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4seventy
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Reged: 07/05/03
Posts: 2210
Loc: Queensland Australia
Breech pressure
      #20225 - 30/10/04 02:23 PM

Purchased a copy of Brown's book "Building double rifles on shotgun actions" yesterday.
Interesting stuff and some good info included.
I must say though that his calculations regarding pressure on the standing breech are a little strange.
I'm no mathematicion nor ballistician but something seems a tad wrong to me.

Page 19 for anyone else who has the book.

One minute he is using the case head AREA in his calculations then he changes to using case head DIAMETER!!!

What the??!! Surely this is a mistake?

Also he states that the 16 bore shotgun cartridge had a max pressure of 12,000 PSI but claims his 16 bore action has been proved at 32,000+ PSI!
I thought most proofs ran at around 30-50% above max pressure not 265%!!
Wow, were any shotgun actions ever subjected to such high proof pressures and would the barrels survive?

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Marrakai
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Reged: 09/01/03
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Re: Breech pressure [Re: 4seventy]
      #20227 - 30/10/04 05:35 PM

You're right there, Alan. Ellis Brown's calculations simply don't add up in his book. The method is sound, however, you just need to use the correct figures!

If you do the sums correctly, you will find that the 17,000-odd psi proof-load of a 12,000-psi 12-bore cartridge will produce a similar force on the standing breech as a .450 NE at 32,000 psi (because of the smaller head-area of the latter). Although its probably dodgy comparing the 12-bore PROOF load with the .450 Nitro WORKING load, I think that the similar force on the breech is the point that Ellis Brown is trying to make.

BTW, I bought my copy of that book when we were only getting about 50 US cents to the Aussie dollar. OUCH!!!


ps: I just edited this post as I had inadvertently used the wrong figures myself! Should have been the 12-bore PROOF load, fixed now!

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Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

Edited by Marrakai (30/10/04 09:11 PM)

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470Rigby
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Reged: 23/02/04
Posts: 328
Loc: Melbourne, Australia
Re: Breech pressure [Re: 4seventy]
      #20263 - 31/10/04 10:41 AM

Actually - to calculate maximum theoretical THRUST on the bolt face or standing breech, you must use the internal sectional area at the base of the cartidge.

In practice, this is mitigated by the strength of the cartridge case, frictional forces between the case and chamber wall, and degree of case taper (heavily tapered cases transmitting more "bolt" thrust).

IMO - What allows some of these dodgy conversions to work, is the ability of the case to contain backward thrust!

Some gunsmiths employ this principle to do a rudimentary "proof test" by oiling a case and firing it, on the assumption that if the maximum theoretical thrust is allowed to develop, this approximates the thrust generated by a proof load under normal circumstances.

So, if you are shooting one of these marginal conversions, you had better make sure you clean the sizing lube off the case, and clean the oil out of the chamber before you pull the trigger! And - oh! - don't polish your cases, or use Nickel plated ones!

BTW - the current CIP Minimum Proof Pressures (PE) for Centrefire Rifles are 30% over the Highest Mean Service Pressure (Pmax), and only 15% over the Highest Individual Pressure (PK) - not much of a margin!

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bonanza
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Re: Breech pressure [Re: 470Rigby]
      #20267 - 31/10/04 11:57 AM

Why not polish?

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470Rigby
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Reged: 23/02/04
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Re: Breech pressure [Re: bonanza]
      #20272 - 31/10/04 01:33 PM

In reply to:

Why not polish?


Reduces case to chamber friction.

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Bramble
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Reged: 29/07/06
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Re: Breech pressure [Re: 470Rigby]
      #60894 - 07/08/06 10:30 AM

I'm sorry if reviving such an old thread is not good form, but I have a query.
In the "Standard directory of proof marks" it states that the English standard of proof for smoothbores (as used for conversions) is 60-80% minimum over service pressure. This conflicts with what is stated here. Is the publication incorrect?

Regards

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Marrakai
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Re: Breech pressure [Re: Bramble]
      #60897 - 07/08/06 12:32 PM

Bramble:
Without looking it up, I'm sure the Directory is correct. There are vastly different factors involved with proving centrefire rifles and shotguns, which 470Rigby has conveniently failed to acknowledge.

470Rigby was a consummate red-herring tosser (or perhaps, just a tosser!) and no longer posts here.

I'm quite biased of course, having taken him to task on a few issues in the past.....


