Bolt guidance system
Firearm comprising a projectile barrel ( 15 ), a firing chamber body ( 16 ) fixed to the barrel, a breech mechanism ( 12 ) for loading a projectile in the firing chamber and ejecting the spent cartridge from the firearm after detonation, a mobile bolt ( 1 ), and a receiver structure ( 13 ) that supports and guides the mobile bolt. The mobile bolt comprises lateral bearings projecting laterally from opposite sides of the bolt, a first pair of lateral bearings ( 4, 4 ′) positioned towards a front portion of the bolt and a second pair of the lateral bearings ( 10, 10 ′) positioned towards a rear portion of the bolt. The receiver structure comprises sidewalls ( 2, 2 ′) each have bolt bearing raceway grooves ( 3, 3 ′) slidably receiving and guiding the lateral bearings of the bolt, wherein a profile of a first portion ( 3 a ) of the bolt bearing raceway groove defines a non-constant height (H(y)) between upper and lower guide edges ( 18, 19 ) that varies as a function of the distance (y) from the firing chamber body ( 16 ), said profile comprising a velocity control portion with a slope (P) configured to impart a braking effect on the bolt during its sliding movement to slow down the rate of fire.
1. A firearm comprising a projectile barrel, a firing chamber body fixed to the barrel and comprising a firing chamber, a breech mechanism for loading a projectile with a cartridge case in the firing chamber and ejecting the cartridge case from the firearm after detonation, the breech mechanism comprising a mobile bolt, and a receiver structure that supports and guides the mobile bolt, the mobile bolt comprising, a first pair of lateral bearings positioned towards a front portion of the bolt and a second pair of lateral bearings positioned towards a rear portion of the bolt, the receiver structure comprising sidewalls each having bolt bearing raceway grooves slidably receiving and guiding the lateral bearings of the bolt, wherein a profile of a portion of the bolt bearing raceway groove defines a non-constant height (H(y)) between upper and lower guide edges that varies along a distance (y) from the firing chamber body, said profile further comprising a velocity control portion with a slope (P) configured to impart a braking effect on the bolt sliding movement to slow down the rate of fire, wherein the velocity control portion has a rearwardly facing angled slope arranged along an upper guide edge of the bolt bearing raceway groove configured to brake the forward bolt movement on a return portion of a firing cycle corresponding to loading of a new round into the firing chamber.
2. The firearm according to claim 1 , wherein the first pair of lateral bearings comprise an oblong shape with a major axis extending in a direction parallel to a first portion of the bolt bearing raceway groove extending from the firing chamber body, and a minor axis orthogonal thereto, a width L of the front lateral bearing in said direction parallel to said first portion of the bolt bearing raceway groove being greater than a height Z of the first pair of lateral bearings.
3. The firearm according to claim 2 , wherein the second pair of lateral bearings comprise a cylindrical shape having a diameter D that is greater than the height Z of the first pair of lateral bearings.
4. The firearm according to claim 2 , wherein the height (H(y)) of the bolt bearing raceway groove at a position proximate the firing chamber body, corresponds to the height Z of the first pair of lateral bearings, and towards an end of the bolt bearing raceway groove at a position remote from the firing chamber body, the height H(y) corresponds to the height of the second pair of lateral bearings of the bolt diameter D.
5. The firearm according to claim 1 , wherein the bolt bearing raceway grooves comprise a first portion parallel to a barrel axis (Y), and a second portion transverse to said barrel axis, the first and second portions connected together to form a “V” shape.
6. The firearm according to claim 5 , wherein the velocity control portion is provided in the first portion of the bolt bearing raceway groove, configured to guide and cooperate with the first pair of lateral bearings of the bolt.