doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Problem: O/U Barrel Regulation

Stan --

Thanks for your note. You are probably right. The gun may be so bad that it is not "fixable"..... no clear way to put it right.

The basic problem is, however, that this B. Rizzini gun is a 2o ga., field gun. I purchased the gun primarily for grouse and woodcock hunting. It weighs about 6.6 pounds. Perazzis are very nice and there is a major dealer not too far away. But, except for the 12 ga. Mirage (I think that is the model) I know of no Perazzi field gun. My impression is that the Mirage is heavier than I would like.

What do know about Perazzi field guns? Perhaps my impressions are wrong.

Regards,

Don

And after I told Phil off for you! You have no sense of gratitude.

Mike

Mike,
My wife says I need to stick up for my dog.

Don,
Pguns do indeed come in field configs. The 20g frames along with slender straight stocks are available and the guns can get down around the weight of your B.Rizz. They are beauties. I have a friend with a .410/28g field gun in a high grade. What a knockout. Prices are the only deterent to me on the small gauge Pguns.

Stan --

I guess my view / understanding of the Perazzi product line was behind the times ... dated to the time when they were represented by Ithaca Gun. ( I live in Ithaca )

Just now, I did take a look at the Perazzi web site and was surprized to see a large number of game guns in all the gauges.

Very nice.

But, after pricing them on the web -- I would have to say that these guns - as new - cost more than I can justify expending. Perhaps, if a great used gun deal came along -- but, otherwise ....

Best Regards,

Don

Chuck -- Mike --

The barrel convergence angle is difficult to accurately determine. As Mike suggests in his appended website thread from 16ga.com, the needed measurements could depend on the design/manufacturing methods used to achieve the needed convergence of the barrels at the muzzle. The barrels could be angled to achieve the convergence with the chokes mounted in line with the barrrel bores. Alternatively, the chokes,alone could be angled to provide for the convergence, while the barrel bores are essentially parallel. Of course some combination of both procedures / designs could be used to achieve the desired final result.

But for the purpose of the measurements -- no matter which procedure is used to achieve the desired convergence for the angle at which the shot charges exit the muzzle -- the angle between the choke bores at the muzzle is the necessary parameter to measure. But, without some special measurement equipment / fixturing / tooling -- this is a difficult measurement to make. I know that I cannot do it well with what I have at home, here. It is essentially impossible to do this in a store, when considering the purchase of a new gun.

The suggestion that the results of careful patterning of the gun for the points of impact (POI) for the respective barrels is best --- is probably the most pragmatic suggestion / approach. But, the intrinsic difficulty here is that one probably owns the gun by the time the patterning is undertaken to assess the guns point of impact (POI) performance. Without a specification for minimum patterning performance, the manufacturers can and do say that the "gun is within spec." -- as can clearly be gleaned from the above postings in this thread. Catch-22, all over again.

If the necessity for barrel convergence does, indeed, derive from the recoil motion of the gun before the shot charge leaves the muzzle -- then there are several parameters that - in principle - affect the necessary convergence to supperimpose the patterns from both barrels. These parameters include:

1. gun mass / moment of inertia for rotation about the stock heel.
2. shot charge mass / weight
3. shot charge velocity at the muzzle.
4. barrel to barrel spacing
5. stock dimensions.

In principle even the physical attributes of the shooter could affect the patterning outcome. This suggests that the patterning should be undertaken off-hand and with the gun mounted in the "normal" way.

The B. Rizzini POI patterening problem I encountered may have been the result of a poor B. Rizzini design, re: convergence ( most important); 1 oz. field loads used in the patterning; and the gun is light (part of the design considerations).

To prove the point, concerning the importance of / necessity for barrel convergence, I may try patterning the B. Rizzini gun with 3 inch - 1-1/4 oz loads -- when I have time (after the wedding). These loads should significantly amplify the problem, if this barrel convergence, design, deficiency is the origin of -- or substantially contributing to -- the problem.

Regards,

Don

I can't for the life of me figure out how an Italian built shotgun is that far out of POI. And the answers Don was given from some noted firms makes even less sense. Within acceptable tolerance, that's useless!!!

