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Thread: 20 gauge rifled barrel dimensions.

  1. #1
    Boolit Master
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    20 gauge rifled barrel dimensions.

    There is a ton of info out there on 12 gauge, however, there is very little on 20 gauge barrels. For some reason I was under the impression a 20 gauge rifled barrel groove diameter would be around .615". I recently lucked into (practically stole) a pair of NEF Tracker II's, both a 12 and a 20 gauge. I have not slugged the barrel, but the 12 gauge seems to be just like every other H&R or NEF at .731" groove diameter. The 20 gauge though, is much larger. I slugged the barrel multiple times, and the groove diameter is right about .6265".

    The 12 gauge shoots great. The 20 gauge, not so much. I've only tried Winchester rifled slugs, and Hornady SST's, which historically have not been all that impressive for me. Still, they both shot around 8" at 50 yards. Oddly enough, all but one of my reloads have proven much better. The best so far has been a Lee 575-492 in a Fed 20S1 wad. Specifically, it has shot best with only a single card wad, then the slug, then another card on top to take up the space. This combo measures about .625". This same load in a Mossberg 500 rifled barrel shot even better, although with some fliers. These fliers appear to be the ones that shear the petals off.

    Long story short, I would like to try some large round balls, maybe .630". My concern is that they may unintentionally find their way into another 20 gauge. My brother has the Mossberg 500, I can't measure that one until he stops by again. I only own the Tracker II. In fact, this is the only 20 gauge I own. I'm hoping some of you out there can provide some measurements of your 20 gauge rifled barrels. Even if it's just a rough measurement with calipers, it would help me tremendously.

  2. #2
    Boolit Master

    Hogtamer's Avatar
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    My savage 220 measures about .614 on the lands, .617 on the grooves.....inexpertly measured with calipers.
    "My main ambition in life is to be on the devil's most wanted list."
    Leonard Ravenhill

  3. #3
    Boolit Master
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    Well that would be great if the trend continues. Thanks.

  4. #4
    Boolit Master
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    msm,
    Using the "inside" jaws of my calipers my 20Ga. M-500 rifled barrel measures .617". My 12 ga. M-500 rifled barrel measures .727". I hope this helps you out.

    I was surprised that th 20 ga. was so small, I was expecting something like .620-.625. But, it's not a really precise measurement, only true way is to push a lead slug through it and measure the slug.
    "We take a thousand moments for granted thinking there will be a thousand more to come. Each day, each breath, each beat of your heart is a gift. Live with love & joy, tomorrow is not promised to anyone......"

    unknown

  5. #5
    Boolit Master
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    For what it's worth, my Tracker II measures .624"-.625" with calipers, and .6265" slugged. I have to wonder if for some reason manufacturers decided to use a .615" bore and .620" groove. This seems odd, as 12 gauge went with a .729" groove.

    Smooth bore's
    12 gauge is .729" nominal
    20 gauge is .615" nominal

    Of course there are variations both ways, but in general rifled barrel 12 gauges run around .729"-.730" groove.

    I think I'll try a .630" ball. I feel a lot better with .010" than .015" oversize. It looks like plenty of guys have ran .626" balls through 20 gauge, so safety problems should be minimal a .630".

  6. #6
    Boolit Master
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    I agree that .630" should be OK, the equator of the ball doesn't offer much resistance even at .015" oversize. The load for my 12 ga. measures .742" O.D. and shows no pressure indications. That is a "sabot" type load using a paper wrapped .662" RB in a Federal 12S3 wad, I should think that a naked RB that is .015" oversize should swage down without problem.
    "We take a thousand moments for granted thinking there will be a thousand more to come. Each day, each breath, each beat of your heart is a gift. Live with love & joy, tomorrow is not promised to anyone......"

    unknown

  7. #7
    Boolit Buddy kaiser's Avatar
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    I too have a 20ga Tracker II with a rifled slug barrel; however, I have not "slugged" it. I have tried various factory slug loads from the "pistol sabot" versions to Foster "pumpkin balls". None of the newer faster sabot slugs in the Tracker worked well, accuracy wise, for probably the reason stated (undersized for the bore).

    I found the most accurate Tracker load for my rifle BBL Tracker to be the Remington 20ga "Sluggers", which is about the cheapest round available! What do I mean by accurate? My gun will put 3 rounds at 50 yards "touching" at their ragged edge holes if I bench the gun and watch my breathing while I pull the trigger. I have no idea what velocity they are "clocking", other than what the manufacture claims. In past years, there was at a time I lived in a couple of states that only allowed slug guns for deer hunting. I tried different brands of factory rounds (different "5 packs) and found the slugs made by manufactures varied a great deal in performance. After checking the dimensions of their slugs, I found they did (indeed) vary in size, at least in 12ga and 16ga guns I used at the time (IC choked). I just bought a supply for each of the gun's favorite load and did not pursue further study.

    With the newer type bullets and components that have come into the market in the last decade, there is a plethora of combinations that can turn a rifled slug gun into a much longer range hunting implement. The only rifled barrel I have purchased in the last 5 years has been the Tracker II, and it was because I got a very good deal on it.

    In my 12ga, peaked by Ranch Dog's experiment, I've loaded and Lee's 7/8oz and 1oz cast slugs in my 870 smooth bore "slug" BBL and found it to be more of a challenge to get the kind of accuracy that I'm getting with my Tracker's factory load than I'm willing time to invest. Plus, with the size and weight of the cast loads, I find better uses for lead with my center fire firearms. (Coincidentally, my 16ga is an Ithaca 37 with a "Deerslayer" smooth bore BBL of 26" that shoots a Winchester slug best, while a "drilling" only like the Brennekee.)

    Thanks for the information regarding the specifications of the 20ga Tracker.

  8. #8
    Boolit Master
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    At this time of the year, there isn't much slug selection in stores. I agree, Remington Sluggers are consistently accurate. Sometimes other slugs do better, but Winchester's are almost never accurate. They were what I had.

    For sabot slugs, the funny thing is the most consistent performer I've found has been the Federal PowerShok sabot slug. It's a soft swaged lead hollow point, and I believe that allows the slug to bump up to a variety of sizes. They are usually in stock everywhere, I'll try them as soon as I find them.

  9. #9
    Boolit Master gpidaho's Avatar
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    Using a slug from "Slugs R Us" that measures .620+ on the lead portion, tapped in to the muzzle until the plastic my Remington 11-87 20ga. rifled barrel measures .612 -.618. I didn't drive the slug all the way through so the barrel may or may not have a slight choke. Again, just a caliper measurement. Gp

  10. #10
    Boolit Master
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    I take it thats .612" bore, .618" groove? Thanks.

  11. #11
    Boolit Master gpidaho's Avatar
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    Quote Originally Posted by megasupermagnum View Post
    I take it thats .612" bore, .618" groove? Thanks.
    Correct. Gp

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check