Cal-gun Fan
Member
Zollen-there are plenty of reliable AR 40 rounders out there that don't use a pressure damper and feed fine...what are you trying to accomplish? Its really unclear.
AR 40 rounds magazine
- Thread starter zollen
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I didn't know 40+ rounds AR magazines already existed and I was told that the spring pressure would be too great for stripping rounds reliably over 40+ rounds. Since there is no such thing as constant pressure springs, so I decided to find another solution for stripping rounds reliably over 40+ rounds. The off the shelf solutions seem to be utilizing carefully calibrated springs for various rounds upward pressure.
Owen
Moderator Emeritus
Well, buy a magazine, buy some dummy rounds, find a friend with a garage machine shop and make a prototype. Your device is simple enough that a "make it and break it" is an easy enough approach.
kwelz
Member
There is no need to think. It has been done.
Sam Cade
Member
I bet you a dollar that won't happen.
The OP is in Canada,does not own a firearm and it would be a crime for him to manufacture a magazine with a capacity over 10 rounds.
Sam Cade
Member
Like all magazines. sheeesh...
Cal-gun Fan
Member
Well why are we wasting time on this then?
Sam Cade
Member
For the same reason I got EMT training I guess..... some of us are just drawn to disasters in spite of ourselves.
Jon_Snow
Member
zollen, welcome to springs 101.
Springs provide a force that is proportional to their displacement from their neutral position. The relationship is F=-k*x, where x is the displacement and k is the spring constant. The minus sign is there because the force is opposite the direction of the displacement. If you’re designing a spring for a magazine, first you determine what the acceptable range of force (not pressure) the rounds need to be under to feed properly for your given gun/magazine combo. You then determine what the length of the loaded stack would be. From this you determine what the spring constant needs to be to ensure you stay within the acceptable force range. You then pre-compress the spring to give the minimum pressure at the unloaded state. Viola! Ever taken a magazine apart and noticed that the spring is a lot longer than the mag itself? The reason is that a long spring constant gives you smaller change in force throughout the magazine but requires greater pre-compression.
Example: Let’s design a single stack mag for a gun/caliber I just made up. Our gun + feed lips will feed properly with anywhere between 20 and 30 lbs of force. We’re feeding rounds that are .5 inches wide at the widest. We want a 10 round mag, therefore our ammo stack is 5 inches tall. Our acceptable force range is 30-20=10 lbsf. Our desired spring constant is going to be 10 lbsf / 5 inches = 2 lbsf/inch. Our minimum force is 20 lbsf, so we need to pre-compress the spring by 20 lbsf / (2 lbsf/inch) = 10 inches.
Example 2: Let’s make a 15 rounder for the same gun. k = 10 lbsf / 7.5 inches = 1.33 lbsf/inch. 20 lbsf / (1.33 lbsf/inch) = 15 inches of pre-compression.
There’re your ‘carefully calibrated’ springs. Not that complicated really. Is that how it works in the real world? No, but that gets you about 95% of the way there, then you make some prototypes and test them out, tweaking as needed. We all appreciate the need for innovation in our fine sport, but this is high school level physics. You might want to work on your education a bit before deciding you can do things better than the professional engineers.
Springs provide a force that is proportional to their displacement from their neutral position. The relationship is F=-k*x, where x is the displacement and k is the spring constant. The minus sign is there because the force is opposite the direction of the displacement. If you’re designing a spring for a magazine, first you determine what the acceptable range of force (not pressure) the rounds need to be under to feed properly for your given gun/magazine combo. You then determine what the length of the loaded stack would be. From this you determine what the spring constant needs to be to ensure you stay within the acceptable force range. You then pre-compress the spring to give the minimum pressure at the unloaded state. Viola! Ever taken a magazine apart and noticed that the spring is a lot longer than the mag itself? The reason is that a long spring constant gives you smaller change in force throughout the magazine but requires greater pre-compression.
Example: Let’s design a single stack mag for a gun/caliber I just made up. Our gun + feed lips will feed properly with anywhere between 20 and 30 lbs of force. We’re feeding rounds that are .5 inches wide at the widest. We want a 10 round mag, therefore our ammo stack is 5 inches tall. Our acceptable force range is 30-20=10 lbsf. Our desired spring constant is going to be 10 lbsf / 5 inches = 2 lbsf/inch. Our minimum force is 20 lbsf, so we need to pre-compress the spring by 20 lbsf / (2 lbsf/inch) = 10 inches.
Example 2: Let’s make a 15 rounder for the same gun. k = 10 lbsf / 7.5 inches = 1.33 lbsf/inch. 20 lbsf / (1.33 lbsf/inch) = 15 inches of pre-compression.
There’re your ‘carefully calibrated’ springs. Not that complicated really. Is that how it works in the real world? No, but that gets you about 95% of the way there, then you make some prototypes and test them out, tweaking as needed. We all appreciate the need for innovation in our fine sport, but this is high school level physics. You might want to work on your education a bit before deciding you can do things better than the professional engineers.
Owen
Moderator Emeritus
<Moderator Hat>
Let's all stick to criticizing the design instead of the posters age, nationality and experience level.
</Moderator Hat>
Let's all stick to criticizing the design instead of the posters age, nationality and experience level.
</Moderator Hat>
Thanks. This is a very useful piece of info. Thanks for your patience! Your calculation clearly showed the length of a spring required for x rounds magazine. It will come in handy in the future.
However in order for a 40+ rounds magazine to be practical, I would need to rethink the 'shape' of a magazine so that it is still ergonomically feasible for shooters who are used to 30 rounds standard magazine.
I have been thinking a 40+ rounds magazine with a shape of 'bend side-way at the middle of a magazine', transforming to a double width 40+ rounds magazine with a total height of 20+ round magazine.
