Bolt-action to semi-auto conversion help

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Jessesky

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0EC9960C-59FC-41BC-B53E-2DEF9E45380D.jpeg Hey guys,

Starting a project to tinker with and help better understand what goes into developing a firearm. I have this old sears .22 rifle lying around worth little more than $50.

Since I don’t want to mess around with the greater forces of a centerfire rifle yet, a 22 is the perfect place to start.

I’m looking to do the simplest of conversions, drilling a gas port, attaching a gas piston and running the piston to the bolt handle where I will craft something like the Howell rifle (pictured). Any tips or issues I may come across?

Any tips on how to prolong the bolt from coming out of battery too soon?
 
All the .22 automatics I know of are blowback, the only thing
to "prolong the bolt from coming out of battery too soon" is the mass of the bolt and the tension of the recoil spring.
 
If you look closely at the Garand type actions, its a bolt action with the handle cut off, and a mechanical hand working it. Of course it was streamlined, but a good place to start. Much simpler than that crazy enfield. As far as early unlock, you start with a small hole and make it bigger until it works. I assume your sears is a bolt action? The issue is where to put the port, but math will help that.
 
[QUOTE The issue is where to put the port, but math will help that.[/QUOTE]
Another issue will be the trigger disconnect to prevent the firing pin from following the bolt forwards and slam firing the gun full auto.

SC45-70
 
No gas driven 22LR. No full rattle trap conversion gun without a disconnector. Back to the drawing board.
True, or else I’ll have the ATF at my door. I suppose I’ll have to figure out how to machine a new trigger group
 
A straight-pull Ross or Steyr already has all of the same innards as, say, a Remington 742 autoloader - a bolt carrier with a separate rotating bolt. The only difference is that the Remington has a gas cylinder and a return spring and the first two require you to use a handle to move the bolt.

You only have to move the straight-pull bolt back and forth; the rotating part is internal, between the bolt and carrier. Makes things a lot simpler than, say, the attempts to convert SMLEs back in WWII.
 
As a humble suggestion, why don't you do the reverse and buy a smg parts kit and do the conversion to semi-auto with a new receiver. Even making a Sten smg into a reliable semi-auto will teach you points of what to consider when converting some sort of bolt action into a semi-auto. Parts kits are relatively cheap and receiver blanks for conversion are available along with communities of interested folks to guide your build. Some of the old Shotgun News/Firearms Talk articles also give good guidance on how to build a safe, legal semi auto from those kits.

Might also want to look up the Mondragon and older Remington/Winchester long action semi-auto rifles as well in design.
 
As a humble suggestion, why don't you do the reverse and buy a smg parts kit
A straight-pull Ross or Steyr
It’s not that it’s the easiest or the best way, it’s the idea of creating something new that hasn’t been done rather than restoring a deactivated gun. I’d like to do a straight pull steyr with a sporterized gun to practice on, but I don’t feel comfortable enough to use it on a full size cartridge yet like the 8x56. That’s a lot of energy to learn with.
 
It’s not that it’s the easiest or the best way, it’s the idea of creating something new that hasn’t been done rather than restoring a deactivated gun. I’d like to do a straight pull steyr with a sporterized gun to practice on, but I don’t feel comfortable enough to use it on a full size cartridge yet like the 8x56. That’s a lot of energy to learn with.

I understand your want to have something unique but bolt actions are childs play compared with making a bolt action into a semi-auto. Either you go gas operated or require a short/long piston or blowback. Perhaps the cheapest route is to take one of those cheap Spanish 93 Mauser receivers floating around (Sarco has them for 19.95 each), convert it to something like 9mm which might have enough umph to cycle a bolt maybe through something like the Garand external piston. Spanish Destroyer 9mm magazines are around as well. You will still need someway to prevent it from going full auto that works in advance as otherwise that can be an ATF problem asap without a license. There is no inventor exception to the NFA.

Given that the Ruck Zuck (aka m95) requires quite a bit of energy to operate the bolt, I would not really consider that as a great option unless you are using full power cartridges.

That is why I suggested learning about the intricacies of how to make a semi-auto first as a means of understanding just how to prevent the ATF from coming down on you for making a machine gun and to make your invention reliable and safe enough to shoot. It took even the famous JM Browning awhile to get semi auto right because a lot of things have to happen in correct sequence for the weapon to be functional.

Pick up the Shotgun News Gunsmithing special collection book and there are a bunch of descriptions of step by step they remade full autos into ATF safe semi-autos. Even if you aren't interested in reactivating these, the steps will be similar. It is possible that Steve Matthews might answer some of your questions if you can get into contact with him. Steve made semi-autos from scratch in at least one series of articles.
 
If Mach IV Shooter was suggesting this, I'd say 'great, go for it." Because I know he knows the laws, is a top-grade machinist, and has built many guns. Judging from your posts thusfar, I agree with Gunny, a foolish endeavor. Much easier to convert a semi-auto to a pump, BTW.
 
I’m looking to do the simplest of conversions, drilling a gas port, attaching a gas piston and running the piston to the bolt handle where I will craft something like the Howell rifle (pictured).

I think the simplest conversion would be to add mass and a spring behind the bolt, gut and machine the bottom of the bolt so a hammer could impact the firing pin and pick up some semiauto trigger group and use that vs the striker. It would be a straight blow back, like every other semiauto .22. Likely wouldn’t look like much when your done but I’d bet you learn something.
 
I'm afraid if you bleed enough gas to cycle the action there won't be enough to propel a projectile, there's a reason tiny cartridges are blowback.
 
Blowback is easier with fewer parts than gas but but the major issue with blowback is finding the proper weight and springs for reliable function plus then ensuring proper feeding and extraction as well as disconnecting to prevent full auto if you hold the trigger down. You will also have to make sure that it fires from a closed bolt per ATF ruling. Steven Mathews in a Shotgun News series made a semi auto .22LR from scratch except maybe the magazine. Might have some useful information in the article. Practical Machinist forum also has a few machinists that like to do stuff like that.
 
One way to slow the opening of the bolt hasn't been discussed. If you look at the cycling action of the gun in the first pic, you'll see the lever is actuated by a diagonal slot that's forced back by gas. If you were to extend the slot horizontally at the starting point, the gas piston could move half an inch (or however long you extend the slot) before the handle is forced up and back by the angled portion of the slot. The slot would end up looking like the hands of a clock at a time of 9:10.
 
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