The question often is asked, "What are the minimum barrel
thickness to safely shoot my gun?" and its a difficult
question to answer without risk. An answer, without a
close inspection of the barrel condition, is impossible without
risk of being wrong.
The use of black powder and corrosive primers is a primary
cause of pitting in some old shotgun barrels, especially if they
were not cared for properly shortly after their use. The
results can be anything from slight to severe pitting and those
pits effectively reduce the barrels thickness by the pits depth
at that location. If the shotgun bore is not mirror bright,
a competent gunsmith will determine the depth of the pitting and
take that into consideration when measuring barrel wall thickness
With that said, here is a general 12 ga. guideline:
In the forward 2/3 of the barrels length, a thickness of
.025" has been suggested as a minimum thickness for safety
reasons. The rear 1/3 length of the barrels, where the maximum
pressures are exerted, requires thicker wall thickness.
The wall thickness at the juncture of the chambers and the
forcing cone is the most critical and is where it has the highest pressure
With some uncertainty, its assumed that a thickness of
.090" at this juncture location would be about
UK Working Standards recommended minimum wall
thickness measured 18" from
the barrel breech from Double
Gun Classics p. 56, Vol. 1, No. 4 Jan-Feb, 2006:
2 1/2" 12g- .028
2 3/4" 12g- .032
Re-proof recommended minimum- .024
And, The Hunter's Encyclopedia from the German
proof house: minimal wall thickness
at end of chamber, regardless of length, for 12, 16 & 20
gauge guns should be 2.3mm (.0906") for 'ordinary good
steel' or 2.1mm (.0827") if a 'Special Steel' was used. For
the 24 & 28 gauges, due to their higher pressures, 2.4mm
(.0945") was recommended.
Minimal wall of .6mm (.0236")
was recommended in the "forward third" of the barrel.
There is greater pressure as the gauges go from 12 to 16 to 20
etc. therefore the minimum values might increase.
Learning the measurement of known original Parker
barrels of the same gauge would be a good example to use to
understand what Parker thought were safe values in the days when
they were making shotgun. The problem with this method is
finding "original" Parker barrels and getting
permission to take measurements.
The thickness of the barrel depends primarily on the frame
size with respect to gauge, and secondarily on length. The
barrels were finished by longitudinal hand filing to fit a
general set of outside diameter checks. The filing was generally
done to balance the gun at the hinge, but it could be muzzle
heavy or light if the customer ordered. The longitudinal hand
filing produced barrels that were not necessarily concentric with
the bore, and wall thickness can vary side to side or top to
bottom. There is no standard thickness.
Some guns appear to have thick barrels because full choke
barrel muzzles are .040 or more thicker than the bore.
Some general observations made on the PGCA forum - Regarding
accepted barrel wall thickness for shooting modern loads, it
seems everybody has an opinion. Many of the gunsmiths that render
opinions on wall thickness of 25 thou or above work more on
modern guns than vintage doubles. If you ask a person who has
spent his life working on fine VINTAGE double shotguns, they
better understand how these guns were made and have much
different opinions on the subject. Most all agree that even 18
thou in the forward half of the barrels is not dangerous from a
bursting or bulging stand point, but rather the risk of dents and
damage that cannot be repaired as there is not enough metal to
work with. More on 18 thou later.
If you ask me, the Brits have been the fussiest about barrels for
almost 2centuries, and set the mark for proof testing. Forget
opinions based upon everybody bloviating and regurgitating what
they have heard or what their friend's opinion is. The British
proof houses regularly try and blow up perfectly good guns! They
see what barrels can handle by passing not one, but two
definitive proof loads through each barrel. I believe the loads
are 18,500psi. We all shoot loads that are below 12,500psi
(magnum loads), and most of us shoot more reasonable loads that
run under 10,000psi. And the guys that have patterned their guns
with loads like RST Shells recognize it is not speed that kills,
but the nice even patterns premium ammunition provide. RST Shells
don't exceed 8000psi. Go to www.rstshells.com
for very affordable, safe loads for your beloved doubles.
If barrels with 20 thou wall thickness were regularly failing the
proof they would not mention that as the recommended minimum. The
facts are that barrels under 20 thou regularly pass proof and are
deemed safe. Barrels with 20 thou and all other characteristicds
in good shape pass proof in overwhelmingly high numbers. It is
extremely rare for failure in the rigid proof testing for barrels
in excellent condition because of wall thickness of 18 thou or
above. Barrels fail for other reasons, but not often from
bursting or changing bore diameters as in bulges. AND REMEMBER,
THIS IS WITH 18,500 PSI LOADS!
