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 Post subject: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Sat Jan 03, 2009 6:38 am 
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Looking for an opionion as to whether a 3" or even a 3 1/2 inch chambered gun will cause pattern disruption when shooting 23/4 inch shells for clays?




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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Sat Jan 03, 2009 6:57 am 
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No.

Most of the guns used for clays nowadays do have 3" chambers, and there is no problem with it. A few gun manufacturers think a target gun will pattern better with 2 3/4" chambers and make them that way, but some others think it actually patterns better with a 3" chamber.

I don't have any actual experience with 3 1/2", but I know a few people use guns like that for clays, and I have not heard of any pattern problems.

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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Sat Jan 03, 2009 12:21 pm 
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The patterning board is the only answer.

Different makes & models of shotgun, different chamber lengths, different forcing cone length, different loads, and different choke constrictions will all affect the pattern.... and not necessarily in any predictable fashion.

Sometimes you'd swear the phase of the moon and the sign of the zodiac are at work in determining shotgun patterns.


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 Post subject: Re: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Sat Jan 03, 2009 1:15 pm 
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Seamus O'Caiside wrote:
No.

Most of the guns used for clays nowadays do have 3" chambers, and there is no problem with it. A few gun manufacturers think a target gun will pattern better with 2 3/4" chambers and make them that way, but some others think it actually patterns better with a 3" chamber.

I don't have any actual experience with 3 1/2", but I know a few people use guns like that for clays, and I have not heard of any pattern problems.


Seamus about summed it up for you. About the only thing to add is that there may be some pattern degradation in longer chambers if you use shells without the protective shot cup. Since I don't know of anyone in this country making target loads with felt or cork wadding, this point is basically moot.

Frank


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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Sat Jan 03, 2009 9:45 pm 
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I've read on the Browning website that 2 3/4" shells fired in a 3" chamber tend to be slightly tighter patterns. My guess is the extra chamber length is akin to a very long throat. See:
http://www.browning.com/customerservice ... asp?id=102

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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Sun Jan 04, 2009 12:57 am 
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If we are talking strictly pattern "disruption", almost nothing might be construed as causing any extremes, but pattern difference- that is entirely possible, and in fact- is a certainty.

Bob K., I believe you have it backwards as to what Browning is saying with their chart.
The range of pattern density is always starting at a lower percentile with the 3" chamber when compared with the equivalent altitude 2-3/4" chamber.

I have stated in some of my previous postings my assertions about shorter shells in longer chambers, and there is ALWAYS going to be a difference from any excess in chamber length, especially when dealing with a deformable lead pellet projectile mass.

That does not mean that many shooters would be able to discern any appreciable difference from different barrels, one at a time, but if you are speaking in physics absolutes, deformity is going to increase and pellet flyer action is going to increase.

Rounder pellets fly straighter and have less extreme spread at longer distances, and I have proven that with my own experiments with chamber design, length, and forcing cone taper alteration.

A shot cup is not any absolute protector of lead shot from deformity, especially in a longer chamber vs. the shell.
The cups do not always totally enclose the top of the shot column and some might say that the top pellet deformity is negligible, but for now, this example pertains to absolutes, so pellets not in a cup can't be protected by the cup.
Every cup also has slits down the side, and those slits meet when the cup is inside the hull. Those slits must spread open a bit when the cup is out of the hull and in the chamber area in front of the crimp, since the chamber is of a larger diameter (about .060") than the inside of the hull, at rest.
A 3.5" chamber will have a large section of the shot cup not in the hull or meeting the forcing cone during a portion of the shot travel. Those slits must be open at that time, and then squeeze back closed when jamming through the taper of the FORCING CONE (after building more velocity and slam action than the shorter chambers). That is one reason for the name, due to the fact it FORCES the ejecta to fit into the bore. Do those pellets feel nothing during that commotion?

Hard lead target pellets will be less affected from any exerted force than softer economy pellets, so keep that in mind, regardless of what barrel you get.
If you have acceptable performance with economy shells in a long chambered gun, I'm happy for you. If you need target loads to be certain of target breakage, you will be spending a bit more money to shoot. You may find that a longer chamber can have the damage factor mitigated a degree or two with a forcing cone alteration, since I have seen such improvements with my own particular method/angle/finish of forcing cone rework.

Your best bet is the natural course of testing with the chokes and shells you prefer at the distance(s) you intend to shoot, and see if the paper tells you what you want to know.

Also keep in mind the very real possibility of crooked choke installation, since a large portion of barrels with screw-in chokes have alignment problems. Some may not shoot near where you point, and a crooked tube can't possibly pattern as well as if it were installed straight.

Best of luck with the choice you make.

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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Sun Jan 04, 2009 10:13 am 
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Quote:
Your best bet is the natural course of testing with the chokes and shells you prefer at the distance(s) you intend to shoot, and see if the paper tells you what you want to know.


That's the facts Jack!

I just measured 5 different wads, from 4 different manufacturers. NONE fill the bore. They all were well under a nominal .725 bore diameter, coming in all very close to .712.

OK, Browning gave us some data. It's probably a safe bet they used Browning guns for the test. Browning overbores to .745. So if we think the shot cup fully protected from deformation at any time during the ride down the barrel; all these wads would leave a .015 gap through the slits in a .745 barrel. In addition some of these wads didn't close up the slits fully even when squeezed down to .712. So pellets being scrubbed and deformed is a given. How much? dunno! What velocity? what wad? chrome bores? how much choke?

