designing a rifle and would like some input

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ive been looking around at some other ideas and found something that is very simple in function.. strong, reliable, and i believe i can simplify it a great deal and make it work for me.. that is the roller locked system (not roller delayed)

the roller locked system appears to work in the same way as the G41/G43 bolt where the firing pin pushes the rollers out of the recesses in the bolt, locking the bolt into the barrel (as is the case on the MG-42) and with this system you need no cam.. firing pin pushes the rollers out, the fact theyre rollers will push themselves in when the firing pin is pulled a bit and the carrier pulls it back.. very simple and can obviously handle 8mm mauser
 
At this point I don't even know enough to know what I don't know. This thread has brought out a lot of knowledge and useful information too.
 
I'm a bit of a tinkerer, myself. I've not so much designed, but copied the designs of others in some of my home built guns. All I've successfully managed so far area couple shotguns, and the .38 I'm building now looks promising.

I'd be very interested in the design if it can be made at home with the simplest of tools. Most of us don't have lathes and vertical mills, so professional grade machining puts most designs out of reach for the majority.

What can be made with minimal tools usually looks like some 3rd world single shot zip gun cobbled together out of various tubing, hose clamps, rubber bands and duct tape, as dangerous to the shooter as it is to the intended target. Then you have things like the Luty BSP SMG, which will win you a fabulous vacation to club fed.

Ideally, I'd like to see something that can be fabricated at home, similar to the Luty SMG, sans federal prison.

AK receivers can be folded out of a shovel, so I'd start with that level of simplicity, using off the shelf components, but not necessarily gun components. If its going to be semi auto, a magazine and bolt that are compatible, and perhaps a barrel, should be all the components needed, and even the bolt, if simple enough in design, can be manufactured at home. Closed bolt Uzi conversion bolts 'look' simple enough (caveat: never handled one, so they may be more complex than I know). So perhaps keep something like that in mind.

The STEN was successful and it was built out of tubing. Semi auto conversion bolts for those exist, too. Simplicity in design will garner the most successful outcome.

Another appeal has to be price expenditure versus time expenditure. For several hundred dollars, you can build an AR in an afternoon. I'm willing to spend less, work more, and if I can build, successfully, a semi auto rifle for a couple hundred dollars, but spend a week or so, I'm more interested. Partly because I'm broke, and have nothing better to do with my spare time.
 
well i actually have two designs im working on.. one is to make a more polished rifle that uses simpler shapes for the receivers.. like tube steel and what not, but be a more polished, more versatile and more adaptable design.. magwells can be removed, calibers can easily be changed, and a full length top rail

the other project im working on which i havent been discussing up till now is i want to make a functioning semi automatic 5.56mm rifle with the least amount of work as possible.. something on the level of simplicity of WWII SMGs like the sten but capable of 5.56mm pressures.. no direct blowback would require an enormous bolt easily jumping the weight up to 15lbs or better.. so i was thinking of utilizing some kind of delayed blowback action or an incredibly simple locking system of some sort

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that aside.. i started just rough sketching out a new bolt design.. below i posted a photo of a new bolt i just worked out.. its an early design.. i could make it completely square if i wanted to but this is a basic roller locked system.. imagine there being a carrier for the firing pin thatll spread the rollers apart to lock into the trunnion.. or maybe just a piece that slides over the firing pin that is held in the locked position by the carrier via a slot cut in the top

10dikp0.png
 
I've actually started a design for a roller locking system bolt design myself.

No fancy computer generated images though, just the ones in my head.
 
well, you can get a free trial of autodesk inventor.. might be worth a try and its so much easier and better when you can see things physically interact with eachother to determine where weakness or conflicts may be

anyway.. i just sketched up a barrel extension.. but this could be machined into the end of a barrel blank if there enough of it.. this shows how you only need the two ears coming off the barrel for the rollers to lock into... now looking at the photos above.. i had the idea.. the upper receiver is square, the barrel extension is square.. say that barrel extension is 1" x 1".. so say the upper is 1" x 1 1/2".. that would allow the block the barrel mounts into to be screwed into the receiver, closest to the bottom of it and offer plenty of clearance for a gas piston above and the guide rods beside the piston (or go with an AUG like system where one of the two guide rods IS the piston

