WALL THICKNESS IN CHAMBERS

[thaynedelange]

I know this subject has been resurrected and flogged like a dead horse many times but I wanted some actual measurements and personal input from members with their own guns. I have a Hosford wall thickness gauge and have found some interesting and varied measurements in my own guns. For example, I have a Parker PT grade 12 gauge with twist barrels. The right tube at the front of the chamber measures .087 and 6" inches from the breech measures .055 The left tube measures .092 at the front and .060 at 6 inches from the breech. I have shot this gun with low pressure shells for years. Does anyone have similar measurements in the their own guns? Please share your info. Thanks!:)

[James L. Martin]

I just measured my 12ga DH Damascus # 94555. I do not have a wall thickness gauge so I measure inside and outside and do the math. Right barrel at 4.125 " in is .202 & 6" in is .132 ,left barrel at 4.125 " in is .209 & 6" in is .134 . I have been hunting with this gun for 4 years using RST 1oz paper. Sorry forgot to divide by 2 . So it's .101 , .066 & .105 , .067

[thaynedelange]

Thanks James. I think those numbers might be a bit high. Several people in the past that have measured that way without a gauge get really high numbers. A wall thickness gauge I think is a must as you can get inside near the ribs. Thank you for taking the time to measure!

[James L. Martin]

Sorry, forget to divide by 2. I have added right numbers.

[thaynedelange]

Ok, that makes sense. Those are good numbers. Your bores have probably not be honed or polished. Nice gun!

[edgarspencer]

James, you didn't say what frame size your DH is, but I think your numbers are just about right for a 2 Frame gun.
Coming up with a reasonably valid number by halving the difference of the ID and OD, will only be reliable at the chamber, forcing cone and perhaps a few inches. Generally, you're more likely to find that, due to striking further down the barrels, the concentricity is less assured. I've seen differences of several thous between one side and another, or top and bottom, at the last 10" or so, then becoming more concentric around the beginning of the chokes.

[James L. Martin]

The frame size is 1 1/2 , the barrels are original 26" and nothing has been done to them as far as I can tell.

[edgarspencer]

In measuring two 1 1/2 frame guns, I find .096", and .092" at the forcing cones. Not a huge drop on two 1 frame guns.

[Dean Romig]

I have 79355 a 0-frame sixteen with .064" and .066" at the front of the chambers, beginning of the forcing cones that were measured by Oscar Gaddy and he pronounced them as "probably safe to shoot with loads under about 7,500 p.s.i."

I've taken a bunch of grouse and a couple of woodcock (and about 50 rounds of skeet) with it using 2.5" RST Falcon Lites.





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[Gary Laudermilch]

My 12 ga 1 frame twist barrels were measured by Mr. Hosford utilizing his equipment. The wall thickness at the end of the chambers was .115 and at the end of the forcing cones .090. Minimum barrel wall thickness was .030 in both tubes.

[thaynedelange]

Thanks Dean,
That is exactly what I was looking for. I know what the old literature says about minimum safe wall thickness 6" from the breech--about .090 but I can only speculate that guns with .040 to .050 might be safe to shoot as well with low pressure loads. I will measure my other two pattern welded barrels and post those numbers tonight.:) Thanks for all the others comments as well. I am hoping more people will post their measurments so we can see what difference between guns and gauges are.

[Drew Hause]

http://parkerguns.org/forums/showthread.php?p=158096#post158096

http://parkerguns.org/forums/showthread.php?t=1565&page=4
English:
James Purdey (1898) 12b., 2.5" chambers: ≥ 0.100.
James Woodward (1909) 12b., 2.5" chambers: ≥ 0.098
James Woodward (1909) 12b., 2.5" chambers: ≥ 0.103
Boss (1897-8) 12b., 2.5" chambers: ≥ 0.090
Westley Richards 12b., 2.5" chambers: ≥ 0.090
James MacNaughton (1895) 12b., 2.5" chambers: ≥ 0.095
Wm. Pape (1898) 12b., 2.75" chambers: ≥ 0.100
EM Reilly (1887-1904) 12b., 2.5" chambers: ≥ 0.091
Henri Egg (1870) 12b., 2.5" chambers: ≥ 0.108
WH Monks (1875-87) 12b., 2.5" chambers: ≥ 0.116
WC Scott (1905-6) 16b., 2.75" chambers: ≥ 0.105
Westley Richards (1905) 20b., 2.5" chambers: ≥ 0.098
WW Greener (1922) 20b., 2.75" chambers: ≥ 0.098

Belgian:
Francotte (1894-5) 12b., 2.5" chambers: ≥ 0.085
Francotte (1896) 12b., 2.5" chambers: ≥ 0.085
Francotte (1930) 20b., 2.5" chambers: ≥ 0.095
Francotte (1938) 12b., 2 5/8" chambers: ≥ 0.098

French:
Verney Carron (1950s) 12b., 2 5/8" chambers: ≥ 0.100

German:
Wilhelm Brenneke (1902) 12b., 2.5" chambers: ≥ 0.110

U.S. maker's doubles usually have a wall thickness at the end of the chamber of > .100

10g and Field grade 12g, and those with a "Double Thick Nitro Breech" frequently much more ;)

http://pic20.picturetrail.com:80/VOL1373/6511424/20991622/408932781.jpg

Note: In heavy barreled turn-of-the-century U.S. maker 12 GAUGE doubles, the angle of the forcing cone is usually greater than the taper of the exterior of the barrel, so it is not uncommon that the forcing cone WT is the same or greater than the end of the chamber WT. THIS MAY NOT APPLY to small gauge American or lightweight British doubles.

WARNING posted on DoubleGunBBS in 2017
“For many years I measured the ID and OD, subtracted and divided by two to get the wall thickness thinking this is close enough. I purchased a wall thickness gauge and began measuring my barrels. One of my guns measured .014 thickness whereas before I thought there was about .025 minimal wall thickness.”

The problem is eccentricity. Freshly cut barrel segments in preparation for tensile testing and composition analysis

http://pic20.picturetrail.com:80/VOL1373/6511424/24532497/409066906.jpg

More infro here
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

[thaynedelange]

great info Drew. Thanks! I promised I would take measurements on my other two Parkers...so here they are. 1. 12 gauge grade 1 lifter mfg. in 1877. RIGHT BARREL .130 WT at forcing cone. LEFT BARREL .128 WT at forcing cone. This gun has the largest wall thickness I have seen on a 12 gauge Parker with twist barrels. 2. 10 gauge grade 3 lifter RIGHT BARREL .096 WT at forcing cone. LEFT BARREL .090 WT at forcing cone. The left barrel has a slight .004 bulge at the forcing cone which is hard to see but it is there. Thanks for taking the time to measure your guns. Keep them coming!:rotf: