parker gun part swapping

Originally Posted by Dave Suponski

Welcome Vincent...Glad to have you aboard..

I'll second that--IMO the best $40 you'll ever spend on anything shotgun related-One great thing about new members in the PGCA- there is most always a new question or quest for info raised, and that's what has spurred the growth in membership in the PGCA--

[Double Trouble]

Regarding barrel regulation being affected by the shortening of the barrels: If that's true, then I guess we are assuming that each barrel is not reasonably straight, but instead, is (minutely) bent in all different directions (but looks straight at a casual glance) ?

Now, every manufactured product has a tolerance, and "straightness" of a barrel has an angular tolerance too. But....... If each tube is reasonably straight, it's centerline will theoretically define point of impact.

OK - now, if one regulates two such tubes together to form a side-by-side barrel assembly, they are "adjusting" the alignment of each tubes centerline to be reasonably coincident at a given distance (let's just say, 50 yards).

Now - these barrel centerlines - being "LINES" - are straight. That's a definition of a line. Additionally, these two centerlines do not change from their original orientation after one, two , or three inches of barrel assembly is cut off. (ie: the two barrels are soldered together for their entire length).

So, by shortening the tubes, we have not "moved" one barrel relative to the other, and we have not changed the same straight "centerlines" of each barrel. So, how then can the point of impact be so drastically changed ?

Additionally, we're talking about shotguns, not rifles. If one was talking about rifles - they are so exacting/accurate that a minute change in barrel "straightness" or barrel vibration/harmonics could affect the apparent point of impact (when the arm is capable of a 1/2" group at 100 yards). But when you're throwing a swarm of pellets in a pattern that can be reasonably measured in feet vs. minute of angle - how much differently can 2" shorter barrels possibly be aligned ?


[BTW: since the thinner walled muzzles of each barrels "touch" (at the muzzle end) - and the breech end of the barrels (which have much thicker walls) also touch, this means that the barrel centerlines are not parallel, and the paths of the shot charges must cross each other (when viewed from above the gun) not too far from the muzzle. Double rifles (when viewed from the muzzle) have the centerlines of each bore separated by a great distance in order to keep them reasonably parallel. Since shotgun bores do not appear to have the parallel centerline, that level of exactness must not be needed.]


I'm playing devil's advocate - I'm not saying that it's a simple task to regulate shotguns. In fact, I still have a beautiful 20 ga. Weatherby O/U that is such a POORLY REGULATED P.O.S. that it shoots like two completely different guns - mounted on one stock. The fine boys at Weatherby said it shot to their specs & did nothing to solve my problem. As a result, I can NEVER recommend that maker, and will never by one of their products again.

Of course, who needs to - with all those amazing old Parkers out there !!!!!


{Damn - my fingers are tired from all that typing !!!!}

[Dean Romig]

John, regarding my statement that a gun with shortened barrels having a tendency to shoot high; The line of the center of the bore is, as you say, a straight line that cannot be altered.... but the shooter's line of sight (also a straight line which cannot be altered) is aligned in direct relation to the center line of the bores and the aid in this alignment is the plane of the top rib with a bead set upon it as a further aid in aligning the shooter's line of vision relative to the center line of the bores. When the barrels are shortened the rib, of course is shortened also, altering the aid to alignment of the two straight lines that the shooter is dependant upon. Now as the shooter maintains his straight line of vision along the shorter rib and the bead the angle of the center line of the bores has been altered upward a bit at the end of the barrels. There is no helping this if the shooter is to shoot as he has always done, i.e. using the rib and bead as his only aid in aligning the center line of the bores with his intended target. This will be more pronounced in smaller gauge guns on larger frames, e.g. a 28 ga. on a 0-frame or a 16 ga. on a 2-frame or a 12 ga. gun on a 3-frame with cut barrels.

[Dean Romig]

Originally Posted by John Mazza

[BTW: since the thinner walled muzzles of each barrels "touch" (at the muzzle end) - and the breech end of the barrels (which have much thicker walls) also touch, this means that the barrel centerlines are not parallel, and the paths of the shot charges must cross each other (when viewed from above the gun) not too far from the muzzle. Double rifles (when viewed from the muzzle) have the centerlines of each bore separated by a great distance in order to keep them reasonably parallel. Since shotgun bores do not appear to have the parallel centerline, that level of exactness must not be needed.]

True, to an extent... however, keep in mind that when the barrels are joined at the breech the sides of the breech end are filed flat and brazed together with a combined wall thichness equal only to the chamber wall thickness of a single barrel which helps greatly in aligning the two bore center lines and aids greatly in regulating the barrels.

[TARNATION !!!]

