Can someone explain the appeal of Low Mass BCGs?

[SgtToadette 59]

So apparently there's a new trend of low mass BCGs in the AR world and I totally don't get it. They are advertised to reduce felt recoil by reducing reciprocating mass, but my understanding is that F=ma, so since we're still dealing with the same force (gas pressure impinging on the carrier), when you reduce mass all you do is increase acceleration of the BCG for a total effect of simply increasing the cyclic rate. Right?

 

To me, having a "normal mass" or increased mass BCG seems like a better idea since it slows the cyclic rate and increased inertia on the bolt's "rebound" and create a better environment for stripping off rounds. Plus if you want to reduce the force of recoil, you're better of reducing the gas pressure (i.e. force) to the lowest, reliable setting.

 

But I'm not an expert and just pulling this out my ass. Am I missing something or misunderstanding?

 

The context for my question is that I'm researching my dream build and want to find the best BCG possible, and it seems the market is flooded with gimmicks.

[Vlad G 345]

You are missing the adjustable gas block.

 

To get most out of a low weight carrier (and often buffer) you reduce the amount of gas the rifle uses via an adjustable gas block. Less mass means you need less gas. Less gas AND less mass means a lot less reciprocating mass. Less mass reciprocating means less muzzle movement.

 

Keep in mind that a hyper effective comp already tames most of the muzzle movement, to the point that the bolt moving back and forth is now actually the biggest component of muzzle movement. Ideally you would want to reduce reciprocating mass to zero .

 

To me this is another one of those things that perfected in competition and it is now moving into mainstream. However, it is not as straight forward as people make it out to be. You do need a reliable gas block, and you tend to tune it to the ammo you are using. You can always run it full open, and you will still get the lesser mass making some difference, but to get the full effect you tune it a bit.

 

The other option is to use a barrel with a small gas hole, or with a gas hole right at the bottom of the spec size. You get most of the effect of the adjustable gas, without another thing that can fail.

[effd27145 0]

Ugh ^^ Beat me to it as I was typing.

 

That^^ haha.

[SgtToadette 59]

Gotcha! Thanks Vlad! I think my confusion was the result of reading manufacturer descriptions which lead me to believe they were drop in components and not part of a larger system.

[Vlad G 345]

Well they are, sorta. I mean they'll drop in, and they'll work, and they'll do something. Its just that to get the most out of them they are part of a larger tunable system.

[Vlad G 345]

They other thing they tend to forget to tell you is that you should be running a titanium firing pin. The lighter BCG moves faster, which means the free floating firing pin moves faster which means it will nudge forward with more energy as it slams into battery. That can lead to unintended boom-booms. It doesn't happen often, but it does happen, which is why the lower mass firing pins come in handy.

 

This is even more important if you don't reduce the gas, because you are going to be smacking that BCG around a lot harder.

[SgtToadette 59]

Makes sense. I think it's really interesting stuff. Still quite a bit over my head at this point. Just makes me want to hit the books and get into reloading!

[Vlad G 345]

That and titanium firing pins look f-ing cool.

 

 

 

 

[SgtToadette 59]

[Vlad G 345]

Well do keep in mind that mostly they'll be black with crud, but it is titanium nitride and there for a reason, looks are secondary.

[SgtToadette 59]

I've actually looked at TiNi BCGs but they don't seem to be the best option. QPQ seems to be more effective from my research.

[Vlad G 345]

I agree, but on a firing pin thats made of titanium, it makes sense.

[SgtToadette 59]

I'm gonna have to peruse the AR pic thread and see some of your builds now.

[Vlad G 345]

Mine are not there. My guns aren't pretty, they are usually scratched and boring looking.