I had wanted a GRS model but could not find one. I ended up buying a bead site model. I liked the bead better than I thought I would but part of me still wanted the GSR. A thread where Nitesite explained to me his reasons for carrying slugs on his service shotgun (put distance between yourself and trouble) made me want the GSR more. I did not want the cost or hassle of having a gunsmith silver solder the base onto my barrel and re-coat it so I decided to make the change myself without soldering.
I started by gathering the items needed:
1) Mossberg Ghost Ring Site Conversion Kit #SKU 95300 which was about $70.
2) #5-40 Thread tap. About $6.60. The hardware stores here only carry #4 and #6 taps and screws. #5 is an oddball. I ordered it from McMaster-Carr #26955A25 http://www.mcmaster.com/#catalog/120/2531/=u62gw2
3) #5-40 x 5/8" long flat head cap screws, black oxide finish. As above I ordered them from McMaster-Carr, #91253A130. 100 for $9.25. I found packs of 10 etc. but they were $6 or so. If anyone wants to do this PM me and I'll send the screws for free. http://www.mcmaster.com/#catalog/120/3116/=u62j7p
I had hoped the base would be solid as it would have been an easier project but it is hollowed out some.
The steps to complete:
1) Insure the shotgun is safely cleared and remove the barrel.
2) Remove the bead site.
3) I put some masking tape on top of the site base and marked two centers for the mounting holes 21/32 apart and center punched the points.
4) I drilled through each with a #30 drill which is a clearance hole for #5-40 thread.
5) I put a screw into the front site base hole and threaded it into the tapped hole for the bead site.
6) I ran the drill into the rear site base hole and lightly marked the barrel with it. Keep the drill (I used a vice and bench top drill) as square as possible to the barrel centerline.
7) I removed the site from the barrel and center punched the mark I made.
8) I used a #39 drill (tap drill for a #5-40) and again, keeping the barrel square to the drill, I drilled the tap drill hole. I went slow to try and help keep the burr down when the bit hits the barrel bore.
9) I used a little tap Majic cutting oil and tapped the second #5-40 hole.
10) Next, I used the 90 degree countersink tool I have for cleaning up MIL crimped primer holes and the holes on the site base were countersunk. I went slow and kept checking the depth with one of the screws. I didn't want the countersink to open up the holes any more than necessary to get the top of the screw flush with the site base top.
11) I screwed the site base to the barrel and noted how much thread stuck into the barrel bore.
12) I drilled and tapped a hole into a piece of metal I had, threaded the screw into it until the amount I wanted to grind off stuck out the other side and then the extra thread was ground off. I did this because I didn't have a #5-40 die to clean up the threads if they were damaged while grinding.
13) I repeated step 12 as needed until the screw was as long as possible but didn't stick into the barrel bore.
14) Some blue Loctite was applied to the screws and the site base was torqued down.
15) I had trouble drifting the front site into the base dovetail. Mossberg tolerances weren't right. A little filing on the dovetail and it went in nicely.
16) The rear site was mounted on existing holes that Mossberg had drilled and tapped into the receiver.
17) The most enjoyable part was sighting it in and practicing acquiring targets. I was a little slower than the bead but slugs at 25 and 50 yards were great! If I ever want to go back I can be back to a bead site in 10 minutes...can't do that with solder.
If I can make any recommendation it would be to wait and get the gun you want. It is cheaper and easier than turning one into what you wanted.
Pictures say quickly what I rambled on above to describe so (sorry for the crappy after pic...lousy phone):
I started by gathering the items needed:
1) Mossberg Ghost Ring Site Conversion Kit #SKU 95300 which was about $70.
2) #5-40 Thread tap. About $6.60. The hardware stores here only carry #4 and #6 taps and screws. #5 is an oddball. I ordered it from McMaster-Carr #26955A25 http://www.mcmaster.com/#catalog/120/2531/=u62gw2
3) #5-40 x 5/8" long flat head cap screws, black oxide finish. As above I ordered them from McMaster-Carr, #91253A130. 100 for $9.25. I found packs of 10 etc. but they were $6 or so. If anyone wants to do this PM me and I'll send the screws for free. http://www.mcmaster.com/#catalog/120/3116/=u62j7p
I had hoped the base would be solid as it would have been an easier project but it is hollowed out some.
The steps to complete:
1) Insure the shotgun is safely cleared and remove the barrel.
2) Remove the bead site.
3) I put some masking tape on top of the site base and marked two centers for the mounting holes 21/32 apart and center punched the points.
4) I drilled through each with a #30 drill which is a clearance hole for #5-40 thread.
5) I put a screw into the front site base hole and threaded it into the tapped hole for the bead site.
6) I ran the drill into the rear site base hole and lightly marked the barrel with it. Keep the drill (I used a vice and bench top drill) as square as possible to the barrel centerline.
7) I removed the site from the barrel and center punched the mark I made.
8) I used a #39 drill (tap drill for a #5-40) and again, keeping the barrel square to the drill, I drilled the tap drill hole. I went slow to try and help keep the burr down when the bit hits the barrel bore.
9) I used a little tap Majic cutting oil and tapped the second #5-40 hole.
10) Next, I used the 90 degree countersink tool I have for cleaning up MIL crimped primer holes and the holes on the site base were countersunk. I went slow and kept checking the depth with one of the screws. I didn't want the countersink to open up the holes any more than necessary to get the top of the screw flush with the site base top.
11) I screwed the site base to the barrel and noted how much thread stuck into the barrel bore.
12) I drilled and tapped a hole into a piece of metal I had, threaded the screw into it until the amount I wanted to grind off stuck out the other side and then the extra thread was ground off. I did this because I didn't have a #5-40 die to clean up the threads if they were damaged while grinding.
13) I repeated step 12 as needed until the screw was as long as possible but didn't stick into the barrel bore.
14) Some blue Loctite was applied to the screws and the site base was torqued down.
15) I had trouble drifting the front site into the base dovetail. Mossberg tolerances weren't right. A little filing on the dovetail and it went in nicely.
16) The rear site was mounted on existing holes that Mossberg had drilled and tapped into the receiver.
17) The most enjoyable part was sighting it in and practicing acquiring targets. I was a little slower than the bead but slugs at 25 and 50 yards were great! If I ever want to go back I can be back to a bead site in 10 minutes...can't do that with solder.
If I can make any recommendation it would be to wait and get the gun you want. It is cheaper and easier than turning one into what you wanted.
Pictures say quickly what I rambled on above to describe so (sorry for the crappy after pic...lousy phone):
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