Above: This 20-bore Merkel double was stamped 1 / 2 and 1 / 1 on the barrel flats. How was it actually choked when it left the factory? The Boremaster helped identify the unique choke configuration.

You’ve seen the gun before. My 20-gauge Ithaca Model 37 was featured along with my hunting companion Zak on the front cover of the July 2012 issue of Shotgun Sports Magazine. Like so many of us, I could hardly wait to take that gun to the skeet range and crunch a few vintage skeet targets. Wow! A 1952 gun in pristine condition. I gave little thought to the choke. The barrel was stamped “Modified”, and I had no reason to doubt that Ithaca’s barrel borer had cut 0.013” of choke constriction into that 0.615 bore. My skeet score was not to my liking, but the pattern board behind the high house indicated the issue was point-of-impact. So I improvised a Browning-style ramp atop the front bead to bring the point-of-impact down to a 50/50 pattern.

With that alteration in place, I headed off to my favorite hunt club in Ubly, Michigan. The little Ithaca didn’t let me down. My favorite upland choke is, hands down, Improved Cylinder, but I was amazed at how forgiving and uniform the Modified patterns seemed to be on those big, gaudy roosters Zak ran down and sent skyward. At an estimated maximum range of 30 yards, the little Ithaca was absolutely lethal on those Rooster Ranch Ringnecks beating a hasty retreat. Later, I shot more Vintage skeet with the gun and abandoned my original thought of having the choke opened to Improved Cylinder. It just didn’t seem to need it. If there is one thing I’ve learned since my early days of shotgunning, “If it ain’t broke, don’t fix it!”

I check the chokes on most of my guns with calipers as soon as they come in the door, and if I have any concerns about the integrity of the choke, they end up undergoing a pattern analysis. But, for whatever reason, the little Ithaca escaped even a minimal level of scrutiny. So when I decided to write an article on the problems I’ve encountered with chokes over the years, my 20 gauge Model 37 was not on that list. Confession time. I’ve not been as diligent as I should have been in accumulating the gun accessories I need to thoroughly evaluate a gun. I should have bought a Bore Micrometer decades ago. But every time I save enough money for the bore micrometer, I find another gun begging me to buy it. That ever happen to you? So I’ve never invested in a Bore Gauge. I purchased an inexpensive Vernier caliper decades ago, and it answered most of my questions about chokes and bores over the years. When I wanted to know the diameter of the bore, I used an even less-expensive inside caliper and took an indirect measurement by reading the setting on the inside caliper with the Vernier calipers. Seemed to works pretty well, but the process takes time and careful attention to detail in order to avoid significant error.

An engineer and shooting acquaintance at the gun club suggested casting a 1”-2” wax plug in the bore, then pushing it out from the muzzle through the breech. I did that on a few guns, then measured the plug with the Vernier calipers. That process seemed to be accurate, but quite time-consuming. And if I really wanted to know how the chokes were performing, I went to the pattern board and shot 3 patterns from 25-35 yards. You can’t get better information than that. Even more important than the points of constriction in your choke is a quantitative performance evaluation. But that takes even more time.

So when I decided to write this article, it was time to give our friend Bob Foege a call at Robert Louis Co. (see ad on page 00). A longtime advertiser in this journal, Bob’s product suddenly appealed to me as a way to get the most accurate information obtainable on the bore and choke dimensions of my guns. You can go on Bob’s website and watch his video outlining the steps in identifying the dimensions of your chokes, bore(s) and barrel wall thickness, along with length and dimensions of the chambers. But this isn’t about Bob’s Boremaster. It’s about the valuable information you’ll gain by tabulating the vital statistics of all the guns in your closet. Bob’s tool just happens to be the quickest way of obtaining that information.