This would mean I would need some form a U-shape upward force in this concept. Let me think...
Cal-gun Fan
Member
....huh?
Zollen: Here is a comparison of a normal 30 rounder to a 40 rounder. And before you ask-YES, it works. It works perfectly.
Please answer me...what are you trying to achieve? The 40 round magazine already exists and works fine. You do NOT need to reinvent the wheel.
Zollen: Here is a comparison of a normal 30 rounder to a 40 rounder. And before you ask-YES, it works. It works perfectly.
Please answer me...what are you trying to achieve? The 40 round magazine already exists and works fine. You do NOT need to reinvent the wheel.
Thanks. The damper would force rounds to shift position in a magazine during a stripping operation, which unfortunately would result of jamming. I think carefully calibrated spring is the correct approach.
I was not entire wrong though. According to Jon Snow's calculation, the 40 rounds magazine (when fully loaded) would still exert greater upward force than 30 rounds magazine, but fortunately AR still have enough momentum to strip rounds reliably.
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Judging user's feedback here, people don't seem to enjoy 40+ rounds magazine because it is not ergonomically compatible with standard 30+ rounds magazine. This is my new direction now.....huh?
Zollen: Here is a comparison of a normal 30 rounder to a 40 rounder. And before you ask-YES, it works. It works perfectly.
Please answer me...what are you trying to achieve? The 40 round magazine already exists and works fine. You do NOT need to reinvent the wheel.
Cal-gun Fan
Member
You're giving me a headache here....
Try this then: It holds 60 rounds and is just about the same ergonomically as a 30 rounder, if heavier:
Drat, pic wont load, here is a link
http://media.photobucket.com/image/...Magazine_60-Shot_AR-15_M16_Box_Magazine_1.jpg
Try this then: It holds 60 rounds and is just about the same ergonomically as a 30 rounder, if heavier:
Drat, pic wont load, here is a link
http://media.photobucket.com/image/...Magazine_60-Shot_AR-15_M16_Box_Magazine_1.jpg
kwelz
Member
While normally I would agree with you I think these three factors all contribute to the level of quality of the posts he makes.
He is young, has no experience with weapons of the theories behind them. Has no knowledge of how they work except for what he "reads on the internet" And finally due to his nationality he has very limited ability to work with these weapons.
I applaud anyone who wants to improve firearms technology. However you can't just make stuff up and then ignore the feedback or pick and choose who you listen too.
Would the weight of 60 rounds AR magazines interfere operator maneuverability and endurance? I deliberately picked 40 rounds magazine to work with because I suspect the weight would be the issue.
Maple_City_Woodsman
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A significant change in the size and/or weight of an individual magazine would indeed change the maneuverability of the weapon. This is why I like 20 round magazines best; the gun is simply lighter and easier to maneuver in all positions and directions.
Over the big picture though, It shouldn't effect the maneuverability or endurance of the "operator" much, because the total weight of gear and number of rounds carried would still be essentially the same.
Over the big picture though, It shouldn't effect the maneuverability or endurance of the "operator" much, because the total weight of gear and number of rounds carried would still be essentially the same.
But an operator would rely mainly with his arms to support his rifle, which could cause fatigue faster. His body would support the rest of his gear.
Maple_City_Woodsman
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You are talking about people who are actually in good physical condition, and use slings and load bearing equipment.
A few ounces add to the gun itself is negligible. It is the physical increase in bulk and the compatibility with existing gear that would be issues.
A few ounces add to the gun itself is negligible. It is the physical increase in bulk and the compatibility with existing gear that would be issues.
Jon_Snow
Member
Only if you used the same spring, which you wouldn't do. You'd design a new one that results in the same range of force from fully loaded to unloaded. The difference is a lower spring constant and the resulting greater pre-compression. This in turn leads to a longer mag since you have to have a longer spring.
Correctly me if I am wrong, the greater pre-compression would implied 40 rounds mag (when fully loaded) would exerted greater upward force that 30 rounds mag.
Jon_Snow
Member
It wouldn't because you use a spring with a reduced spring constant. F=-kx, x is larger but k is smaller so F is the same.
Look back at my two examples.
Unloaded it’s pushing up with F = - (2 lbsf/inch) * (-10 inches) = 20 lbsf, which is the lower operating limit. The displacement, x, is negative since I’m calling up positive in this instance. Fully loaded it’s pushing up with F = - (2 lbsf/inch) * (-15 inches (10 inches pre-compression + 5 inches worth of ammo)) = 30 lbsf, which is the upper operating limit.
Now look at example 2, same gun, 15 round mag, same operating limits.
Unloaded it’s pushing up with F = - (1.33 lbsf/inch) * (-15 inches) = 20 lbsf, which is the lower operating limit. Fully loaded it’s pushing up with F = - (1.33 lbsf/inch) * (-22.5 inches (10 inches pre-compression + 7.5 inches worth of ammo)) = 30 lbsf, which is the upper operating limit. Same force in both cases because both the pre-compression AND the spring constant changed.
I assumed the k remained the same. Ok. If a spring length is increased for a higher capacity magazine, then we must use a 'softer' spring to compensate the greater tension, hence lower (k).
(The extra length of pre-compression * y lbsf/inch) >= minimum operating limit.
(The total height of fully loaded x rounds * y lbsf/inch) + (The extra length of pre-compression * y lbsf/inch) <= maximum operating limit.
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Owen
Moderator Emeritus
and to answer the next question from zollen, you change the spring rate (k) by changing the spring material, the cross section of the wire, or the the helix angle of the spring.
its really pretty straight-forward and while the actual derivations used to arrive at the equations above High School math, the derived, working equations are simple algebra.
its really pretty straight-forward and while the actual derivations used to arrive at the equations above High School math, the derived, working equations are simple algebra.
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