The official Mike Bellm's

Bellm TCs


TC Contender, G2, Encore/ProHunter Performance Center

 





Some general guidelines follow.


Wherever possible and practical, choose a smaller diameter chamber to minimize the thrust back on the frame.

Think of the chamber and cartridge as a cylinder and piston. Maximum pressures for the higher intensity cartridges are more or less a constant.

In an engine you want more force on the piston. In a firearm, you want less force.

To get less force on the frame, you want a smaller diameter chamber, not larger.

For prime example, velocity from a .280 Rem. Ackley Improved with a 140 gr. bullet at 3140 fps is essentially the same as you get from a 7mm Rem. Mag., but the larger diameter belted mag case exerts more force on the frame.

In this example, you give up nothing with the smaller diameter chamber, but help insure you are not overworking the frame or the lower lip of the barrel lug and risking stretching either one.

Use a rimmed case wherever possible.
It is an easily demonstrated fact that rimless cases with long, sloping shoulders are driven forward in the chamber, slightly crushing the case shoulder when the firing pin hits the primer.

This does several things.
1) It cushions/softens the impact of the firing pin,
2) adds to headspace, case stretching, shortening of case life, and
with the result that,
3) it gives less consistent ignition than when the case is stopped by the rigid, solid rim of a rimmed case.

There are a multitude of applications where a rimmed version of a rimless cartridge can be done by simply necking down .444 Marlin brass and trimming back where necessary for any cartridge 2.250" or less in length, such as the very efficient 7x57 Improved that rivals .280 Remington.

.309 JDJ, also made from necked down .444 Marlin brass, does NOT belong in a Contender, contrary to Mr. Jones, but makes a most excellent alternative to .30/06 with .30/06 ballistics in an Encore barrel and is a good rechamber option to bump up and improve the accuracy of a .308 Win. barrel.

Any of the chambers based on the .308 Win. case body can have a rim counterbore cut in the barrel for shooting either rimless or rimmed ammo interchangeably. .308 Win. and .356 Win. let you shoot either standard rimless or rimmed factory ammo. For 7mm-08, just neck down .307 Win. brass. .260 Rem and .243 Win. will require turning/thinning case necks since the brass thickens when necked down and creates a loaded case neck diameter too large for most standard chambers.

When no rimmed case is available choose a sharper case shoulder.
Like the case shoulder collapse described above, just the opposite can be demonstrated with the sharper 40 degree shoulder attributed to P.O. Ackley's designs.

If you remove the extractor from a barrel, measure where the head of an empty primed case is in relationship to the end of the barrel, then measure where the case head is after firing just the primer, you will find all of the common rimless cases will be driven forward in the chamber.
A few years back we did some fairly extensive demonstrations of this with .308 Win., .35 Whelen, and .280 Ackley Improved.

The .308 Win. case was driven into the chamber about .003".

The .35 Whelen with is longer shoulder angle and smaller shoulder area was driven in about .006".

The 40 degree shoulder of the .280 Ackley Improved hardly let the case budge even .001".

In standard factory chamberings, the Bergara barrels I work with cover the range of applications for hunting fairly well.

Some quick comments follow, but are not meant to tell you anything you have not read in magazines or experienced yourself over the years. This is mostly for those less versed in cartridges.

.243 Win. has proven itself over and over for years as an ample game round up through deer and even elk. It is inherently accurate, mild recoil of course, and a superb varmint round as well. This is common knowledge in spite of the trends for bigger, badder, louder, and harder kicking rounds.

7mm-08 offers a good trajectory and energy for medium sized game while .308 Win. lets you shoot heavier bullets.

In standard factory chamberings, .270 Win. is still at the top for combining the flattest trajectory and energy rivaling the harder kicking belted mags like 7mm Rem. Mag.

The old standby .30/06 has been doing the job on deer, elk, and bear quite well since it was introduced over 100 years ago. Recoil with 150 gr. bullets is moderate while being more than enough "gun" for most game. Recoil with 180 gr. bullets gets a bit stiff while the 165 gr. bullets are a good compromise.


My personal prejudice.........
.270 Win. for everything where ranges might approach the 400 yard mark.

Loosely speaking, inside of 300 yards, the differences in trajectory and effectiveness from one cartridge to the next hardly show up in the real world unless the target is a larger animal that needs more bullet weight and penetration.

With any cartridge choice, still the determining factor is bullet placement, and from that standpoint I emphasize choosing a cartridge you can manage well, shoot well, and consistently place shots with.
If you can only do that with a .243 Win. you are far better off reliably placing a good 6mm game bullet low behind the shoulder with a .243 Win. than you are making a bad shot on game or simply plowing a deeper furrow in the dirt when you miss with something you can't manage well.

The "authorities" would have us believe .22 caliber is not suitable for deer and larger game, but interestingly those astute enough to know better still continue to utilize varmint gun accuracy killing deer and elk every year with well placed shots.

The short version in summation is accuracy, what I emphasize, not bigger, badder, louder that kills on one end and maims on the other.
And if bigger is warranted, it should be just as accurate as the smaller rounds.



 

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