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Bolt Action Barrels & Blanks

MPA Spencer Barrel Manufacturing Process Summary

In June of 2013, MPA purchased Spencer Rifle Barrels. In addition to the equipment needed to produce world class barrels, Clay’s methods and practices are followed to a “T”. As those who are familiar with Clay Spencer and his world class barrels and bolt action rifles, the methods used by Clay were developed over 30+ years of painstaking effort with the goal of producing the BEST barrels possible, delivering long life and extreme accuracy. No shortcuts are ever taken. The process is slow, exacting and very specific. The results are impressive. His products are legendary in the Benchrest community, particularly in the 1000 yard IBS competitions. Clay’s barrels have set over 43 world records and won 75+ major matches and National Championships.


For our match grade barrels, the process starts with a specific grade of 416RQ series stainless steel. This grade of Stainless is the best for manufacturing rifle barrels. Each and every bar goes through Immersion Ultrasonic testing – which verifies that no surface  or internal inclusions are present. Each lot is independently tested prior to the start of the barrel manufacturing process. The best material gives us the ability to produce the highest quality barrels.


MPA Colchester AFor the gun drilling operation, we use specially modified Colchester lathes. Although these single spindle lathes may not be as productive as dual spindle gun drills such as Pratt & Whitney, Eldorado or others, these specially configured machines offer variable speed control of the spindle and the feed mechanism down to 1 RPM increments. This allows us to fine tune the cutting parameters to provide extremely straight barrel blanks with reduced tool marks from the drilling process. 1500 psi Oil Pump system provides efficient chip evacuation from the drilling process.


The reaming operation is performed immediately after the Gun Drill process. Specific size reamers are pulled through the Gun Drilled barrel blank, controlled through exacting cutting parameters with respect to feed and speed, flushed with a high pressure cutting oil system.


MPA Rifling MachineThe MPA/Spencer Rifling system has taken years to perfect. We use a pull button rifling system. The rifling button is created on CNC grinders to extremely tight tolerances with respect to twist, size and uniformity. The “Twist Guides” are created on multi-axis CNC machines and control the rate of twist to an extremely high level of rotational accuracy. There is absolutely no variation to the twist rate over the entire length of the barrel. The depth of the rifling and twist accuracy are extremely consistent. As a side note on the Rifling method….There are many different opinions on the best method to rifle a barrel. Push or pull button, cut rifling or hammer forge. The Hammer Forging process is very productive, however it’s typically not used when producing world class barrels. The arguments typically surround cut vs. button. The truth is that both methods produce very good barrels, providing the entire barrel manufacturing process is sound. They each have pros and cons but you will see both types of barrel rifling methods on rifles in the winner’s circle of competitions across the globe.

Stress Relieving

MPA Cress Stress Relief OvenThe Stress Relieving operation is performed after the rifling process. This removes any stress caused by the previous operations and ensures a stress free barrel – allowing impressive performance for the life of the barrel. The process is performed in a specially designed Cress Oven with PLC controller. The program is specific with respect to time and temperature to achieve maximum results. The process is slow, taking over 24 hours to complete.


MPA Air Gage AThe hand lapping operations are performed after the rifling process. This process removes the cutting tool marks created by the drilling and reaming operation. These tool marks are perpendicular to the direction of bullet travel and must be removed to ensure consistent performance of the barrel. The “lap” is poured to match each individual barrel and a lapping compound is mixed and applied to the lap. The lap is pushed and pulled, by hand, through the bore of the barrel until both size and surface finish tolerances are achieved. This is verified using a Sheffield air gage system, Mitutoyo Skidless Profilometer and Bore Scope. Bore size uniformity of .0001” or better is required.


MPA ChamberingMPA Chambers our barrels for both our MPA “BA” series Bolt Action Rifles as well as the barrels we sell to the general public. Using Clay’s methods, each bore is indicated on the breech end of the barrel to below .0001″ TIR prior to the chambering operation. This ensures proper concentricity  between the chamber and the tenon threads. We use only the best removable piloted carbide chamber reamers and throaters to fine tune the chamber for optimum results.  We can provide a wide variety of chambers, from 17 HMR to .338 Lapua.  Although Clay’s entire methods are slow, they do produce an outstanding chamber – fitted specifically to the application.


Please use this standard Contour Chart to specify the Contour required.

For any questions or inquiries, please contact Masterpiece Arms.

866-803-0000 or

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