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 Post subject: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 7:10 am 
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It was brought up at the Gun Club today that another Red Label shooter found his patterns at least one choke tighter. As mine patterns one tighter, almost two on slow small rounds, wondered if it was the nature of the beast, or the fact that they are over-bored. They come factory with Briley chokes, and pattern quite well. Still tight, and even tighter with Carlsons extended. Any takers on reasoning?




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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 7:27 am 
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Working with 12-gauge guns and trap-appropriate chokes & shells (and counting holes) I haven't found any particular relationship between bore-diameter and the tightness of the resulting shot pattern. There are tight and less tight examples with either smaller, standard, and larger bore diameters.

My three tightest guns in general have been an Ithaca-era Perazzi (0.724 bore, 0.038 choke), a Bowen (0.740 bore, 0.040 choke), and the tightest of all, an 870 (0.732 bore, 0.038 choke.).

Neil


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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 7:37 am 
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I'm no expert on this, but I can give you the basic theory: an overbored gun allows the shot to spread out into a wider cross-section (think pancake), which in turn makes for less deformation due to setback, as well as fewer pellets in contact with the bore (ie. less barrel-scrub). All of that supposedly translates into tighter patterns due to fewer fliers.

Whether one subscribes to all that is another story...


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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 8:12 am 
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I agree that's the sort of thinking you might read or hear anywhere, S2r, but remember, for almost anything like this, one can make up "explanations" which are just as good, but opposite. (I'm not saying any of the following is true, just that to some it may sound true.)

1. Deformation in the shell is the same, since the pellets there don't know anything about bore-diameter yet. Deformation at the choke is a theory, since while it may happen, you have to wonder why tight chokes, which should deform the shot most, have the tightest patterns.

2. In a bigger bore more pellets are in contact with the bore and getting scrubbed, widening the pattern.

My point is that the way to find out about patterns is to shoot and count them; not just think about them.

Neil


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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 8:21 am 
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Totally agreed. As I hinted, I don't totally subscribe to the theory, but that's the generic answer to expect.

My big argument against it has to do with wad design: with a larger bore the shotcup expands to a larger diameter opening up the slits more. If you envision the other extreme (a very tight bore), the wad has little opportunity to splay outward and contains the shot better.


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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 8:28 am 
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Concerning overboring as an aftermarket feature:

The reason some people see tighter patterns after getting their barrels averboard as an aftermarket feature is because they use the same chokes as before. By opening up the bore you are essentially making the constriction difference between the bore and choke larger. So a bore ID of .730" with a choke that is .720" has .10". Now you go and overbore the barrel to .742" and use the same choke you know have .22" of constriction.

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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 8:32 am 
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I subscribe to the thinking of slightly "looser" bore means less shot deformation. The shot is 100% contained in the shot cup, no shot protruding above the wad when crimping. That being so, it would seem the wad can provide a better layer of protection from the barrel as the shot is traveling down the tube, translating to less shot being flattened out before it leaves.

Well, after shooting and looking, the 7/8 oz at 1250-1300(published) fps pattern extremely tight through a L.M. As in almost two chokes. The 1 oz. load at 1250-1300(published) fps also pattern tight, but only to a modified % at 30 yards. So one choke tighter. It's much more visually evident on a skeet field, where a 3/4 oz or 7/8 oz will absolutely crush a clay through the factory Briley Skeet chokes. Next thing to do is pattern those two, and see just how well they are patterning at 15, 25, and 35 yards. Curious to see if they DO hold together closer to the I.C. in my Benelli, rather than a true skeet %. Never shoot much skeet, so wasn't concerned how those chokes pattern, but yesterday really got me thinking about how loose you can go with a choke and get a commanding break. The Ruger can produce the same results with the Carlson L.M. that would otherwise be somewhere between a modified or I.Mod. Curiousity is killin the cat here....


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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 8:36 am 
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TDKK wrote:
Concerning overboring as an aftermarket feature:

The reason some people see tighter patterns after getting their barrels averboard as an aftermarket feature is because they use the same chokes as before. By opening up the bore you are essentially making the constriction difference between the bore and choke larger. So a bore ID of .730" with a choke that is .720" has .10". Now you go and overbore the barrel to .742" and use the same choke you know have .22" of constriction.


That makes perfectly good sense. The Ruger has a factory barrel with factory chokes. Do any others with factory over-bored barrels find tighter groups? Since there doesn't seem to be one specific thing to point to and say this IS the reason, I'll settle for "that's the way it is". Again, curious if it holds true on a majority of over bored barrels, or maybe it's just a specific thing that happens to these Red Labels.


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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 8:47 am 
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The only way to know is to find the inner bore diameter and compare it to the measured choke constriction. Just because a choke says LM on the side, it does not mean it will perform like a LM out of your barrels. Its also proven that some choke companys are "loose" with their choke tolerances.

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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 9:13 am 
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Hillbilly, the look of light-load patterns can be deceiving. As the table near the end of the post below shows, the center of 7/8 ounce patterns hold up pretty well when compared with heavier loads. It's the outside that suffers. The result is a pattern which looks a good deal tighter than counting tells you it is, though the 4% general gain in pattern density when going down to 7/8 ounce is nothing to entirely discount wither.

http://www.trapshooters.com/noframes/cf ... eid=534960

Neil


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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 10:09 am 
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I'm curious as to the significance of the leading diameter of choke tubes. IIRC I measured the leading diameter of some optima chokes and they measured something like 0.738 or so - so about 0.006 or so larger than the Optima bore on my DT10. I wonder if that may behave like a jug choke. This is prob not significant - but I remember a guy who measured the bores on a 471 optima at something like .723 diameter. So those optima chokes have an expansion of 0.015 before you get into the choke itself. It seems to me that he said that the gun tended to pattern tighter than the choke would indicate - i.e. the mod choke patterned more like imp. modified.

john

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 Post subject: Re: Overbored Barrels Pattern Tighter?
PostPosted: Mon Sep 20, 2010 12:19 pm 
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Hmmm. Interesting graph. But why discount anything outside the circle as a flyer? Enough "flyers" just equals a larger usable pattern, or looser choke equivalent, assuming the density is great enough, right? The lighter loads DO actually carry a heavier core density, hence pattern tighter. You have a good point, that with less pellets and less flyers the core begins to look tighter, and one may never really know without counting. BUT that doesn't change the fact that through 3 different loads 1-1/8, 1 oz, and 7/8 oz, and two different shotguns (Legacy, Red Label) the core densities were noticeably stronger through the Red Label.

Here's the first 7/8 oz load I ever patterned, with standard shot. Now all I use is magnum shot, so not sure what change that would have made to these numbers, but with confidence in the load, not gonna recheck em.
7/8 oz load of #7.5 Lawrence Shot= 178.72 Pellets from a Carlson's Light Mod in the Legacy at 1250 (published) f.p.s Thats an average of 5 shots counted, and a long waste of my life countin. :) On the Red Labels end, same day, same load, same choke manuf. and constriction, it worked out to be 201.42 pellets. Not significantly different, but still. It's a better core density. Should have done each with a box to be a little more accurate, but not really patterning for pellet count, looking for holes. Wanted to know that neither gun was just blowing shot to the four corners of the earth and the bird was giggling all the way to the ground.




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