Bolt design

[ShottyUK]

Hello.

I've just joined the forum, but have been visiting and reading for a while now. I'm based in the UK, and until now have only worked with shotguns and air rifles (there are much easier to work on from a legal perspective over here, as I do it for a hobby).

I am in the process of getting licensed for a 22LR, which of course I intend to build myself (with the exception of the barrel). I'm happy with my design so far (receiver, safety, trigger, stock) but the bolt is causing me concern, and I have some questions;

I like the idea of a bolt with locking lugs at the front (mauser style, I think). Obviously the bolt needs to rotate, whilst the sleeve and cocking piece remain in place. This sounds fair enough, but am I right in thinking the bolt rotates about a thread on the sleeve? There is something about constantly working a standard thread that doesn't sit right with me, which is why I'm asking.

Alternatively, I've seen a .22LR bolt where the bolt and cocking piece remain still, whilst the sleeve rotates about the bolt (single locking lug on the sleeve) - this was on a 'Brno' rifle. This would be easiest to manufacture, but I wonder if this design would scale up to larger rounds (the sleeve would probably be very large for a .270, for example, and there would be no safety lug).

Finally, are there any recommended books that cover design considerations and conventions? I have read "a master gunmaker's guide to building a bolt action rifle" which is a good start, but isn't much more than a set of plans whereas I'm more interested in design. For example rules of thumb regarding the size of locking lugs, or suggested barrel/action threads. I will subject my final design to CAD simulations, but currently I'm working on paper.

Any advice would be appreciated.

Thanks.

 

[marky123]

Hello.

I've just joined the forum, but have been visiting and reading for a while now. I'm based in the UK, and until now have only worked with shotguns and air rifles (there are much easier to work on from a legal perspective over here, as I do it for a hobby).

I am in the process of getting licensed for a 22LR, which of course I intend to build myself (with the exception of the barrel). I'm happy with my design so far (receiver, safety, trigger, stock) but the bolt is causing me concern, and I have some questions;

I like the idea of a bolt with locking lugs at the front (mauser style, I think). Obviously the bolt needs to rotate, whilst the sleeve and cocking piece remain in place. This sounds fair enough, but am I right in thinking the bolt rotates about a thread on the sleeve? There is something about constantly working a standard thread that doesn't sit right with me, which is why I'm asking.

Alternatively, I've seen a .22LR bolt where the bolt and cocking piece remain still, whilst the sleeve rotates about the bolt (single locking lug on the sleeve) - this was on a 'Brno' rifle. This would be easiest to manufacture, but I wonder if this design would scale up to larger rounds (the sleeve would probably be very large for a .270, for example, and there would be no safety lug).

Finally, are there any recommended books that cover design considerations and conventions? I have read "a master gunmaker's guide to building a bolt action rifle" which is a good start, but isn't much more than a set of plans whereas I'm more interested in design. For example rules of thumb regarding the size of locking lugs, or suggested barrel/action threads. I will subject my final design to CAD simulations, but currently I'm working on paper.

Any advice would be appreciated.

Thanks.

Sounds interesting,but I can't think of any .22 rifle with front locking lugs.What sort of things have you built shotgunwise?
MARK

 

[Dave W]

Since you're doing this for a project, you might want to take a look at "The Bolt Action Rifle" by Stuart Otteson. There are two volumes. The first covers military rifles, the second commercial rifles. The books get down and dirty on just the sort of things you're asking about, along with trigger mechanisms, etc.

The paper volumes are long out of print, but you can get scanned CDs through Amazon for $25 or so.

I know "read the book" isn't a very satisfactory answer, but either or both of those volumes will answer questions you probably didn't even know you had!

 

[Alpacca Fortyfive]

There are two reasons for the apparent lack of front locking bolt actions in .22RF.


Most importantly, the short rimmed case runs the risk of catching in the locking recesses, and those locking recesses also provide a longer than optimum feeding path for the short length of the loaded round.

Second, with the small diameter of the case head, and the low pressures which rimfires must be kept to

( there is a balance to be achieved in rimfire cases, in order to avoid needing too strong a striker blow to initiate a thicker case, and to avoid bursting the thin case needed to allow a moderate striker blow to initiate it reliably)

Coupled with the relatively large size of the bolts used to allow easy operation with normal sized hands, bolt and receiver deformation during firing remains within acceptable limits with rear locking, and as you won't be reloading rimfire cases, it doesn't matter if there is a few thou of stretching.

Regarding the Brno / CZ, the root of the bolt handle forms a second lug on the locking sleeve.

I think Krico produced a .22 hornet with that type of bolt, and IIRC, Savage produced larger rifles with a similar layout.

For design formulae, I posted a link here a few weeks back to Forgotten weapons blog and a design manual which they posted.

Check out the furrer threads at Forgotten weapons, as one of the Gentlemen posted a link to a HTML version of Chinn's "the machinegun" , Vol 4, which contains design formulae. .pdf scans of Chinn's books are up on SCRIBD.

Back about 2007, I also posted some bolt design formulae quoted from Alsop, Popelinsky et al on this forum, the book is currently unavailable, and was hideously expensive a couple of years back (£700+ on Amazon!) .

good luck with the paperwork!

