LW BCGs: I Hear So Much and Know So Little

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Skylerbone

Skylerbone

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Anyone have a primer or some insight? If I understand what I’ve read, coupling a LW BCG and carbine buffer with an AGB should allow for a softer impulse that stays on target thanks to the reduced reciprocating mass.

My question is whether the difference is substantial in a 10.5” carbine barrel set up and if so, which one for a forward assist lower?
 
I've got one in my light weight upper. I ran it with a reduced power mainspring as well, and found it extremely flat and comfortable. Add a brake and it would probably just shake. Mine isn't a very high quality, or particularly light example either.
 
I wouldn't say substantial in a 10.5" S/A,.... noticeable ? yes.
That comment will vary quite a bit... dependent on so many variables.

I would suspect a F/A would benefit more.

I did this same thing to a 18" RLGS 3G AR, softer shooter for sure, enough softer to make me do it again ? ... Nope

A decent muzzle device, combined with a good recoil pad ( Limbsaver for Magpul carbine stocks ) produced better results for me.
 
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My 3Gun rig has

SLR AGB
Low mass BCG (Rubber City)
H Buffer with reduced spring
Precision Armament M4-72 brake

and it is a remarkably light and flat shooting gun, even with it's LW profiled barrel. Once "tuned" for the ammo I haven't found it any less reliable than any other AR15 I've owned. Every gun I've put together since has had at least an AGB, that alone goes a long ways in recoil and keeps the action cleaner.
 
Skylerbone said:
Not looking to SBR right away, just an SBA3 and KVP Magnum XL linear comp.
Click to expand...

Consider a short reset trigger as well... ( since you are spending money , Lol ) , they can be dramatically different.

I'm not a huge fan of cassette triggers but... reading this article showed some wildly computer measured differences.

A short quick reset , with little creep, little overtravel for reset etc... basically a hair trigger , can make for some fast shooting in a competition gun.

The Geissele Super 3 Gun (S3G) flat bow or curved... can also be super, crazy fast shooting.

BEAR in mind, if you decide on a fast trigger... under stressful conditions ( combat type ) your muscles will involuntarily tense up and / or contract... so with a fast trigger, you could discharge the firearm unintentionally... repeatedly.

So until you are very well trained on the short pull trigger.... 3G only.

https://www.thetruthaboutguns.com/ar-15-drop-in-trigger-roundup/
 
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without writing a book, i'd say keep in mind it's a SYSTEM. when you dramatically reduce dwell time, you have to increase pressure to make up for lack of volume.

i could be leaving something out but all of these work together
ammo
-powder burn rate - need to stay in a certain range to make gas guns work
-powder amount - mil ammo is typically hotter than civ stuff like wolf and white box and cycles a lot harder.
diameter of gas port hole - usually the point of restriction in the gas system unless there's an AGB
AGB if any, which is typically used to reduce the volume of gas heading back toward the carrier
length between chamber and gas port - the closer, the higher the pressure
length of gas tube (usually this is a standard size but some people make pigtail ones that effectively reduce the pressure)
weight of reciprocating mass - the more mass, the slower the chamber opens
-BCG
-buffer
muzzle devices like suppressors which put some back pressure and cause the action to cycle much harder

as far as goals are concerned, i think the general consensus is that super fast "snappy" and low mass gets you back on target quicker, but lots of people like slow and soft recoil "impulse"
most people will try to adjust the system until the bolt doesn't lock back on an empty magazine and then back off a bit. if you do this, you better keep it clean. if it gets dirty, it may not cycle
the third thing is reducing gas coming back into the action from a suppressor by trying to slow the chamber from opening until chamber pressure drops by adding mass to the carrier and heavy buffers

so obviously some of those conflict.

you can go with a regular buffer and lightweight carrier, which will cycle faster, and then use an AGB to reduce the gas to make it softer. but doing so typically reduces reliability. keep in mind most systems known for reliability have really heavy bolts. and dirt or mud or powder fouling, maybe cold weather, etc could cause it to not cycle properly (won't pick up the next round in the mag because it's not going back far enough)
you may also start noticing your brass has dirty necks, may stretch more, etc
 
I’m planning to use a SOLGW 10.5” Carbine Gas .078” port barrel, KVP 3.25” Magnum Linear Comp, JP clamp-on AGB, and from there the hard list stops.

I do have a SI flat wire spring and a standard (3oz) buffer in a carbine extension but would consider a captured spring system or reduced power spring if appropriate. Not sure on trigger yet, I may try the LaRue everyone raves about but an Elftmann is leading the list based on those I’ve tried.

As for cleanliness I clean after every range outing and rarely run more than 100 rounds through any given AR. I also tend to use plenty of lube.

