What causes ring bulged chambers.

M

Murphy98

Guest
Had a Martini Cadet rifle rifle rechambered from 25/20 to 256 Win. Mag. After about 50 shots the barrel came loose and the chamber is bulged, most of the reloads were mild but the one that finished it off may or may not have been but I am not sure if the load was hot or if the rifle had just developed a condition of excess head space, but the barrel become obviously loose and the chamber was bulged about 7thou on the case just back from the junction of the neck. My gunsmith found some squashed unburned powder grains in the chamber from a load that was too light and did not combust properly {14g Benchmark8208}, he is adamant that the unburned grains would have caused the barrel to come loose and the chamber to bulge. Seems to me that the bulged chamber would cause the barrel to get tighter not looser. The end result was quite unspectacular with no burning of the bolt face , no smoke or flying particles. The load that seemed to cause the rifles demice was 14g of Alliant Unique. Case capacity is about 22g of fine grained powder to filled the top of the neck. Is my gunsmith correct, just trying to cover his backside , or are other factors involved. Do chamber bulges occur in strong rifles such as Rugers and Remingtons or are they simply a lever action thing?:mad:
 
What kind of barrel was used? Cadet barrel tenons are 3/4" x 14(15?), and if I recollect correctly, .25-20 (Repeater), and the. 310 Rook cases are about the same. The .256 is bigger; maybe that caused some chamber swelling, especially in a relatively soft steel barrel. Original Winchester 92s had that problem when rechambered to high pressure cartridges.

If you can believe it, I once had a Cadet that had been rebarreled to. 219 Donaldson. I had that barrel pulled right away! And some importers rechambered original Cadets to .32 Special...

You had some bad luck; hopefully, your receiver is OK.

The guys on the Martini forum at Rimfire Central might have some helpful ideas.
 
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To Fussy 1

The barrel that was rechambered is a Sportco Martini barrel straight out of the 1960s. I to have owned a Martini Cadet in a much larger calibre [ 25/35] with no problems. Fortunately the action is not damaged, and this time it is being rechambered to 30/30 using a Howa barrel. Thanks for your interest.:cool:
 
Murphy98 said:
Had a Martini Cadet rifle rifle rechambered from 25/20 to 256 Win. Mag. After about 50 shots the barrel came loose and the chamber is bulged, most of the reloads were mild but the one that finished it off may or may not have been but I am not sure if the load was hot or if the rifle had just developed a condition of excess head space, but the barrel become obviously loose and the chamber was bulged about 7thou on the case just back from the junction of the neck. My gunsmith found some squashed unburned powder grains in the chamber from a load that was too light and did not combust properly {14g Benchmark8208}, he is adamant that the unburned grains would have caused the barrel to come loose and the chamber to bulge. Seems to me that the bulged chamber would cause the barrel to get tighter not looser. The end result was quite unspectacular with no burning of the bolt face , no smoke or flying particles. The load that seemed to cause the rifles demice was 14g of Alliant Unique. Case capacity is about 22g of fine grained powder to filled the top of the neck. Is my gunsmith correct, just trying to cover his backside , or are other factors involved. Do chamber bulges occur in strong rifles such as Rugers and Remingtons or are they simply a lever action thing?:mad:
Click to expand...

That's a lot of UNIQUE!! I have worked with the .256 quite a bit.
 
What I know about Unique.

Have used it quite a lot in other rifles and consider it to be one of the slower pistol powders, fairly close in burning rate to Alliant 2400 by perhaps a little quicker. 9g in a H:mad:ornet is about max. where as 2400 might go to 11g. Works well for reduced loads in the 25/06 with 15g giving a 70g Sierra Blitz 2100fps 18g will 2400fps 19g, which I consider maximum,2560fps. Having said all that I may well have destroyed my rifle with just one load,but I would have expected a bit of a show and there was none, just a loose barrel and a bulged chamber. In any event I dont think I would recommend that load to any one with a 256, if they want to keep their rifle in one piece.
 
Bill,

My old third edition Hornady manual lists 9.1 grains of unique behind a 60grain soft point in a Marlin Model 62 which admittedly wasn't the toughest action around. Then again, the .256 was designed as a pistol cartridge, wasn't it?

John
 
Murphy98 said:
The barrel that was rechambered is a Sportco Martini barrel straight out of the 1960s. I to have owned a Martini Cadet in a much larger calibre [ 25/35] with no problems. Fortunately the action is not damaged, and this time it is being rechambered to 30/30 using a Howa barrel. Thanks for your interest.:cool:
Click to expand...

I would need the thickest Sorbothane recoil pad on that .30-.30. ;-) Will the breechblock need grinding to allow a round to be chambered?
 
To Fussy 1

Am not too sure about the breech block,as my 25/35 Martini just had an ordinary breech block to the best of my knowledge and the rounds are very similar. My rifle already has a thick rubber recoil pad but not sorbathane, but really a 71/2 lb rifle in 30/30 shouldn't bother me too much as I already own a 71/2 lb 300 win. mag. Really these Martinis are getting out of hand as I have now comissioned another .256 as well the 30/30. When I get them up and running I will try and post some pictures and accuracy results. I think the secret with the .256 is to treat it as one would one would a SMLE or a shotgun,but it is a bit of a balancing act as the temptation with such a small cartridge is to throttle it up a bit.;)
 
A 7 1/2 pounder should be OK. Some of those Martinis are very light. There were rumors that someone was tooling up to make some new ones... I'm still waiting, LOL!
 
To Fussy 1

Some new ones would be very interesting, what about a rimless extractor model. I would buy 2 straight off, one in 221 fireball and one in 6ppc. the original ones are really getting a bit past it as both of my actions were made in the 1920s. If you remove the internals the vintage is stamped on the side of the mechanism.:D
 
To r4astro

A new action made of modern steel should handle the pressure, but the weak extraction problem might be more difficult to over come. Ruger must get around the problem with their falling block models, but I have not looked inside of one and therefore am not sure how they go about it. I just love Martinis because of the way that slab sided action handles, a bit like an 1892 Winchester with better accuracy. I feel that we are digressing a bit here as this a guns smiths forum and from what I can see most gun smiths hate the things because they are slow and fiddly to work on. Can't say I blame them when three bolt actions can be rebarrled while they fiddle around with one Martini.:(
 
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