I own a mechanical contracting company. I have had lawyers tell me there is NO time limitation on liability for defective materials or defective workmanship. There have been lawsuits over copper hot water water pipes that had been installed for several years and then started leaking. The building owners claimed, among other things, that the installing contractor had not reamed the lip out of the pipe when he cut it and this set up turbulence causing erosion. It broke some very large mechanical contractors.

Best,

Mike

I guess the Rizzini could be restocked or the stock bent so that the top barrel shot 8 inches high and the bottom barrel shot 8" low but that still seems out of reason.

Mike

Contrary to a published recommendations, a friend occasionally unscrews the choke on his gun and shoots a round or two without any choke in the barrel, then reinstalls it like normal. Apparently with no damage. He's been doing this during our sporting clays shoot once a week for yrs.

Don, If you're comfortable with shooting without a choke in the barrel, I'd think that would tell if the choke machining in the barrel was the culprit. Just shoot it for POI at a closer range, say 20 or 30 yds.

Chuck --

This is my last note / entry for a while -- daughter's wedding and all. Leaving momentarily.

But, in response to your last entry -- you are certainly correct with respect to your suggestion. (You have the makings of a very good experimentalist / researcher.) But I have never fired the gun without the chokes in place. (You should have seen how I cared for this gun.) I have heard that shotguns can be fired with no screw-in chokes in place -- "without damage". While I thought the gun was worth something, I was very hesitant. But, realistically -- with what we, now, know about the gun -- what do I have to loose! And your suggested experiment would shed some, much needed, scientific light on the origins of poor double gun barrel regulation. So .... We will do it!

.... But, "the plot thickens".

Here is what has happened since my last response to you.

I finally got in contact with Rizzini / Galazan. ( My initiative.) Galazan is clearly caught between me and Rizzini. They have offered to sell me new barrels at their (Galazan) cost. .... And, now, the barrels will be patterned and assessed before shipment. This may be the best compromise I can achieve without following up on Mike's suggestion and dragging Rizzini into court. (In deference to Mike, I think we could win in court -- especially if Mike argues the case.)

But, I will call Jim Eyster on Monday and depending on what they think they can do, technically, and the cost structure, I may accept Galazan's offer.... or I may proceed with Eyster. On the other hand - if Eyster is confident and the cost is not too high - I may do both. (Yes, I am just a bit crazy.)

Either way, I think the experiments we have discussed could be undertaken without compromising either potential barrel solution. I will discuss this point with Jim.

So, there are two experiments I will do, which should shed some light on the barrel regulation considerations we have discussed.

1. Your suggested, "chokeless", patterning of the barrels should quickly sort out the contrbutions that the chokes were making to the divergence of the patterns from the two barrels. Actually, I do not think this will harm the barrels, after examining the geometry of the barrels into which the chokes are normally screwed. You may recall that we exchanged chokes between the barrels - in our original experiments - without affecting the patterns' POI's. As previously mentioned, the chokes appear to be very much parallel. Based on these two considerations, I expect that the chokeless patterns may have different POI's -- but, the divergence of the patterns will closely approximate that which we found with the chokes in place. This last statement discounts the importance of the small change in the gun's effective moment of inertia for recoil with the choke removed. We will see.

2. I will pattern the gun with 3 inch, 1-1/4 oz, shells and compare the pattern divergence to that associated with the, previously used 1 oz loads. (Chokes in.) Since these loads have ostensibly very closely approximated muzzle velocities, the differential in recoil kinetics can be easily understood. If the lack of barrel convergence is the primary / controlling source of the POI impact divergence for the two barrels, then I should see an increase in POI divergence of more than 25 %. This experiment will shed light on whether the "toe in" barrel geometry is indeed an important consideration ... and if so by how much.

But, it will take some time to undertake these experiments. I want to make sure I have a back-up barrel plan in case the chokeless experiments go "wrong". And, then, there are my daughters wedding plans and all..... my present house reconstruction, ... consulting work ... trout fishing ... etc.

I promise to send you and the rest of the group a posted report on the outcome of the experiments. This is getting all very interesting. I actually think we are learning about this barrel regulation "stuff".

Best Regards,

Don