Effect of Delayed Unlocking

SonoranPrecision

Gunny Sergeant
Full Member
Minuteman
Sep 12, 2019
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Phoenix, AZ
I know this will be a little long winded, but the details might be important on this one.

So I’ve gone down this rabbit hole before, without specifically knowing it. At the time primarily focused on the negative effects of an extremely overpassed system. At the time I was seeing abnormally large groups after adding a suppressor, which was resolved by reducing the gas via a BRT gas tube. It worked quite well, and resulted in the rifle going back to shooting as well as it did prior to adding the can. That said, I would still get random fliers (true fliers, on a 30 shot group, 28rds into 1.2”, the 2 would fly wide and increase the es to 2”) which I chalked up to me just sucking, or getting sloppy.

Fast forward, I built a new upper specifically to help reduce receiver flex/positional poi shift (which was done reasonably successfully with an Aero Enhanced upper and rail). This meant a whole new upper, and allowed to be built with an adjustable gas block this time. Long story short, new upper shoots great, gas is tuned perfectly, still getting random fliers as discussed above, so same conclusion, I must still be doing something weird to cause the fliers.

Then a buddy of mine who works in a local gunshop hits me up and is telling me about this new BCG they have from VKTR (turns out it’s exactly the same as the Leitner Wise bgc) and that I should try it out. After looking into it, their claim to fame is an altered/delayed cam path, that is supposed to unlock the bolt/extract the case 10-15% later than a standard BCG, thus keeping full pressure in the barrel longer, and extracting at lower pressures, which should reduce gas to the face running suppressed. It’s also hard chromed, and a couple other minor advantages, so I figured sure, why not. Worst case it does nothing, and I could use another BCG anyway.

Turns out, it definitely does something. The rifle went from locking back on empty to not locking back. And most interestingly to me, the fliers seem to have disappeared. It was just one group, but it’s August in AZ, so laying on the ground to shoot a group is not comfortable this time of year, and it was a 20rd group in about 2 minutes, so the rifle got quite hot. All that to say, if there were ever conditions that would justify having some fliers it was that.

Obviously I need to do some more testing, but has anyone observed anything similar? Maybe not with the Leitner Wise/VKTR cam path, but I know LMT and Surefire do something similar with a delayed cam path. Does it even make sense that delayed unlocking would have that much of an effect?
 
I don’t know the answer to your question, but the Griffin Enhanced Gas Pocket BCG has some delayed unlocking feature too.

From the product page:

“Increased Cam Pin Travel Length for delayed bolt unlock”


I can say that that BCG is definitely quieter than a stocker. I bought the whole kit sans the buffer stuff. Gun feels smoother too, but that might be in my head.

Listen to this, much of it is over my head as I’m not an AR-master.
 
I know this will be a little long winded, but the details might be important on this one.

So I’ve gone down this rabbit hole before, without specifically knowing it. At the time primarily focused on the negative effects of an extremely overpassed system. At the time I was seeing abnormally large groups after adding a suppressor, which was resolved by reducing the gas via a BRT gas tube. It worked quite well, and resulted in the rifle going back to shooting as well as it did prior to adding the can. That said, I would still get random fliers (true fliers, on a 30 shot group, 28rds into 1.2”, the 2 would fly wide and increase the es to 2”) which I chalked up to me just sucking, or getting sloppy.

Fast forward, I built a new upper specifically to help reduce receiver flex/positional poi shift (which was done reasonably successfully with an Aero Enhanced upper and rail). This meant a whole new upper, and allowed to be built with an adjustable gas block this time. Long story short, new upper shoots great, gas is tuned perfectly, still getting random fliers as discussed above, so same conclusion, I must still be doing something weird to cause the fliers.

Then a buddy of mine who works in a local gunshop hits me up and is telling me about this new BCG they have from VKTR (turns out it’s exactly the same as the Leitner Wise bgc) and that I should try it out. After looking into it, their claim to fame is an altered/delayed cam path, that is supposed to unlock the bolt/extract the case 10-15% later than a standard BCG, thus keeping full pressure in the barrel longer, and extracting at lower pressures, which should reduce gas to the face running suppressed. It’s also hard chromed, and a couple other minor advantages, so I figured sure, why not. Worst case it does nothing, and I could use another BCG anyway.

Turns out, it definitely does something. The rifle went from locking back on empty to not locking back. And most interestingly to me, the fliers seem to have disappeared. It was just one group, but it’s August in AZ, so laying on the ground to shoot a group is not comfortable this time of year, and it was a 20rd group in about 2 minutes, so the rifle got quite hot. All that to say, if there were ever conditions that would justify having some fliers it was that.

Obviously I need to do some more testing, but has anyone observed anything similar? Maybe not with the Leitner Wise/VKTR cam path, but I know LMT and Surefire do something similar with a delayed cam path. Does it even make sense that delayed unlocking would have that much of an effect?
I've never really heard much of anything about the gassing of a rifle causing flyers. There are way too many other factors to consider than just chalking it up to the gassing of the rifle.