BTW, if you will forgive me the intrusion Bramble, I just re-read this thread and it is clear I mis-understood 4seventy's original post concerning the 32,000 psi figure quoted on page 19 of Ellis Brown's book. He indeed states that in East Germany, after 1950, shotguns were proved at 32,000+ psi, and refers to the Standard Directory of Proof Marks as his source of information.

My copy of the Directory is a little unclear, but in no way supports Ellis Brown's statement! Rather, it refers to a 'standard proof' (for 650 bar operating pressure) where the chamber-pressure must reach 12,329 psi measured by copper crusher. Apparently the proving cartridges must average 13,085 psi for 10 shots, and 14,507 psi for 10 shots if 3" or more long. A 're-enforced proof' was also available in East Germany (presumably for 850 bar guns) which had to record 17,405 psi chamber pressure during proof-firing.

So 4seventy' I would agree entirely with your observation, and join you in asking where Ellis Brown found the 32,000 psi figure?


My 'SD of PM' is undated, but is the Jolex publication distributed by Blacksmith Corporation, if that means anything. The East German data is on page 92.



--------------------
Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

Edited by Marrakai (07/08/06 02:31 PM)

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Bramble
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Reged: 29/07/06
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Re: Breech pressure [Re: Marrakai]
      #60922 - 08/08/06 12:31 AM

I agree with you. That is what my copy shows also.

This is where I am becoming totally confused with so many conflicting pieces of information.

The crux of it is this, I have scrimped and saved and finally after 24 years of longing have booked a trip to Africa. Now I dont need a double, but I want to use one for what may be the only trip I am able to take. I cannot afford even an old double so I will build one. Not the first gun I have built by any means.
I am not too concerned as I will use .450 No,2 in a quite pretty, modern Spanish action I have forund that has 3 1/2 inch chambers 1350 bar service pressure and by design has the facility to dicharge both barrels simultainously( though hevens knows why you would wish to (1750 grains of shot at 1400fps ouch).
If that isent enough action then goodness knows what is?
But with a project that has a 20,00 psi bomb 12 inches from my face I would like as much empirical data as I can get.

It is apparent that many people have built doubles on shotgun actions and they work from OK-very well, but are they just using the safety margins that are built into any gun to acchieve that and constantly exceeding the design criteria for that action. On the face of it Ellis Brown is using the proof pressure to secure a new service pressure, with due deference to him, that is like firing any gun with proof loads constantly, that isent safe or sane. Constantly appraching the elastic strain margin of any piece of steel will eventually lead to stress induced failure from work embrittlement.

I got A squares book today and they absolutly do not recommend fillers, however all the loads on this site talk about RL15 and filler, whereas they use RL22. Now you guys shoot these rifles all the time, but they have all the lab facilities, whom should I believe?

Do you know of any data where somebody has tested a double action to destruction to assertain where the limits are, and do barrels fail before actions. All the horror stories I have read refer to the failures of barrels, I have not read of a failed action?

Regards

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Marrakai
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Re: Breech pressure [Re: Bramble]
      #60947 - 08/08/06 01:10 PM

Bramble:
Here's how I look at it: use the proof data to help you choose an action, but be sure that it is well-built, obviously robust in construction, has a third fastener preferably a cross-bolt, and is made with (relatively) modern steels. Then when the barrels are fitted, fire a couple of proof loads 30% above the mean working pressure of the chosen cartridge. If it passes, it is now 'in proof' for the new load, regardless of what it was proved for before.

There are several ways to estimate a 30% overcharge, contained in previous threads on this subject. As I recall, most employ an over-weight projectile, rather than over-charge of powder. A search should give you a starting point.


In reply to:

all the loads on this site talk about RL15 and filler


Like hell! Many of us here in Oz are very leery of Reloader powders for the big nitro expresses. I know Seyfried and others have popularised them in the States, but neither I nor any of my close friends use the stuff, being unashamed AR2213 or IMR4831 fans for the NEs. Filler is usually not required, but a felt wad or tuft of dacron would probably be needed in the over-sized .450 No.2.

If you match published factory velocity with AR2213 or IMR4831, you will invariably be well below the pressure for which the rifle was originally proved. All modern published pressure tests support this assertion.


BTW Bramble, I would give serious consideration to disabling that 'both barrels' feature when converted to .450 Nitro!

