There is a website www.rediscovered-shooting-treasures.com/mossberg that offers copies of the original factory instruction sheet for the 810 models. This is the "manual" that came with your rifle and covers a lot of information including trigger adjustment.
Get an owner's manual from the maker. It may not be user adjustable. It might take a gun smith or factory trained armorer to do it.
try: http://stevespages.com/page7b.htm
This is the same rifle as the Mossberg 810.
Original maker is Mossberg, Model 810. hoosiergunworks.com has magazines
Recommend you let a gunsmith do it.
Type your answer here... how do I adjust the trigger on Remington 799
Best left to a qualified gunsmith
Mine has it.
I believe this rifle was made by Mossberg and is the Mossberg 46B. Do a search for photos of the 46B Mossberg to see if it is a match. If so, try Havlin Sales & Service as they may have a replacement trigger guard.
Check Mossberg Customer Service thru their website. They will need the serial number of the gun in question- model changed during production.
No. Trigger guards for these were made of plastic.
No, the Gyphon does not have an adjustable trigger