The first gun to get the Boremaster treatment was my 1926 New Ithaca Double. A Grade III gun, it’s one of my prized possessions. Not for its value so much as for its performance. You can see the gun draped over my shoulder in the same July 2012 issue of Shotgun Sports. Both barrel flats on the Ithaca are stamped 4, indicating it left the factory with Full choke constriction in both barrels. I purchased it from a previous owner in the East who decided he would rather have a Parker. The price was right, so I decided I would purchase the gun and have the chokes opened to Improved Cylinder and Modified. But a quick check with the Vernier calipers indicated some previous owner had come close to doing that! My Vernier calipers indicated the constriction at the muzzle was probably producing Light Modified and Improved Modified patterns if the bore dimensions were standard. I cast a wax plug, and the Vernier calipers confirmed a plug diameter of 0.662”. I shot the gun so well I abandoned any thought of further evaluation or choke alteration. It turned out to be perfect for our annual Gentleman’s Cup Double Gun Sporting Clays events at Freeland Conservation and Gun Club, and I turned to the gun on a Georgia quail hunt as well. It was a little hard on the breasts, but all of the birds were dead! But now I could quickly evaluate the bore, choke(s) and chambers with minimal effort. Turns out both bores are actually 0.660” diameter (slightly under-bore). According to Boremaster, the right choke actually contains a full 13 points of constriction (perfect Modified), and the left barrel has 23 points (three points shy of Full Choke). The left barrel most likely possesses the original Full choke constriction. The chambers are 2 5/8”, as I had suspected, and the chamber dimensions are right on specification. You can check the barrel wall thickness with Bob’s Boremaster if the integrity of the barrels is in doubt. The barrels on my New Ithaca Double clearly have never been refreshed and are more than adequate strength. But I still feed it 2½” RST Best Paper cased loads. Both the gun and my shoulder thank me for that.

Only a year or two before that purchase, I discovered a Merkel 147E, 20-gauge SxS double being offered by an internet dealer (but not an authorized Merkel dealer) with a compelling price. He claimed to have four of the guns, all marked Modified (1/2) and Full (1/1) on the barrel flats. They were described by the dealer thus: appears “new in box”. When the gun arrived, careful inspection revealed it was, in fact, flawless. Not a handling mark on the stock or metal finish. So I took it to the gun club and shot a round of Sporting before I messed with the chokes. I was NOT getting Modified and Full choke breaks. So back to the bench to measure the chokes with the calipers, and the bore with a wax plug.

I concluded the chokes were actually I.C. in the right barrel and Modified in the left. But now I had the Boremaster to verify my previous work. My calipers and wax plug got me close. Both bores were overbore by American standards. The right and left bores were essentially the same at 0.628, about 0.013” overbore by American standards. The left barrel was nearly Improved Modified with 18 points of constriction, and the right barrel was approaching Light Modified with 10 points of constriction. My guess is the choke specifications were just far enough outside of Merkel’s standards for a gun choked Modified and Full, that they decided to dump these four doubles off through an internet outlet for liquidation. I think the chokes are near perfect. What are your thoughts on this boring?

But lest you think your bore and choke analysis will be limited to Fixed choke guns, it will not. Ever wonder if your choke tubes were properly matched to the bore? I purchased a Beretta 20 gauge O/U about 1990, and a 20 bore Beretta Teknys 15 years later. The former came with four MobilChokes, and Beretta supplied five identical tubes with the semi-auto. Carelessly, I had mixed up the choke tubes for the two guns, and now wondered whether both guns had exactly the same bore diameter and, more importantly, whether the choke tubes had the same dimensions. If I mismatched a slightly oversized MobilChoke from one gun with a slightly undersized bore in the second gun, the pattern performance could conceivably vary by an entire choke designation. That might mean the difference between anchoring that South Dakota pheasant with an ounce of 5’s, or having it fly off with a dropped leg. Time to check out the bore diameters of all three barrels, and the points of constriction on all nine chokes. That took about five minutes with the Boremaster.

As it turns out, all three bores have identical inside diameters of 0.628, and each pair of chokes representing the major choke designations provide identical points of constriction. Both I.C. Chokes measure 0.617, both Modified chokes measure 0.612, and both Full chokes measure 0.595. One skeet choke measured 0.625 (3 points of constriction), while the other measured 0.635. The latter I would call a bell choke, but I suspect the patterns from both skeet chokes are quite similar. The Improved Modified MobilChoke supplied with the Teknys measures 0.601, providing enough constriction to meet the traditional Full choke specification in 20 gauge. It breaks trap targets with authority. A tip of the top hat to Beretta. Their manufacturing tolerances appear to be phenomenal, given the decade-plus span between the manufacture of the two guns. The I.C. choke is slightly more constricting than the traditional standards, so it might be expected to produce Light Modified patterns. Naturally, the only true confirmation of the chokes is at the pattern board, and you would have to shoot a minimum of ten patterns with each choke to differentiate between Improved Cylinder and Light Modified patterns. Our time is too valuable for that. Better to be modestly over-choked than under-choked.

