I looked at the web site for x-tream.
They indicate 1500fps as a max velosity.
These are from Freedom Arms for their guns only: bullet, powder, start load, fps, pressure, max load, velosity, pressure.
FREEDOM ARMS
FA300JFP H4227 27.0 1494 41,400 30.0 1634 53,700
FA300JFP H110. 28.5 1589 44,400 31.5 1780 55,000
+FA300JFP H110 31.0 1625
FA300JFP HS7 16.0 1111 33,400 22.0 1501 50,200
FA300JFP HS6 15.0 1084 31,100 19.0 1450 46,200
FA300JFP HP38. 8.5 820 32,000 11.5 1076 43,200
FA300JFP W296 28.0 1537 41,000 31.0 1750 54,800
FA300JFP W571 16.0 1107 33,000 22.0 1494 50,700
FA300JFP W540 15.0 1100 32,600 19.0 1440 46,000
FA300JFP W231 8.5 824 31,800 11.5 1062 42,400
FA300JFP 2400. 24.0 1461 42,000 27.0 1656 55,000
FA300JFP BLUE DOT 16.0 1240 39,100 19.0 1534 54,000
FA300JFP UNIQUE 10.0 1049 30,600 14.0 1275 38,600
FA300JFP BULLSEYE 6.5 804 20,100 9.5 1026 33,400
FA300JFP A.A. NO. 9 20.0 1177 17,100 +27.5 1625 51,900
FA300JFP A.A. 1680 31.1 1346 27,300 34.5 1622 54,500
FA300JFP N110 24.0 1505 34,500 26.6 1634 49,380
FA300JFP N120 27.0 1290 29,300 31.0 1491 43,760
+ Factory Equivalent loads. Testing done in 7 1/2" Revolver & 7 1/2"
Given the barrel length and cylinder chamber, I would lean towards the 16 grain Blue Dot load in your gun.
They indicate 1500fps as a max velosity.
These are from Freedom Arms for their guns only: bullet, powder, start load, fps, pressure, max load, velosity, pressure.
FREEDOM ARMS
FA300JFP H4227 27.0 1494 41,400 30.0 1634 53,700
FA300JFP H110. 28.5 1589 44,400 31.5 1780 55,000
+FA300JFP H110 31.0 1625
FA300JFP HS7 16.0 1111 33,400 22.0 1501 50,200
FA300JFP HS6 15.0 1084 31,100 19.0 1450 46,200
FA300JFP HP38. 8.5 820 32,000 11.5 1076 43,200
FA300JFP W296 28.0 1537 41,000 31.0 1750 54,800
FA300JFP W571 16.0 1107 33,000 22.0 1494 50,700
FA300JFP W540 15.0 1100 32,600 19.0 1440 46,000
FA300JFP W231 8.5 824 31,800 11.5 1062 42,400
FA300JFP 2400. 24.0 1461 42,000 27.0 1656 55,000
FA300JFP BLUE DOT 16.0 1240 39,100 19.0 1534 54,000
FA300JFP UNIQUE 10.0 1049 30,600 14.0 1275 38,600
FA300JFP BULLSEYE 6.5 804 20,100 9.5 1026 33,400
FA300JFP A.A. NO. 9 20.0 1177 17,100 +27.5 1625 51,900
FA300JFP A.A. 1680 31.1 1346 27,300 34.5 1622 54,500
FA300JFP N110 24.0 1505 34,500 26.6 1634 49,380
FA300JFP N120 27.0 1290 29,300 31.0 1491 43,760
+ Factory Equivalent loads. Testing done in 7 1/2" Revolver & 7 1/2"
Given the barrel length and cylinder chamber, I would lean towards the 16 grain Blue Dot load in your gun.