One thing you should do though is put each BCG on a scale. Compare the original one to the new one. Odds are they have a weight difference hence the locking back concern.

If you really want to go down the rabbit hole about what an increased unlocking actually does we can absolutely do that, however if you are strictly talking about flyers I think you are chasing a ghost.
 
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I've never really heard much of anything about the gassing of a rifle causing flyers. There are way too many other factors to consider than just chalking it up to the gassing of the rifle.

One thing you should do though is put each BCG on a scale. Compare the original one to the new one. Odds are they have a weight difference hence the locking back concern.

If you really want to go down the rabbit hole about what an increased unlocking actually does we can absolutely do that, however if you are strictly talking about flyers I think you are chasing a ghost.
What I can say is that I have one rifle that absolutely had the accuracy destroyed by being over gassed. Like doubled the group size, so I know for a fact that unlocking too soon absolutely CAN cause dispersion issues. So it follows that it’s likely not an on/off switch, but rather a sliding scale. But you’re right that causing/curing random fliers MIGHT be a stretch. More likely to see an overall increase in group size, and not fliers. Either way, it seems to me that as long as everything still cycles, delayed unlocking can only benefit the system.

As far as the locking back, it’s not a concern, as adjustable gas took care of it. But I hadn’t thought about the weight of the BCG playing a role. Just put them both on a scale and they weighed exactly the same. Meaning the different cam path is either robbing some energy, the carrier has some other mechanism of ditching excess gas, or the delayed unlocking is lowering residual pressure in the bore during extraction. Or more likely a combination of more than one of those.
 
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Didn’t think they finally translated that idea into an AR bolt carrier, glad they did.

Love the idea of the long, slow, smooth helical cam track.

I imagine that the design enables a slower, higher - torque camming action.

I always wondered if this design would be friendlier to brass.


Long Recoil designs typically have these long cam tracks…

Examples from Singapore are the CIS Ultimax and the SAR-21.

Not entirely sure if the machineguns from Knight’s Armament use a similar cam track in addition to long recoil travel.

Then a buddy of mine who works in a local gunshop hits me up and is telling me about this new BCG they have from VKTR (turns out it’s exactly the same as the Leitner Wise bgc) and that I should try it out. After looking into it, their claim to fame is an altered/delayed cam path, that is supposed to unlock the bolt/extract the case 10-15% later than a standard BCG, thus keeping full pressure in the barrel longer, and extracting at lower pressures, which should reduce gas to the face running suppressed. It’s also hard chromed, and a couple other minor advantages, so I figured sure, why not. Worst case it does nothing, and I could use another BCG anyway.

Any chance you could photograph the cam tracks of a regular BCG and that one by VKTR side by side for comparison?

I’m curious about the differences.
 
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Any chance you could photograph the cam tracks of a regular BCG and that one by VKTR side by side for comparison?

I’m curious about the differences.
So where the cam path of the LMT is elongated with regard to bolt travel forward, the VKTR has an elongated travel in rotation. Standard BCG has 20.7 degrees of bolt rotation, whereas the VKTR has 22.5 degrees. Additionally, looking at them side by side, it appears a standard carrier, as well as the LMT, have straight line movement in the cam path while the bolt is in the fully locked position. However the VKTR flips that around, and puts the straight line travel AFTER the bolt has fully unlocked. I imaging that helps reduce the chance of the cam pin gouging the upper receiver, although I’ve never personally seen a rifle with that issue.

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So where the cam path of the LMT is elongated with regard to bolt travel forward, the VKTR has an elongated travel in rotation. Standard BCG has 20.7 degrees of bolt rotation, whereas the VKTR has 22.5 degrees. Additionally, looking at them side by side, it appears a standard carrier, as well as the LMT, have straight line movement in the cam path while the bolt is in the fully locked position. However the VKTR flips that around, and puts the straight line travel AFTER the bolt has fully unlocked. I imaging that helps reduce the chance of the cam pin gouging the upper receiver, although I’ve never personally seen a rifle with that issue.

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Thanks!

I see now.

Instead of “slow unlocking” associated with a long helical path, it’s more of “delayed unlocking.”

Something closer to changing the timing of the “bolt twist.”
 
Instead of “slow unlocking” associated with a long helical path, it’s more of “delayed unlocking.”

Something closer to changing the timing of the “bolt twist.”
Definitely a change to the bolt timing. I would almost lean more to a “delayed extraction”. Because the bolt probably is technically unlocked around the same time, but that linear travel in the cam path is after the bolt is unlocked. So the bolt is held in a technically unlocked position for a split second before actually starting to extract the case from the chamber.

I read that you were trying to minimize gas as much as you could, but does your rifle lock back on the last round with just slightly more gas?
Really it only failed to lock back when the can was removed. But yes, a little extra gas and regained full function.
 
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