Now if I’m understanding things correctly, with a low mass carrier and buffer I want a low power spring and substantial reduction in gas from the AGB?
 
it's your AR and you can do it for no other reason than you feel like it, but there's no way i'd build a gun like that.
1. short barreled ARs are LOUD
2. short barreled ARs with comps/brakes are crazy ridiculous loud. plugs and muffs loud. i wouldn't want to shoot it indoors even with plugs and muffs
3. because it's loud, i'd want a suppressor. and a suppressor is probably going to be less reliable and super gassy with all the light weight stuff
4. if you're making a weapon, don't use clamp on gas blocks, and realize if you touch that thing off at night, muzzle flash is going to be wild

if you're making a 3gun style race gun, use an 18" barrel and rifle gas and a brake
if you're making something reliable, use a gas block like noveske's switchblock, which is simple 3 position (normal, suppressed, off) and PINNED
 
taliv said:
1. short barreled ARs are LOUD
2. short barreled ARs with comps/brakes are crazy ridiculous loud. plugs and muffs loud. i wouldn't want to shoot it indoors even with plugs and muffs
3. because it's loud, i'd want a suppressor. and a suppressor is probably going to be less reliable and super gassy with all the light weight stuff
4. if you're making a weapon, don't use clamp on gas blocks, and realize if you touch that thing off at night, muzzle flash is going to be wild
Click to expand...

If I may address these:

1. I’ve built a 7.5” and 10.5” in 5.56 already and I agree they are LOUD.
2. I’ll be using a linear comp. (blast forwarding) 1.25” dia. X 3.25” length to help attenuate noise. If correct, that gives me the equivalent of a ~13.5” barrel before that blast begins to shred my ears. I know it’ll never be an 18” rifle gas but they have made the other two tolerable. I do have several 18” barrel rifles to shoot as well.
3. Right now a suppressor is out until I dig in and do my homework. Purpose wise this is strictly a fun gun for now but may at some point be double stamped in the future. I am glad you mention these issues however as I’d be happy to skip the low mass carrier if it is counter to the objective of flattening impulse.
4. I realize for a defensive carbine a pinned gas block is a no-brainer but I’ve yet to encounter problems with low pro blocks. The JP came recommended and is what I chose on the other 10.5” build.

I sincerely appreciate the feedback because I honestly don’t know everything I want to know about setting things up. I will say that working with the first AGB made a noticeable improvement but that was compared to a 7.5” barrel pistol gas which may get a replacement 11.5” in the future. Apart from the pistols, all other ARs are 16” or 18” middy and rifle gas.


The AGB model in question; 4 clamping screws, and I use a torque driver to set them.
7BD1D5A4-3B3E-4CCA-BF42-01F8474C673B.png

The actual build barrel and gas block.
3B92F5E6-DDF4-494D-90F5-45C68A0AC1AE.jpeg

Unless I’m mistaken, this blind hole is a starter if you wish to pin the block.
55B93561-693F-45A9-A78B-8B65C21580C4.jpeg

A pair of KVP linear comps, the Magnum is on right.
BF8D7639-7228-437D-9CC4-5DDFFF5EF143.jpeg
 
js8588 said:
Velocity flat 3.5lb trigger. You'll be very, very happy with it.
Click to expand...

I’ll look into it, never had the opportunity to try one yet. My personal ARs, those not built by/for my kids all use 2-stage RRAs at 4 and 3 1/2 lbs. I dare say I’m not qualified to use an ultralight but do have several bolt action rifles that dip below 3 lbs.
 
Skylerbone said:
Now if I’m understanding things correctly, with a low mass carrier and buffer I want a low power spring and substantial reduction in gas from the AGB?
Click to expand...

Correct, but you can use a standard spring and heavier buffer combination. Some guys go with a full power spring to ensure feeding. I ran this combination for a couple of match seasons.

This is where the "tuning" to your load comes in. Since you've reduced the mass/weight, and the spring & buffer weight, it's just a matter of allowing just enough gas to reliably work the action with that load, whereas most ARs are over-gassed top allow functioning with a wide spectrum of ammo. I always start at a click or 3 above closed, load and fire 1 round from a magazine, opening the gas port 1 click at a time, until you reach bolt lock. I then open up 1 more click for reliability.

For a lot of guys/gals, the lesser recoil and more importantly muzzle climb isn't going to matter one bit, but for gamer gun it really does help. Also IF you're going to suppress it's a huge benefit.

As far as clamp on GBs VS Pinned or setscrew, I've only used setscrew on my builds and dimpled the barrel and I've never had a problem with that setup. I'm putting together a SPR now and am researching the possible accuracy benefits in going to a clamp-on. Some have stated that it provides a better seal and places less stress on the barrel. Since the barrel maker builds match rifles for a living, I'll go with his recommendation. His barrel (White Oak Armament) did come dimpled, and they sell setscrew as well as clamp-on blocks.

UPDATE: I contacted WOA reference Clamp VS. Setscrew and accuracy differences between the two methods. Their reply was that they see no differences in accuracy between the two installation methods. Good enough for me! For my SPR build I'll stick with set screw.
 
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You might move the JP Adj. GB forward of the barrels shoulder, just slightly ( .025' ) I am pretty sure , on the JP Adj. GB's you place it against the barrels shoulder if it is a JP barrel.

If it is being installed on a barrel for possible use with a USGI handguard and hardware ( your SOLGW 10.5" would fall under that ) , you place the Adj GB slightly forward ( making up for that thickness of a USGI handguard cap. .... Gizmo that holds the front part of USGI handguards )
 
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