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First things first:

There are only two ways to increase the rigidity of a tube. Simple physics and a little knowledge of structural engineering confirms that you can only increase the rigidity of a tube by increasing the overall diameter of the tube (think varmint or target barrel....or at the extreme, unlimited bench rest or rail guns), or, you can shorten the tube.

Please note: I did not use the term stiffness here. Stiffness is an inherent property of the metals used in the barrel, and cannot be easily altered. And short of custom gunsmithing, we can't exactly drop a super-heavy weight varmint barrel on a Mini. So, our obvious option is to cut the barrel to increase its rigidity.

Now, and most importantly, why and how does shortening the barrel on a Mini-14 work to improve accuracy?

Well, in addition to the increased barrel rigidity, it also involves what many shooters call "barrel harmonics".

However, a more accurate description of these "harmonics" is what can be defined as pressure wave induced deflections. These pressure induced deflections in the barrel cause the muzzle end to exhibit a 'whipping action'...however slight...during and after each shot. These pressure waves can actually be seen (using some very sophisticated ultra-high-speed videography) traveling down a barrel. The description I read a while back of a cartoon character putting a finger in a gun barrel and the barrel expanding along its length is not far from what really happens.

Gas dynamics meets structural engineering here.....

Both air and gas pressure travels in waves, and you can think of the pressure waves traveling along a barrel just like the waves in the ocean. The distance from wave crest to wave crest is called the wave period, or in some instances, the frequency. Any competent gunsmith will confirm that the chances of a mass-produced barrel matching the pressure wave signature of a particular load is almost an infinitely remote ideal. It would be kind of like winning a multi-million dollar lottery and then getting stuck by lightening on the way to cash the check. You see, given all the different possible variables, it's usually much easier to adjust loads to a barrel, than the other way around. (That's what keeps the reloading companies in business....lol)

Now, if we could create an adjustable length barrel, matching a particular load to a particular barrels' pressure wave signature wouldn't be a problem whatsoever. In fact, the Browning BOSS system is an example of altering the effective barrel length to change the tuning for individual loads. Granted, it's a rudimentary systems, and not really effective at doing much more than making the gun louder…but on certain guns, in certain calibers, it does have some pretty noticeable success at bringing the gun into "the grove."

Ok…think of the waves in the ocean again, but this time, float a six-foot long board in the water. The waves are passing under it and the board is bobbing up and down. It won't take long for the casual observer to see that the only time that each end of the board remains perfectly level from wave to wave is when the waves have a six foot period. The board may rise and fall along the waves, but it will remain perfectly level form end to end if the waves are six feet long.

But wait…what about shorter waves? Sure enough….there other wave periods in this example that would support the board in a level position, including 6in, 1ft, 1.5, 2, 3ft periods.

So, what exactly does all this gobbledy-**** really mean? You'll understand in just a second...I'm getting to that...

Since we are dealing with a Mini-14, and since by nature most of us are cheap bastards, the super easy way to decrease the effects of pressure wave deflections on a low-mass barrel is to shorten the barrel to the point where the pressure waves have a period that is "in phase" with the actual barrel length.

See my simple graphic at this link:

http://www.videoplanet-xxx.com/images/Ruge...rrelPhasing.jpg

The graphic shows the entire concept better than I can explain it.

As you can see, matching a barrel length to the unique pressure waves created during firing and having the barrel / bore axis in phase with the pressure wave at the exact point the bullet leaves the muzzle CAN be achieved by shortening the barrel.

Another thing you might notice from the chart is that regardless of the actual barrel length, it can be either too short or too long at the same time. It all depends on which side of the pressure wave you are on. And you might also notice that there are several points along a barrel length where the barrel length is in phase with the pressure waves. This means there might be numerous possible successively shorter barrel lengths that could be cut while still keeping the barrel in phase with the wave signature.

Bottom line - as long as you can get the pressure wave in phase with the barrel length, you WILL increase the accuracy out of ANY long arm, using ANY barrel, even if you have to cut off barrel length to bring the gun into phase.

Hopefully, this clears up some areas of confusion, and why it is possible to both shorten the Mini-14 barrel, increase the overall rigidity of the unit, significantly decrease the effects of the pressure induced barrel deflections, and subsequently increase the overall accuracy of the firearm.

I guess the magic question on everyones mind is "so what is the ideal length of the barrel for a Mini-14"?. And my answer to that is I really don't know. We all shoot different loads, in different climates, under different circumstances. But what I can say is this...there appears to be a "sweet spot" with the Mini using many of the readily available commercial .223 rounds that appears to fall in the 15.75" to 17.25" range depending on the loads being used.

Like all things in life, your mileage may vary...and any alterations are your own responsibility.

Lastly….let me say the before anyone attempt to cut their barrel, get the right tools or find a person who has the skills to properly cut and recrown the barrel. Don't be a dumbarse and simply whack off the barrel with a hacksaw and call it done. Further, only take off small amounts of barrel with each cut….1/4" steps are a good amount. Make sure you fire measured rounds before you start cutting, and then fire at least 50 measured rounds per step. Make sure you use your preferred ammo and use the same ammo for all testing. I strongly urge the use of a bench rest and a high-powered scope for the type of precision testing that is necessary with cutting a barrel. If you don't know what you're doing, don't even attempt this...you will be disappointed.
 

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Z Man. Great work!! NRA, after WW11, tested German M98 barrels to try to see why the steps. Arranging rods equally spaced along the barrel and firing disclosed that the rods gathered at the steps. Confirmation with non/stepped barrels. Conclusion was, as I recall, that the steps were to "tune" the barrel. From jaded memory.

I thought GCA 68 fixed the minimum rifle barrel length at 18" measured from the face of the bolt.
Hence factory lengths of l8 1/4". Am I missing something or does adding the muzzle brake count in establishing the length of the barrel? If no response to this question I get the message. TIA, Billc

PS: MERRY CHRISTMAS TO THOSE WHO CARE AND HAPPY HOLIDAYS TO THOSE WHO DON'T.

COMPARE YOUR RIGHTS NOW TO THOSE YOUR PARENTS HAD IN 1946..............
 

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It's 16 inches including the flash suppressor. Shotguns are 18 inches.

Dennis Jenkins

Originally posted by Billc
Z Man. Great work!! NRA, after WW11, tested German M98 barrels to try to see why the steps. Arranging rods equally spaced along the barrel and firing disclosed that the rods gathered at the steps. Confirmation with non/stepped barrels. Conclusion was, as I recall, that the steps were to "tune" the barrel. From jaded memory.

I thought GCA 68 fixed the minimum rifle barrel length at 18" measured from the face of the bolt.
Hence factory lengths of l8 1/4". Am I missing something or does adding the muzzle brake count in establishing the length of the barrel? If no response to this question I get the message. TIA, Billc

PS: MERRY CHRISTMAS TO THOSE WHO CARE AND HAPPY HOLIDAYS TO THOSE WHO DON'T.

COMPARE YOUR RIGHTS NOW TO THOSE YOUR PARENTS HAD IN 1946..............
 

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ZMan

Thanks for posting this item. It seems like there should be a formula one could plug powder charge and bullet weight into for given barrel parameters.
 

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I bet it differs from rifle to rifle.

Dennis Jenkins

QUOTE]Originally posted by dvdstdg
ZMan

Thanks for posting this item. It seems like there should be a formula one could plug powder charge and bullet weight into for given barrel parameters.
[/QUOTE]
 
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