Sigarms Sig SG 550 SP, SG 551 SP Instructions Manual
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![Page 48
5.1.2. Discharging the shot
By pressing the trigger [11] the hammer [7] is released. The hammer
is under pressure from the main spring [12] and strikes the firing pin
[10] which, in turn, impacts against the cartridge primer of the
cartridge [P] thus discharging the shot.
Discharging the shot
48](http://img.usermanuals.tech/thumb/5850/93802/w64_sig_550_551_d-47.png "Page 48
5.1.2. Discharging the shot
By pressing the trigger [11] the hammer [7] is released. The hammer
is under pressure from the main spring [12] and strikes the firing pin
[10] which, in turn, impacts against the cartridge primer of the
cartridge [P] thus discharging the shot.
Discharging the shot
48")
![Page 49
5.1.3. Unlocking and recoil of bolt
The gas pressure, generated by the burning powder, drives the bullet
up the barrel [13]. As soon as the projectile passes the gas port [15], \
the propellant gas flows through the adjustable gas valve [14]. The gas
pressure acts on the gas piston [1] which pushes the bolt carrier to the
rear.
Bolt carrier recoil begins
49](http://img.usermanuals.tech/thumb/5850/93802/w64_sig_550_551_d-48.png "Page 49
5.1.3. Unlocking and recoil of bolt
The gas pressure, generated by the burning powder, drives the bullet
up the barrel [13]. As soon as the projectile passes the gas port [15], \
the propellant gas flows through the adjustable gas valve [14]. The gas
pressure acts on the gas piston [1] which pushes the bolt carrier to the
rear.
Bolt carrier recoil begins
49")
![Page 50
During the rearward motion of the bolt carrier [4] the bolt head [5] is
rotated by the control cam [3] so that the locking lugs [8] are
disengaged. The bolt is now unlocked.
Unlocking begins
50](http://img.usermanuals.tech/thumb/5850/93802/w64_sig_550_551_d-49.png "Page 50
During the rearward motion of the bolt carrier [4] the bolt head [5] is
rotated by the control cam [3] so that the locking lugs [8] are
disengaged. The bolt is now unlocked.
Unlocking begins
50")
![Page 51
The bolt assembly moves back along the rails in the receiver [16] as
far as the stop [17] whereby:](http://img.usermanuals.tech/thumb/5850/93802/w64_sig_550_551_d-50.png "Page 51
The bolt assembly moves back along the rails in the receiver [16] as
far as the stop [17] whereby:")
![Page 52
5.1.4. Bolt advance
The force of the compressed recoil spring [2] thrusts the bolt forward.
The bolt head [5] feeds the next round from the magazine [20] into
the chamber.
Bolt advance
52](http://img.usermanuals.tech/thumb/5850/93802/w64_sig_550_551_d-51.png "Page 52
5.1.4. Bolt advance
The force of the compressed recoil spring [2] thrusts the bolt forward.
The bolt head [5] feeds the next round from the magazine [20] into
the chamber.
Bolt advance
52")
![Page 53
In the final stage of the advance, the bolt head [5] locks up and the
release bar [6] is depressed. The weapon is ready to be fired.
Locking
53](http://img.usermanuals.tech/thumb/5850/93802/w64_sig_550_551_d-52.png "Page 53
In the final stage of the advance, the bolt head [5] locks up and the
release bar [6] is depressed. The weapon is ready to be fired.
Locking
53")
The bolt assembly moves back along the rails in the receiver [16] as far as the stop [17] whereby:
5.1.4. Bolt advance The force of the compressed recoil spring [2] thrusts the bolt forward. The bolt head [5] feeds the next round from the magazine [20] into the chamber. Bolt advance 52
In the final stage of the advance, the bolt head [5] locks up and the release bar [6] is depressed. The weapon is ready to be fired. Locking 53
6. Appendix 6.1. list of parts 100 receiver 111. Receiver casing 141. Bolt cover 142. Rivet 151. Rear sight drum 152. Drum spring 153. Drum stud 154. Luminous ampoule* 155. Insert 156. Rubber disc 161. Pivot 162. Drum axle 163. Spring washer 164. Safety washer 165. Leaf spring 171. Windage correction screw 172. Click stud 173. Rear sight spring 174. Limitation spring 175. Spring pin 181. Elevation correction screw 200 Barrel / gas system 211. Barrel* 212. Front sight mount* 213. Roll pin 214. Spring ring** 221. Bayonet lug** 222. Spring pin 223. Stop pin 224. Compression spring 225. Spring pin 231. Front sight 232. Night front sight 233. Positioning bolt 234. Night front sight spring 235. Spring pin 236. Front sight screw 237. Front sight disc 238. Spring pin 241. Gas valve 251. Gas tube 261. Gas piston 262. Recoil spring 263. Spring pin 264. Spring pin 265. Spacer 268. Support washer 300 Handguard 311. Upper handguard 321. Lower handguard 330. Bipod complete** 331. Leg left** 332. Leg right** 333. Bipod carrier** 334. Stud** 335. Circlip** 336. Click stud** 337. Bipod spring** 400 Bolt 411. Bolt head 412. Firing pin 413. Firing pin stud 414. Firing pin spring 415. Extractor 416. Extractor spring 417. Pin 421. Bolt carrier 422. Bolt handle catch 423. Axel of bolt handle catch 424. Spring of bolt handle catch 425. Bolt handle * Can not be ordered as individual parts **Not on SG 551 54
500 Trigger assembly 501. Trigger casing 521. Magazine catch 522. Magazine catch spring 523. Magazine catch pin 524. Bush 541. Pistol grip 542. Floorplate 543. Allen screw 544. Stop nut 545. Nameplate 551. Pressure point screw 552. Stop nut 553. Pressure point spring 554. Trigger guard 555. Trigger guard bearing 561. Hammer 562. Hammer axle 563. Main spring 564. Bolt catch 565. Bolt catch spring 566. Spring bolt 571. Safety lever 572. Safety shaft 573. Locking spring 576. Spring pin 578. Stop ring 581. Trigger 582. Trigger spring 583. Trigger rod 584. Pivot trigger 585. Trigger bush 586. Trigger rod spring 591. Trigger casing stud 592. Spring –pressure pin 593. Spring for trigger casing stud 594. Spring pin 595. Pin 596. Cup spring 600 Butt 611. Buttstock 612. Butt catch 613. Butt catch spring 614. Clip 615. Spring pin 616. Butt 700 Magazine 711. Magazine casing 712. Magazine floorplate 713. Floorplate catch 714. Feeder 715. Magazine spring 6.2. Exploded drawing Information to be supplied when ordering spare parts: