Help me understand the benefits of a JP VMOS vs Full Mass carrier on a permanently suppressed platform?

[Volarus]

So I’m starting the long process of building a higher-end suppressed AR308, and the internals are likely to be JP.

One thing I can’t figure out, is what are the inherent advantages of the VMOS when compared to their full mass BCG?
I mean other than the two obvious advantages of being adjustable and being slightly heavier.

I see that that the VMOS is 0.7oz heavier when configured with two tungsten weights, so - if you need that additional 0.7oz, then the advantage is clear.

Also, if you’re going to be switching up your configuration - the benefits of the VMOS is crystal clear.

So I don’t plan to change up my configuration at all, once the rifle is tuned - I don’t plan to do anything with it other than shoot it and clean it. So the variable part doesn’t mean a lot to me. Whether or not the +0.7oz matters to me or not remains to be seen.

In my mind, the simpler the moving part system - the better. Basically - given the option, I would rather use the JP Full Mass BCG than the VMOS purely because it is a simpler system with less failure points.
That being said, I’ve never handled a VMOS so I thought there might be some other design feature I was missing - so I emailed JP asking what them if there was any reason I would want to purchase their VMOS over their Full Mass BCG if I already knew I would be shooting suppressed all the time without changing my configuration at all.




The response I received didn’t make a lot of sense to me.
I was told that the VMOS doubles the deadblow hammer effect over the Full mass BCG because part of the weight was dynamic because it moves, the effect being increased reliability, particularly when dirty.

So - as I understand it, a deadblow hammer has a hollowed area in the hammers head containing something like sand or lead shot that follows the blow of the hammer face in order to stop the hammer from bouncing like a normal hammer would.
So to me this translates into stopping bolt bounce in a BCG. This makes perfect sense to me.

***My confusion*** primarily stems from the following:
From what I’ve read and videos I’ve watched about the VMOS - I’m not seeing anything that says or suggests that the weights on the back of the VMOS move within the BCG at all. They appear to be nothing more than fixed weights that are held in place securely with o-rings to keep them tightly in place.
If these weights are not moving within the BCG itself - then they are not performing any sort of deadblow hammer effect over a solid/ fixed mass BCG of equal mass. Am I missing something? Are these weights actually dynamic and moving on the BCG?


I’m assuming that some part of this explanation simply went over my head and I’ve never handled or shot a VMOS so I’m coming here to ask those who know better than I.

Do the weights in the VMOS move?

Is there something inherent to the VMOS that would make it in some way more desirable than a fixed mass BCG other than being able to change the mass or gain a little more weight?

 

[Bigjake83]

Do the weights in the VMOS move?

Yes! Just like when you shake a buffer and you hear the weights shift, It's not as pronounced as that but they do have play In between each weight that is dampened by a rubber o-rings.

You are overtaking the shit out of this.

Suppressed AR's have been running just fine for decades with the conventual Heavy Buffer and Full Mass BCG's combos, both will work the VMOS just gives it a little more Pushinn for the cushion.

 

[Volarus]

Yes! Just like when you shake a buffer and you hear the weights shift, It's not as pronounced as that but they do have play In between each weight that is dampened by a rubber o-rings.

You are overtaking the shit out of this.

Suppressed AR's have been running just fine for decades with the conventual Heavy Buffer and Full Mass BCG's combos, both will work the VMOS just gives it a little more Pushinn for the cushion.

Perfect, thanks for the info!

Yeah definitely overthinking it - but to me, if I’m building what will ultimately be a ~$5k setup - overthinking it is part of the fun.

Having never operated a rifle with a VMOS installed, I’ve no doubt they aren’t needed.
But if using one offers notably smoother operation - I’d like to have it in my rifle. But I certainly wouldn’t buy something without understanding why I’m buying it.

If the VMOS isn’t bringing a lot to the table though, I think a Full Mass BCG with a headspaced bolt is the ticket.

 

[Huskydriver]

Fmos also has serrations for a fa the others do not fyi if that matters to you

 

[Volarus]

Fmos also has serrations for a fa the others do not fyi if that matters to you

that’s a good thought!

For 5.56 it doesn’t matter to me - I’ve never needed to use an FA before.
I’ve heard that ar308s have more of a use for them though - but I would hope I wouldn’t need it.

At the end of the day I’m not taking the rifle to war and it’s not a home defense weapon. It’s for hunting and ranges. I’ll probably go to some courses for fun. But ultimately not too concerned if I can use a FA.

 

[TimK]

I have a VMOS for small frame. Different from your situation, I know. As already stated, the weights do move and provide some additional hammering effect. I got mine for a high reliability.223. It’s enough heavier from the typical LMOS I usually use that I REALLY noticed the difference in the recoil impulse. Significantly higher. I ended up moving it over to a Valkyrie just to make some use of it.

in your case, it might have value in that you could test for reliability with one or two steel weights. If it proves to be good in the lightest configuration, I think you’ll notice a reduction in recoil.

You can achieve very similar results by fiddling with the weights on an SCS. And, IIRC, you can change the overall reciprocating mass of the BCG and buffer combined by 4-5 ounces in the .223 versions. That’s a lot of flexibility to try to find the minimum total mass required to achieve the level of reliability required. My stupid Valk gums itself up very quickly. I experimented with the masses of both BCG and buffer until I found the minimum to get me 250 rounds of reliable function. You could do the same with your setup. Get it good and filthy and then start reducing weights until it quits running.

in the .223 version, the weights are interchangeable with those in the SCS. Not sure if that’s the case in the large frame versions.

