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.357 Remington Maximum Main Page, Click Here!
Loading data, accuracy tests, expansion tests, extensive information about the Max.
After you read what follows, be sure to go to the main page for the Max!



I finally stumbled across how the forcing cone chamber below came to be!
The March 1982 issue of The American Rifleman Magazine had an article by C.E. Harris, page 30, detailing the source of this well intended, but in reality, abomination you are stuck with yet years later.

The title of the article is "Proper Throating Is The Key To Accuracy."

Older versions of .357 MagNUM chambers had only a very short, abrupt cone between the end of the chamber neck and the start of the riflings. Accuracy was usually rather dismal in the Contender.

What the principals working with the Contender did back then was to theorize that the Army Marksmanship Unit (AMU) version of the .38 Special chamber used in their 1911 type target pistols was the answer, and the long forcing cone ".38 AMU" designated chamber DID in fact improve accuracy when that design was incorporated into the Contender barrels being tested.

HOWEVER, without going back and researching the bullets used in .38 AMU ammo, common practice in those days especially was to use hollow base 148 gr. wadcutter bullets in the NRA Bullseye competitions the AMU guns were designed for.

I can see how the very thin, very frail soft lead skirts of those bullets would NOT work in the old style chamber but WOULD expand pretty uniformly and flow more smoothly through the long forcing cone diagrammed in the .357 Maximum drawing below.

Thus, I can somewhat understand now the logic behind the long forcing cone, especially with plain lead bullets, either soft swaged hollow base or cast lead flat based.

While the .357 Remington Maximum IS an excellent cartridge for shooting cast lead bullets, it is perhaps arguably (cast lead shooters may disagree) at its very best with jacketed bullets, and jacketed bullets just don't expand, "obturate", sufficiently in the oversize forcing cone and thus enter the rifling at random angles with the shank of the bullet not supported and held in alignment with the bore.

Unfortunately, the long forcing cone chamber design has been applied to all of the straight walled, revolver type rimmed chambers found in Thompson Center's barrels today with the result that accuracy still remains far below the potentials of these rounds such as the .357 Magnum, .357 Maximum, .44 Magnum, .454 Casull, and .460 S&W frequently encountered in TC barrels.

(Then they put essentially NO throat in .375 Win. and .45/70 barrels and a very short almost non existent throat in .444 Marlin barrels. Go figure.)

Interestingly, the article goes on to state that a cylindrical section of throat was recommended to the researchers as an alternative to the forcing cone. Harris even acknowledges it would reduce flame cutting of the bullet shank.

But this brings to mind the Winston Churchill quote:
"Most men occasionally stumble over the truth, but pick themselves up and continue as if nothing ever happened."

My advice is to rechamber the forcing cone chambers for a longer cartridge, thereby cutting out most or all of the forcing cone and permitting cutting a cylindrical throat that DOES guide and support the shank of the bullet as it enters the rifling.

That, or the best solution shooters have come up with for accuracy with the forcing cone chambers is to use long shanked, wide flat nose cast lead, gas checked bullets +/- 200 gr in .35 cal. for example, that seal off the bore sooner than shorter bullets do. The LBT designs such as put out by Cast Bullet Performance and others are recommended.

What you have in a forcing cone SAAMI factory chamber is basically the same thing as a barrel that is literally SHOT OUT!
If you do a chamber cast of a barrel that has thousands of rounds run through it and no longer gets decent accuracy, you will find the same approximate shape in front of the chamber neck...... a cone worn into the opening of the bore.

If there is any logic applied to throats in the close breech guns, it sure does not show.

It is a real travesty that dim wits in high places dumped this bad chamber design on the American shooting public! You just can't fix stupid.



In the diagram of a TC factory, SAAMI .357 Rem. Maximum chamber below note the gap between the base of the bullet and the red outline of the forcing cone:


DO THE MATH......THAT IS A .358" DIAMETER BULLET STARTING OUT IN A .381" DIAMETER HOLE. THE DIFFERENCE IS .023" OR .0115" OFF THE AXIS OF THE BORE THAT THE BASE OF THE BULLET CAN DEVIATE IN ANY RANDOM DIRECTION!

It is amazing this design shoots as well as it does!

But when the shank of the bullet is contained and guided by a cylindrical throat centered with the bore, distortion of the bullet from entering the rifling at an angle is virtually eliminated and accuracy is much improved.

