Semi-auto with locking bolt?

[campergeek]

I hope this question won't make me seem really daft.

I have a semi-auto .22 rifle built by Savage but store-branded by the "Coast-to-Coast" chain. It's a clean, well-functioning and accurate rifle, but it has a feature that somewhat perplexes me. The bolt handle extends through the other side of the chamber and the other end can be pushed through one of two holes - one locks the bolt open, the other locks the bolt shut. I can see the utility of locking the bolt open, but for what reason would one want to lock the bolt shut?

Doing so does not act as any sort of safety; if there is a round chambered the rifle will still fire. However, it will not eject that round and load the next. The best I can figure, this is an attempt to provide a "best of both worlds" between a bolt-action and semi-auto. Leaving the "lock" unengaged allows the rifle to function in semi-auto mode, but locking it shut provides the rigidity (and theoretically greater accuracy) of a bolt gun, also requiring the shooter to cycle the next round manually.

Does anyone have any insight on such an action? The model number stamped on the rifle is 285N, and I have found one cross-reference that identifies the rifle as a Savage "7J", but I can't find any info about a Savage 7J. Any knowledgeable insight, blind guesses or mad theories are welcome.

 

[Jim Watson]

These guns were rated .22 short, long, or long rifle, but they probably won't function in auto with anything but LR, unlike the Remingtons. The manual mode is for the shorts and longs.
Also, as Henry Stebbins, one of the best writers of the '50s said, it would be good for teaching a kid to shoot. You could require him to operate it manually to keep from getting trigger happy.

My Weatherby XXII has a manual mode, too.

 

[FlyingBohonk]

Many years ago I used the lock mode on my Coast to Coast rifle to get more power out of the gun when coon hunting or for long shots. It makes the gun a single shot bolt action. Unfortunatley, sometimes you push it in by mistake when carrying it and you won't get the next round loaded. That was a bummer.

 

[rcmodel]

I think the original intent was to lock the bolt closed on an empty chamber for safe storage in loaded mag ready condition.
IE: No chance of it loading itself if the bolt handle snagged on a gun case or something.

Also the ability to use it as a single-shot while training kids and such.


It does not add any power, speed, or accuracy to the bullet to lock it shut.

The bullet is gone and pressure is down before the bolt blows open anyway.
If it wasn't, the case would rupture.

rc

 

[Maverick223]

It's what is often described as a "gill-gun" (derived from the slots in the receiver, which vary by model). I have a Stevens 87D that is similar (it's tube-fed and the charging handle is smaller/longer).

As mentioned above the locking feature is used for cleaning (in open position) and shooting low-powered ammunition (like shorts and CBs) in the closed position. My example will feed just about anything from the magazine (being a detachable box magazine fed model, I'm not certain that your's will do likewise), making the feature very practical IMO. To expound a bit, they tend to be very accurate, but reliability is often reported as spotty (though mine has been very good in this respect).

I've attached a schematic for the tube-fed version, as well as a key (there is some parts interchangeability).

 

[MachIVshooter]

Many years ago I used the lock mode on my Coast to Coast rifle to get more power out of the gun when coon hunting or for long shots.

There is absolutely no velocity increase by locking the bolt; Bullet has left the muzzle long before the bolt opens.

 

[Owen]

I have one of these, Sears branded, and would to love to know more about them.

Is the trigger supposed to hold the bolt back until released?

Is yours accurate? (mine is not at all)

 

[Maverick223]

Is the trigger supposed to hold the bolt back until released?

Yep, it's designed that way. It should also be noted that you must pull the trigger to fully extract and replace the bolt for dis/re-assembly.

 

[kBob]

Yep. Also the tube feeded as others have said feeds S, L, LR and I have seen one cycle with CCI CB Longs even.

Now I have to break the Chrono out of storage to see if these guys are correct and find buddy with gun.

-kBob

 

[Maverick223]

Yep. Also the tube feeded as others have said feeds S, L, LR and I have seen one cycle with CCI CB Longs even.

I'll have to give that a shot; I don't know that I have ever tried it, but I wouldn't be terribly surprised if that was the case.

 

[Steel Horse Rider]

That feature is for when you are using the grenade launcher attachment......

 

[holdencm9]

There is absolutely no velocity increase by locking the bolt; Bullet has left the muzzle long before the bolt opens

I am confused doesn't the bolt have to start moving the instant the bullet starts moving, if it is blow-back operation? Due to the much greater weight of the bolt, friction, and recoil spring pressure, the bolt may only move 0.01" by the time the bullet exits the muzzle, so it is probably a negligible difference in velocity of the bullet, but you said absolutely. In concept, there is nothing that holds the bolt forward so if it isn't moving by the time the bullet leaves the barrel then what starts it moving?

 

[Maverick223]

I agree, physics proves that the bolt and bullet begin moving simultaneously, they do not, however move at the same rate. The bolt has much greater mass, and therefore moves very slowly by comparison. There would be a reduction in velocity as a result (pressure is reduced, because volume increases), but it's certainly negligible and perhaps immeasurable, which I think was rc's point.

 

[holdencm9]

I hear ya maverick. I think we are all on the same page then. I just heard "absolutely" and as an engineer I rarely deal with absolutes. So then it got me wondering if maybe my whole understanding of blowback operation was errant! I agree that with the much much much larger mass of the bolt it will not move much at all. I did a quick calc and figured about 0.2" and that doesn't even figure in the recoil spring force or friction. Thanks for clearing that up.

 

[Maverick223]

Don't forget the added mass of the spent case, & powder (which will be divided between forward & rearward momentum), in addition to static and dynamic friction for both bullet & bolt (which will change dependent upon the lubricants & fouling present), and the spring compression...it becomes an equation that I'd rather leave to the ballisticians.

I remember doing a "simple" calc. to determine the optimal bbl length of a ceterfire rifle cartridge before friction deteriorated performance...not something I'll be doing again.

 

[MachIVshooter]

Holdencm9-

As Maverick already pointed out, and as you seem to have understood anyway, the amount of rearward travel the bolt exhibits before the bullet exits the muzzle is miniscule, and the corresponding increase in volume of combustion chamber equally small.

Yes, if one were able to consitently and exactly replicate pressures, friction and all other varibales, you would see a tiny change in velocity from locking the bolt. In reality, however, the standard deviation from shot to shot will be far greater than the difference created by the small change in combustion chamber volume and resulting pressure.