I've posted this before.

By the mid-1920s, Ithaca had beefed up their Flues doubles quite a bit. In the 1912 through at least 1915 Ithaca catalogues they give their smallbore weights as --

16-ga 5 3/4 to 6 1/4
20-ga 5 1/4 to 5 3/4
28-ga 4 3/4 to 5 1/4

In the July 1919, Ithaca catalogue --

16-ga 5 lbs. 14 ozs. to 6 1/2
20-ga 5 1/2 to 6
28-ga 5 to 5 1/2

In the December 1, 1919, Ithaca catalogue --

16-ga 6 to 6 3/4
20-ga 5 3/4 to 6
28-ga 5 1/4 to 5 3/4

In the 1925 Ithaca catalogue --

16-ga 6 1/4 to 6 3/4
20-ga 6 to 6 1/2
28-ga 5 3/4 to 6 1/4

At the time the two Ithaca No. 1 1/2s in question here were new, North American 20-gauge shells were offered with 3/4 and 7/8-ounce loads. When the 1-ounce, progressive burning powder, high velocity, load came out in 1922, Western Cartridge Co. put their Super-X load in their 2 3/4-inch FIELD shell. Remington with their Model 17 pump made for 2 3/4-inch shells followed with their 20-gauge Heavy Duck Load put up in their 2 3/4-inch Nitro Club shell. Winchester with a boat load of their Model 12 20-gauge pumps out in the world made for 2 1/2-inch shells stuffed the 1-ounce high velocity load in their 2 1/2-inch shells.

Attachment 106689

Winchester continued to offer the 20-gauge 2 1/2-inch Super-Speed load up to WW-II --

Attachment 106690

In support of this information, I have a Flues 28 gauge serial # 369437, which dates it to 1923 and it weighs 5lbs 13 oz.

I like those 2 1/2 inch Winchester shells....charlie

I have a nice 28" 1-1/2 Flues 12ga with dam bbls that has the same engraving as the Whitley gun. My uncle got it in a bar one night for $35!!! and gave it to me when I was 16, along with a 16ga Remington Mod 11. The Gunbroker gun is apparently the earlier(corrected) version of the 1-1/2 grade? I could shoot that 3-1/4" DAH on the Whitley gun just fine! Nice looking gun; very nice bbls. I wouldn't hesitate in buying it at all, especially considering how high the prices on Parker small gauge guns are getting these days. I got a nice 28" VH20 with 3-1/4" DAH from J Thynne & co for the price of the Whitley gun not that many years ago, and I shoot it better than all but one of my other Parkers....

Other way around, Richard. The Gunbroker gun is of 1912 vintage and the Whitley gun is between mid-1915 and 1918.

Jeezo Pete.... seems that the folks in the know recommend keeping your loads at 6,000psi and lower to prevent frame cracking on these light Flues 20ga guns. Easier said than done. I don't see any 20ga loads in any of my books that are that low pressure. My 1200fps loads using PB in AAHS and STS hulls are 10,300psi. I don't find anything usable in the Lyman 2,3, 4 and 5th editions.