 

[speerchucker30x3]

Front locking lugs in a 22RF? Easy Peezy, just figure out a way to get the nose of the cartridge into the chamber before the rim leaves the feed rails. Or it can be done with a modified tiny control round feed Mauser. I made two of them about 20 years ago. There is no lower locking lug on the bolt. Where the lower lug should be in the action is the cartridge guide box. It forces the cartridge up into the extractor after the cartridge has left the magazine and then drops out of the way when the bolt nose comes up against it. Sort of a little teeter totter arm or hand that holds the cartridge as it travels into the chamber. The extractor has a fake locking lug just behind the claw to give the illusion of two lugs when the bolt is pulled back. I saw the original at a gun show and with the permission of the owner stripped it and traced the parts and took pictures of all the parts. I had over 50 hours into the first one 40 into the second. I never built another and never will at $2,000.00 a copy for just the action. I used Remington 581 magazines, hangers and catches in the same way the Anschutz single shots are converted to clip repeater without the expensive Anschutz magazine. I also used a modified Remington 541T trigger. The hardest part was broaching the two raceways without the action expanding or cracking. After wreaking a couple I did it with the action body in a heavy sleeve. The drawback is the long travel of the bolt required to make it feed which is almost 2 1/4 inches.

 

[wesg]

Bleiker, and Grunig & Elmiger, both make a rimfire action (same thing afaik) with front locking lugs. You can get a sense of scale from the pictures and renderings.

Only other modern action I'm aware is made by Time Precision. Basically a Rem 700 clone with a cone breech, no feed ramp. Genuine pita to load from what I've read.

 

[LBrooks]

I have pictures in my files of the Japanese design of the 98 Mauser bolt. It has the sleeve which rotates, but is not threaded into the bolt body. I believe it would be worth playing around to see if you can redesign to fit your own 22 LR design. If interested I can make up a PDF file and send it over in an email as an attachment. This design was made during WW11 for some of their rifles.

 

[ShottyUK]

Thank you very much for your responses, I'm glad I found this forum.

It hadn't occurred to me that front locking lugs would be harder to feed. I initially jumped at the idea because it would allow me to scale up the design for a larger round at a later date (I'm also getting licensed for something slightly larger; .222, .223 etc - TBD). The reason I thought the front lugs were common because I've seen lots of larger rifles, but only one bolt action .22LR.

I'll now focus on a sleeve lug design, and see what I come up with, paying attention to usability too.

I'll read up on all the suggested resources. I'm in no rush & want to do it properly, and like to understand the theory behind what I'm doing.

@LBrooks I'd be very greatful to see the pictures you have. I'll have a go at sending you a private message if I can work out how.

@Mark Recently I've just been fixing guns & making the occasional part when I get the chance. As I'm not licensed (day job is behind a computer 9-5 in an office) I only tend to repair the 'old faithful' and tired clay guns, where it wont be the end of the world if I screw up! I can only legally keep other peoples shotguns for 72 hours at a time too, which anyone paying real money would not put up with. A fair few years ago I made a .410, but it was embarassingly ugly, it looked like a pipe attached to a wooden fence post. I'm expecting to do a bit better this time round

Thank you for the advice, it is appreciated!

 

[willbird]

On many 22lr the cocking piece is free to rotate, but then has a key to orient it, the key rides in the cut for the bolt handle. When threads are used they sometimes are square threads, and maybe even buttress if memory serves me right....but plain old threads too in some cases work just fine....generally only 90 degrees or less of rotation.

For a 22lr I suppose you could use an interrupted thread lockup, but that has it's own issues even though some rifles used it anyway.

Bill

 

[marky123]

Thank you very much for your responses, I'm glad I found this forum.

It hadn't occurred to me that front locking lugs would be harder to feed. I initially jumped at the idea because it would allow me to scale up the design for a larger round at a later date (I'm also getting licensed for something slightly larger; .222, .223 etc - TBD). The reason I thought the front lugs were common because I've seen lots of larger rifles, but only one bolt action .22LR.

I'll now focus on a sleeve lug design, and see what I come up with, paying attention to usability too.

I'll read up on all the suggested resources. I'm in no rush & want to do it properly, and like to understand the theory behind what I'm doing.

@LBrooks I'd be very greatful to see the pictures you have. I'll have a go at sending you a private message if I can work out how.

@Mark Recently I've just been fixing guns & making the occasional part when I get the chance. As I'm not licensed (day job is behind a computer 9-5 in an office) I only tend to repair the 'old faithful' and tired clay guns, where it wont be the end of the world if I screw up! I can only legally keep other peoples shotguns for 72 hours at a time too, which anyone paying real money would not put up with. A fair few years ago I made a .410, but it was embarassingly ugly, it looked like a pipe attached to a wooden fence post. I'm expecting to do a bit better this time round

Thank you for the advice, it is appreciated!

I'm not quite sure what you mean here but all the best

 

[ShottyUK]

I'm not quite sure what you mean here but all the best

Ha, yes I should have chosen my words more carefully considering the subject. I mainly refer to cosmetics (eg if I were to scratch a farmers old Spanish go-to SxS, they wouldn't be as concerned as if it were new).