The pattern on the paper is the bottom line. If you are shooting 2-3/4 in a 3 inch gun; how would you tell if your gun would shoot different/better with a 2-3/4 chamber? It's the gun you have, you've gots to shoot it that way.

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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Wed Jan 07, 2009 1:35 pm 
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None that I have seen and I have patterned several 3 1/2", 3" and 2 3/4" models with a bunch of differentent loads.

Sometimes the longer chamber gun is better with a particular load and other times it's the shorter chamber gun that patterns with another load.

Each gun, load, and choke will pattern differently for the next one even if they are all the same.

There is only on true way to know for sure. That would be to start with a 2 3/4" gun and pattern it with several loads. Then lengthen the chamber to 3" and lengthen the forcing cone. Then pattern those same loads. Then lengthen the chamber again to 3 1/2" and the forcing cone. Then again pattern it with the same loads. Once done repete with a few more guns, preferable some with differnt bore diameters. Now you would have some data that would be useful and less subjective.

Since I don't seem to have patterning issues with 2 3/4" shells out of my 3" and 3 1/2" guns I won't be doing the above testing.


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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Wed Jan 07, 2009 11:35 pm 
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That is handy to have someone verify one of my points i.e. about wad slits, for starters.
Of course, my posting was not strictly about wads, but was one useful detail to consider.
I would not expect that any appreciable difference in bore diameter (if Browning exclusively used backbored barrels for testing) to change the outcome from chamber length difference, since the bore change is strictly a minor change in forcing cone length since only the very end of the forcing cone is altered when the bore is enlarged, not the bulk of the chamber-induced deformities.
Physics doesn't change, regardless of any deeply-held beliefs not based on scientific principles.
The bore reduction shown in this backbore example (based on Browning before/after) is under 5% difference in bore area reduction.

Image

If a shooter is unable to notice differences between guns/barrels that have differing chamber length (but believe that the chokes and results might be considered equivalent), much of the discrepancy may be attributed to differences in bores and chokes, as well, such as:
constriction variance or choke variance between manufacturers or even daily differences at the same plant
tube fit to bore
tube alignment to bore
bore finish
barrel length, harmonics
difference in crown precision

Any noticed details between barrels of different chamber lengths that does not take any choke differences into account would not even rise to the level of anecdotal evidence- in other words, a skeet choke couldn't be compared to an improved modified, for instance.

Any chamber length difference would not be able to be satisfactorily tested by lengthening a chamber again and again, according to one fellow questioning my detailing of chamber length degradement of lead shot patterns. He expected it would be impossible to change the length and also duplicate the forcing cone finish and so on.

Nay-sayers tend to set up impossible (to them) conditions for tests that would be required to convince them to change their mind to a new conclusion.

He just couldn't fathom that I knew a way to make a proper test of an individual barrel that would meet such demanding (and he thought, impossible) standards of repeatability.
After I explained the process for that specific scientific test, he then had to resort to another lame form of belittlement, since his argument was otherwise full of holes.

(First off, I had never made any comments that anybody had been mistaken, just that they hadn't seen proper experimental results because they had only been exposed to individual and distinct examples, not specific examples that had critical alterations tested. That is the scientific method to test alterations, by inducing the least amount of variables. Using data from just changing barrels is much more imprecise.)

He had started with name-dropping a couple of authors that wrote shotgun books and had stated that THEY hadn't noticed differences between barrels enough to happen to tell if one was a 3" or a 2-3/4", so consequently, if they hadn't noticed any anecdotal evidence, then the possibility of mr. no-name (me) knowing something that they hadn't discovered made me seem to be trampling their good reputation, in that fellow's eyes, at least. I was not fit company for such August personalities, I suppose. I never said I was, in the first place, and so what? The authors had merely stated that they had seen some 3" barrels out-pattern some 2-3/4" barrels, or not noticed differences in barrels enough to worry about those differences.
The books referenced had been from some years back before there was any 3.5" 12 ga., so the data could very well have been presumed dated, if giving the benefit of the doubt to my statements had been given any consideration. I don't expect to be given slack, just not have imposed standards applied to just me, alone.

I only state that I have done chamber length experiments that prove a change in length to match the shell is a definite pattern enhancement, and the converse must consequently be true. The is no other alternative.
One numerical expectation that I have seen:
lead shot turkey load, 3" shell in 3" chamber, good turkey choke vs. same load in 3.5" chamber- something near 20% difference
Hevi-shot loads have had less difference in my tests as expected due to pellet hardness vs. lead deformability.

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Gunsmithing website:
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Articles on every page.
Article 3 pictures improper or dangerous choke installations, article 1 has explanatory illustrations, and article 2 has info. about bore/forcing cone improvements/limitations.


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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Thu Jan 08, 2009 12:12 pm 
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Dang, I got a head ache. :cry:


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 Post subject: re: Pattern Deteriation - 3 1/2 inch chamber
PostPosted: Thu Jan 08, 2009 1:55 pm 
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The only way to know for sure would be to lengthen the chamber and forcing cone each time on the same barrel. You can't use a differents barrels with different chamber lengths nor is using a 3 1/2" chamber and then putting the correct length plug in the chamber for the next shell size down any good. Different bore diameters would also be a good experiment to see if there were any additional effects. Just saying there would not be any is less scientific and just speculation.

If someone is going to do the test, all of the variables need to be the same or otherwise it nothing more than a waste of effort.




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