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Thread: How reliable are Low Mass BCGs

  1. #21
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    Quote Originally Posted by ryu_sekai View Post
    Reliability means no malfunctions with any type of ammo.
    I think that this is impossible, for any weapon. There are too many things that can cause malfunctions on any kind of auto loading weapon. Unless you can somehow have a perfectly sized gas port, a perfectly aligned gas tube, a perfectly weighted bolt carrier group, a perfectly tuned gas system (either "piston" or DGI), a perfectly tuned buffer system, perfectly lubricated at all times, other perfect parts that never fail, perfect magazines, perfect environmental conditions, etc. Every weapon will malfunction eventually if not properly taken care of.

    The *best* you're going to do is to buy a quality weapon from a reputable manufacturer, do all required preventative maintenance on a fixed schedule, properly lubricate it, use quality magazines, and use ammo from a reputable manufacturer.

    That's the easy part.

    At that point, the most important thing is for you to train so you know how to utilize the weapon and quickly clear any malfunctions that occur.

  2. #22
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    Quote Originally Posted by justin_247 View Post
    I think that this is impossible, for any weapon. There are too many things that can cause malfunctions on any kind of auto loading weapon. Unless you can somehow have a perfectly sized gas port, a perfectly aligned gas tube, a perfectly weighted bolt carrier group, a perfectly tuned gas system (either "piston" or DGI), a perfectly tuned buffer system, perfectly lubricated at all times, other perfect parts that never fail, perfect magazines, perfect environmental conditions, etc. Every weapon will malfunction eventually if not properly taken care of.

    The *best* you're going to do is to buy a quality weapon from a reputable manufacturer, do all required preventative maintenance on a fixed schedule, properly lubricate it, use quality magazines, and use ammo from a reputable manufacturer.

    That's the easy part.

    At that point, the most important thing is for you to train so you know how to utilize the weapon and quickly clear any malfunctions that occur.
    I think you took that a little to literal. I don't have malfunctions with my AR's and don't want to start.

  3. #23
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    Quote Originally Posted by ryu_sekai View Post
    what is the narrower margin?
    Quote Originally Posted by ryu_sekai View Post
    If i used a lighter bcg, will that jack everything up?
    I wish I could give more specific guidance, but as I stated my info is second hand from a few weeks or research. I dont have any low mass stuff but I have considered building a race rifle.

    Think of it like this. Lower mass equals less stored energy. Less stored energy means less reserve to make things "work".

    Now you can "tune" the gas pressure down to only what is needed to move the low mass items and overcome things like the drag caused by the loaded magazine on the BCG just to name one. But the total energy transfered from combustion to moving parts is lower, that is what narrows the safety margin.

    Remember, things that are in motion tend to stay in motion unless acted on by an outside force. The mass of those items in motion directly effects what "counter action" is required to stop or lesson that movement (like the mag drag on the BCG).

    You may be able to "tune" your system down so light and low pressure that a mere cricket fart on the BCG could cause a short stroke...

  4. #24
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    Quote Originally Posted by Mall_Ninja View Post
    I wish I could give more specific guidance, but as I stated my info is second hand from a few weeks or research. I dont have any low mass stuff but I have considered building a race rifle.

    Think of it like this. Lower mass equals less stored energy. Less stored energy means less reserve to make things "work".

    Now you can "tune" the gas pressure down to only what is needed to move the low mass items and overcome things like the drag caused by the loaded magazine on the BCG just to name one. But the total energy transfered from combustion to moving parts is lower, that is what narrows the safety margin.

    Remember, things that are in motion tend to stay in motion unless acted on by an outside force. The mass of those items in motion directly effects what "counter action" is required to stop or lesson that movement (like the mag drag on the BCG).

    You may be able to "tune" your system down so light and low pressure that a mere cricket fart on the BCG could cause a short stroke...
    I understand now. My 11.5 Duty Rifle will have the M16 BCG. Im going to throw the LO MOS in my 16". Not gonna lube or clean it and log my rd count. Ill see how long it can go without a malfunction. The JP LO MOS is as slick as my NIB, which is pretty impressive.

  5. #25
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    Quote Originally Posted by ryu_sekai View Post
    what is the narrower margin?

    Seems seems like people generally "tune" their rifle by changing out Buffers or BCGs, because they cant change the size of the gas port. If the gun is under gassed they make it more reliable by going with a lighter buffer. If its over gassed, they increase the buffer weight. seems like if you have a set weight for the buffer, BCG and tune the gas port, it should be reliable. Although people have said the lighter BCG makes it have less force to seat a round, but others say they run it in carbine classes and shoot the piss out of it and it works great.


    So far both my tuned rifles (11.5/16) have been 100% after a lot of shooting and no cleaning. If i used a lighter bcg, will that jack everything up?
    That narrower margin is a specific type of ammo, in a specific atmospheric condition and at a specific level of cleanliness that is needed to run "gamer" parts reliably. Throw any of those out of whack and you will probably run into problems.

  6. #26
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    To make a gas driven rifle work properly, there are three things that need to be balanced out-
    -Mass of the reciprocating parts
    -Control of the gas flow including mass, velocity and pressure
    -Spring compression rate and rate of relaxation

    Change any one of these and the others will need to be adjusted to match.

