Low mass BCG, buffer/spring weights, gas lengths...?

[Scotty454]

I'm relatively new to ARs, and my upcoming SLR build will be my first ground up build.

I bought an 18.6" barrel with a mid length gas system (Non-adjustable gas block). I'm curious about low mass BCGs, and the relationship between them and the gas system length/buffer mass/spring weigh. What are the advantages of a low mass BCG, and playing with buffer weights?

 

[tharkhold]

I'm relatively new to ARs, and my upcoming SLR build will be my first ground up build.

I bought an 18.6" barrel with a mid length gas system (Non-adjustable gas block). I'm curious about low mass BCGs, and the relationship between them and the gas system length/buffer mass/spring weigh. What are the advantages of a low mass BCG, and playing with buffer weights?

In the simplest terms, a low(er) mass BCG requires less energy to move around, and hence would cycle faster in the action of the firearm.

A stiffer spring would affect this back-and-forth movement though... the advantage of the AR platform is that you can play around with various springs/weights/etc relatively cheaply... It may all come down to how you like and feel your rifle with X spring, Y buffer weight and Z BCG.

One you start down this hole, there's no coming out!

I'll let the Physics PhD's chime in.

 

[adamg]

I'm relatively new to ARs, and my upcoming SLR build will be my first ground up build.

I bought an 18.6" barrel with a mid length gas system (Non-adjustable gas block). I'm curious about low mass BCGs, and the relationship between them and the gas system length/buffer mass/spring weigh. What are the advantages of a low mass BCG, and playing with buffer weights?

The advantages of low mass BCG is less reciprocating mass in the firing cycle, so the gun moves less. It moves less at the back of the BCG stroke, when the gun is impacted backward, and less at the front of the stroke, when the gun is impacted forward.

Personally I wouldn't run a LW BCG with a 18.6" midlength barrel and non adjustable gas block. That's a lot of gas going into the BCG, which gives it a lot of energy, and it lacks the mass to absorb it, so it is going to cycle very hard. I think some of the LW BCG manufacturers would even advise against it.

If anything, a LW BCG is a disadvantage in the setup you listed. A LW BCG can only offer less gun movement if it is receiving less energy from the gas system than that same gun ran with a milspec BCG. And you lessen the gas by using shorter-than-normal dwell time gas systems (i.e. intermediate or rifle length on a 16", rifle length on a 18.0") and also restricting gas with the adjustable gas block.

The other piece of the lightweight, low impact puzzle is a reduced weight buffer and buffer spring. I have all these parts in the EE at the moment except the buffer parts.

There's some talk about LW BCGs on JP's website, for instance here where they recommend use with adjustable gas system:
https://jprifles.com/document_pdfs/JPBC2JPBC3JPBC16_641.pdf

 

[mileageman]

Running a LW BCG is pointless without a adjustable gas block and is not recommended. The longer the gas system the better. If you look at the top 3-gun shooters in the US they are for the most part all running 18” barrels, rifle or mid length gas systems, adjustable gas blocks, and very effective muzzle brakes. Perceived recoil and muzzle rise will be significantly less.

 

[sky52]

^^ correct. A low mass BCG without an adjustable gas block means that the bcg will now travel at a higher velocity then the regular full mass bcg, how will that translate to felt recoil? I do not know, it may even defeat the benefit of lowering the felt recoil that would have been there, as i run both an adjustable gas block and a rubber city light weight carrier on a 16" mid length. It shoots and recoila like a 10/22 now.

 

[Scotty454]

Hmm... So basically, don't bother with lowering the mass of the bolt carrier and buffer unless you can meter the amount of gas coming into the system. Decreasing the mass of the carrier will increase the cyclic rate, but probably also increase felt recoil?

The barrel I ordered came with a gas block, but it might be worth getting an adjustable so I can play around, and get it where I want it? The intended purpose for this rifle is 3 gun, and general (NR )plinking/target shooting. Though for the latter purpose I'm not overly concerned about recoil/performance, moreso just reliability.

 

[sky52]

If its reliability you are looking for...leave everything the way it is. Adjustable gas block and low mass operating system tends to be finicky

 

[Scotty454]

If its reliability you are looking for...leave everything the way it is. Adjustable gas block and low mass operating system tends to be finicky

Finicky in what way? I have no problem playing to get things right, but I'd like to be able to figure out what works and then leave it that way. I'm going to start reloading .223 (Just got my XL650 set up), so I could also dial in loads as needed?

 

[ffgats]

get an adjustable gas block if you want to use a Light weight BCG, Superlative and Odin are availiable in Canada by one of the site sponsors, get some springs with different weights and buffers. much better if you reload yoour ammo so everything can be tune and balance.