Japan) has gone to overbore and porting, but has refused to lengthen cones. It makes you wonder why.

Gun makers are like any other mass merchandiser. They sell what the public thinks it wants. If the average guy thinks that porting his barrels will actually do something other than make noise, then the makers will supply ported barrels until the craze passes. We are seeing that now as many shooters are starting to avoid ported guns. Beretta is still laughing at Browning for that one.

The bottom line to all of this is:

1) Yes, you can get someone to do work on chrome barrels if they have the right hardened tools, and

2) be a bit careful of the work you ask for.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)

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Velocity Loss In A Gas Gun


This isn’t really a question, but an observation I thought you may be interested in.

Over the years, I have heard the same question asked several times. “Do you lose velocity in a gas auto due to the amount of gas bled off to work the action?” I decided to waste some time on finding the answer to this question. Being somewhat of a Jr. Technoid wantabe, I figured out right away that for the test to have any validity, I would have to use the same gun and barrel. So I took my trusty AL390 and my chronograph and all the different shells I could find and ran some five shot strings. Then I tapped the gas ports and installed set screws in them. I ran the strings again (but for some reason I had to work the action manually). To make a long story short, there was no difference in velocity between normal operation and having the ports plugged. However, I was very surprised at the deviation in some of the popular factory loads. My reloads were generally much more consistant.


Dear Randall,

The tiny amount of gas vented by the little teeny weenie gas ports, as well as the timing of the venting (well after the shot has reached most of it’s eventual velocity) just about guarantees the conclusion you observed.

But, hey! You did the work. No armchair surmising for you. It’s easy to just sit back in the easy chair and sagely opine. I do it all the time. It takes a certain mindset to drill and tap to find the truth when others are just tapping their feet. You have done us all a service. Now, when I get asked the frequent question about velocity loss in a gas gun, I can state some facts instead of my usual groundless opinion.

Randall, for your indomitable pursuit of the TRUTH, you are hereby awarded the coveted Junior Technoid Order of the Palm (third class). This award is granted to those who actually do the work, rather than just talk about it. Henceforth you will be allowed to add the letters “JTOP3” to your signature. In token of this honor you will soon receive (by email, of course) a genuine hand-painted plastic shirt pocket protector, suitable for framing or even wearing if you are into ball point pens and slide rules in the breast pocket.

Well done!

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)

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Legendary Rhode with Skeet Bronze; Prone Rifle Recap & Saturday Preview | USA Shooting

Source: Legendary Rhode with Skeet Bronze; Prone Rifle Recap & Saturday Preview | USA Shooting

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