Shot shells pressure.. how important..

[Gary]

For a Parker or other vintage SxS from 1900-1930's with Steel barrels (not Damascus) how important are the shells we use as far as pressure is concerned.
I always stay under 1200 fps..
I have used RST 2 1/2 1125 fps and 1187 fps shells with no issues as the pressure is supposed to be around 6500, was wondering if I could use some Winchester AA Extra Light Target 1oz #8 1180 fps.. but dont know the pressure on those as Winchester doesn't share that data.
Dont want to have issues with the 2 nice Parkers (and other vintage SxS's) I have so want to make sure I am using the correct shells not to cause any damage.
Thanks.

PS moved this from Parker Hammer Gun Forum..