the other way i see you can go about this is to use that barrel extension piece and rivet it into the trunnion.. then use the savage system of changing barrels where you headspace by hand, then use a barrel nut to tighten down over the top the threads

i was willing to go to 1.5x2" for the receiver dimensions, this would offer plenty of room to simply use what you see below as an extension of the barrel and make a separate trunnion, riveted to the receiver that that extension would fit into.. to make it easier the barrel extension edges can be rounded off, so the internal machining of the trunnion would be rounded off eliminating the need to use anything like a broach for it

lastly.. i just rounded that bolt off to see what it would look like when its smoothed out.. i could just as easily leave it square and cut the entire thing out of a piece of 9/16" square bar, only needing to cut the slots in the bolts for the roller and do some internal boring

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just another thought unrelated to the bolt carrier group.. but i was thinking about the gas system.. if the gas system is above the barrel and i extend the top half of the receiver out to the gas block for a full length top rail it would also make it pretty difficult to work on the gas system if it needed to be taken apart or worked on unless the barrel was removed to do so.. do its another reason why ive considered going with a gas system that was under and off to the side of the barrel like on the AUG, because then the gas system and if i place a forward non reciprocating charging handle on the rifle, both things could be accessed simply be removing the lower handguard



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"AK receivers can be folded out of a shovel"
The sheet metal can be, at least. The FCG, trunnions, bolt, carrier, and gas system are all about as complicated as anything else.

Justin,
The one drawback with roller locks is that you have a line of contact with the bolt and recess, rather than a planar contact, so the interfaces have to be made with very similar radii in order to get a broad effective contact area. Also very hard metal. Otherwise, the rollers will need to be much larger than a comparable planar lug would need to be (also, the Hertzian Contact Stress formula is a bit of a bear to wrangle). The drawback with a milled extension like you have shown is that the rollers will thrust outward nearly as much as they push back, and there is no continuous ring to take the load; this is why MG42 and MP5 trunnions have continuous ring forged trunnions, and why CZ52 roller-locked pistols have a problem with splitting slides due to outward pressure & metal fatigue. Your barrel extension looks essentially like an MG42 barrel's except its locking grooves are cut through windows in the sides (as opposed to completely open sides in the trunnion). If the barrel extension was supported by another ring of material (like if it was pressed/screwed into a strong collar on the receiver tube) this would be a non-issue.

As far as the locking piece, you will definitely want to go with a firing pin sleeve as part of the bolt carrier. If the pin itself does it, the BATFE would probably categorize the device as an open-bolt gun. This would also have the benefit of allowing the bolt/carrier spring to be lighter. Pretty cool ideas so far, though. What magazines do you want to use? This will define a lot of things, and mags are actually one of the more impossible parts to make yourself.

TCB
 
well those are some interesting points to consider.. i was actually thinking the rollers dont seem to offer too much contact surface between the bolt head and the receiver.. so.. there may be some incentive to lean more towards the G41/G43 system.. but the flapper system isnt ruled out yet though.. i can extend the barrel extension a bit more.. move the hinge for the flapper up behind the bolt head and be able to have simple rear locking flappers lock into the barrel extension of a similar design

so.. if the systems im looking at now theres the roller locked, the flappers, and the G41/G3 front locking retractable locking lugs.. im fairly certain i want to go with one of these systems over a rotating bolt and i do believe it will be a much better design than the tilting bolt

as for the flappers.. just how long do the flappers actually have to be?

as for magazines, im focusing on using two magwells from the start.. magwells will screw to the bottom of the receiver and ill space the four screw holes out enough for .308 length magwells.. for .223 length magwells the front of the magwell will be all the way forward and itll have a tail on the back side to cover the rest of the opening in the receiver and screw into the same screw holes in the back.. im focusing first on the FAL magwell and AR-15 magwell but of course any and all magwells could be made at a later date

i think later on im going to draw up a rough model of what the finished product may look like
 
for anyone who is interested.. this is a G43 bolt disassembled, you can see the two retractable locking lugs removed and you cans eee how simple the bolt itself is.. barely more than a piece of tube steel with a few slots cut out

