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Double Rifles, Single Shots & Combinations >> Single Shots & Combination Guns
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TilleyMan
.333 member


Reged: 23/08/05
Posts: 272
Loc: Melbourne, Australia
Case taper, extraction... and the Martini Cadet
      #140723 - 17/08/09 09:35 PM

Interested in people's thoughts on case taper and ease of extraction in the Martini Cadet based conversions?

I've always liked the idea of the .357 Max as the basis for a whole range of Cadet wildcats, and am keen on the idea of a .25/.357 Max... sort of a .256 Win Mag Improved using the increased case capacity. Quality brass (ie not Bertram) is much cheaper and easier to find than .222 Rimmed and a bit more punch in 25 cal... sort of a rimmed 250 Myra or 25 Copperhead.

I know first hand problems with sticky cases in the .222 Rimmed Cadets and I've no intention of going into the field with a cleaning rod to clear the chamber every third shot!

I think the Hornet and derivatives, the .32/20, .25/20 and.218 Bee and the .222 Rimmed fit the action very well, leaving a fairly safe chamber wall to barrel tenon thickness ratio. The .357 Mag has the largest case head size I'd be comfortable rechambering a Cadet action to... I know some people have done .30/30's in a Cadet and other variations on that case...

Even the .25/35 in my mind always looks a bit out of scale with that action (much better in a Martini Enfield), and I don't want to fiddle around with changing the block ramp angle or radius.

Case taper seems to be the issue with the Cadet's fairly marginal extraction... I know some of the old timer cartridges like the .25/35 have a pronounced case taper, just wondering how tapered a .25/357 Max case needs to be?

More taper than a .222 Rimmed seems like a good starting point!
But should it look like a mini .303/25

Cheers

TM

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Tatume
.400 member


Reged: 09/06/07
Posts: 1091
Loc: Gloucester, Va USA
Re: Case taper, extraction... and the Martini Cadet [Re: TilleyMan]
      #140724 - 17/08/09 10:08 PM

Since you've brought it up, I'd like to also hear discussion on the 30-30 derivatives in the Cadet action. A 7-30 Waters Cadet with 20-inch barrel and Stutzen stock has great appeal to me. The same configuration (or perhaps a 16 or 18 inch barrel!) chambered in 357 Maximum is also attractive. I wish I knew where to get an action and who to have do the work?

--------------------
Take care, Tom
NRA Life Member

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Otto
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Reged: 15/09/05
Posts: 111
Loc: Arizona, USA
Re: Case taper, extraction... and the Martini Cadet [Re: Tatume]
      #140727 - 17/08/09 11:49 PM

I built a 30 Super (300 H&H rimmed) for a customer on a high wall action that has had extraction problems. My reamer cut a tight chamber and, with any loads at greater than 308/30-06 velocities, the cases stuck. I even bought another reamer that is .003" larger in all dimensions. The larger chamber helped, but still requires a bump on the lever to kick out the cases. I own a 22 Hornet on a German Martini action and a Bill Sukalle barrel that also has extraction issues. Yes, a 22 Hornet! My suggestion for anyone wanting to build on a Cadet, is to be sure the reamer is NOT a Minimum dimension reamer. Then, polish the chamber to a mirror finish. Then, be prepared to shoot modest loads. For a trouble free single shot, build on a Ruger #1 action.
Otto

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DarylS
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Reged: 10/08/05
Posts: 26992
Loc: Beautiful British Columbia, Ca...
Re: Case taper, extraction... and the Martini Cadet [Re: Otto]
      #140739 - 18/08/09 02:05 AM

Buddies .17Ackley Hornet in a thick side Martini, minimal taper case has no trouble running 3,940fps with 20gr., not a light load by any stroke, and cases kick completely out of the action upon extraction.

Another friend's .30/30AckImp also has no extraction problems from his Martini Cadet using loads that duplicate .300 Savage fctory ammo. It's the tapered cases that usually give grief in extraction, not the straight sided ones from what I've seen.

I've never had any extraction issues with straight-sided cases with heavy loads as there is little or very minimal bolt or block thrust, the barrel handling the pressure. The case then conracts roughly .001' away form the chamber walls and usually 'falls' from the chamber. Rough chambers don't work, anywhere.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

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xausa
.400 member


Reged: 07/03/07
Posts: 2037
Loc: Tennessee, USA
Re: Case taper, extraction... and the Martini Cadet [Re: DarylS]
      #140740 - 18/08/09 05:16 AM

I know that it's counter intuitive, but I am convinced that straight sided cases extract better than tapered ones, particularly in single shot actions with little or no primary extraction. I think the reason is simply that single shot actions, as opposed to bolt actions, have a certain amount of "give" in them, and when a tapered cartridge is fired, the action springs slightly, which allows the cartridge case to obturate to slightly more than the normal chamber size. Then, when the pressure subsides, the action snaps back, and the now oversize cartridge case is driven forward into the chamber, where it is tightly wedged and resists extraction. A straight sided case would not have the same wedging action and therefore extracts easily.

