How to Calculate Bolt Thrust

Bolt thrust is the force exerted on the lug in a rifle.

Responsible gun owners know the importance of the proper use and handling of locking lugs. According to Lilja Precision Rifle Barrels (LPRB), the strength of the bolt lugs is extremely important; their strength depends on several factors, including the number of lugs on the bolt, the axial length of the lugs and the width of the lug. Bolt lug thrust is the amount of force exerted on the bolt that the locking system must accommodate.

Instructions

1. Review the components. Bolt thrust is comprised of peak pressure and case head area.

2. Identify the formula. According to LPRB, bolt thrust is defined as peak chamber pressure measured in PSI times the area in the case head, where area is defined as 3.1416 times the inside diameter of the case head squared.

3. Calculate bolt thrust. Given a Remington 223 with a PSI of 65,000 and an area of 0.070787 square inches, compute bolt thrust as 0.070787 x 65,000 = 4601 PSI.

References

• Lilja Precision Rifle Barrels; A Look at Bolt Lug Strength; Dan Lilja; 2011