g4330.JPG


this is a flapper style bolt from a DP28 and DPM

DPM050.jpg

and this is the roller locked system (had to go with an MG42 because a smaller, lighter, simpler gerat 06 is hard to find photos for)

mg42%20bolt%20(1)-500x500.jpg
 
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of those three systems above, flapper, the front retractable lugs, and the roller locked systems.. what do you guys like the most?.. what do you think would be the simplest and most reliable system to go with and why?.. im fairly certain id like to go with one of those three over a rotating bolt (which has been done to death, and frankly bores me)

one downside i see to the roller locked system is that realistically you have the entire pressure of the cartridge being places on a relatively small surface area.. look at the grooves the rollers travel in on the bolt.. when you put a round surface against a flat surface theres only so little contact surface between the two

with the flapper locked system, im not sure how accurate this system can be when you have essentially two free-floating plates between the bolt and the receiver to lock it... seems like if there is ANY play at all you could end up with a very sloppy system

and the downside i see to the retracting lugs is its rather difficult to get a large contact surface with the locking lugs because the larger you make them, the further inside the bolt they need to retract and theres only so much space available

___

the route im taking right now with the roller locked system is to take a lot of inspiration from the G3.. but slim down and simplify the bolt while also changing the cam surfaces so the rollers will lock on a flat surface and not an angled one.. thus making it roller locked... but im going to use essentially the same little roller pack for it and design a new bolt to better suit my needs
 
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so.. i have kind of a rough grouping of bolt parts that i think could work.. they are two rollers not too dissimilar from the ones in the HK91 rifle and it uses that little clip on top to hold them inside the bolt so they cant fly out.. also, i designed a cam block that will slide inside the bolt and be the surface which pushes the rollers apart

now.. if a roller locked rifle accidently fires when its not in full battery, there will be a major failure.. so im designing this safety feature into it.. the firing pin which protrudes through this cam block will have a section of it that will be a tad larger than the hold in the cam block to stop the firing pin allowing it to only travel a certain distance..

what that means is since the firing pin can only go a certain distance through the cam block, the firing pin simply wont reach the primer of the cartridge until the cam block is fully forward, and that cam piece cannot go fully forward unless the rollers are fully pushed aside and the rifle is fully locked

im thinking about these kind of safety features as i go along.. judging each mechanism to make sure the rifle cannot fire unless its completely safe to do so

this is a rendering of what i have so far.. as you can see its not too dissimilar from an HK91 bolt except ive made the cam block as so that it will be roller locked and not roller delayed.. and i just designed the head of the cam surface for now.. havent decided how this will interract with the bolt carrier but maybe something similar to the G43 bolt carrier

i will admit though that the further i progress with the roller-locked system, the more im realizing that it requires a lot more internal machining that i had hopes as i would have preferred to keep most internal machining like that to just drilling and boring.. hmm, but now that i think about it, all the forces absorbed by the bolt when locked are going to be on the surfaces in front of the rollers, not on the surfaces behind the rollers.. i wonder if i could cut off just behind the opening for the rollers and then use a piece of thick walled steel tubing to make up the back half of a two-part bolt.. that would eliminate all internal machining

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anyway.. put that aside for now..does anyone have any other ideas?.. maybe some other kind of locking mechanism not yet discussed, or any ideas relating to other features?

i was looking through some different rifles.. and i noticed the FG42 and its side magazine which wasnt uncommon for other designs and it got me to thinking... people quickly cast aside the thought of using them.. but i mean there are tradeoffs.. if the magwell is on the side.. then it would be much easier to remove that magwell and design something like the HK21 magwell which would allow feeding from belts.. also when laying prone the size of the magazine wouldnt be an issue

or what if it used a helical magazine (like the calico .22 and the russian PP-19.. but was perhaps top loaded like a P90 to keep the weight and balance rearward?

about the only thing i DONT want to do here is just make some cookie cutter rifle thats just like all the rest that are already out there but instead make one easier to make, as reliable as can be, and still add a bit of something different to it

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a question someone may be able to help me with.. its relating to primary extraction.. primary extraction is when the rearward movement of the bolt or the cartridge itself is slowed down to allow a slower pull of the cartridge out of the breach before it gets jerked violently to the rear.. without primary extraction and something that unlocks immediately, this can tear case rims off... now i was thinking about the roller locked system.. it seems like this includes its own primary extraction.. as the rollers begin to move inwards, the amount of contact surface with the locking recesses lessons and the bolt should begin to open slowly as the lugs are being pulled inwards before they are completely unlocked and the rifle completely recoils.. much in the same was a case is partially extracted during firing with a roller-delayed system only this doesnt occur until after the bullet leaves the barrel

so this seems like it would be a good advantage to roller locked... i could be wrong though?
 
