newbie has a chamber question

[Bruce Day]

There are dozens of posts here answering your questions.

Parker answered it directly:
1 1/8 oz 3 dram is the standard load
1 1/8 oz. 3 1/4 dram heavy load
1 oz. 2 3/4 suitable for most upland birds.

Your gun was patterned with the first load for best pattern

Moving from 2 1/2 to 2 3/4 " expanded length shells results in an average of 5 percent pressure increase.

Your gun was made to use shells of about 10,000 psi maximum service loads, or 80 percent of proof loads.