doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Advice on Chamber Sleeving

I am looking at chamber sleeving from 12ga 2.5 to 16 2.5.

How much weight does it add?

What are the issues with leakage around 16 ga wads in the 12 ga bore if any?

Which 16 ga wad bases expand best for the 12 ga bore?

If you have done it would you do it again and why?

Sherman Bell published this study of GaugeMate adapters back in 2006. It would make sense that 16g to 12g bore would not diminish, and possibly increase, fps

28g Gold chamber adapter in a 16 gauge gun:
(Both Remington and AA factory loads were nominally 1200 fps)
A Remington 28-gauge STS factory load of 3/4 ounces of #8 lead shot, gave a velocity (at 4 feet) of 1215 ft/second and developed a pressure of 5100 psi at the front of the forcing cone.
A Winchester 28-gauge AA factory load, also with 3/4 ounces of #8 shot, gave a velocity of 1252 ft/second and developed a pressure of 5800 psi.

Drew, I'm wondering what the measurements would show for pressure in the same location in a 28 ga gun? My thinking is that the overbore situation shooting 28ga cartridges in a 16ga gun would lead to a substantial pressure decrease, or is that correct? I know peak chamber pressure is usually in the neighbourhood of 11000 psi but no idea what it should be in front of the forcing cone.
John

You are certainly correct John that increased volume yields decreased pressure, and it would have been helpful for Bell to have measured the "just forward of the forcing cone" pressure with the factory loads.
I've never seen a pressure-distance curve for a 28g load.
The SAAMI 28g max. is 12,500 psi and most 28g target loads have a 1" chamber pressure of about 11,000 psi as you said, and the powders are rapid burning.
This is a pressure-distance curve from the old Alliant site; for 1 1/8 oz 3 Dram 12g load



It appears that the 4" pressures are about 1/2 of the peak pressure.

Really nothing to add other than I chamber sleeved a 24bore to 28. Worked out great with and shoots great.

Added weight is almost nothing, a couple ounces per chamber or less and perfectly place between your hands. I did this with a Fox 16 to 20 project. The chambers on the 16 were bad, real bad. Stored in a closet for 40 years with two paper shells in it. The shells looked like a corncob. I knew sleeving them would restore them to function, but decided to go down a gauge to make a long barreled, tight choked 20 gauge, for late season Dove. Plus I liked the idea of a over bored 20 which is what I ended up with. If you look at the bore differences you just end up with a 16 which shoots 2 3/4" shells perfectly. A lot like the chamberless guns. The chamber size was the bore size. As I recall the chamber size for the 16 is .732. With plastic wads sealing will be easy. a 16 bore is .662-.670, the 12 should be about .729. The plastic wad should seal difference. Pressures matter and there are tons of low pressure 16 gauge load information. Pressures with the chamber sleeve should be fine, it is the barrels I want to keep within reason. Sounds like a fun project.

Rough math is about .9 oz for steel inserts per chamber