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on the CZ-58, the two locking lugs are linked together right?.. and the bolt carrier hits that bridge to push the locking lugs up and pushed the bolt back on that same surface..

you know.. you see so many rifles where you have a giant bolt carrier that does all the work, has the rails, and most the weight that it feels foreign to make the bolt the heavier part, to put the rails on the bolt and use the carrier just to push it

___

heres an idea that may work well for a bullpup design.. that is, put a catch on the op-rod so the trigger forward of the receiver catches the op-rod before it goes completely forward.. that op rod would be attached to the firing pin and then have an extra inch or so of travel after the bolt locks in which that carrier and oprod can still travel, essentially combining the op-rod into a striker as well.. this is what the FG-42 did, and a company out of texas is making legal semi auto versions.. to use it in a bullpup you could just place the trigger pack and the catch further forward

now to do this in a roller locked or falling breach mechanism is just as easy.. just provide an extra half inch to an inch of travel after the carrier has completely and fully locked the rifle (so it cant be classified as an open bolt mechanism)

one of the reasons i thought about having a side magazine is you can have it eject out the opposite side and be able to reverse it as well so you can switch the magazines and the ejection port.. this would require only two sides of the receiver to be cut for an ambidextrous system as opposed to three and also makes for a fairly straightforward belt-fed option too.. just throwing some more ideas out there to see what people think
 
More pics of the bolt. English is not my native language, so I still don't have the full firearms vocabulary implemented, so what do you mean with locking lugs?

2ilbm14.jpg



3451o8x.jpg
 
that reminds me of a flapper system... but one that pivots vertically from the rear.. i think its a very good system.. question though.. would it be unsafe to make a similar system that actually pivoted on a large pin?.. then you you could have the blocks lock even with the bolt face and move the system even further forward because its my understanding that block falls between the a ledge on the side of the bolt and into recesses in the receiver to lock.. basically falling between the two.. but would a large pin should it pivot on one instead be able to handle the pressures of a .308?.. benefit is you can then add a tail above the pivot point for the bolt carrier to hit.. makes it a bit simpler.. but then again i could probably simplify what the cz58 does too.. and it looks very simple since it seems to be all external machining

you know, when i really think about it.. the CZ VZ 58 system doesnt seem like its going to work for what i need it for.. no way to access the bridge across the top of the locking pieces and still have the bolt lock in the barrel.. and of the DP-28 style flapper system even if i did make one with really short flappers, they still couldnt lock in a barrel extension without the bolt carrier being able to go over top to actuate them

what i need is a solution that will be front locking.. but actuated or operated from the rear of the bolt so the bolt can be inside the barrel or barrel extension when it locks.. and can be unlocked from the rear.. this leaves me realistically with only three systems.. rotating bolt, roller locked, and the G43 type front locking flappers which are locked and unlocked from the inside of the bolt by a piece that can be set up to be operated from the rear if needed

im going to focus my further efforts from here on on the G43 front locking flapper setup.. its internally locked and unlocked, can be unlocked with the bolt head into a barrel, and itll be easier to machine a locking recess inside the barrel, which means you wouldnt even need a barrel extension... what i will have to do however is add a bigger margin for safety over the G43 system by increasing the contact surface of each lug to a point where the rifle could safely be fired if for some reason it only locked on one of the lugs.. say the other one was worn or broken.. and im going to do the thing i discussed above with the firing pin. put a stop on firing pin so the firing pin cant even contact the primer until that bearing surface is fully forward and the rifle is fully locked

