The Accurized Action: What Makes A Long Range Rifle Great
Every APS rifle shipped out is built on an accurized action. The vast majority being the Remington 700 actions for several reasons. The Rem 700 is very desirable because it is extremely strong, it is one of the best designed factory actions (receiver), and has the fastest lock time of any factory action. One of the best receivers for consistent, accurate bedding to the stock.
As a properly accurized action, the Remington 700 action will stand with any match grade action offered today as long as it is used within its design limits.
This is a typical factory Remington 700 Magnum receiver showing the threads and locking lug recesses. This action is in pretty nice shape but will really shine after a total accurized action job is performed. This article explains the accurizing process for a conventional receiver and doesn't include reaming the receiver bolt raceway or fitting bolt sleeves to tighten up bolt to receiver clearances. Please contact Mr. Kirby Allen of Allen Precision Shooting at kballen@3rivers.net for full details of its benefits to accuracy. All modern receivers are accurized in the same manor. The Rem 700 is covered in this example but all are very similar in procedure. First, the receiver is fitted into an accurizing fixture. This fixture is an aluminum cylinder with two sets of four bolts. One set spaced around the front of the cylinder and four around the rear. The receiver is held, suspended in the cylinder by the bolts. The receiver is then dialed in to be turning perfectly true to the axis of the receiver bolt race way.
This picture shows the receiver in the fixture ready for dialing in. The receiver is fitted with cylindrical bushings that fit in the bolt way. One in the rear and one in the front of the receiver. These bushings vary by 0.0005 so the correct bushing must be chosen to for a tight fit in the receiver. Once a bushing is fitted to the rear and front of the receiver, a precision ground mandrel is slipped into these bushings. The mandrel is held in place by the two bushings and extends 6 in front of the receiver in perfect alignment with the axis of the receivers bolt way. This is critical as we are only interested in the internal alignment of the receiver as the external dimensions are always off axis to the bolt way axis. To get a truly accurized action, all internal dimensions must be square and true to produce the result desired, extreme consistency.
The mandrel, fitted correctly is perfectly on center with the axis of the bolt way. To dial the receiver in, two 0.001 dial indicators are positioned, one at the receiver face at 12:00 and the other positioned 6 out on the mandrel again at 12:00. The lathe chuck is then turned by hand and the run out in the dial indicators is observed. The front four bolts are used to dial in the indicator at the receiver face and the rear four bolts are used to adjust the indicator 6 out on the mandrel. When the front indicator is dialed into less then 0.001 run out, the back four are then adjusted until that indicator is reading less then 0.001 run out. Which in turn will have induced run out into the front indicator. The process is repeated again and again until both indicators are reading less then 0.001 run out which generally takes 15 minutes to accomplish.
With the receiver perfectly zeroed, the mandrel is removed and the lathe is set up to single point cut the threads so that they are in perfect alignment with the axis of the bolt way which they are never even close to. Generally the threads are opened up by around 0.010 to completely clean up the old threads to produce a perfectly trued and fresh cut thread. Sometimes the treads may need to be enlarged by as much as 0.025 in diameter to clean up the old threads.
Pictured above are the same threads after they have been single point cut in the accurized action fixture. The quality is clearly seen. Once the threads are trued, it is time to clean up the bolt lug locking recesses. This is done by inserting the proper length boring tool and taking very light cuts off the locking lug recesses until they are totally cleaned up.
Here is the freshly cut recess surface which is perfectly square to the axis of the receiver. The next step is to clean up the receiver face. This is accomplished by facing off the receiver by taking 0.001 cuts until the receiver face is clean and square. The least amount of material removed is best, we only want to clean up the surface for a perfect non stressed barrel shoulder bearing.
This is the receiver face after it has been cleaned up and trued. The inside edge of the receiver has been bevel cut and polished to aid in threading the receiver. The accurized action process is complete, and it is time to true up the bolt dimensions.
This is the factory original Remington 700 magnum bolt. Truing critical dimensions of the bolt are very important to produce a rifle that will shoot very tight and consistent groups. The first step is to strip the bolt totally removing striker assembly and plunger ejector. Then a precision ground threaded arbor is threaded into the rear bolt threads. This stub/bolt are then chucked up in a 4 jaw chuck in the lathe. The live center on the tail stock is then positioned in the firing pin hole so that the bolt will now turn perfectly on center to the axis of the bolt when the bolt body is dialed in properly. A special very light weight live center is used for this procedure so that it turns with very little force so that it will support the bolt for the cutting operations but not bevel out the firing pin hole while doing so. This is the only use for this ultra light live center in my shop. With the bolt zeroed, the rear locking lugs surfaces are then recut perfectly square to the axis of the bolt. Next, the front surfaces of the locking lugs are trued up allowing a tight consistent fit between the forward surface of the bolt lugs and the barrel which will be fitted for only 0.005 clearance. The front face of the bolt nose is then cut square to the axis of the bolt way which in the Remington 700 will also be fitted for only 0.005 clearance in length inside the bolt nose recess in the barrel. The diameter of the bolt nose is then cut true. This will allow the barrel bolt nose recess to be cut for 0.005 total (0.0025 preside) clearance in diameter when the barrel is fitted to the receiver. With these cuts made and all edges chamfered so there are no sharp edges to hang up on during bolt cycling, a collar is then fitted to the bolt head. With this collar securely fastened to the bolt, turning cuts are made on this collar until it is perfectly concentric to the axis of the bolt. The steady rest is then used to support this collar with its three support fingers and the live center is pulled away from the bolt face.
The first picture shows the collared bolt in the steady rest and the second show the results of cleaning the bolt face up true and square to the axis of the bolt body.
The receiver has now been through the accurized action process and a final measurement is taken to ensure that all the critical dimensions and baring surfaces are square and true and ready for lapping the lugs in and sleeving the bolt if desired by the customer. The stripped bolt is inserted into the action after everything has been cleaned of any chips or oil left from the machining. With the receiver face pointed vertically, a dial indicator is used to measure the distance from the receiver face to the bolt face. Four measurements are taken, one at 12:00, 3:00, 6:00 and 9:00 on the bolt face. If there is a measurable variation over the bolt face which means anything more then 0.0001 to 0.0002 total variation across the bolt face, the process is repeated until this measurement is 0.0001 or less over the entire face of the bolt with the bolt in the receiver. This ensures all critical surfaces are perfectly in line and square with each other and the receiver is ready to have the locking lugs lapped and the barrel fitted.
The final product, a perfectly accurized action. This Remington 700 magnum receiver ready to be the building platform for a big game rifle capable of placing three rounds inside 1 at 500 yards. Truly a piece of art!
Kirby Allen of Allen Precision Shooting with 350lb Russian Boar Another route to Long Range Perfection is to build your rifle with a Fully Custom Action. Modern Custom Actions are precision made, with the Accuracy built in and ready to go, and are less time consuming to install. Most have the "Remington 700 footprint" and will "Drop-In" and can be fitted quickly into your rifle build. There is a price for every budget for custom actions ranging from $550.00 to $1700.00 for a quality, precision made custom action.
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