MK18 Vs. Geissele Super Duty 10.5

[okie]

I think he means this: https://www.m4carbine.net/showthread...tock-A5-spring

Weird. I used to have an A5 system with a milspec rifle spring and the next heaviest buffer. Never had any trouble with it. Standard M4 barrel extension.

[17K]

I’ve had many A5 systems in use over the past 11-12 years and the only thing they’ve ever done is cause the occasional, yet persistent mystery malf.

They’re not a reliability upgrade. Period.

[Wake27]

I’ve had many A5 systems in use over the past 11-12 years and the only thing they’ve ever done is cause the occasional, yet persistent mystery malf.

They’re not a reliability upgrade. Period.

I honestly don't think I've ever seen anyone else have issues unless its a known conservatively gassed barrel and paired with a green spring.

[okie]

I’ve had many A5 systems in use over the past 11-12 years and the only thing they’ve ever done is cause the occasional, yet persistent mystery malf.

They’re not a reliability upgrade. Period.

I'm a sample size of one, and honestly didn't shoot it that much.

Trying to wrap my head around the physics of what might be going on. Should be pretty much identical to using a rifle lower. Since we're just talking about chambering a round in this context, barrel length, port size, etc. can all be ignored.

So the one and only difference is that it's chambering that next round into the M4 feed ramps. However, aren't there a lot of rifle length AR15s out there now with M4 feed ramps? Seems like if anything that would potentially mitigate issues with chambering.

As far as the mechanical differences between carbine and A5 (which should be identical to rifle for all intents and purposes), it's just the compression rate of the spring. But since the force drops off slower as the rifle spring decompresses, you would think that would improve things.

Well this is interesting to say the least. I wonder if it has something to do with the spring in the A5 buffer? I never understood that myself, as it seems to contradict what the weights are there to do. I wonder if the spring in that moment when it's chambering somehow neutralizes the inertia of the weights, momentarily rendering them weightless? I suppose if the timing of that were just perfect it's possible.

[1168]

I wonder if it has something to do with the spring in the A5 buffer? I never understood that myself, as it seems to contradict what the weights are there to do. I wonder if the spring in that moment when it's chambering somehow neutralizes the inertia of the weights, momentarily rendering them weightless? I suppose if the timing of that were just perfect it's possible.

I think thats what it is. I think that the weights are forward during feeding and chambering, and the lack of deadblow effect in that moment is enough to cause occasional first round stoppages.

I’ve had them, too, with mags where the 30th round was a tight squeeze, and with ones that are supposed to hold 30 but don’t. Before 17k spoke up earlier this year, I assumed it was the mags, but in retrospect, they did manage to function in regular lowers.

If anyone has any mags that meet that description, shoot me a PM.

17k, are your modified A5s still solving the problem? I’ve returned from my travels, so I’m going to start testing it, also, if I can consistently reproduce the problem.

[17K]

The one I have going has about 2K through it, so far so good, but it’s mostly been ran with Pmags, which help a lot.

I have running my gun that I swapped back to the carbine-H with all the mags I thought were bad and believe it or not, they all run fine.

[Diz]

Tuning AR's has become just as complex as tuning 1911's in the old days; there are just so many after-market parts and combinations that it's easy to get things out of balance. But to be expected for such a modular weapon that is relatively simple to build.

Kuhnhausen said it in his 1911 manuals and I think it applies here. If you have a set of mil-spec parts that have been mic'd and confirmed to be GTG, then you're half-way home when it comes to diagnosing a lot of this stuff. Then when you "upgrade" the original design, you frequently run into issues. Case in point, shortening bbl length, along with gas length, and buffer/buffer spring weights. When you changed just one part, it could create a huge down-stream effect.

When you talk about buffer/buffer spring weights you also have to consider the other end: bbl/gas length, gas port dia, and length of bbl past gas port. (Not to mention ammo/mags). It's no wonder these mfg's just crank open the gas port; it will cover a multitude of sins.

So yeah we all know that you can find combinations that don't work well. I think one way to approach this is to put everything back to "stock" as much as possible, see if you can get a base line, and then add in parts one at a time, to see if you can isolate the problem. This may sound like a big DUH to some, but frequently it's the little things that bite you in the ass.

Case in point, with so many mfg's out there, you can get tolerance stacks that are just a few thou too far for things to work/work well. There are three key measurements in a bolt carrier. The front bolt hole dia, the back hole dia where the gas rings run, and the hole the bolt tail sits in. And the various mfg's are all over the place with them. They all effect how "gas-efficient" your BCG is. If the fit-up is tight with your bolt, very little gas is wasted, so it is all gonna work to power the system, for better or worse. If there is excessive clearance in any or all areas, then it will leak gas, with less gas available to run the system. Again this can work for or against you.

Now normally we'd want a very gas-efficient system. With everything running right, it gives you the most bang for the buck. But if you're way over-gassed, you might WANT a looser fitting bolt to help piss off some of that excessive gas (in fact some mfg's do this on purpose for suppressed weapons). So mic'ing out the parts, and knowing this, might help you isolate other problems. And it's not just a matter of throwing more money at it to guarantee a good part. Sometimes PSA has better overall dims than a high-end boutique mfg. Point is, it pays to check.

[bear13]

Has anyone with a overgassed 10.3 ran a adjustable gas block to help? Gives you ability to tune if you throw a can on?


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[georgeib]

Has anyone with a overgassed 10.3 ran a adjustable gas block to help? Gives you ability to tune if you throw a can on?


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Adjustable gas blocks are not considered reliable enough for a serious use or high volume weapon. You are much better off with a restricted gas tube from Black River Tactical.

[okie]

I think thats what it is. I think that the weights are forward during feeding and chambering, and the lack of deadblow effect in that moment is enough to cause occasional first round stoppages.

I’ve had them, too, with mags where the 30th round was a tight squeeze, and with ones that are supposed to hold 30 but don’t. Before 17k spoke up earlier this year, I assumed it was the mags, but in retrospect, they did manage to function in regular lowers.

If anyone has any mags that meet that description, shoot me a PM.

17k, are your modified A5s still solving the problem? I’ve returned from my travels, so I’m going to start testing it, also, if I can consistently reproduce the problem.

Or worse, the weights are only maybe a fraction of a mm back, effectively cancelling them out, meaning your buffer weight is only the buffer body itself, which I think is less than an ounce.

Strange though because the one I had could strip the first round of any mag I owned, even if loaded to 30. Primarily that's pmags, lancers, and USGI, but I also have some hi cap mags that I've played around with. The Surefires were the most notorious for not wanting to feed that first round when fully loaded, as you can imagine, but the A5 didn't have any trouble with those either.

I still don't understand the spring in them though. Seems like it would totally defeat the purpose of what those weights are there to do, which is to be a dead blow hammer when the bolt closes. The AR has a very short cam path with no runway, so the bolt can't bounce at all. You look at other cam paths and they have a long runway so when the carrier bounces off the breach face it doesn't cause the bolt to rotate out of battery.