Remember that little Remington Model 11 I reviewed in the June 2015 issue of this journal? It turns out the bore on that 1941 gun has a nearly perfect I.D. of 0.616. Remington was also spot on with the traditional six points of constriction in the Improved Cylinder choke, making it an ideal gun for Michigan grouse and woodcock. No wonder my old friend Tom Hatton was such a deadly instinctive shot with his Remington humpback 20 gauge back in the early ’60s. And my 16-gauge Winchester Model 12 I use exclusively for trap? I reviewed that 1942 gun in the January 2013 issue of this journal in an article titled, “I Just Bought this Used Gun”. The bore has the traditional inside diameter of 0.662, but the choke Winchester cut in that barrel is a full 30 points of constriction. And consistent with the beautiful patterns I’ve seen from my old Winchester guns, that little gun makes dustballs of trap targets at 16 yards.

Image Left: The author’s 20 gauge Ithaca 37 is stamped “Modified” on the barrel, but it carries and shoots like a 28 gauge with an Improved Cylinder choke. Ithaca configured the bore and choke perfectly for the sportsman hunting in the uplands of Michigan, but that was accomplished more by accident than by design.

But wait, you don’t have access to calipers, a bore gauge or a pattern board? And you don’t want to go through the laborious process of casting a wax plug to determine the bore diameter? You just want to drop something in the muzzle and be done with it, right? I frequently browse gun shops, and I don’t want to hassle the proprietor every time I come across a “gun of interest”. If this describes your gun-buying habits, you need a “Choke Gauge”. You can order one by calling 1-800-676-8920. Order item #PLACG (see page 47). It just might be all you’ll ever need.

So what about that 1952 Ithaca 20-gauge pump we discussed at the beginning of the article? The gun that carries like a 28 gauge and shoots like it had an Improved Cylinder choke? Well, Ithaca’s barrel-boring traditions notwithstanding, the barrel is modestly under-bored by seven thousandths, with an inside diameter of 0.608 (0.615” is standard). And the barrel stamped “Modified” measures six points of muzzle constriction, essentially configured to deliver Improved Cylinder patterns. It appears the under-bored barrel ate up half of the intended modified choke constriction, turning that little gun into the perfect upland companion. But to be sure, the Improved Cylinder constriction actually delivered Improved Cylinder patterns, I ran next door and shot two 25-yard patterns. I used Winchester Super-X one-ounce loads of #6 shot (count 220/0z). If it was delivering Improved Cylinder patterns, it should place 83% of the pellets in a 30” circle at 25 yards. The first pattern placed 85% of the pellets in the 30” circle, and the second placed 83% in the same area. The average 30” pattern density of 84% was nearly perfect for an Improved Cylinder pattern at 25 yards. I checked the core density of the two patterns and they averaged 66%. The Oberfell and Thompson 20” core density standard for an 83% pattern is 67%. I didn’t need more pattern samples to declare the little Ithaca a winner!

One final observation. If you were evaluating my Beretta or Merkel chokes by just measuring the inside diameter of the chokes tubes, you would seriously under-estimate the amount of choke in the three guns. And if you had measured the muzzle constriction of my 20-bore Ithaca pump, you would have surmised, as I did, that the gun had a Modified choke. I’m sure Ithaca thought it did when it left the factory. SS


Ron Jones is a retired pharmacist of 49 years who confesses his first love after family and God are shotguns and hunting. His first shotgun experience was his grandfather’s 1911 Ithaca Flues 20, and that experience nearly caused him to look for more pleasurable avocations. He admits to missing all 50 targets his father threw with their Remington hand trap, and the experience resulted in a headache which wouldn't quit. But his love for guns, particularly vintage scatterguns, has remained with him in the ensuing 60 years. Our heritage is important. Preserving and embracing the values and traditions which our forefathers have handed down will enrich the experiences of those who follow. In some small measure, Ron hopes to contribute to that body of knowledge the younger generation embraces.