Caution to the reader. The following may be true/false or none of the above. Do I need to understand aeronautics to fly in an airliner? Do I need to understand automotive mechanics to drive a car?? Do I need to understand barrel regulation to shoot a gun?? Maybe not but now I want to, even as the midnight hour is swiftly approaching.

After asking questions and getting answers and thinking about it all, I'm less confused (or more) and may or may not have it straight.

SXS barrels have a straight bore
SXS barrels Outside Diameter is greater at the breech and narrower at the muzzle but the bore Inside Diameter is consistent so... the wall thickness is greater at the breech and less at the muzzle and the least midway along the barrel length.
That we can see with this diagram posted a few times on the forums.



From this diagram the breech OD is 1.205 and the muzzle OD is 0.825. OD midway is 0.799 The variance from breech to muzzle is 0.38 but midway the variance is greater, being 0.406
To have the two barrels become a single unit, Dean just explained that the breech end is filed to half its thickness and the two brazed together. The filing would have to start at half thickness and continue at an angle toward the muzzle that allows the two muzzles to just touch. That angle changes according to the length of the barrels. Now there is a lot of space between the two barrels from the brazed join at the breech and the touching barrels at the muzzle. This space is filled at intervals with soldered shims - more shims midway than at either the breech or muzzle end. Shimming has an effect on regulation as does the angle of breech wall filing, as I understand it. The gun can be fired without the rib being laid and adjustments can be made in the shimming to achieve the desired regulation. I think

As I understand it, the purpose of regulating the barrels is to have the payload from either barrel hit the same point of impact at a specified range. A waterfowler may be regulated for 40 or 50 yards and an upland gun may be regulated for 20 or 30 yards. It could be regulated to a customer's specification.

Beyond the point of regulation, the shot strings will cross each other. Before that point, the two shot strings will be converging and beyond that point, the two shot strings will be diverging.

Given that the diameter of an effective pattern is approx 30 inches, a bird in the center of the point of regulation is quite dead. Moving the bird further down range and not moving the barrels, the bird will be closer to the edge of the pattern until it is eventually not in the pattern. Same effect moving the bird closer (but of course the pattern diameter is less and less so if you connect you have a dead bird but nothing left to eat ).

I'm still unsure how shortening the barrels, with the shims not having been touched, changes the regulation. I can see that the choke may be changed, thus opening the pattern earlier and reducing effective range. For example, a heavy waterfowler is now a short range upland gun. This part remains unclear to me.

I may or may not see Dean's point regarding shortened barrel causing a shooter to hit high. Now if one were used to a 32" gun (uncut) would this shooter hit high with a 28" gun (uncut) ???

I know when I close my eyes and pull the trigger, sometimes I'm high, sometimes I'm low, sometimes there's a dead rooster sometimes there's not. I guess I need to concentrate on seeing just the bead and bird, but when I try that, the bird inevitably carries on untouched. But I am glad the Parker Bros got it all figured out for me, even if I don't quite understand it all yet.

Cheers,
Jack

Here are some images of a barrel set with ribs removed showing the soldered shims. Sent my way from Jent to help explain some of this.

[Holeshot]

I agree with Bill. Shoot the gun and check point of impact. Only a pattern board will tell if there is any concern. I have shot both and the open chokes help cover up the loss of regulation. I tend to pattern all my sxs's, after having a 20 that crossed over past 20 yards and it was factory length and tight choked. Didn't make much of a dove gun.

[Dean Romig]

Originally Posted by Jack Cronkhite

I may or may not see Dean's point regarding shortened barrel causing a shooter to hit high. Now if one were used to a 32" gun (uncut) would this shooter hit high with a 28" gun (uncut) ???

No Jack because we're talking "cut barrels" not barrels that were manufactures to a particular length. A gun has its barrels regulated not only in relation to each other but also in relation to the placement of the rib and bead on the barrels. You will note that on many live bird or trap Parkers and other live bird or trap SXS shotguns of the day the top rib was somewhat narrower at the muzzles than at the breech end.... a finely tapered rib in other words, allowing the rib to lay lower between the muzzles facilitating the angle of the center line of the bore somewhat upward in relation to the line of vision of the shooter. This allowed the gun to shoot high to a rising bird.
This placement of the rib wasn't necessarily on every gun of this description but was on many of them. Even later the placement and angle of the ventilated rib allowed for the same angle.

[TARNATION !!!]

The part I like best is "shoot 'em"

[Hammer Gun]

Vincent, There were guns that left the factory that were not exactly on the inch!

[Double Trouble]

Good information, guys !

It sure would have been fascinating to have watched the workers at Parker assemble one of these fine guns !