Here is a graphic example of the exact same forcing cone arrangement from a factory .357 MAGNUM chamber. Note the gap between the base of the bullet and the case neck. While the bullet is moving this distance, powder is being blown around the bullet since the bore is not sealed off at the nose of the bullet.
With the chamber cast, .357 MAGNUM case, and bullet laid side by side, you get a better picture of what is going on inside the chamber. Bullet is placed at approximately where it will first contact the rifling. (photo courtesy D.W. Murphy)


The only difference between a current vintage factory .357 Magnum and a factory .357 Rem. Maximum chamber is the 1.610" length of that portion roughly .380" in diameter for the longer .357 Rem. Max. case.

You can see the shape of the cone compared to the shape of the bullet shank and see that while the nose of the bullet may get centered at with the bore at its nose, the base of the bullet is sitting in a much, much bigger hole that cannot align it with the bore.

Close up of the .357 Mag. chamber cast. (photo courtesy of D.W. Murphy)
Again, note the gap behind the bullet before it makes contact at the nose.

The spot where the bullet is sitting is the point where it hits the rifling.

If you were to do a chamber cast of an old totally worn out barrel that had thousands of rounds shot through it, a cast of it would look almost exactly the same as the above factory SAAMI chamber!

Is that what you want? Do you want to pay hard money for something worn out and useless? Not likely.

But that is what you are buying with a brand spanking new, out of the box .357 Magnum or .357 Remingtom Maximum barrel with a SAAMI factory chamber, a throat cut too large in diameter and cone shaped.

As you can see, with this long forcing cone in the stock .357 Magnum factory chamber, the bullet is completely free of the case by the distance shown between bullet and case above before it hits the rifling. Between the long jump and no alignment of the base of the bullet, a chamber like this can hardly be expected to give good accuracy. Again, you have the same long forcing cone arrangement in factory .357 MAXIMUM chambers as well.

Rechambering to the longer .357 Max. case cuts out all but about .1" of the long Mag. forcing cone. Note that a SHORT cone IS necessary when shooting lead bullet to prevent lead from shearing off the bullet as it enters the throat. Thus the .1" of factory cone remaining after rechambering to .357 Maximum is a benefit. In fact, if there is no short cone, I use a separate reamer to create one since quite a few shooters do find the .357 Rem. Max. is excellent with cast lead bullets. The cylindrical section of throat then extends forward of the short, abrupt cone.

Quoting Mr. Murphy, "I dropped the bullet into the barrel and used the depth rod on my calipers to get a reading of 1.4" from the back end of the barrel to the bullet. I did my best to align the case, bullet, and chamber cast as accurately as possible to show how much room there is for improvement. I should still have at least 0.20" left before the rifling starts. the cannelure of the bullet is about 0.10" to the right of where the (.357 Maximum) case will stop."

Once again, cast lead bullet shooters seem to have the key to accuracy with the forcing cone chambers.
The consensus is to use a long shanked, heavy cast lead gas checked bullet with a wide flat nose. Cast lead shooters claim the heavier weights of wide flat nose bullets kill as well or better than lighter weight jacketed bullets.

And since there is a distance the bullet travels TOTALLY unsupported before even sealing off the bore at the muzzle, the longer shanked lead bullets eliminate powder blow-by around the nose of the bullet by sealing the bore off sooner. Ie, seat these bullets out as close to or just contacting the riflings at then forward end of the cone.

What you are looking at in the above drawing and photos is what you DON'T want.

This forcing cone arrangement above is what you get in factory .357 Mag, .357 Rem. Maximum, .44 Magnum, .454 Casull, .460 S&W, and other similar straight wall chambers. However, this same cone is also cut in .22 Hornet and .22 rimfire Mag. chambers as well. On the other hand, some factory chambers such as .30/30, .375 Win., and .45/70 have NO throat in them.

Older Vintage .357 Magnum chamber for comparison to the current long forcing cone design.
Top, cast of a current .357 Magnum TC factory chamber long forcing cone design. Below it, an '80s vintage .357 Magnum TC factory chamber cast with a much shorter forcing cone design. Bottom, .357 Magnum case. (Courtesy, D.W. Murphy)


Second from the top is a chamber cast of an older vintage of .357 Magnum chamber with a short cone, as opposed to the current long style that is about .4" long. Note how much farther forward the rifling start in the top cast.

This one is still a cone, but it is quite short in comparison and a much better choice either to shoot as is as a .357 Magnum or to rechamber to .357 Maximum, which will cut out all but about .1" of the forward end of the factory cone, then I cut a new, proper throat as shown in the diagram below.

