by Gunsmith Advisory Panelist
Provided to Varmints Den, Home of the Go Go Varmint Go Message Board
Michael Donaldson (aka Doc)
In order for you to achieve the best possible accuracy from your varmint rifle, it must be bedded properly! There are many types of bedding styles; block bedding, two-point bedding, pillar bedding, and then pour some epoxy into the stock, cinch the screws and call it good!!
In this "How To" article we'll deal with the pillar bedded system with a free-floated barrel. Our barreled action is a Remington 700 fitted into a McMillian fiberglass stock.
The most important aspect of bedding is that the action is STRESS free!!
My pillar system will give you this 99% of the time. I've seen bedding jobs that you have to pry out of the stock, and others that by tightening the action screws the stock flexes .030 - .050 in the forend. On a properly-bedded rifle you should be able to remove the barreled action from the stock easily. If done correctly, they should fall free from the stock with the screws removed!
With this style of pillar bedding we'll bed the recoil lug to the magazine box and the rear tang; the center of the action is free floated. This system works equally well for wood stocks.
Step 1: We will machine out the areas to be bedded in the milling machine.
These cavities will be the areas bedded. Tape the barrel at the end of
the forearm to fill the gap between barrel channel and barrel. This levels
the barreled action in the stock. Set the barreled action in the stock,
making sure it does not bind. I like .010 - .015 clearance all around to
ensure it does not bind in the stock. Next we will bore 5/8 holes in center
line of the action screws
through the stock.
Step 2: Lay the barreled action on the bench and set the stock over it. With a depth mike or dial calipers measure the depth to the receiver. Add .050 to the front pillar and subtract .050 from the rear.
Step 3: We are now ready to machine our aluminum columns. I use 7075 T-6 or 2024 T-3 for columns. It's hard and will machine very well. Shy away from 6061 as it machines poorly by comparison. Turn the rear column to .615 X the length; the front column is hat-shaped with the larger section measuring .800 and stepping down to .615 where it goes through the stock. The front column is counter-bored 82 degrees for the screw head. Its depth should be four threads in the receiver and be below the stock line. Don't worry about the rear column as it will be .050 below the trigger guard. Drill the columns with a letter "F" drill .257 for screw holes. Attach the columns to the receiver with the guard screws.
Step 4: With the columns attached set the barreled action in the stock. The columns should set into the 5/8 holes in the stock. There should be no binding; make sure you have clearance all around the receiver area. If the columns fit tightly into the stock, look for the area that binds and file or sand to free the tension. It is very important that these steps are followed because if the columns are not set in the stock correctly stress will occur.
Step 5: Clean columns with acetone and dry them. Mix up some five-minute epoxy, re-attach columns to receiver and coat areas that set into the stock with epoxy, and a light bonding coat on the 5/8 holes in the stock. Set the barreled action into the stock and hold together with one wrap of surgical tubing around the receiver. ONE WRAP ONLY! Just enough tension to hold it together. Wait ten to fifteen minutes before removing screws from columns. This will free the barreled action from the stock, leaving our columns in place. If done correctly this will give us two pillar supports for our action to rest on when we fill the cavities with our bedding compound.
Step 6: With the columns held in place by our five-minute epoxy we'll mix some Brownell's Acra Glass and pour into the cavities to within .250 of the top of the columns. Set the barreled action onto the columns and snug the screws. Let set for 24 hours. Remove barreled action from stock and look over your job. I use the Acra Glass as a filler only and use Marine Tex, Devcon, or Bisonite as our final bedding compound. The Acra Glass will be hard and slick and will need to be roughed up; a foredom tool with a carbide burr works well for this.
Step 7: We are now ready for final bedding. In order to have a neat free-floated barrel we will mask the barrel with five layers of plumber's pipe tape. This is .010 thick and 3" wide; very similar to electrical tape. Run five layers lengthwise on the barrel. Using the same tape, mask the recoil lug with one layer, the sides, bottom, and front side toward muzzle. The front receiver ring will have a strip .250 below stock line on the sides. With the masking done set the barreled action back into the stock. It should set on our columns without binding. Snug screws and check over. Make sure the barrel and action are not high-centered on the taped areas!
If all looks well remove from stock and coat metal with release agent. Two coats are fine. Use good "Mold Release." I like a product by Synair: it's water thin and works well. Don't forget to coat the screws.
Step 8: Now the moment you've all been waiting for!! Mix the bedding compound of your choice. Mix the resin and hardener EXACTLY: not close but EXACT! An Ohaus triple beam balance scale works well. With the bedding compound mixed I use a plastic syringe (available from your local feed store or drug dealer). A large nozzle works best with a tip length of 1-1 1/2". Inject the compound into the stock, filling the voids like you would decorate a cake (if in doubt ask your wife, she'd love to help!). Fill the cavities pretty full. The excess will ooze out. Next, use an ice cream stick to work the compound. Removing all air pockets, take a Q-Tip and push it through the hole in the column to remove the bedding compound. Push from the bottom up. Dip your Q-Tip in release agent and coat the inside of the column hole. This prevents the screws from sticking.
Take the barreled action and set it in the stock, taking care to keep it centered, and aligning the tang to the column hole. Lower the barrel into the compound. Start the tang screw into the action and snug it down against the column. This will allow the receiver and barrel to settle into the compound without creating air bubbles and voids by rocking and shifting to align screw holes. Use a Q-Tip to remove the excess compound from the front column hole. The compound will ooze out around the barrel, etc. Wipe the excess away. Insert the front screw and tighten snug against the front column. Take a razor blade and remove the excess along the barrel channel. Do not allow the compound to be above the center line of the barreled action as removal will be very difficult. The compound is now left to cure for five days. Yes, five days. All epoxies will require a five-day cure at 70 degrees.
After three to four hours crack loose the screws and re-tighten. This will keep the screws from freezing up.
Step 9: Well, five days have passed. It's time to remove the barreled action from the stock. Remove screws from stock and strike barrel and action smartly from the top with a plastic mallet. Turn upside down, hit barrel just ahead of forearm to pop it loose. You may have to see-saw the barrel and action out, depending upon the recoil lug. Remove the tape from the barrel, recoil lug and the sides of the receiver.
Step 10: The finished job, NO VOIDS! The column contact can be seen through the compound. The recoil lug with the tape removed has .010 clearance on the bottom, sides and front. The five layers of tape on the barrel will give us .050 of free float. Clean up the stock and magazine well. Rough up the column in the trigger guard and bed the trigger guard. After it cures, drill out the column holes to .9/32 - .302 letter "N". This will give us clearance for our screws.
Step 11: Points of interest: The screw holes need .015 -.020 clearance per side, the barrel .050 free float to front of receiver, the recoil lug .010 clearance on sides, front, and bottom. The bolt handle should have .020 clearance on all sides and bottom out on the action only, not the stock. The magazine well should have .050 - .060 clearance on all sides. The trigger and pins should not contact the stock. Assemble the gun and put into the stock. It should not bind. With the screws snug, loosen the front screw and watch the barrel and forend tip. It should not move. I use a dial indicator on a magnetic base attached to the barrel with the indicator on the stock. You should not have more than .002 movement when tightening and loosening the action screws. If you have a lot of stress in the action it will not shoot well and you'll need to locate the problem (usually a high spot or something is touching; bolt hand screws, magazine box). Or re-do the bedding process.
After doing a few bedding jobs you'll be a pro, so go slow, don't get
in a hurry, and use plenty of release agent. Make sure that the initial
column setting is stress-free and you'll never have a problem.