My 2x Great Grandfather, George Bell was born in East Farleigh, Kent, England in 1817.
In 1837 he and his brother, James emigrated to Australia as sailors on a convict ship.
George Bell married Sarah Sargent at Sutton Forest, New South Wales in 1844.
This couple settled in Picton, New South Wales and had a family.
Their eldest son, George was born at Picton in 1845.
James Bell, the second son was born in Picton in 1847.
I checked for references in the online index for the Registrar of Births, Deaths and Marriages in Sydney at https://bdm.nsw.gov.au/ and found the following.
BELL JAMES 517/1847 V1847517 49 son of GEORGE and SARAH
Using these reference I was able to search for entries in the Archives Authority of New South Wales (now State Records) Genealogical Kit (1988) for baptisms 1788-1855. The early colonial baptism, marriage, and burial records of some 164 volumes cover the time before civil registration in New South Wales. This includes Victoria and Queensland which was part of New South Wales at that time. These are held as Government records by the Registrar of Births Deaths and Marriages for New South Wales in Sydney.
Many of these records were microfilmed and released to the public in the Archives Authority of New South Wales Genealogical Kit in 1988. Of the 164 volumes copied, only 123 volumes were released in the kit covering the time frame 1788-1855. Volumes 124-164 were not included in the kit.
This was because some of the records contained in the volumes were after 1855 so fell outside the parameters of the historical project and were subject to state privacy laws. Other volumes were not included because they were so fragile and the handling of those volumes would have destroyed them.
Returning to our Bell research I found Volume 49 in the above-mentioned records, and I was able to view a microfilm copy of the original record on AO Reel 5018.
Although you can view these records at your library you cannot make a printout as it is a condition of use of these records and is stated at the beginning of each film. The copyright belongs to the Registrar of Births Deaths and Marriages. I was able to make a transcription and add appropriate notes.
As the Presbyterian Church in Picton was not built until after this date , the baptism most likely took place at a service in the old courthouse with the Rev Hugh Robert Gilchrist on Saturday 28 November 1847
The history of the [Picton ]district might be said to have begun with the settlement of the Antills at “Jarvisfield” in 1820, and the land must have been taken up rapidly, for very soon there was a strong Presbyterian group in the area, including such families as the Harpers, Inglises, McDonalds, McAlisters, McLeans, Dunns, Mclntyres, and Grahams. To minister to their spiritual needs, in 1838, the Rev. H. R. Gilchrist began to ride over from Campbelltown to preach in the barn at “Abbotsford.” Later services were held in the old Court House, which stood at the corner at the top of the hill where the Hume Highway from Sydney enters Picton. 
I also have a certified copy purchased from the Registrar of Births, Deaths and Marriages in 1983. The reference is identical and the information is the same including the birth and baptism dates so I believe the this is the same document at the Registrar’s office.
I also checked in the newspapers to see if there was a birth notice or report, but found none.
James Bell’s birth entry in the Bell family bible is also the same date, so after adding all these references to my Birth Data sheet for James Bell I am confident he was born at Picton on 18 September 1847.
My share document for this baptism can be found under the Resources and Examples Tab on this website under-
BELL, James, 1847, Picton, Baptism Transcription
 The Picton Post (NSW), 31 March 1937.