That port cover is still pretty heavy compared to the other polymer offerings.

I've got a JP LMOS that I like. If you don't want to go JP, I also have experience with the 2A Armament Lightweight BCG and it's running flawlessly for me.

Just stumbled upon this thread.  Tried a super lightweight build years ago.  Cav-15mkII + bushmaster carbon 15 upper.  Adco profiled a 14.5 inch barrel to "pencil" for me and permanently attached a vortex flash hider.  This was years before all these high quality LW components were on the market.  

Well the carbon 15 upper was junk.  Broke on me.  They no longer make a polymer upper in that rifle and have went to aluminum.  

Anyway...

The old Cav-15 lowers, are they lighter or heavier than the standard configuration (lightweight) lowers that need a buffer tube when built out?

Just curious

It depends man. It can be done. Just gotta build it light I think my tegra carbon fiber lower with  smoke composites stock, hogue grip and aluminum grip screw weighs less than 10 oz. Add about 3 oz to that for the lightest stock and buffer tube combo. Cav arms lower weighs over 20 oz if I recall. If you're asking about a mil spec aluminum lower then the cav arms is definitely lighter

2A, BAD, or Master of Arms lower with the hogue grip and a smoke composite's stock is going to be pretty light, lighter than a Cav lower.

I need to put my old cav-15 on a postal scale.  It has standard lower parts kit in it.  Of course they don't require a buffer tube, castle nut, or retainer plate.  The pistol grip is integrated and it doesn't need a grip screw.  Some other small parts can be omitted as well.  

I was just wondering if anyone here had done any comparisons (this thread is 43 pages and will take me a while to read).  

I'm sure with today's lighter lower components I could make mine even lighter.  The CAV's stock can also be cut down to save more oz's.  

I was thinking more of a comparison between the 2A armament and BAD offerings to the old Cav receivers.  I'm sure there are also more out there.  Magnesium and carbon fiber lowers, etc.

This is what I was wondering.  Thanks

You can compare all kinds of different build options with the PWD. Link is in my Sig.

Man, classic firearms wants to charge me a $15 fee to change my ffl. The stupid website wouldn't let me order unless i chose an ffl, and my ffl wasn't listed!!! So i tried calling and ordering but noone answered. So i just chose one that wasn't on file. And bang, fee. What a perfect ending to a perfect day. An FFL change fee??? Who's even heard of that? I'd cancel the order but the cancellation fee is more than that $15 fee!!! Just a heads up for anyone who wants to buy the fostech lower.

use a jp aluminum carrier in my sub 3.5 lb build. I use the rubber City armory adjustable gas key and it has practically zero recoil. The whiskey arms aluminum carrier is alot cheaper and it's cut for full auto. No forward assist serrations but who needs those??? ;) The lightest steel carrier is the faxon Gunner. Any titanium carrier is g2g, I've used a few. They're very durable and lightweight. If you want even less recoil use a taccom lightweight 2 piece buffer. I use it with all my rifles.

Awesome!  Thanks for the buffer suggestion. Is it preferable to run with a standard carbine spring?

Well that is starting off on right foot :/
Thanks for heads up.

Since there is variance with the weights of light weight bcg, is there a certain weight/threshold where lessened recoil becomes noticeable.

I use a wolff reduced power recoil spring. Less forward recoil impulse.

It's kinda hard to tell, 5.56 doesn't have a whole lot of recoil to start with. Get the buffer/carrier combo under 7 oz and you will be pleased with the results!!!

I ended up putting an A-hole brake on mine, because even with the super light bolt carrier and buffer and a tuned gas system, recoil got really snappy and annoying.  The brake turned it into a staple gun.

I ended up getting my Hogue 15° poly grip down to 1.058 oz. without cutting the length. I hollowed out the grip and skeletonized the upper area.
I used router bits in the drill press for the most part but made the mistake of useing a roto zip bit and got a little too close to one edge and now have a visible cut.
I ordered a new grip to start over a little neater this time.

With the grip installed i wrenched on it as hard as I felt safe and there is no perceptible flex or weakness, so I feel it's as good as it's going to get w/o weakening it.

