Action type and accuracy


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Surefire
July 1, 2006, 02:12 PM
What properties makes the bolt and single shot inherently more accurate than other action types (lever, pump, semi-auto, etc?)

I've never understood why some actions are more accurate than others.

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taliv
July 1, 2006, 03:50 PM
the more simpler the more better

bolts have fewer moving parts, and most of those parts move inline with the barrel, so there's not a lot of force put on the action in other directions. bolts are often free-floated, while lever and pump guns usually have a magazine that connects to the barrel in one or more places, and it's usually attached in a fashion designed to keep the magazine from falling off, rather than to dampen or control muzzle harmonics.

with a bolt, the only thing that moves after the firing pin is the bullet. with semi-autos, you've got a lot of movement in the gun that has an effect on the bullet's path.

beerslurpy
July 1, 2006, 04:05 PM
There are two major things that will hurt accuracy in a rifle:

1) things attached to the barrel, especially the entire length of the barrel. If a stock or a tube attached at both ends of the barrel has a different coefficient of expansion than the barrel metal, the barrel will be fine initially, but bend slightly when conditions are cooler or warmer than when assembled. The inaccuracy comes from the bending being of a different direction and magnitude depending on temperature. When you start shooting the gun, the barrel will expand and slightly lengthen, introducing another source of inaccuracy. This problem also shows when the bore is not in the center of the barrel or one part of the barrel (top vs bottom, left vs right) cools quicker than another. Tanks have this problem.

2) things acting upon the barrel during firing. Like gas systems that bleed off gas from the end of the barrel and feed it to a piston at the other end. This aids in timing, but every force exerted on rotating the bolt and pushing it back will be exerted in an opposite direction on the barrel. This causes it to gyrate. How much of an effect this has upon accuracy depends on how repeatable the gyrations are and whether there are other gyrations overlapping (as during full auto fire).

Float-barreled bolt actions tend to have neither of these problems since they lack barrel attachments, have thick barrels that function as heat conductors and heat sinks and naturally lack a gas system. Any unevenness in cooling will be dissapated by the barrel metal and any expanding effects on the barrel from heating will be greatly delayed by the large mass of the barrel and relatively large surface area of the outside.

Fosbery
July 1, 2006, 04:11 PM
the more simpler the more better

Bad...grammar...overload...must....resist....urge to....correct:o

JohnBT
July 1, 2006, 06:01 PM
Using the .22 LR as an example, the autoloaders typically have a larger chamber than the bolt actions. The fit needs to be a little sloppy to get reliable feeding. Of course, an autoloader can have a tighter chamber such as the Bentz, but the bolt guns can have, and will feed just fine with, an even tighter than normal match chamber. A tight match chamber does a better job of consistently lining the bullet up with the bore and actually makes the bullet touch the lands. When a bullet has to jump to the lands it can enter the barrel a little crooked and throw the shot off.

From: www.shilen.com/rugerBarrels.html

10/22 Barrels
Barrel grade: Match Grade Only
Material: Chrome-moly or Stainless Steel
Groove diameter: .2215"
Twist: 16"
*Chamber: Shilen/Bentz, designed for optimum accuracy in semi-autos
Crown: Target


77/22 Barrels
Barrel grade: Match Grade Only
Material: Chrome-moly or Stainless Steel
Groove diameter: .2215"
Twist: 16"
*Chamber: Tight match, designed to land-engrave bullets
Crown: Target

Vern Humphrey
July 1, 2006, 07:37 PM
the more simpler the more better


Bad...grammar...overload...must....resist....urge to....correct

Let me correct it:
The more simplerer the more betterer. :p

mc223
July 1, 2006, 08:01 PM
I own a Bushmaster/White Oak semi that shoots better than most bolt/singles.

rangerruck
July 1, 2006, 08:02 PM
Niceingly done, Vernk! Also on a bolt action , the receiver tends to be shorter and thicker, therefore, stiffer. Stiffer actions means less "whip" effect to the shot. So really you could say that the rifles that would TEND to be most accurate statistically, would be ones with no hinged floor plates, or even no internal magazines at all, such as a rolling or falling block , or a single shot, all other portions being equal.

esldude
July 2, 2006, 01:51 AM
Yeah, a falling block is about the only action that could give the bolt a run for the money accuracy-wise. But the most common rifle from Ruger, that has many redeeming features, tends to have a long chamber. Brownings don't seem to suffer from this, and are reputedly very accurate. Though I have only a Ruger #1 which will flirt with one inch groups at 100 yards in 45/70 with store bought ammo.

redneck2
July 2, 2006, 10:52 AM
You can hang out at Benchrest Central for a while and you'll figure out what affects accuracy. On a bolt gun, BR shooters take a factory receiver and square up the bolt face to the bore, the lugs to the notches in the receiver, tighten the chamber, etc.

For example, if only one lug is contacting (not unknown on a factory rifle), the action twists and binds during firing. Suppose the chamber is oversized. In effect, the round can lay with the tip pointing down.

There are (or used to be) a tons of threads about Savage vs Remington accuracy. I suspect it has a lot more to do with when the rifle was made and how good the tooling was versus brand. If your barrel was the first one of a production run, it's probably real good. If it's number 1,000 out of 1,000, it's probably not so good because the tooling is not as sharp.

As for action type, I have an AR that is accurate beyond belief. If I had to win a shooting contest, I'd take it over my 22-250 Rem 700, and it's plenty accurate for most anything.

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