    Let's clear up a few misconceptions. First, the only reason a change in the mass of the reciprocating parts will change how much free recoil the firearm generates is because it changes the mass of the whole firearm, not because the mass of the reciprocating parts was changed.

    Firing the same ammo at the same velocity, a firearm with greater mass has less free recoil than one with less mass. It doesn't matter where that mass is. If you were to lighten the carrier by 4 oz but added 4 oz to the barrel, the rifle will still generate the same free recoil because it still weighs the same. If you just add 4 oz to the barrel, the rifle has more mass and thus less free recoil. Will that recoil feel the same as would if those 4 ozs were added to the carrier instead? Probably not because a heavier carrier moving back and forth in the upper will feel differently than a lighter one.

    badazz posted inaccurate information about springs. Will a spring relax faster when pushing less mass than it would pushing more mass? Definitely maybe. A spring pushing a good amount of mass will relax at a slower rate, but even when pushing no mass, it has a finite rate at which it relaxes. The more you lighten the load on the spring, the less gain in velocity. It's the law of diminishing returns.

    In an AR, the spring pushes the BCG back into battery with energy that has been stored into it from the momentum of the BCG opening. The gas gets everything moving but after a short distance the gas is cut off and from there, the whole shebang is just coasting. Less mass in the BCG/buffer, the less momentum it has to compress the spring, the less momentum it has to compress the spring, the less energy the spring has stored. It's possible that the spring will not have enough speed or stored energy for reliable function.

    A heavier reciprocating mass does not mean the rifle will have softer recoil. In fact, the greater the reciprocating mass, the more likely it will cause the muzzle to move off target while in motion. If the BCG/buffer were to account for 20% of the whole mass of the rifle, it will move the rifle around more than if it were only 10%. The trade off is that the lighter BCG/buffer has to move faster to load the rifle with the same energy- or use a stiffer spring. Note that a stiffer spring isn't always a faster spring.

    A lighter BCG/buffer isn't more likely to bounce than a heavier one. There's more to it than velocity. What causes bounce is the carrier hitting the barrel extension in such a way that energy is reflection cause the two parts to bounce away from each other, like striking a hardened steel surface with a steel hammer. There's bounce. But strike that same hardened surface with a deadblow hammer designed to spread out the energy, it won't bounce at all, even if the deadblow weighed the same and strikes with the same velocity.

    The JP low mass carrier can be made to run with the same reliability as a standard full auto carrier but the rest of the system has to be tuned to make it happen. 3 gun guys don't tune their rifles that way. They tune their rifles to run at the very edge of reliability with a certain ammo for the softest recoil and least movement of the muzzle from target. When everything is in balance, a "race gun" will work every time. But that balance is delicate and easily upset.

    Bottom line is the rifle gas system with a 20 inch barrel, rifle spring and rifle buffer or A5 buffer is the most reliable and forgiving set up for an AR firing the 5.56x45. Everything else trades reliability for some other advantage such as a shorter package
    Last edited by MistWolf; 08-30-13 at 19:21.
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  7. #27
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    I would expect it to be somewhat more sensitive to ammo and dirt or lack of lube.

    It's also important to understand that "weak" ammo from what we can measure easily (velocity) doesn't always equate to low gas pressure at the gas port. You may have some other "hotter" ammo that has lower pressure at the gas port. I recommend against gaming "low recoil" systems on defensive weapons because you are unlikely to shoot enough expensive defensive ammo to really know it's reliable.

    How much lighter is the JP?

  8. #28
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    If for no other reason than finding out the purpose for the drilled out BCG I've seen advertised, glad I read this thread.
    Let me rephrase that; maybe I understand the reasoning behind these BCGs...
    Carry on.
    Moon

  9. #29
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    Looks like LMOS is 3.21 oz lighter than an M16 carrier


    Quote Originally Posted by Robb Jensen View Post
    bolt carriers (w/o bolts in them)
    Colt non shrouded 1/2 circle carrier 8.63oz
    Colt shrouded 1/2 circle carrier 8.87oz
    Bushmaster non shrouded AR15 carrier 8.92oz.
    Bushmaster shrouded AR15 carrier 9.26oz.
    CMT M16 carrier 9.46oz

    Quote Originally Posted by JP web site View Post
    JP Low mass carrier
    Not for use in .308 AR-type rifles.
    Weight: 6.25oz with key installed.
    Quote Originally Posted by JP web site View Post
    JP Full mass carrier (AR15)
    Not for use in .308 AR-type rifles.
    Weight: 8.5oz with key installed
    Black River Tactical
    BRT OPTIMUM HFCL Barrels - Hammer Forged Chrome Lined 11.5", 12.5", 14.5"
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 12.5" MRC, 11.5" CQB, 9" PDW
    BRT EZTUNE Preset Gas Tubes - CAR and MID
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  10. #30
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    I can recall a time when the lighter 'half circle' semiauto carrier was considered less reliable and less desirable than the 'full circle' auto carrier, and recall substituting the latter for the former for just that reason.
    Times change I 'spect.
    Moon

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