Submitted By: John Picher
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The 504 was shooting pretty well out of the box, but had too many flyers and strung groups for my liking. I grabbed the Moto-tool, the drill, and the Brownell's Acraglas kit and had at it.
Behind the rear stud, a piece of 1/8" plated stove bolt was inletted into the stock, laying across to keep the stock from spreading under stress.
The front screw hole was drilled out to 5/8" to take a pillar made from a piece of an old Rem 581 barrel. The front pillar was cut and placed tight to the lower screw boss and just a couple thousandths short of touching the receiver, to allow for a skim of Acraglas to mate with the receiver.
Due to the thin wood between the rear stud and trigger guard, a 3/8" bolt was modified to serve as a pillar. The head of the bolt was sliced about half way to create a flange, then chucked into a drill and spun against a file to cut off the corners. It was drilled through the middle, with a bit just one size larger than the rear screw and cut off 3/8" long, so there would be adequate clearance between it and the receiver stud.
Blue modeling clay was used to keep bedding material out of key parts. The clay was also used to keep bedding material from going under the rear stud. I didn't want the action to rock on the stud, but be cradled by the Acraglas in the rear.
A piece of the bolt end was cut to create a tap, then screwed into the stock to form threads in the wood that would hold the flange tight in the stock while assembling the rifle during bedding. The flange was recessed into the stock so the trigger guard rested against it.
The picture below was taken as a "Before Acraglassing" shot. Note the routing on most surfaces and the small original height "pads" at the beginning of the barrel channel and the bridge ahead of the rear scores that were left to hold the action in position while the bedding material set up. The blue modeling clay is quite evident , but there should have been more around the magazine well.
Masking tape hadn't yet been placed around the trigger assembly when the picture was taken. The trigger group and magazine well should probably been removed to make the bedding job easier, but I was working around the Super Bowl broadcast and wanted to get everything done quickly.
Acraglas was mixed with glass powder and some chopped-up fiberglass insulation to keep it from running so much and to increase its strength. It was also colored to match the stock using the dye supplied with the kit. I like Acraglas because it actually soaks into wood a bit, providing a great bond while increasing the wood's strength. After fitting, pillars and the cross-bolt were removed and coated with Acraglas, then re-inserted.
The Acraglas, before inserting the barreled action. Actually a little more was added over the cross bolt before the action was installed. Before inserting the screws, Qtips were used to remove bedding from the pillar holes and receiver threads.
The bedding came out very well, mating the steel to wood perfectly and expanding the contact surfaces dramatically, but the proof is in the shooting. Some of the modeling clay had been removed at this point, but more was cleaned out later. Testing the cured Acraglas with a sharp point, it was found to be about the strongest mix I've ever done.
I placed a work light with a small spotlight over the action to help the epoxy set up a bit quicker. The Acraglas was mixed and placed during the Super Bowl half time (plus two touchdowns - video taped).
The action came out a little hard, since I didn't put enough clay around the magazine well. Good thing I decided that it had set up enough after two and a half hours . If I'd waited any longer, it would have been really bad! After the bedding was done, I opened the barrel channel and free-floated the barrel.
I shot the rifle from the bench at 50 yards under pretty good conditions. Temp was about 45* and wind was under 4 mph and variable. Mirage was pretty bad, though, causing some groups to open up. Average of 10 5-shot groups, using several types of ammo, was .368". The smallest groups were 0.154" and 0.162". The average group size for five groups of Lapua ammo was 0.252", exceeding my goal of .300" average.
I may make a pressure pad out of Acraglas, then rout out the bottom and top to create dual pads, centered at 4:00 and 8:00, but the rifle is shooting very well right now.