Bolt handle bounce

[memilanuk]

Anyone here familiar with the cause/effect of bolt handle bounce?

Recently swapped the original bolt handle on my 10BA Stealth for the big knurled 110 BA style handle, and I'm seeing a lot of bounce while dry-firing

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[Fotheringill]

Is the handle snugged down tightly at the rear, very large hex?

[memilanuk]

Yup

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[Stumpkiller]

Does it occur if you have an empty cartridge in the chamber?

[memilanuk]

Haven't tried that yet...

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[sharpshooter]

Bouncing during dry firing probably seems annoying and concerning, but chances are it won't do that with a cartridge in the chamber. Reason being that without a cartridge case to center the bolt in the receiver, it will lock up slightly off center on an empty chamber.
When you operate the bolt by pushing the bolt handle, you are pushing from the right side of the centerline of the bolt body, essentially preloading and tilting the front of bolt to the left. With the clearance between the bolt body and receiver, plus the float in the bolt head, this will position the bolt head slightly off center. When you start the rotation of the bolt, the left locking lug will engage it's lug abutment first. At this intersection, the point of engagement will act as a pivot point, and the bolt will rotate on this axis instead of it's true axis with the bore. With in a few degrees of rotation, the right locking lug will engage on it's abutment, and because of the tension from cocking, and the ability to float, it has enough friction to hold this position throughout the full bolt rotation. At this point, the bolt head is off center from it's true axis. When fired, the tension of the main spring is released and the whole bolt is relaxed and the stress is relieved from the engagement surfaces, causing the abrupt "jump". When it jumps, it just doesn't go back to center, it goes past center to the opposite side with momentum. Changing the bolt handle to the heavier version would actually multiply the bounce because of the increased mass at the end of the handle.
When a cartridge is loaded, the case itself centers the bolt with the chamber, and also acts as a buffer. Now being centralized, both locking lugs engage at the same time and there is no off center stress.

If you have bolt handle bounce with a cartridge in the chamber, it could be from a collection of 3 things: 1. Bolt handle out of spec, causing over/under rotation. 2. Bolt body machined out of phase, causing over/under rotation. 3. Closing ramps machined out of phase, causing one side to engage before the other. I have only seen the latter on older receivers made with the old machinery, but I have seen bolt handles and bodies out of spec in current production.

[Robinhood]

Good stuff there Fred.