Try the reduced power recoil spring from wolff. That might be the missing piece! Because i can shoot mine all day, follow up shots are a piece of cake! They were even when i had a flash suppressor.

Well i explained the situation to them and they have waived the fee as a one time courtesy. The angry email threatening to take my business elsewhere and call my bank and dispute the transaction probably didn't hurt my cause either.

Thanks for all the info!

Shame you even had to go through that.

No problem. I run taccom lightweight buffers with adjustable gas systems on all my ar's, 223, 308, and the 50 beowulf. On my lightweight 5.56 and 308 i use RCA adjustable gas keys and reduced power springs. I could be wrong but the RP springs seem to reduce recoil. On my "duty" builds i use SLR sentry adjustable titanium gas blocks with sprinco XP springs. In my beowulf i use the 2a regulated bolt carrier and sprinco XP red spring. There's no need for the extra buffer weight for semi auto.

Yeah, well i know about the FFL transfer fee now. I should've just waited till today to call. They are a good company, their prices are great, especially on surplus and trade in stuff. That just goes to show you, always read the terms and conditions carefully.

both of these are already in the PWD...

I wasn't aware that they have 3 variants of port door now. Thanks for bringing this to my attention. Data added to the PWD.

Thanks amigo. It's been a labor of love. I'm always trying to get more exposure for it, so if you "know people" or run a youtube gun channel or whatever, feel free to spread the gospel.

I hadn't heard that 2A had a new end plate out, but that's a 'good add' for the PWD. Very light...

Nope, you're not wrong. Reduced power springs dampen the recoil. I started off using the JP OSC, which if I'm not mistaken, is rated 7 percent above a standard spring. When I switched to a Sprinco Yellow, which is reduced power, I instantly noticed the difference in recoil.

Besides that, using standard or extra power springs in LM systems slows the action on the rearward stroke, which can prevent lock-back, and prevent the next round from being stripped. More often than not, folks assume it's the gas system, start fiddling with that, introduce more gas, which complicates things further.

If you're successfully using standard or extra power springs with a LM system, you're probably using too much gas and battering your LM components.

Yeah, the plate just kinda "appeared" on their site one day. I have a short list of websites that i check daily for new products and 2a is one of them. I'm afraid i'm not anyone special, just a basement builder. No channel or anything like that. I will tell anyone i know who wants to build lightweights about it though. In the pwd i saw the notes by the smoke composites castle nut and end plate, the answer is yes they are compatible with all buttstocks and buffer tubes. V7 also has a new line of ultralight 2099 keymod handguards, they have 7068 aluminum barrel nuts. The weights are pretty good, not quite as light as the brigand or original KMR (with lightweight hardware) though.

I agree with everything you said. I run lightweight buffers and standard mass nitrocarborized STEEL bolt carriers with xp springs, i do not use xp springs with aluminum or titanium carriers. I see no extra signs of wear and reliability is exceptional, even when firing with a fouled gun using the echo trigger.

Forgive me.  What are "LM" components?  Brand?  I'm lost on the acronym

LM = low mass?¿

With a super light bolt carrier group, reducing the spring rate is asking for reliability problems.  As it is, the gas is dialed down and the bolt carrier group does not 'bottom out' in the receiver extension.  I would put a stronger spring in it (and adjust the gas accordingly) before I put a lower strength spring in it.

Seems like I've had that endplate since early March. Great piece of hardware.

Reliability will not be an issue if you get the gas right. I tune the gas until the bolt will just barely lock back while the bolt carrier is dry. Then i give it just a little bit more. I've not had any problems, and the recoil is barely there, even when i had the flash hider on it. Give it a try dude.

Nope, not accurate, but I understand why folks adopt that theory. Seems logical, but defies physics.

Keep in mind, the system operates under direct impingement, so the gas created from the spent cartridge is what propels the carrier into the rearward motion. When that gas is spent, the carrier is solely using the energy created from the gas, weight and momentum to overcome the action spring. Conversely, in addition to an over-sprung spring, using underpowered ammunition is another variable that slows the rearward travel of the carrier.  

