FYI - Rifling - Lands & grooves ...
I've been somewhat fuzzy on this, especially when someone talks of loading bullets so they reach (or almost) the lands...
Rifling consists of grooves cut or formed in a spiral nature, lengthwise down the barrel of a firearm.
Rifling is placed in the barrels of firearms to impart a spin on the bullets that pass through it.? Because bullets are oblong objects, they must spin in their flight, like a thrown football, to be accurate. Looking down the barrel of a firearm you might see rifling like that depicted on the right.? This image shows a pattern of rifling containing six grooves with a right twist.
THANKS TO http://www.firearmsid.com/A_bulletIDrifling.htm FOR THESE IMAGES
Rifling consists of grooves cut or formed in a spiral nature, lengthwise down the barrel of a firearm.
Rifling is placed in the barrels of firearms to impart a spin on the bullets that pass through it.? Because bullets are oblong objects, they must spin in their flight, like a thrown football, to be accurate. Looking down the barrel of a firearm you might see rifling like that depicted on the right.? This image shows a pattern of rifling containing six grooves with a right twist.
THANKS TO http://www.firearmsid.com/A_bulletIDrifling.htm FOR THESE IMAGES
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What they mean by almost reaching the lands, is that the ogive of the bullet shouldn't actually engage the rifling on a loaded chambered cartridge, but for best accuracy it should be just barely off (this depends on the gun, it's trial and error).
Also, rifling works regardless of whether it's a roundball or an oblong object (look at the changes in muzzleloaders in and around the civil war era)
Does that clarify what you're after?0 -
Rifling, as previously stated, stabalizes the projectile/bullet regardless of the dimensions of that bullet, e.g. round, conical, etc.
Generally speaking the greater the length to the diameter (more oblong) the more spin (stabalization) needs to be applied. This is also true to the same general shape bullets as the bullet weight is increased.
The amount of spin is governed by the twist rate of the barrel and that is where you will see references to 1 in xx or 1:xx and the "xx" is stated in inches ... so a 1 in 7 or 1:7 is that the rifling makes one complete (360 degree) turn in 7 inches. Thus a 1:7 barrel has a higher spin rate than a 1:10
Now as for the cartridge length being set to have the ogive of the bullet just short of touching or touching the rifling, this practice relates to the quest for the greatest accuracy and is based on the theory that the less distance the bullet has to travel before encountering the rifling the better the accuracy. In concept this is a valid theory but not all rifles are the same, so in handloading you have to adjust your loading setup to the rifle and that is basically a trial and error practice. Once you have what appears to be a good charge weight for a given bullet shape and weight you can then experiment with the cartridge length to see if you can reduce your group sizes, and in this process you have to be aware of pressure changes as the bullet comes closer to the rifling (stiffness of bolt action to eject, flattening of the primer, etc.) And it is not uncommon to have to slightly reduce the charge weight. All of this length change is done in thousandths of an inch increments and for hunting purposes, IMHO, is a waste of time as any quality, modern, field grade rifle will be chambered to SAAMI Specs. and commercial ammo or handloaded ammo to standard reloading specifications will produce more than adequate hunting accuracy.
Hope this helps clear it up. If not and all we've succeeded in doing is giving you a headache ... take a couple asprin and ask us to try again[:D]
+++Update+++
Valudude is absolutely right ... I got a little overfocused. There can be value if your going after prairie poodles, chucks, etc. at long ranges. However, when you get to this level of precision loading, generally, your looking to tighten groups at distances (repeatability) -vs- putting a single (first) shot on a small target. But I'm glad he caught my oversight ... thanks "V'dude"!
If you only have time to do two things so-so, or one thing well ... do the one thing!0 -
quote:...and for hunting purposes, IMHO, is a waste of time...
I think this depends on what your quarry is and at what range you will be shooting. Small target at long range, maximize accuracy.
Otherwise I agree.0 -
Not to add to Jsergovic's headache, But why the need for a variable twist rate, and what are the pro's and con's to having one? 0 -
Trapp55
The biggest potential advantage to using a "Gain Twist" barrel is with long (pure) lead bullets moving at high velocity. Start out almost streight and increase the spin gradualy (over the length of the barrel) as opposed to trying to get the spin speed up fast (IE: in the length of the bullet). As these bullets will "strip" (shave the outer layer of lead in the rifling, leaving the bullet at bore diameter with little or no spin) in a fast twist high velocity loading.
Other than that, it's advantage is pure (unproven) theory.
Some guys like a mag full of lead, I still prefer one round to the head.0 -
Thanks Tailgunner, Learn something new every day! And just when I thought I knew it all![:D] Just proves you can teach an old dog new tricks.[;)] 0 -
I load everything AT the lands and work the load. Then,..take that recipe and work both into,.. and away from the lands to see what appears to be the best group. Almost all guns will shoot better AT the lands (that means touching the lands,...not shoved into them) All my loads will leave a slight scar on the bullet jacket when chambered and ejected. I have rarely seen a rifle NOT shoot it's best when touching the lands. Some will like to be up to .010" off the lands,.but others will like to be .010" into the lands. It is rifle specific,..and only a lot of loading and range sessions will prove the best for your gun. Once you have the accuracy load for a good powder at 100yds,..then the load testing while moving into and out of the lands is best tested at 300yds and further. this distance will allow the subtle differences to appear and be clear cut.
why chase the game when the bullet can get em from here?....
Got Balistics?0 -
Justin started this whole thing. And explained it in a most succinct way.
Thanks, all !!0
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