 

[beenjammin]

With adjustable gas blocks I dont see the advantage of a heavy vs light anymore. Just adjust the gas until it cycles. Heavier is going to take more gas and lighter is going to use less is would seem. before when a rifle was over gassed I could see a heavier carrier coming into play, but with blocks like the JP,SLR, or Seekins having 30 or so adjustment settings, it would seem you could fine tune either

 

[Volarus]

I have a VMOS for small frame. Different from your situation, I know. As already stated, the weights do move and provide some additional hammering effect. I got mine for a high reliability.223. It’s enough heavier from the typical LMOS I usually use that I REALLY noticed the difference in the recoil impulse. Significantly higher. I ended up moving it over to a Valkyrie just to make some use of it.

in your case, it might have value in that you could test for reliability with one or two steel weights. If it proves to be good in the lightest configuration, I think you’ll notice a reduction in recoil.

You can achieve very similar results by fiddling with the weights on an SCS. And, IIRC, you can change the overall reciprocating mass of the BCG and buffer combined by 4-5 ounces in the .223 versions. That’s a lot of flexibility to try to find the minimum total mass required to achieve the level of reliability required. My stupid Valk gums itself up very quickly. I experimented with the masses of both BCG and buffer until I found the minimum to get me 250 rounds of reliable function. You could do the same with your setup. Get it good and filthy and then start reducing weights until it quits running.

in the .223 version, the weights are interchangeable with those in the SCS. Not sure if that’s the case in the large frame versions.

All excellent points and things for me to think about!

Coming into this I’ve just had the thought of using standard/full mass reciprocating parts for maximum reliability on a suppressed platform.

But the more feedback I get and the more I think/read about it - maybe that’s not necessary?

I sure wouldn’t mind a lighter recoil impulse on a Semi .308.

With an adjustable gas block perhaps I could get away with a standard/all steel weight VMOS.
I am planning to use a Nomad 30 with E-brake, which is in sort of an in-between place in terms of gas flow-through. I don’t know that if want to go all the down to an LMOS carrier though.
Which really emphasizes your point on being able to tweak and fiddle with the weights in the VMOS.

Lots to think about - thank you very much for your input!

 

[Volarus]

I'm using a LoMass on a 16" rifle length gas suppressed .308W. I just opened the gas enough to cycle the gun. I am more concerned about the additional mass cycling back and forth adding to the effect of the recoil.

I think a heavier mass BCG would be useful for a 6.5 Creed where the pressure is higher from a smaller bore.

Oh wow, very nice.

Are you near the limits of what you’re gas system can get you?
Wondering how gunked up it will run?

 

[Volarus]

I don't understand what you mean. I tuned it. The gas block isn't maxed out one way or the other if that's what you mean. I don't think it's going to struggle to fight thru carbon build up in the receiver. The whole point is that it has way more cycling power available on tap to move that lighter BCG than it needs so I tune it down. I haven't set the gas so that it just barely cycles. I guess a way to explain it is imagine a see-saw. Gas port and dwell time on one side of the pivot and BCG/ buffer mass on the other. With spring power related in a supporting role to the cycling mass. More cycling mass = more gas required. Less cycling mass = less gas required. I don't think a heavy mass BCG fights thru carbon in of itself. Spring power helps a lot with that. And just because you have a lower mass BCG doesn't mean you have to have an underpowered spring.

Yes that’s all I meant, if it had to be tuned nearly to the limit of its ability to get it to slow down such a light BCG on a suppressed platform.

 

[Volarus]

I don't think it's tuned to an extreme limit. The gas setting seems to be about the middle of the screw adjustment range. In fact I was actually kind of surprised how much I had to open it up. I expected that it would only be a couple of clicks off of fully closed. I think it's just over middle on the "more open" side. I've shot about 200rds so far and haven't had a single malfunction outside of adjusting the gas during the first 11 rounds. It's been dead reliable with 4 different types of ammo. The recoil is like a bolt gun punch. I don't at all feel the two-stroke recoil-push back and then the reciprocating forward slush of the mass returning forward. I've shot suppressed M110's and SR25's a lot. They all have a two-cycle, back-forward motion of recoil. When they get carbon caked the forward reciprocation of the BCG becomes a sluggish "ca-chunk". They have full mass BCGs. I'm pretty sure, with a suppressed AR-10, you can grind any rifle to a halt eventually without cleaning and lubing. And we definitely tested those limits.

That’s a lot better than I would have expected. I would have thought you would be putting near min gas into that BCG trying to slow it down with a suppressor!
Thank you very much for sharing!

 

[SMTGWKD]

With adjustable gas blocks I dont see the advantage of a heavy vs light anymore. Just adjust the gas until it cycles. Heavier is going to take more gas and lighter is going to use less is would seem. before when a rifle was over gassed I could see a heavier carrier coming into play, but with blocks like the JP,SLR, or Seekins having 30 or so adjustment settings, it would seem you could fine tune either

Just my $.02, but I run suppressed 90% on many rifles - nearly all with AGB. For 5.56 - I agree. For 6 ARC, .308, and especially 6.5 Creed my experience is that mass regulation was very useful for reliable, consistent function with various loads, powders, bullets, etc and to really dial in the system. If we are spending this much on a great rifle, why not make it epic by adding that extra adjustability to both tune the rifle for as broad a spectrum of ammo as possible?

I actually had overpressure issues on the brass and primers before weight regulation. There is an interesting, but long and kinda boring, video from JP discussing their perspective on mass regulation on "wildcat, high pressure" cartridges like the 6.5 Creedmoor. Definitely worth a watch.