Doesn't repeated, large sample, empirical testing that occurs
in very controlled circumstances trump untried opinions?
Especially with DEFINITIVE PROOF LOADS?
The British Gun Trade Association clearly states that 20 thou is
the generally accepted minimum for judging healthy guns. This is
stated in the Jan/Feb 2012 issue of Shooting Sportsman, and in
another Shooting Sportsman article from Sept/Oct 2009 issue.
Unless you are shooting guns with obstructions in the barrels,
there is no measurable risk shooting reasonable loads in guns
with 20 thou wall thickness at least 15" from the muzzle,
provided all other issues are sound, like tight ribs, no serious
dents, etc. This is not opinion, but data collected for decades
under controlled testing.
Now, from my experience I think many Parker collectors and
shooters may be surprised that I have measured at least 20 guns
that were 20ga. or 16ga. guns on "O" frames that were
definitively factory original in the way of blue and bore
diameter. They were never backbored or polished inside, and never
filed or machined on the outside since leaving the factory, and
they had areas 6-12" back from the muzzle that were 18 thou,
FROM THE FACTORY. This is almost always in a 3-4" area very
close to the top rib or bottom rib, and only on one side of the
tube. As one person on this thread mentioned, virtually all
vintage American doubles have a very noticeable lack of
concentricity, ie thicker on one side than the other. There is
also the matter of soldering on the ribs, with the required
filing of overflow solder tight in to the rib, creating these
All of these guns were very lightweight Parkers. Where most 20ga.
Parkers weigh in the neighborhood of 6 1/4lbs., often a few
ounces more, how do you think the factory came up with the guns
that weigh less than 6lbs. or even 5 3/4lbs.? It is damn hard to
hawg a butt and remove 3 oz. of wood. It is usually more like 2
ounces with a lot of hawging. And once hawged out, how do you
think they keep the gun from being barrel heavy? They filed metal
from the barrels, that is how.
The guns I refer to have been shot for generations, and 10 years
ago hunters would regularly use high base shells for everything.
After 70-100 years of use they are still unchanged and have
How many of the opinion makers actually own high quality barrel
wall thickness gauges? Not many I can assure you. I travel the
country and am surprised how few buyers of fine shotguns own one,
let alone know how they are used. If you are going to buy more
than a few shotguns in your life, I recommend looking at the
Hosford and Co. barrel wall thickness gauge. One mistake in
buying a bad set of barrels on an expensive gun will pay for the
gauge 5 times over. The Hosford gauge is very convenient and
portable. Either that or rely on someone that has one before
finalizing any deal in which the wall thickness is not guaranteed
by the seller. Just my opinion on that. No dog in the race.
Just examing 100 Parkers I have sold over the last 3 years, 24 of
them had at least one of the two barrels with wall thickness
under 23 thou. Without a lot of researching each individual gun,
I can generally say I don't buy or sell any guns you all would
consider unworthy at least as a sound shooter, and in general I
have above average shotguns. THAT IS 25% OF THIS SAMPLING THAT
PROSPECTIVE PARKER OWNERS WOULD DISMISS IF THEY WERE FOLLOWING
THE 25 THOU RULE.
I guess my point is this: It seems there are quite a few folks
that come to this forum as being inexperienced with buying and
shooting Parkers, and are looking for sound info from members to
utilize in getting started shooting and collecting Parkers.
Rather than use guesstimates and opinions, why not recognize the
results of strict empirical data gathered over the decades of
testing provided to us by the Brits? It is certainly better than
having fellows looking for a light weight Parker for the uplands
simply give up because they can't find one with both tubes over
25 or even 30 thou, as some have stated in this thread. Many of
those following that advice would pass over some very fine
Parkers for no reason at all. And then they would have to buy Fox
guns, as most of them are much lighter than like Parkers! We
don't want that do we?
And again, most of the members of our association have no clue
what their Parker's barrel wall thickness is. MANY of them are
shooting guns that are under 25 thou, and have for decades.
Again, a word of caution - without a hands on inspection, these numbers mean
little; don't risk life and limb shooting bad
them inspected by a competent and knowledgeable gunsmith before
shooting an older gun of unknown history or condition.
Here is a link to a
video that demonstrates how barrel wall thickness is tested.