Hi William, the R has no real significance. Bud’s has another item with the same number 51414, so they added the R at the end to differentiate the items. The R is from RIA.
Stay safe & have a great day!

the r is a typo checked by ups correction email sent. RIA specs show it as ca compliant see *****
SKU 51414
SERIES ROCK
CALIBER 45ACP
CAPACITY 8
BARREL 5″
OVERALL LENGTH 9.625 INCH / 244 MM
OVERALL WIDTH 1.31 INCH / 33 MM
OVERALL HEIGHT 5.5 INCH / 140 MM
WEIGHT 2.5 LBS / 1.13 KG
FRONT SIGHT MOUNTED DOVETAIL CUT
REAR SIGHT MOUNTED DOVETAIL CUT
GRIPS WOOD
FINISH MATTE STAINLESS
ACTION SEMI-AUTOMATIC
TRIGGER PULL 4 – 6 LBS
PURPOSE PERSONAL PROTECTION, RECREATIONAL SHOOTING
****CALIFORNIA COMPLIANT YES
https://armscor-rockislandguns.com/efs-stainless-steel-1911-fs8rd-45acp-8rd/

Hi William and welcome. This looks to be a Buds error as this is the correct UPC and Model: 51414 that is CA compliant as listed on other vendor websites. Cheers, stay safe and enjoy!