Incidentally, I have a .25-.222R on a Winchester Low Wall action and it extracts flawlessly. Of course, the lack of strength of the Low Wall limits me to rather mild loads.

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DarylS
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Reged: 10/08/05
Posts: 26992
Loc: Beautiful British Columbia, Ca...
Re: Case taper, extraction... and the Martini Cadet [Re: xausa]
      #140752 - 18/08/09 11:15 AM

Quote:

I think the reason is simply that single shot actions, as opposed to bolt actions, have a certain amount of "give" in them, and when a tapered cartridge is fired, the action springs slightly, which allows the cartridge case to obturate to slightly more than the normal chamber size. Then, when the pressure subsides, the action snaps back, and the now oversize cartridge case is driven forward into the chamber, where it is tightly wedged and resists extraction. A straight sided case would not have the same wedging action and therefore extracts easily.





Exactly - bolt or block thrust with tapered cass - no such (or minimal) bolt/block thrust with straight cases.

I've had Ackley Imp chamberings that I stopped progression of loads due to working past where I thought the absolute max point should have been, not due to any pressure signs. When a .257 AckImp beats a .257 Weatherby magnum for speed with 100 and 120gr. bullets, it's time to back up a hundred fps or so and take a good look at the stats. There were absolutely no pressure signs by case measruement nor with no expansion of primer pockets, yet the chronographed results were there - same day/same time testing as well.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

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TilleyMan
.333 member


Reged: 23/08/05
Posts: 272
Loc: Melbourne, Australia
Re: Case taper, extraction... and the Martini Cadet [Re: DarylS]
      #140755 - 18/08/09 11:53 AM

Thanks for the advice guys...

I've heard similar stories about the .222 Rimmed sticking with Bertram brass, but not with the original Super brand cases... seems to point toward case head expansion issues, as the .222 Rem case doesn't seem to have a lot of taper to it.

Xausa and Daryl that is an interesting theory... sounds very plausible!

BTW does anyone know if the BSA International action body will accept 'standard' Martini Cadet internals?

That way, the .22RF BSA International action body, with its adjustable trigger and thicker sidewalls, hopefully could be converted across to CF just by swapping the .310 CF falling block and bushing the firing pin for the higher pressures?

While they ARE drying up, there's still plenty of Cadet action parts at regional gunshows in Australia... and while Francotte actioned Rook Rifles are going through the roof, BSA Internationals are often found at bargain prices.

Tatume
Plenty of complete Cadets come up for auction here (and he will send to the US):
http://www.australianarmsauctions.com/

Ray Jansa also has Martini actions from time to time, one listed now for A$225
http://www.jansa.com.au/access2.php

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DoubleD
.400 member


Reged: 23/11/03
Posts: 2437
Loc: Retired in Oklahoma
Re: Case taper, extraction... and the Martini Cadet [Re: TilleyMan]
      #140756 - 18/08/09 01:46 PM

International action are different and will not interchange.

The Thin side Cadet will interchange with some fitting in to the thick side M-12 and 1215's. It a fairly simple process to convert the thick side BSA 12's and 1215's to Centerfire.

--------------------
DD, Ret.

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TilleyMan
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Reged: 23/08/05
Posts: 272
Loc: Melbourne, Australia
Re: Case taper, extraction... and the Martini Cadet [Re: DoubleD]
      #140839 - 20/08/09 09:54 AM

DD

Thanks for the info, a pity things aren't quite as straightforward as I had hoped

What are the known weaknesses of the thin sided Martini Cadet?
Seems the preferred actions all have thicker sidewalls and a reinforce bulge around the barrel tenon seating area...
I tend to steer clear of the Sportco Martini conversions, as the action side walls were all surface ground (~.030"+ per side) to remove rust pits and proof marks, Govt stampings etc before reblueing... which further weakened them. They also fitted an annoying cross slide safety just behind the trigger.

In Australia there's two main conversions I've seen... the quick'n'dirty way which involves chamfering out and TIG welding the off-centre RF firing pin hole at the end of the falling block. Danger of overheating and distorting/weakening the block if anything other than TIG or MIG is used.
Facing off flat and re-drilling (from the rear to ensure concentricity) and remachining a smaller central CF firing pin hole. New or replacement CF .310 firing pin then reprofiled to match the new hole ; and

The 'proper' way:
Counterboring and a threaded bushing made up (similar to the refinished blocks on a Martini Enfield .303 factory refurbishment), new or replacement CF .310 firing pin then reprofiled to match the new hole.

