Action vs distance and accuracy

[theboyscout]

Is it true the athe action of your rifle affects the distance and accuracy of the rifle. Growing up I was always told that a break barreel rifle closes and seals better than a bult action and a bult action better than a semi auto or pump. And with the action closed or sealed tighter more gasses have to go out the front of the barrel thus pushing the the bullet more effectively to it's max distance and accuracy better. Is that true?

 

[wanderinwalker]

OK, I *think* I know what you're asking, so I'll take a stab at answering it.

First off, a break action single shot is NOT the best choice from an accuracy standpoint. It is in fact a matter of how the action closes and "seals", but the hinged actions are flexy and not always consistent in lockup. Case in point, the NEF/H&R single-shots are notorious for how variable their accuracy is. Some are very good, others are at best mediocre.

The bolt action rifle is truly the best choice from a precision standpoint, based on how consistently they can be made to lock-up and how the action can be bedded to the stock. Plus the lock-time can be shortened and a number of factors that are well beyond my understanding. Accuracy is all about having everything happen the exact same way every single time. Variety is good for ice cream flavors, not for rifle accuracy.

Semi-autos can vary as much in accuracy as the break-action single-shots I mentioned above. This is also due to inconsistencies in lockup, multi-piece stocks, and the fact that the cycling of a semi-automatic throws lots of wonky vibrations into the system. Many semi-auto rifles can be very good; witness all of the AR-pattern rifles that can shoot sub-MOA. The reason the AR-pattern allows for this is because the barrels can be free-floated quite readily, and there are no heavy reciprocating parts riding around on top of, or below the barrel that don't return to the same place every shot. My personal match-ready AR-15 Service Rifle would outshoot the Thompson Center Encore (break action single shot) I used to have and is quite likely more accurate than either of the bolt-action sporters I currently have in my gun cabinet. This particular AR-15 has a very good stainless steel match barrel and a heavy steel free-float sleeve.

Now to the point you were mentioning about "maximum velocity and accuracy". Accuracy generally doesn't have anything to do with your ammunition achieving maximum speed. Target shooters frequently find their best accuracy with reloads that are below the maximum possible velocity for their bullet/powder combination. Action type doesn't really impact the muzzle velocity of your ammunition as much as the specific barrel on your rifle. While theoretically you'll lose some velocity with a gas-operated semi-automatic versus a fixed breech action (bolt action, single shot, pump), in actual practice it isn't significant enough to matter.

Short version: pick a rifle you like and shoot it.

 

[Bushpilot]

Growing up I was always told that a break barreel rifle closes and seals better than a bult action and a bult action better than a semi auto or pump. And with the action closed or sealed tighter more gasses have to go out the front of the barrel

It's the brass case that "seals" the gases in the action by expanding tightly under pressure against the walls of the chamber when fired, not the action itself... The "action" holds the case in place and keeps it from backing out of the chamber which would allow the case to stretch too much and rupture..

 

[taliv]

as others have said, it's not a question of "sealing" per se. for sure, when shooting most ARs you will get gas back in your face so it may seem like it's not "sealing". However, this is because the case is ejected before the pressure in the chamber has returned to ambient. But the bullet left the barrel a long time before the chamber is opened, so it doesn't affect the velocity.

generally, people will run lower powder charges to get less pressure in semi autos vs bolts, and they'll often run powders that burn at different rates.
this means you typically get a little less velocity in a semi. There are a few reasons. imho, the biggest one is that a semi is going to eject the case before it has time to cool. Semis are more sensitive than you might imagine, as the difference in an ounce of weight in the buffer (say going to an H or H2 buffer) will make a difference in how reliable your ejection is. Obviously, ejecting a bolt gun is manual and takes much longer, giving the brass time to shrink back a wee bit from the chamber walls. I believe you'll see some differences in reloading manuals and mfg powder recommendations for bolts vs semis.

A separate issue is that the semi typically redirects a portion of the gas out of the barrel to operate the action. It might be interesting to chronograph a semi with an adjustable gas port and see how much of a change you get in velocity with the port full open vs closed. offhand my guess is it's probably worth 10-20 fps depending on length of the gas tube.

 

[Varminterror]

The content in the OP doesn't really match the Thread title.

Yes, it is true the action of the rifle does affect the accuracy, or rather precision, of the rifle. No, this pseudoscience of action "air tightness" isn't a factor. As @Bushpilot mentioned, the brass is the effective seal for the system. Consistency and symmetry of lockup is what matters. A bolt action rifle will typically have a more symmetric lock up - long term - than a break barrel.

"Distance," or effective range, is a factor of retained velocity at range. Retained velocity at range depends upon initial velocity, Muzzle velocity, as well as bullet aerodynamics, ballistic coefficient, and upon environmental conditions, density altitude. None of that really affects PRECISION, really, but it is easier to shoot long distance with a flatter shooting bullet and cartridge.

Semi-automatic, centerfire rifles are typically NOT sealed bore, so they lose some muzzle velocity compared to a sealed bore action with the same barrel length, like a bolt action or break action. Semiautos use some of the expanding gases to operate the action. The action lock up design and reciprocating mass also tends to rob semiauto rifles of some precision. They trade a bit of precision for an increased rate of fire. But for most practical pursuits - that is hunting or soldiering - the target size is sufficiently large such the difference in impact velocity really doesn't change the effective range terribly.