Since the action spring is in fact what returns the carrier to battery, if the carrier doesn't have enough energy, weight or momentum to effectively overcome and compress the action spring, among other issues, the carrier will not lock, strip a round, etc.

Instead of using the correct action spring, a lot of folks simply introduce more gas, which works to some extent, but you're basically slamming and bouncing the carrier off the buffer face using gas instead of using compression, stored energy, then momentum to create positive lock-back, strip the next round, and return the carrier to battery.  Assuming that your buffer is aluminum, smacking a slab of steel with a ballpeen hammer is the near equivalent of what's happening, which is why I say that components are being battered.

The most common misconception is that you need a slightly enhanced or extra power spring to slam the bolt face into a fouled chamber, but  when properly tuned with a reduced power spring, that bolt will slam home with complete and absolute authority, no different than a full mass system.

Needing more lube than a standard mass carrier is another common misconception, which is why so many chambers are full of muck. Since its debut, I use Geissele thin grease, and recommend it. In DI systems, combustion quickly burns off your average lubricants, which is why manufacturers started using veggy-based lubricants in recent years to resist burning off.

When you're using the correct action spring, you can actually take full advantage of an adjustable gas system instead of over-gassing the system to compensate for an incorrect action spring, which defeats the purpose, and introduces the law of diminishing returns. You can tune the system to work with a very light and specific load exclusively, or you can tune the system to run with any ammunition you find on sale without over-gassing the system.

That said, a low mass system can and will run just as reliably as any full mass system. I've shot everything from Tula, PMC, Federal Premium, M855, and my own handloads without adjusting the gas. I've been using Taccom buffers in LW carbines for years, dating back to when their buffers were yellow. Literally, thousands of rounds without issue.  

For some reason, some folks simply can't grasp that. They spend $2,000 assembling a LW carbine, then call it a range toy based on their lack of confidence in the system, or their lack of competence in tuning the system. Hell, my LW carbines are good for hunting, scouting, backpacking, or defending life and limb, right alongside my Colt and BCM carbines.

For the record, Sprinco markets their reduced power, yellow spring as a solution to the rare occurrence (LOL) of an under-gassed system, which speaks volumes about the springs purpose. Under normal circumstances, depending on how over-gassed your system is, reduced power and sometimes standard springs and buffers induce short-stroking.

What about buffers, you ask?

What would tubbs flatwire springs be classified as as far as over or underpowered spring?

Tubbs are rated in the enhanced to extra power category, above the mil-spec standard rating.

So for recoil I would be better served with the standard carbine spring if I have adjustable gas block? Also is there a flatwire spring that is lower power but would still provide the perk of longevity?

In reference to recoil, yes, but that's assuming we're talking about a low mass BCG, and you didn't mention what weight your buffer is.

I'm not aware of any reduced power, flatwire springs. As a whole, there is not a high demand for reduced power springs simply because the bulk of rifles out there are over-gassed.

An ultralight could be built for many reasons. I personally wouldn't take mine to a war because the strength/versatility/capability of various components has been sacrificed in the name of dumping weight. All guns are a compromise, hopefully based on design objectives. If you build all of your LWs for the purposes stated, that's cool...but others are also free to build for other reasons. At this point it's the comp crowd and the 'ditch weight at any cost' crowd that is pushing new developments in LW parts, so let's not throw those builders out just because their guns aren't war-ready. Plenty of room for all kinds of LW builders here.

I don't have a low mass bcg at the moment but do have adjustable gas block.  Planning on getting low mass bcg.  I have ran my rifle with h2 and carbine buffer and the gas block setting was the same with each locking back on same setting.

Trust me, I get that, but the typical "I built it to have fun at the range, and I wouldn't use it in a defensive situation" response implies that LW carbines are good for nothing more than that purpose. Fun and games, shits and giggles. That, in particular, is getting old, and what my commentary is based on. In short, it would be somewhat productive to dispel that perception. On the opposite end, and on a positive note, I do see more and more SBR's being assembled with LW receivers and components, which is a good thing.

