During headspace adjustment on the M2HB the gauge is placed where?

• A. Bolt lug
• B. T-slot
• C. Receiver milled groove
• D. Gas block

Answer: (B)

Headspace is the distance from the bolt face to the fixed datum surface in the receiver when the bolt is locked. For the M2HB, you place the headspace gauge in the T-slot of the receiver because this slot provides a stationary reference surface that aligns with the locking mechanism, giving an accurate measurement of headspace. Placing the gauge in the bolt lug, the gas block, or any receiver groove wouldn’t give a correct reading because those areas don’t serve as the proper reference for headspace and can be affected by moving parts or the gas system. So the T-slot is the correct place to check and adjust headspace.