___

now im getting bored of discussing locking systems.. im looking to discuss other features.. such as magazine placement.. front of the trigger, bullpup, or on the side.. either way its going to be ambidextrous so if its a side magazine the magazine well and ejection port will be made to screw in in place of eachother.. if its a front or rear mag then i will have to make two ejection ports and cover one (like on the FAL)

id also like to discuss gas systems.. i will not go with direct impinged but i can either go with a short stroke or a long stroke.. i thought about copying the AUG a bit with the two guide rods being attached to the carrier.. which also allows them to be used as rails so welding rails in the receiver wouldnt be necessary, and with springs inside them the action can be shortened considerably and the function of one of these rods can be a gas piston, the other used for a non reciprocating charging handle.. even make the functions swappable for ambidexterity.. but im not opposed to welding rails into the upper prior to heat treating it and just going with a single piston system

so lets discuss something besides locking systems for a while.. anyone have anything else theyd like to discuss or ideas theyd like to share?
 
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About the gas systems, well, the obvious disadvantage of the Direct Impingement is that you have hot gas and carbon fouling blowing into the action... but you said you will not go with DI so let's discuss long stroke and short stroke. Let's start with the long-stroke gas system... the gun that comes to mind when I think about a long-stroke is an AK-47. This system has the advantage of being reliable, but is not as controllable as a short stroke or a DI would be, because the center of mass changes during cycling. So the POA is disrupted. I don't think this is much of an issue in semi-auto though. Then you have short-stroke gas system, here the piston is not fixed to the bolt, so it moves separately. FAL, VZ58 and AR-18 are examples of rifles with short-stroke gas systems. Short-stroke is more controllable than long-stroke but IMHO it won't be an issue with semi-auto. Personally if it's for a semi-auto I would go with long-stroke, because it's very reliable, simple and robust.

I will share pictures of the VZ58 short-stroke gas system shortly.
 
actually, the AKs reliability has absolutely nothing to do with its gas system, if you look at an AKM (7.62 or 5.45) gas block youll notice the gas vents after only a short distance similar to a short stroke system.. so the AK is essentially a short stroke system as its under pressure from the gas for only that short distance... piston travels with the carrier though but thats all besides the fact.. a true long stroke in which the piston is under pressure until its fully rearward would impact the back of the receiver with quite a force, likely damaging internals

the AKs added reliability is in the mass of its bolt carrier group.. because of the added weight of the BCG it carries more momentum as it travels rearward allowing it be be better at overcoming friction, debris, etc and therefor offers more reliable extraction.. now if the AK was a complete short stroke system like the SKS, and the BCG still had the same mass youd see zero change in reliability

also, efficient cycling isnt the only issue to be concerned with but if the bolt yanks too hard and too fast on the cartridge, it could tear the rim off and leave you with a serious jam

lets face it though, the gas system is just as important to the rifle as the BCG.. true short stroke systems are incredibly snappy as it requires enough force to be placed on the carrier to allow it to cycle on its own.. but im wondering if we could actually achieve a more gentle extraction cycle perhaps with longer stroke (distance from where the piston rests to where the gasses stop pushing it, where the gas vents) you could decrease the pressure of the gas system and smooth out and lighten down that stroke

for the purpose of smoother extraction i had the idea of making sort of a two-strage gas system.. the gas block would be fed by a single gas port in the barrel, but where the gas vents into the gas tube there would be two holes, one small one closer to the barrel that would release a smaller volume of gas to more gently push the carrier forward at a slower rate, and then the upper hole will be the full size one that will carry the energy to send the entire BCG rearward.. and since the gas will have to travel a little bit longer to get to that top hole youve momentarily delayed the second stage

the only downside i see to having a true short stroke system over the AKs basically short stroke but attached piston is that with the AKs setup it means one less spring and another less moving part (the separate piston).. honestly, what is the point of the system the SCAR uses where it has the big chunk of metal almost the full length of the gas system with a tiny little piston head on the front that is separate in the gas block?

thats just a couple ideas i had for the gas system
 
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Yes, you're right, AK's reliability is because of the BCG mass. But the BCG added weight is in some way related to the gas system. The definition of a long-stroke gas system is that the piston is fixed to the Bolt Carrier.
 
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