“Bolt thrust”的意思、由来-开放百科全书

词条

Bolt thrust

释义

Calculating bolt thrust
Formula Friction effects
Practical method to estimate bolt thrust
Bolt thrust estimations for various pistol/revolver cartridges Bolt thrust estimations for various rifle cartridges
References
External links

Bolt thrust or breech pressure is a term used in internal ballistics and firearms (whether small arms or artillery) that describes the amount of rearward force exerted by the propellant gases on the bolt or breech of a firearm action or breech when a projectile is fired. The applied force has both magnitude and direction, making it a vector quantity.

Bolt thrust is an important factor in weapons design. The greater the bolt thrust, the stronger the locking mechanism has to be to withstand it. Assuming equal engineering solutions and material adding strength to a locking mechanism causes an increase in weight and size of locking mechanism components.

Bolt thrust is not a measure to determine the amount of recoil/free recoil.

Calculating bolt thrust

With a basic calculation the bolt thrust produced by a particular firearms cartridge can be calculated fairly accurately.

Formula

^[1]

where:

F_bolt = the amount of bolt thrust
P_max = the maximum (peak) chamber pressure of the firearms cartridge
A_internal = the inside area (of the cartridge case head) that the propellant deflagration gas pressure acts against

Cartridge case heads and chambers are generally circular. The area enclosed by a circle is:

where:

π ≈ 3.1416
r = the radius of the circle

Equivalently, denoting the diameter of the circle by d.

A practical problem regarding this method is that the internal case head diameter of a particular production lot of cartridge cases (different brands and lots normally differ dimensionally) can not be easily measured without damaging them.

Friction effects

A complicating matter regarding bolt thrust is that a cartridge case expands and deforms under high pressure and starts to "stick" to the chamber. This "friction-effect" can be accounted for with finite elements calculations on a computer, but it is a lot of specialized work and generally not worth the trouble.^[2]

By oiling proof rounds during NATO EPVAT testing procedures, NATO test centers intentionally lower case friction to promote high bolt thrust levels.

Practical method to estimate bolt thrust

Instead of using the internal case head diameter, the external case head base diameter can also be measured with a caliper or micrometer or taken from the appropriate C.I.P. or SAAMI cartridge or chamber data tables and used for bolt thrust estimation calculations.

The basic calculation method is almost the same, but now the larger outside area of the cartridge case head is used instead of the smaller inside area.

where:

F_bolt = the amount of bolt thrust
P_max = the maximum (peak) chamber pressure of the firearms cartridge
A_external = the outside area of the cartridge case head

This method is fine for getting a good estimate regarding bolt thrust and assumes an overly large area that the gas pressure acts against yielding pessimistic estimations, generating a safety margin in the process for worse case scenarios which can result in increased maximum (peak) chamber pressure of the firearms cartridge, like a round that is chambered in an already very warm chamber that can result in cooking off (i.e. a thermally induced unintended firing).

Bolt thrust estimations for various pistol/revolver cartridges

Chambering	P1 diameter (mm)	A_external (cm²)	P_max (bar)	F_bolt (kgf)	F_bolt
.22 Long Rifle	5.74	0.2587	1,650	427	4268\|N\|lb-f\|abbr=on}}
9×19 mm Parabellum	9.93	0.7744	2,350	1,820	17847\|N\|lb-f\|lk=on\|abbr=on}}
.357 SIG	10.77	0.9110	3,050	2,779	27248\|N\|lb-f\|abbr=on}}
.380 ACP	9.70	0.7390	1,500	1,130	11085\|N\|lb-f\|abbr=on}}
.40 S&W	10.77	0.9110	2,250	2,050	20101\|N\|lb-f\|abbr=on}}
10 mm Auto	10.81	0.9178	2,300	2,111	20701\|N\|lb-f\|abbr=on}}
.45 ACP	12.09	1.1671	1,300	1,517	14879\|N\|lb-f\|abbr=on}}
.454 Casull	12.13	1.1556	3,900	4,507	44197\|N\|lb-f\|abbr=on}}
.500 S&W Magnum	13.46	1.4229	4,270	6,076	59584\|N\|lb-f\|abbr=on}}

The P1 (cartridge case base) diameters and P_max used in the calculations were taken from the appropriate C.I.P. data sheets.

Bolt thrust estimations for various rifle cartridges

Chambering	P1 diameter (mm)	A_external (cm²)	P_max (bar)	F_bolt (kgf)	F_bolt
5.45×39mm	10.00	0.7854	3,800	2,985	29268\|N\|lb-f\|lk=on\|abbr=on}}
.223 Remington	9.58	0.7208	4,300	3,099	30396\|N\|lb-f\|abbr=on}}
7.62×39mm	11.35	1.0118	3,550	3,592	35223\|N\|lb-f\|abbr=on}}
.303 British	11.68	1.0715	3,650	3,911	38352\|N\|lb-f\|abbr=on}}
7.92×57mm Mauser	11.97	1.1197	3,900	4,367	42824\|N\|lb-f\|abbr=on}}
7.65×53mm Mauser / 7×57mm	12.01	1.1329	3,900	4,418	43327\|N\|lb-f\|abbr=on}}
6.5×55mm	12.20	1.1690	3,800	4,442	43563\|N\|lb-f\|abbr=on}}
.30-06 Springfield / .308 Winchester	11.96	1.1234	4,150	4,662	45722\|N\|lb-f\|abbr=on}}
7.62×54mmR	12.37	1.2018	3,900	4,687	45964\|N\|lb-f\|abbr=on}}
8mm Lebel	13.77	1.4892	3,200	4,765	46734\|N\|lb-f\|abbr=on}}
7.5×55mm Swiss GP 11	12.64	1.2548	3,800	4,768	46761\|N\|lb-f\|abbr=on}}
.375 Holland & Holland Magnum / .300 Winchester Magnum	13.03	1.3335	4,300	5,734	56230\|N\|lb-f\|abbr=on}}
.300 Winchester Short Magnum	14.12	1.5659	4,400	6,890	67567\|N\|lb-f\|abbr=on}}
.300 Remington Ultra Magnum	13.97	1.5328	4,400	6,744	66139\|N\|lb-f\|abbr=on}}
.338 Lapua Magnum	14.91	1.7460	4,200	7,333	71914\|N\|lb-f\|abbr=on}}
.300 Lapua Magnum	14.91	1.7460	4,400	7,807	76556\|N\|lb-f\|abbr=on}}
.50 BMG	20.42	3.2749	3,700	12,117	118829\|N\|lb-f\|abbr=on}}
14.5×114mm	26.95	5.7044	3,600	20,536	201387\|N\|lb-f\|abbr=on}}

The P1 (cartridge case base) diameters and P_max used in the calculations were taken from the appropriate C.I.P. data sheets.

References

1. ^A Look at Bolt Lug Strength By Dan Lilja {{webarchive |url=https://web.archive.org/web/20100303024616/http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm |date=March 3, 2010 }}
2. ^Stolle Panda Bolt Stress and Deflection Analysis

External links

[https://web.archive.org/web/20130505030534/http://lutz-moeller-jagd.de/Waffen/Blaser/R93/Blaser-R93.html Blaser R93 Unfälle - zur Verschlußbelastung {{de icon}}]
[https://web.archive.org/web/20130603114006/http://lutz-moeller-jagd.de/Waffen/Technik/Zylinderverschluss/Zylinderverschluesse.htm Zylinderverschluß - Verschlußkräfte {{de icon}}]

4 : Firearms|Firearm actions|Firearm terminology|Ammunition

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