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Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

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wombat
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Reged: 06/03/04
Posts: 163
Loc: Australia
Re: Breech pressure [Re: Marrakai]
      #60956 - 08/08/06 09:23 PM

With great respect to those with more experience than I-
may I say that with my 500 Searcy the Aussie powders 2209 and 2213sc worked very well BUT after 30 odd rounds the action was full of unburnt powder.I did not have a problem with the functioning of the gun but I was worried I might.I still go to the trouble of R15 and a filler because it is very clean burning (in my rifle)

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Marrakai
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Reged: 09/01/03
Posts: 3591
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Re: Breech pressure [Re: wombat]
      #60959 - 08/08/06 09:42 PM

Hey Wombat, that's interesting. Can't be the short barrels (your Searcy is 24 inch?), because I get no unburnt powder using AR2213 in my 24"-barrel Jeffery .400, clean as a whistle. My .470 burns clean too. The .500 NE Vic used to have left no unburnt powder with IMR4831 either.

Fed 215 primers all round, I assume. Are you using full-weight bullets?

I haven't 'graduated' to 'short cut' 2213 yet. When the writing was on the wall, I bought a couple of 4-kilo cans of the old 2213. The new stuff is a tad slower I believe. Perhaps that's it, although unburnt AR2209 is a concern.

Mate, you gotta do what's best in your own gun, of course.





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Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

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Bramble
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Reged: 29/07/06
Posts: 950
Loc: England
Re: Breech pressure [Re: Marrakai]
      #60967 - 09/08/06 01:26 AM

Thanks Marrakai

and you bet that both barrel system will be disabled.
Even as a shot gun with 2x 3 1/2 inch 2oz loads that aproximates the old 4 to the pound rifles of the 1800's and I read they were most unplesent (worse perhaps with tubes, this gun only weighs about 9lb)

This is a current action I will be using, it doesent have a third fastner but it is massivly built and I figure that if it was built for double discharge then the design criteria with 12 guage is a total of 24,300 lb approx breach thrust one hell of a lot more than 1 .450No.2. (about 6,300lb)

I know some people do not care for us home builders of doubles but could you or some other kind soul give me the outside diamiter at the muzzle of a .450 barrel and also at the 1/2 way point so that I may get the profiles correct.

With regards to the loads, thanks very much, I dont like the idea of fillers and I am please to learn that you are using the same powders that A square tested. It appeared from their data that the tests were very through and I wondered about the RL15 route.

With thanks and best regards

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NE450No2
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Reged: 10/01/03
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Re: Breech pressure [Re: Bramble]
      #60982 - 09/08/06 04:59 PM

Bramble
Here are the measurements of the bbl on my British double a 450 No2.

Just in front of the water table where the barrel becomes round. 1.19 [1.91 was a typo]
At 6" .915
At 12" .755
At 18" .677
At 24" .650
At 28" .660

The bbls are 28". I measured both bbls at 24 and 28 inches, the measurements were the same.

Hope this helps.

Edited by NE450No2 (10/08/06 09:46 AM)

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banzaibird
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Reged: 18/09/05
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Re: Breech pressure [Re: NE450No2]
      #60987 - 09/08/06 09:41 PM

In reply to:

Just in front of the water table where the barrel becomes round. 1.91




Is that a typo? Almost 2 inches accross the barrel? Or is it supposed to be 1.19?

Bill

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Bramble
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Re: Breech pressure [Re: banzaibird]
      #60993 - 10/08/06 02:51 AM

Thank you very much, that was most kind of you.

I know that this will never compete with an English best rifle, however I will try and stay in the spirit and do justice to a great line of guns.

Would the group like me to post pictures as I progress?

Thanks again

Best Regards

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NE450No2
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Reged: 10/01/03
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Re: Breech pressure [Re: Bramble]
      #61000 - 10/08/06 09:47 AM

1.91 was a typo. Post corrected, thanks.

Yes show us pictures.

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bulldog563
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Re: Breech pressure [Re: Bramble]
      #61041 - 11/08/06 04:05 PM

I would like to see it progress. Should be interesting.

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Bramble
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Re: Breech pressure [Re: bulldog563]
      #63587 - 05/10/06 10:34 AM

As promised the first of the pictures of this build.

The gun has been stripped and the action dismantled, cleaned up and re-blued.
The barrels cut off before the monoblock and awaiting faceing.
The drawings of the barrels have gone off to Lilja tonight and I await their quote.
I have done the calc's on the barrel weights and it appears that the finished rifle should weigh 10 1/2 - 11 lbs.

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