Once again this is a .357 Magnum case which demonstrates where the case mouth ends and where the riflings start.

Bear in mind that a number of companies have supplied reamers to TC over the years, and that there are a number of variations that are all construed by the reamer manufacturers to be "SAAMI Standard." There are apparently choices that are acceptable, but some of the designs TC has adopted over the years exhibit a gross disregard for the accuracy you are presumably expecting and paying for.

(Chamber Throat Misalignment Click on this link also for a cast of a misaligned chamber throat.)

Below is the .357 Remington Maximum chamber WITH a true throat, what you DO want.



The chamber I cut for .357 Rem. Maximum has a throat in it, NOT the forcing cone you see in red in the top diagram above.

The riflings only are cut away, leaving a true throat, one that is cylindrical and does support the shank of the bullet.

When starting from a fresh barrel, the cylindrical throat starts immediately in front of the chamber neck. But when rechambering a factory .357 Magnum barrel to .357 Remington Maximum, approximately .1" of the smaller end of the forcing cone shown in red above will remain. The .381" diameter of the Magnum chamber body is extended forward into the cone area, cutting it away, all but for about the last .1" of the cone.

Forward of the very short section of cone remaining will be a true cylindrical throat.

The approximate .1" of forcing cone remaining after I rechamber to .357 Maximum IS beneficial when shooting cast lead bullets. If there is an abrupt ledge at the end of the chamber, lead will expand into the void between the case neck and the end of the chamber neck and leave a sheared off ring of lead in the chamber. In new unchambered barrels I DO put in a short cone to accommodate cast lead bullet shooters with NO adverse effects on jacketed bullets.

For barrels I rechamber to .357 Rem. Max., seat the bullets out as far as practical or to the limits of the throat length.

Where book maximums for 160 gr. bullets with 4227 for example are about 22 gr., I am test firing routinely with 25 gr. and have no excess pressure signs at all.... no primer cratering even.

However, I should note that WW-296 is probably one of the very best powders in the Max.

With the .357 Maximum, you can load it to essentially the same pressures as you would a .223 Rem. in both Contender/G2 barrels and Encore barrels since the two rounds are within just a few thousandths inch of being the same diameter.

The .357 Maximum pretty closely equals .35 Remington performance in standard loadings.... a long time, proven meat getter out to about 150 to 200 yards in the hands of a good shot who knows the distance and his ammo's trajectory.

Bumped up to the full potentials of the round, the .357 Max. will actually out shoot the .35 Remington in rifle length barrels, making it fully a 250-300 yard cartridge fired from rifle barrels and delivering essentially the same muzzle energy as a 180 gr. bullet from a .308 Winchester.

.357 Remington Maximum is one of THE very best choices for 10 and 12" Contender barrels. When custom chambered correctly with a true throat, it is extremely accurate.

With the broad range of .357-.358" bullets available, excellent powders in the correct burning rate range, inexpensive brass, and the readily available .357 Magnum dies used to load the Max. as well, it is a "natural" for any Contender/G2 or Encore/Pro Hunter barrel collection.

The new untapered TC factory 12" Contender barrels with the two forend screw attachment for more substantial forends than on the 10" "bull" barrels make it better suited for hunting where field conditions vary a lot. But either length of barrel works great.

As a plus, the crowns on the factory 12" barrels I have examined so far have been quite cleanly cut, clearly showing the outline of each land and groove, and should not require any recrowning work to make them shoot well. Any that look a bit burred get touched up automatically before they go out the door.

If you are deer hunting in a state that requires straight wall handgun cartridges, don't trip over the .357 Maximum!

.357 Remington Maximum is one of the most versatile rounds there is fired from either handgun or rifle barrels.

For information about rechambering your .357 Magnum barrel to .357 Remington Maximum, please call Mike Bellm at (541) 956-6938.

Send barrels with NO sights or scope base attached and include $95 payment to:

Mike Bellm
6721- 6150 Road
Olathe, Colorado 81425

Phone: (541) 956-6938
email address: mike@bellmtcs.com


.357 Rem. Maximum Main Page, Click Here!
Loading data, accuracy tests, expansion tests, extensive information about the Max.

More Chamber Casts
along with more explanation of what a throat is supposed to be compared to what you get in factory chambers and from anyone cutting chambers with SAAMI spec. reamers...... exactly what you DO NOT want if accuracy means anything to you at all!



 

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