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Grenadier
.375 member

Reged: 20/02/08
Posts: 570
Loc: North of the Columbia, USA

Backthrust table - anyone have one?
#268251 - 20/07/15 10:48 AM

Does anyone know of or have a table or listing of backthrust for various cartridge candidates for rifles built on shotgun actions? It would be nice if it also included backthrusts for 20, 16, and 12 gauge shotguns.

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Carpetsahib
.333 member

Reged: 29/04/07
Posts: 435
Loc: Western NC

Re: Backthrust table - anyone have one? [Re: Grenadier]
#268268 - 21/07/15 01:05 AM

I made some calculations awhile back on a limited list of cartridges. Let me know what cartridges you are interested in, and the pressures involved. I haven't done this for the gauges you mention, but could do so if I had the internal head diameters.

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Grenadier
.375 member

Reged: 20/02/08
Posts: 570
Loc: North of the Columbia, USA

Re: Backthrust table - anyone have one? [Re: Carpetsahib]
#268274 - 21/07/15 04:43 AM

Quote:

....but could do so if I had the internal head diameters.

I also lack that information or I would try some rough calculations myself.

At the moment I am interested in:

12 gauge shotgun
7x65R
9.3x74R
.375FL NE 2-1/2"
.375FL Mag
.405 Winchester
.450/400 NE

But it would be nice for everyone if we could find a more comprehensive list.

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Carpetsahib
.333 member

Reged: 29/04/07
Posts: 435
Loc: Western NC

Re: Backthrust table - anyone have one? [Re: Grenadier]
#268282 - 21/07/15 10:01 AM

Well, I have information for 4 calibers.

The 9.3x74R should be about the same as the .30-06. The internal head area is .1164 in^2. Simply multiply this by the peak chamber pressure to obtain the back thrust.

The .405 is the same as the .30-40 Krag at .1134 in^2.

The .450/.400 is the same as the .450 NE at .1676 in^2.

The .375 H&H is .1385 in^2.

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Grenadier
.375 member

Reged: 20/02/08
Posts: 570
Loc: North of the Columbia, USA

Re: Backthrust table - anyone have one? [Re: Carpetsahib]
#268305 - 21/07/15 06:20 PM

Thank you for the help, Carpetsahib.

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eagle27
.400 member

Reged: 24/01/09
Posts: 1123
Loc: Nelson, New Zealand

Re: Backthrust table - anyone have one? [Re: Grenadier]
#268306 - 21/07/15 07:51 PM

Wikipedia has a good article on measuring backthrust and lists backthrust for some common cartridges- Google it,

Carpetsahib is correct in that it is the internal head area (on which the powder exerts the pressure) that is used in the calculation but you can also use the outside case head diameter in the calculation which then provides a safety margin for those loads that can give higher peak pressures.

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Carpetsahib
.333 member

Reged: 29/04/07
Posts: 435
Loc: Western NC

Re: Backthrust table - anyone have one? [Re: eagle27]
#268312 - 22/07/15 12:18 AM

Quote:

Wikipedia has a good article on measuring backthrust and lists backthrust for some common cartridges- Google it,

Carpetsahib is correct in that it is the internal head area (on which the powder exerts the pressure) that is used in the calculation but you can also use the outside case head diameter in the calculation which then provides a safety margin for those loads that can give higher peak pressures.

I agree that the outside head diameter can be used to provide a safety factor. I will point out that the adhesion of the body of the case to the chamber wall can also be taken into consideration. If you do so, it will provide an additional safety factor.

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Bergen
.224 member

Reged: 31/10/15
Posts: 17
Loc: England

Re: Backthrust table - anyone have one? [Re: Carpetsahib]
#274132 - 27/11/15 10:49 AM

Grenadier, I have QuickDesign which is a cartridge design software and for every cartridge in the database there is a bolt thrust figure.
The units differ depending on whether the data is CIP or SAAMI but when I have a minute I'll post up the data on there for the cartridges you mention.

If you read this before I post the numbers feel free to add as many cartridges to your list as you wish.

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Matabele
.300 member

Reged: 16/09/10
Posts: 230
Loc: Zimbabwe

Re: Backthrust table - anyone have one? [Re: Bergen]
#274231 - 28/11/15 11:01 PM

Bergen, If you don't mind could I add a few cartridges in addition to Grenadiers?

.303 British
6.5x57
7x57'
22 Hornet

Thanks for your help!

Edited by Matabele (28/11/15 11:02 PM)

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