There are shooters, enthusiasts, hobbyists, preppers, and guys that simply like assembling rifles, and I fall into each of those categories, no different than anyone else. Whichever crowd is leading the charge in new developments, my sincere thanks.

But the tubb's flatware is tunable due to its extra length. David speaks about this in his buffer spring YouTube video.

Exactly.  Which is why going both lightweight, and reduced power spring, can reduce reliability.


There is no 'correct' action spring, because we've deviated from the design on all counts; gas port, reciprocating mass, and recoil spring. 'Correct' is the spring that best meets our performance goals; one of mine is that reliability should not be sacrificed.

The gas needs to be balanced; the bolt carrier group needs to go far enough to lock back after the last round, but not so far back to strike the end of the receiver extension...which is exactly where I am at.

That may be a common misconception, but it isn't mine.  The system needs to be balanced, but retain sufficient energy to work.

..and, if you reduce the weight of the reciprocating mass AND reduce the spring, there is less force to strip rounds out of the magazine... which is what I didn't want to happen.

I hope no one is building a LW rifle just to say it's super light but not function.

My 3.5 lb rifle is built to be as light as possible but it also has to function properly 100% of the time. Becaue if it does not function, what good is it?

With that being said, is it my "go to" rifle when things go bump in the night. No. Becaus my go to gun is set up differently for my needs. It has a different sighting system, light, sling and a redi mag.

If I needed my ultra lite and it was handy, I would not hesitate to grab it and put in work.

That's why I built it with my own specs such as absolutely no polymer anywhere.

It's just like my mustang. Very fast but not my first choice for comfort or a cross country drive. But it works and if I needed it to make a get away then it would absolutely work.

It's been a while since I have watched his video. I may have to watch and see what he says cutting a coil equates to. Most reduced power springs seem like they are 10% less than standard so wouldn't want to exceed that

I went back and watched. In case anyone was wondering every 3.6 coils cut is approximately 1 lb of pressure decrease. Anyone know what the numbers are for the wolf reduced spring not locked back vs locked back. Tubbs was 10.3 not locked vs 16.3 locked back

I've found my carbon fiber sub 3.5 lb ar to be very reliable, i wouldn't hesitate to grab it in a fight. I used the reduced power action spring, I will say that it doesn't like metal magazines as much a polymer ones but i've never had any problems or malfunctions with it after i tuned it.

even if the cycling is 100% reliable, an ultralight may not be all that suited to being a fighting gun. For example, some people run CF rails that have no (or little) in the way of mounting options for a light, or BUIS. The optic on it (if there is one) may be on the lighter side, relative to being built like a tank and ultra-durable like you'd want in SHTF.

So sure, you COULD use an ultralight as a fighting gun, but how many people here actually use their ultralight as the primary SHTF weapon? Personally, a tavor is my SHTF gun...and if not that I have 2-3 other ARs I'd grab first. Not that I couldn't use a LW to shoot at people...it's just not optimal for how it's configured. So whether it is WWIII ready or just a range toy, the more the merrier, I say.

As I see it we can tune the system to run on the least weight, spring and gas pressure, but if the forward force of the carrier isn't enough to overcome the resistance of stripping a round from the magazine (variable no doubt, between all kinds of magazines) you're reducing the reliability.

That said, if you've tuned yours and it does reliably strip rounds, party on!

Theoretically you could use so little reciprocating mass, spring pressure, and gas that it would stop when the bolt runs forward to grab a round, and that, I think, is what people are worried about. The rest can be tuned/compensated for.

I just found the under 6 lb thread :) When i have the a-hole micro and stitchclimber barrel nut installed on my baby this weekend i'm gonna post!!! If only i could figure out how to make pictures work... :/ My 308 is under 6 lbs (soon it'll be under 5 ;) I won't spoil the surprise on how yet though!!! Actually, i just changed my mind, i'm spoiling :P Next paycheck i'm ordering the new faxon PENCIL 308 barrel!!! it'll shave over 2 oz, that and the hogue grip will have me under 5!!! Hopefully with the red dot still on there but i will remove it temporarily if i have to!!! :)