Do you have any links or recommended books on the M12 or M1215 conversion please?

Cheers

TM

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TilleyMan
.333 member


Reged: 23/08/05
Posts: 272
Loc: Melbourne, Australia
Re: Case taper, extraction... and the Martini Cadet [Re: TilleyMan]
      #141397 - 31/08/09 09:16 PM

Spent a bit of time sectioning some cases suitable for the Martini Cadet... nice change from 9.3mm bullets

As you will see below. the .222 Rimmed (original Australian Super brand) has a quite thick web vs the 357 Max... and lastly a .223 case for comparison.

Look at the brass thickness just below the primer cup on the .357 Max
It would seem the .222 Rem has a working pressure of 38,000 CUP vs the .357 Max's ~46,900 CUP and the .223's ~43,500 so the case should handle it

I've heard the .256 Max was quite popular some years ago (basically a .256 Win Mag based on the .357 Max case) which should give a fairly solid improvement over the original round (can't seem to find any ballistics data), in a more compact package that still leaves a good thickness in the barrel tenon. Some say it will approximate the old .25/35...



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DoubleD
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Reged: 23/11/03
Posts: 2437
Loc: Retired in Oklahoma
Re: Case taper, extraction... and the Martini Cadet [Re: TilleyMan]
      #141403 - 01/09/09 01:34 AM

.256 Win is based on the .357 Mag case.

Got no clues on the reason for different web thickness. Although two things strike me. Both thick webs are rifle cartridges and both have a smaller bottle neck. Don't know if there is any significance.

The weakness of the Martini Cadet or more correctly the BSA Francotte Martini:

1. weak extraction
2. small barrel tenon
3. difficult load geometry-entry angle

The common misconception is that the striker hole in a Rimfire cadet breech block is off center. It is not. As many as I have looked at I have never seen a Rimfire BSA with an off center striker or striker hole. The proper way is to simply adjusted the block height to lower the point of impact. No other changes are needed. Striker diameter is already correct. You may also need to adjust the load position. No MIG, No TIG, no facing off, No reheatreating.

The .thin side ..310 cadets do need their strikers modified and breech blocks bushed…the striker diameter being to large for smokeless powder use.

You will find the adjustment instructions buried in the LoC for Armorors of the Martini Henry. You can find them reprinted in several locations including in Ian Skennerton’ SAIS 15 on the Martini Henry.

Remember the Francotte is a Martini Henry with all the internal parts moved to a subframe, nothing more.

The thick side actions are generally rimfires. I don’t think I have seen a thick side centerfire. Some do enlarge the barrel tenon hole on the thick side, but I don’t feel the need.

--------------------
DD, Ret.

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TilleyMan
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Reged: 23/08/05
Posts: 272
Loc: Melbourne, Australia
Re: Case taper, extraction... and the Martini Cadet [Re: DoubleD]
      #141439 - 01/09/09 08:37 PM

DD

Thanks for the update... yes, the .256 Win Mag is basically a .357 Mag case necked down to .25 cal with a 25 degree shoulder, good for ~2400fps with a 60gr bullet.

The .256 Max is essentially the same, but based on the longer .357 Maximum case.

Sportco in Australia bought up many thousands of ex-military .310 Cadet Martinis (mainly BSA, some Greener) and were then 'reconditioned' by surface grinding off all the serial numbers, unit and proof marks from the already thin walled actions, and rebarrelling them to .22RF, .22 Hornet, .25/20 and .32/20 in the early post WWII years when ex-military .303's were illegal for private citizens to own in some states.

They also fitted a rudimentary 'cross bolt' safety behind the trigger... not needed IMO, but perhaps required in order to sell to the public even in the 1950's.

http://www.sportco.org.au/intro.htm
http://www.sportco.org.au/models.htm

The breechblock below is from an ex-Sportco converted .22RF... note the off centre hole for the replacement Sportco rimfire pin. Someone has since converted it back to CF by dropping in a standard .310 firing pin.



Overseas Francotte Martinis and the BSA thickwall Martinis like the 1215 may well have central RF firing pins, but the Sportco converted ones I have seen here in Australia were all off centre... I'd say this is where the confusion arises, as quite a few converted Sportco Martinis have ended up in the USA

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DoubleD
.400 member


Reged: 23/11/03
Posts: 2437
Loc: Retired in Oklahoma
Re: Case taper, extraction... and the Martini Cadet [Re: TilleyMan]
      #141444 - 01/09/09 11:37 PM

They didn't know what they were doing. I have never seen one of those up here.

All they had to do was draw the horns and raise the block and nothing else.

--------------------
DD, Ret.

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