Rifle with straight pull bolt action

A modular rifle system comprising:

• a receiver;
• a first barrel assembly removably secured to the receiver, the first barrel assembly configured for a first ammunition caliber;
• a bolt assembly comprising:
• a bolt body with an open front end;
• a first bolt head removably secured to the bolt body, the first bolt head configured for the first ammunition caliber and having a plurality of extendable roller balls spaced around a circumference of the first bolt head for locking the first bolt head to the first barrel assembly;
• and
• a latch on the bolt body configured to secure the first bolt head to the bolt body,
• wherein the first barrel assembly is replaceable with a second barrel assembly configured for a second ammunition caliber different from the first ammunition caliber, and
• wherein the first bolt head is replaceable with a second bolt head configured for the second ammunition caliber.

A straight pull bolt action rifle comprising:

• a receiver;
• a barrel assembly extending from the receiver;
• a bolt assembly comprising:
• a bolt body;
• a bolt head at a forward end of the bolt body;
• a bolt handle rotatable about an axis transverse to a longitudinal axis of the straight pull bolt action rifle between a forward rotational position and a rearward rotational position;
• a bolt operation mechanism configured to lock the bolt handle in the forward rotational position when the bolt assembly is in an in-battery position;
• and
• a thumb-actuated release member positioned at a rearward side of the bolt operation mechanism, the thumb-actuated release member configured to unlock the bolt handle from the forward rotational position,
• wherein the thumb-actuated release member is positioned such that a user can depress the thumb-actuated release member with a thumb while fingers grasp the bolt handle, and
• wherein the bolt operation mechanism comprises a linkage system configured to gradually push the bolt assembly away from the receiver upon rotation of the bolt handle from the forward rotational position toward the rearward rotational position.