[WKUHilltopper]

I’ve heard this all my life—that bolt action was more accurate than semi-auto—but no one can really explain to me why. Is it just a “thing” people just parrot—because that’s what they’ve always heard too—without any proof?

[RC one]

you can generally get a more consistent “weld” between the barrel and the forearm with a bolt gun. Bolt guns allow you to use “neck sized” ammo which is also much more accurate.

[AnalogReigns]

I believe with a bolt action you seat can the cartridge tighter—the tolerances are necessarily greater when you are mechanically trying to blow out the shell after each firing as with a semi-auto.

At least that’s what makes sense to me. A bolt is a much simpler and cleaner design and since speed of extraction is not an issue....you have the ability to have much tighter tolerances, which equals more accuracy.

[fso301]

I’ve heard this all my life—that bolt action was more accurate than semi-auto—but no one can really explain to me why. Is it just a “thing” people just parrot—because that’s what they’ve always heard too—without any proof?

As I've always understood it, a semi-auto has more moving parts. Each of these parts moves in multiple directions, some directions are primary movement while some are just due to mechanical tolerances. With each moving part comes variability and variability is the enemy of accuracy.

The end effect of all this variability is that each round tends to seat ever so slightly differently from the previous round. Head spacing will be slightly different. Gas pressures will be slightly different which results in slightly different functioning of the action. When fired, the firing pin doesn't strike the primer dead on either.

These points of variability and others tend to adversely effect the accuracy of a semi-auto more than that of a simpler bolt action rifle.

[omega4179]

Semis have a necessarily looser chamber tolerances and parts start moving around as they function.

[PugetSoundSoldier]

The breech and chamber don’t move at all; after you close the bolt, it’s essentially a single piece that will hold the entire action still until well after the bullet has exited the barrel.

[NVDave]

There’s several reasons, but they all cumulate in “looser tolerances of moving parts.”

Some accuracy techniques are applicable in both types of actions - eg, better barrels, with better crowns and better chambers. A technique that is sometimes used on bolt guns that probably wouldn’t be ideal in a semi-auto would be to tighten the case neck reaming diameter. In both types of rifle, paying closer attention to the chambering of the barrel, improving the stock mounting, free-floating the barrel, insuring that the barrel is co-axial with the receiver and bolt all help.

Bolt guns striving for maximum accuracy often sleeve their bolts - something that just doesn’t apply to semi-autos. Likewise, lapping lugs usually won’t make any sense on a semi-auto.

The point comes down to this: In a bolt gun, if you have the time and experience (or your gunsmith does), you can create an environment whereby the bullet is pointed down the bore in line with the bore’s centerline at the point just forward of the chamber. In the bolt gun, you can carry this to the fullest extent by such techniques as sleeving the bolt, lapping the lugs, facing the bolt, facing the receiver, etc, and then using a tight chamber, or fire-forming your brass. The result will be seen downrange, especially if you’re paying attention to your loading practice, which might include setting the bullet seating depth to use up most of the leade. Semi-autos are often shooting ammo that is uniformly loaded to a specification, not custom-made for that particular rifle.

As you try to achieve tighter and tighter groups at distance (say, 1000 yards), the importance of the ammunition loading, the quality of the components, etc all become much more important than at short ranges.

As for proof: Look at the benchrest records for accuracy. There’s no semi-auto that can come close to the current benchrest records. Here’s an example:

http://accurateshooter.wordpress.com/2007/07/09/sarver-shoots-1403-group-at-1000-yards/

[Armedanddangerous]

The bolt action IS definately more accurate than a semi auto, however, the semi is better for quick follow up shots, and if I understand what I hear on the sniper show on the military ch, quick follow ups are often needed.

Also, keep in mind, if you have to make a followup shot with a bolt gun one must cycle the empty round out and a fresh one in, that effects the point of aim ever so much, which a semi auto rifle does not have that problem.

[sig226]

In essence, the bolt fit is tighter in the manually operated rifle. It also uses a tighter chamber. Since you typically have two lugs on a bolt action, it’s relatively easy to fit both lugs to the barrel. An AR style bolt has eight lugs, one of which is on the extractor and will always be a weak spot. As noted, the tolerances are made a little looser in a semi auto to allow the action to operate in adverse conditions. The mechanical advantage of a bolt handle is significantly greater than a semi auto. It means the shooter can overcome more friction when chambering a round.

Also, the actions on bolt guns tend to be very thick. The extra steel resists deformation under pressure. Chamber pressure is 65,000 p.s.i., so even a slight movement affects long range accuracy.

This does not mean that a semi auto can’t achieve good precision. It can. But if all quality standards are equal, the bolt gun will shoot tighter groups.

[archy]

I’ve heard this all my life—that bolt action was more accurate than semi-auto—but no one can really explain to me why. Is it just a “thing” people just parrot—because that’s what they’ve always heard too—without any proof?

As a former match armorer and shooter who has built some winning team rifles and also worked on the Navy's M84 bolt-action sniper's rifle program, I can offer you a few generalities I've come to believe based on my 40 years-plus observing and participating in such things.

1: The person behind the rifle is of much more importance than the rifle itself. It is not a *magic stick,* whetjer boltgun, semiauto or other.

2: the ammo is of at LEAST as much importance as the rifle, probably more so.

3: A semiauto can indeed be tuned to shoot as well or nearly as well as most boltguns. But the semiauto's operation bay be destructive of a sniper's rifle's telescopic sight [not an issue with a match rifle using iron sights] and may require additional preparation and care in setting up the ammunition.

4: After a season of match rifle competition, the semiauto match rifle will likely need to be rebuilt and retuned for the next season's competition and intervening practice shoots. This is acceptable for match rifles, and happily keeps match rifle armorers at work in the shop instead of being sent off on other details and helps keep the civilian armorers' wives and kiddies fed. However, a military weapon thatr has to be rebuilt at the shop every 5-18 months is not acceptable.

Note that the Brits have reached similiar conclusions, and have gone with the very similiar L129A1 rifle, though the lovely .338 Lapua Magnum L115A1 bolt-action sniper's rifle will also remain in use.

[SBprone]

The inherent superiority of bolt rifles was due to extremely true bolts and chambers, finely honed locking lug engagement, custom chamber reamers and ammunition designed to work together, solid bedding of actions in rigid stocks, and free-floated barrels machined to very high standards by the likes of Kreiger, Obermeyer, etc.

When match smiths and armorers began to work with the M-16 about a generation ago it was discovered that this rifle’s bolt with its radial locking lugs was inherently very accurate and a good foundation for an tack-driving match rifle. Since then armorers and civilian tinkerers have experimented with chamber dimensions, bullet shapes and weights, propellants, barrel twist rates, barrel float tubes and adjustable two-stage match triggers. The fruits of all this experimentation have naturally been applied to the larger 7.62mm rifles that use the same basic design features as the M-16.

This new sniper system is only new to the military but the technology has been available on the civilian market for several years.