Tuning the Remington Model 700 Firing-Pin Assembly

A typical example of the kind of challenges that face the gunsmith is the reworking of the firing-pin assembly found on the Remington Model 700-Series rifle bolts. In this particular case, the reason I was asked to look at the rifle was a sluggish bolt assembly. The cause of the "warped" spring was the considerable difference in diameter between the firing-pin shaft and the inner diameter of the main thrust spring.

The Right top: A Remington Model 700/ 40X firing-pin assembly is shown here in the spring compressor detailed in the March 08 article. The warp in the spring leads to a bind within the bolt, producing a sluggish and inconsistent lock time. Right bottom: The factory firing pin at the bottom of the photo shows the taper, which has been removed on the upper firing-pin shaft.

The upper assembly also shows the sleeves used as a corrective measure to keep the spring straight. differences in diameter result in a warped spring, which in turn produces drag. This drag can be considerable and tends to vary from one gun to the next. In some cases, lock time is more noticeably affected than in others. Fortunately, there is a simple measure that can be taken to remedy this problem, and the necessary parts in the corrective process can be made in the shop at minimal cost.

If you’re familiar with the Remington Model 700-Series, then you know that the shaft used for the firing-pin assembly is made with different diameters and configurations. Some are of the full inner-spring diameter, while others have a diameter well under the inner diameter of the spring. Some are fluted with four grooves, while others lack this feature. Some are tapered, while others are not. And the weight of these shafts can vary considerably.

The smaller-diameter firing-pin shafts are the ones that result in warped springs, and the correction of this problem is what I’ll deal within this article. From the many bolts I’ve examined, these tapered, smaller-diameter shafts appear to be the ones used by Remington most often. Disassembly of the Remington Model 700-Series firing-pin assembly is best performed with a spring

The drag or "hysteresis" of a crooked spring can dramatically affect lock time and thus the accuracy of the rifle. compressor. A spring compressor is available from Brownells or you can make your own unit, as I did. My spring compressor is detailed in my article in the March 08 issue of American Gunsmith. While the compressor makes the job easier, the firing-pin assembly can be disassembled and reassembled without special tools, if proper care is exercised.

The principle involved in my method for changing the diameter of the smaller firing-pin shaft to a larger one involves making and installing a split sleeve. The outer diameter of the sleeve is a few thousandths under the inner spring diameter. The inner sleeve diameter is determined by the smaller diameter section of the turned-down firing-pin shaft. Thus, before making the sleeve, the firing-pin shaft must be turned to a uniform size.

When the firing-pin shaft is put in the lathe for turning, chuck the shank end where the cocking piece attaches. Here, the tapered shaft is turned to the size most uniform along its axis. The metal removed will be along the taper for a length of about an inch. The entire taper need not be removed. A good, clean lathe bit cut will leave the Left top: At the top in this photo is the turned firing-pin shaft. Below it are the sleeve halves used to achieve a match-up of the inner bolt/spring diameter.

Left bottom: This before-and-after photo of the Remington Model 700-Series firingpin assembly shows the warped mainspring (top) and the altered firing-pin shaft with sleeves installed to straighten the spring (bottom).

shaft dimensionally uniform for a good inside sleeve fit. Making the split sleeve is accomplished easiest by drilling a hole in a length of metal the size of the turned down firing-pin shaft. The part is then turned to the inner diameter of the firing-pin spring and cut to length. Following this, the piece is split lengthwise into equal halves. For this, I used a fine-tooth saw and just cut by eye as straight as I could. While most any machinable metal will work for this part, I used brass.

A smooth outside surface will help to eliminate friction for a more uniform lock time. The split sleeves are then put in place as the spring slides over the major diameter of the firing-pin shaft in preparation for a trial fit and final reassembly. A light coating of a lowviscosity oil over all surfaces is recommended. Conclusions The lock time of a rifle is negatively affected by any drag or friction as the firing-pin assembly is released and the cocking piece moves over the sear connector.

This is particularly noticeable when a kinked or crooked firingpin spring causes undue drag or friction. This condition is easily checked on the Remington Model 700-Series rifles by unscrewing the shroud and testing the firing-pin assembly for friction as it is moved forth and back inside the bolt channel. Any friction will affect accuracy to at least some degree. This procedure will greatly reduce the friction drag caused by a warped spring.

The cost involved is very low and the job can be accomplished in only an hour or two. I