doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Inherent inaccuracy of a SXS-How Much?

I believed I could see the right barrels of four different Parkers I owned that were bent(very slightly, of course) about 2/3 of the way to the muzzle and paralleled the left barrel from there on out. To me, this made a lot of sense but I discussed it once with Oscar Gaddy and he said he had never noticed this. Am I the only one who has ever observed this, or thought I had? This was observed by looking through the bores, at the rings.

The issue here is that "inherent inaccuracy" is undefined, so explaining it or measuring it is somewhat difficult. That said, I'm enjoying the discussion. So far, I see three possible definitions. 1 - the static geometric relationships among the muzzles and the line of aim. 2 - the static geometric relationships of the barrels and the aiming line. 3 - the dynamic relationship between aiming line and barrel line upon firing during barrel time.

It is clear to me that the dynamic result depends on the shooters physical reaction to the shot, as well as the design and construction of the barrels. Just as a handgun must be sighted in by the shooter to be truly sighted-in (rifles to a lesser extent), the shotgun would have to be custom regulated to the individual shooter to truly converge at a predetermined distance. Practical experience shows that this is a minor consideration in a very high percentage of cases.

So, Bushmaster, what is it you really want to know? Try some other words.

Yeah, Doug, I thought I had been fingered...in more ways than one. All of 'em happened in a short period too. Maybe over 4-5 yrs. Stuff for elbow to elbow beer drinkin.

If they converge at 40 yards-how much are they off at 20 and 60 and does it matter.
Because it is at most an inch or two I assume it does not matter.

Jim;
The drawings from the Smith Plans & specs book seem to indicate the bbls remained straight & were set to the convergence I mentioned in the previous post. I didn't get the book back out for exactitude, but the figures I cited are extremely close. They in fact gave the point of convergence of the bore axis a few feet from the muzzles & the seperation of the axis at the 40 yd range. It may not have been the exact 15" I gave but was within a half inch of that.
Upon acquiring this book many years ago & seeing these figures I did a rather informal check on some of the Lefevers I owned at the time. The first check of muzzle vs breech spacings revealed they were about the same as those given for the Smiths. Then working from the outsides using a good set of Starrett dial calipers I measured the bbls OD's at regular intervals & then at the same places measued the total widths across the two bbls. Going this method one of course is simply assuming bore to OD concentricity but plotting the centerlines of the bores revealed essentially a straight line & on several differnt guns of varying weights they all plotted very close to that .011" per inch convergence of the Smith drawings.
In measuring a good number of bbl OD's on various doubles over the years I have found the vast majority of them are slightly "Beefed Up" in the choke area,IE the dia runs larger over & slightly ahead of the chokes than from behind the chokes back to about the mid point of the bbls.
If the bbls were squeezed in anywhere near to paralell for much length behind the muzzles this would be readily apparent just looking down their OD's. In all the guns I have owned or handled much over the years I don't recall ever seeing this condition, "BUT" I certainly am not saying it has never been done, just that I have never personally noted it.
While admitting I am not real experienced at reading the internal shadow rings, on those on which I have tried I have never observed what I took to be a distinct & intentional curve. My observations have been the bbls as set in are as straight as build tolerances allowed & then set to that converging angle, which is incidently about 0°38' included, trigging from the .011" per inch of convergence.

Miller,
My recollection was that the .011"/1" you got was about what I got on a sampling of my 12g doubles.

Jim,
I measured a handful of my 12g dbls, including 2 Pahkas and none had any "Kentucky windage".

It's entirely possible that I imagined what I think I saw. I don't have any Parkers now, so I can't even look through the bores again. I'll look through some, at the next gun show.

My biggest chuckle, whenever this topic comes up, is how many people believe you could shoot around a tree @ 20 yards, left barrel to the left and right barrel to the right, and kill a quail at 40 yards, with either barrel. After all, that's where they are regulated to converge, right?