Why are bolt action rifles considered more accurate than semi-auto ones?

--Terry--

--Terry--

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Hi,

I'm having a disagreement on aonther forum with some people on why semi-autos are not as accurate as bolt guns.

Actually I don't know the answer.

But some guys are saying that semi-autos are less accurate because of the movement of the bolt WHILE the bullet is leaving the barrel which causes the gun and barrel to shake/vibrate and thus affects the trajectory of the bullet.

I believe that the bolt doesn't move at all until AFTER the bullet leaves the barrel on semi-autos. But they are not convinced, and I myself cannot come up with an answer of why semi-auto is less accurate.

So, could anybody enlighten me on this question?

Thanks in advance.
 
the bolt starts to move as soon as the bullet passes the gas tube. so its possable.

im deffanetly not an expert. but what i would think is a major part of it is that with a bolt action it kinda forces you to cool down after each shot.

im sure other guys here will have other reasons and are more experianced than i am.
 
Aries- said:
im deffanetly not an expert. but what i would think is a major part of it is that with a bolt action it kinda forces you to cool down after each shot.
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I always thought of it the same way. The bolt gun kinda keeps you from resorting to "spray and pray". Every shot has to count. Also, significantly less chance of a jam (less moving parts).

As far as mechanically, or scientifically, why bolt guns are more accurate... There are several threads on this subject on the american "sniper" forums. Try googling "bolt action vs semi auto".
 
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A lot less moving parts involved in the process. So it is easier to have them all fit tight together to produce consistency shot after shot.

My 0,02$ :)
 
IntelGDR691 said:
A lot less moving parts involved in the process. So it is easier to have them all fit tight together to produce consistency shot after shot.

My 0,02$ :)
Click to expand...

+1

And as stated before, the bolts move backwards as soon as the bullet passes the gas tube.

In a bot action, there's less moving parts, and the bolt is tightly shut. Not an expert too, but that's what I know/think.
 
Check out the videos I have linked. The projectile leaves long before the action opens. Semi's are less accurate due to a loose and/or inconsistent lock up between bolt and barrel. In the past semi's had poor triggers as well when compared to bolt action rifles. Bolt guns generally have longer barrels which produce higher velocities and inherently provides for consistent accuracy at greater ranges over short barrel firearms.

http://www.youtube.com/watch?v=G0VjdI_S_HM&feature=related

http://www.youtube.com/watch?v=qNmqMlm7i8g&feature=related

At 50 seconds in this video you can see the bullet just ahead of the muzzle. Seeing as how he's firing a carbine length gas system and the projectile has left the barrel prior to the action opening. It would be safe to say a longer radius gas system will have similar results.

http://www.youtube.com/watch?v=dHG2IWV1caE

Here is another great site with some excellent high speed of a shotgun and the action of an AK.
http://www.photron.com/content.cfm?n=gallery

TDC
 
Well, there are more to that, I think.

On a semi-auto with a float barrel, I can't see why "moving parts" could affect accuracy because they move AFTER the bullet leaves the muzzle: In a semi-auto, for the high pressure inside the barrel to start pushing the piston/bolt back, it has to overcome the tension of the recoil spring, and the inertia of the still bolt. So there is a slight time difference between the bullet leaving the muzzle, and the bolt start moving back.

So, what factor was affecting the trajetory of the bullet which flies out of muzzle right after it passes the gas port?
 
Less moving parts, closer tolerances, it all means repeatability, which some people call accuracy ;). The critical moving parts in a semi's case are the ones related to the gas system usually, but anything touching the barrel, even a looseish fitting bolt will affect the harmonics right there, and if your gas piston gets wacked by the propellant gases as the bullet passes the gas port and causes a weird vibration right before the bullet exits the muzzle, and you have a completely screwed up trajectory.
 
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Bolt has stronger camming effort on the cartridge thus neck sizing fire formed brass is more reliable in a bolt gun. Shooting factory ammo, a good auto loader can rival many bolts.
 
The biggest issue with semis (especially the military derived ones) is that they are designed for 'reliable' function. That usually means oversized chambers with very long throats. It's the long throat that can lead to bullets wiggling around in the throat before engraving in the lands.

Cockeyed bullets don't travel very straight towards the target.

The barrels on semis are also poorly made as the primary concern is surviving high rates of fire vs bug hole groups.

Then they usually have alot of slop. Ease of maintenance and function under conditions means parts can rattle around.

Poor bedding is also very common.

Add in heavy, gritty, spongy trigger pulls and you have the worst aspects for accurate fire.

In all semis that I have seen, the bullet leaves the barrel BEFORE the bolt fully unlocks. It better or else the shooter is going to wear ALOT of hot gases.

The shining example of how well a semi can shoot is the AR15/10 and variants.

The gas impingement reduces parts moving and crashing around which can upset barrel harmonics. The entire gas system is designed for modern pressures so normal 'factory' ammo doesn't throw the moving parts into a spasm.

The barrel is free floating and well isolated from the handguard and other accessories. A very solid action mounting system.

Todays AR's have some of the best barrels in the business mounted. They are of larger profiles for more rigidity. Chambers have better throat designs. Triggers also mimic some of the better working bolt rifles.

Add in optics so you can see what you are aiming at and the AR platform is now a true 1/2 min or SMALLER rifle. Amazingly, reliable function has been retained in many respects.

There are a few custom tuners that have done wonders for the Mini 14 too.

I have worked on several M305's and have gotten MOA performance just by proper tuning and load work up. The barrels on some of these even came with match chambers.

Certain semis can shoot as well as many bolt rifles. The bolt rifle will still be the platform of choice for BR type accuracy but for sub MOA, there are plenty of other choices today.

Jerry
 
bolt action is more accurate than a semi-auto

On a semi-auto u loose gas pressure because it uses the gas to force the bullet out and force the action back open. So the bullet looses speed on a semi auto and so it also looses its distance. On a bolt action however ALL of the gas is presses against the bullet thus more speed, more range, and a more accurate shot.
 
In the past I think it was more true that bolt actions were more accurate then semi auto do to all the previously listed reasons above which i wont bother repeating. But presently both actions are on par do to the aid of current ballistics technology.

Barrett and Accuracy International as well as several other weapon contractors have built new semi automatic sniper platforms which perform as well as their bolt action counter parts for multiple unit engagements. So in short both actions are capable of the same accuracy but getting a semi automatic action to the standards of a high performance bolt action weapon system takes quite a bit more work and alot more money but is possible.
 
D) All of the above except losing gas pressure. It has more to do with stability of the action in the stock than anything else.
 
Thank you guys for all the answers.

In a word, it is not about the movement of the bolt. It should not affect accuracy because the bullet should have left the muzzle before the bolt starts moving.

It is actually many other factors working together.

And semi-autos can be made with very good accuracy if somebody is willing to pay a lot more money for it than a same-level bolt rifle.
 
I'll play devil's advocate and say that a gas gun can be every bit as accurate as a bolt gun of equal quality. The difference is the triggers. Bolt guns are easier to shoot well because it is exceedingly difficult to get a very good trigger on a gas gun.
 
Manually cycling the action is cool, and therefore more accurate. Pump actions are even cooler than bolt actions, and even more accurate.:cool:

Semi-autos can't have as tight tolerances, or they would jam frequently.
 
there are extremely accurate autoloaders out there - repeatability is the key, and tolerances. for instance, a good autoloader will return to battery exactly the same way each time, but does everybody throw the bolt the same way each time?. There's also the human element - its easier to do the same thing the same way with an auto and get tight groups than with a bolt action that recoils and takes more work to return to the same position each time.


To my mind its a tossup
 
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