Im going down a path I have never been on before and I have a LOT of questions. Good news is I am only going to start with one. When switching out the bcg to a lightweight bcg, is it necessary to switch out the buffer spring to what is advertised as "lower power" spring?

I have a diamondback db15 300blk 16" barrel which has the mid length gas system. I just want to make sure that in my quest for ultra lightweight, I don't mess up its reliability

Don’t do it.

Don't do the buffer spring, or don't try to make it lighter with a lighter BCG?

Both/either reduce reliability

Whats the best route to take to make it lighter but still reliable/accurate?

What is the weight loss objective - where are you trying to go, and to what purpose?

There's no wrong answer - but there is the probably of wrong advise if the objective is not known.

This isn't about talking you out of it, but hopefully giving input that has value, rather than a guess at what the desired end state is.

Your best source of easy weight loss is the barrel - going with a skinny profile barrel will net more loss typically than a lightweight BCG.

And, as noted above - you're most likely going to run into reliability issues without some investment in specialized buffers, buffer springs and gas management.

IMHO - most shooters going with lightweight BCGs are trying to increase cycle rates to cut down on competition times vs the weekend p-dog hunter.

The next easy weight cut is the hand guard - assuming a free floated tube or rail?

Going with the smallest diameter handguard, and no quad rails will pick up a few more ounces of savings, especially if you can use an alloy barrel nut.

If you can find a minimalist buttstock - a few more ounces shaved - all things I'd do before going to the BCG route.

Switching the upper to a "slick side" will have some savings, again - we're shaving fractions, not pounds.

JMHO

300 BLK with a mid-gas system. Interesting. Might not want to stray too far off the design specs. I'm just thinking out loud, it might be on the verge of under-gassed.

The objective is to make it a good lightweight deer/hog hunting rifle. Currently as it sits, its is 6lbs 13oz ready to hunt. Since the 300blk isnt a long range cartridge anyway I didnt put a magnified scope, only a vortex red dot (crossfire). I know sub 7lbs ready to hunt is pretty dang good, but as all of you know one can't help but think "how light can I get it?". Ultimately, if I could shave 1lb off I think I could be VERY happy with that

In the AR game, that's fairly light.

Keep the rifle as is and build a lightweight rifle using the latest components. It will keep you shooting and you will end up with 2 rifles.

Pay attention to published weights and don't hesitate to call the manufacturer and ask if you can't find it.

Now the caveat, you'd be surprised how hard and much more expensive it is to build a lightweight AR.

I built a low 5lb rifle yrs ago using a Plum Crazy polymer lower and a heavily skelentonized upper, magnesium buffer tube, carbon handguard and a pencil barrel. It was crazy light but was crazy expensive, at least 1/2 the cost of a quality build more expensive than the most expensive rifle I had built to date.

I have seen 4lb rifles, but those guys are anal and the majority are extremely talented with access to a machine shop, you couldn't put a price on those rifles.

The 4 1/2lb Ar15 Article

3.25lb AR15

I have a Del-Ton light weight 16" carbine length barrel with an A2 front sight on a Tennessee Arms polymer lower. It has an AR15 BCG instead of the M-16 BCG and a standard GI collapsible stock. It's just under 6 lbs without a rear sight. Putting a plastic Magpul rear sight and it's just 6 lbs. I supposed I could take off the A2 flash hider and put on a thread protector and get back under 6 lbs. Everything beyond that is going to get pretty expensive.
kwg

KWG, did you ever get that barrel to shoot last year? Did the handguard make any difference?

I recently put together a new one in 5.56. Faxon 16” pencil barrel, ALG handguard, KE arms polymer lower, larue mbt2, full auto BCG, H2 buffer, holosun RDS on reptilla mount. It’s 5.51#. There are better ways to reduce weight than going to a lighter BCG.

Yes I did. The free float hand guard made a difference. Another member here turned me on to Unbranded. An AR parts vendor and I picked up several free float hand guards. But, it was a Midway barrel and after using my pistol (10") bore scope I see the rifling was a bit rough with machine marks so I could never get it to shoot like I thought it should. I haven't spent the money yet but my next barrel is going to be a Ballistic Advantage stainless. As I recall, 79S who lives in Alaska has the BA stainless barrel and he likes the way it shoots. I have 2 other BA barrels and they shoot well. Just because it's a bargain doesn't mean it's a real value.

kwg

You’d be better off starting from scratch than replacing parts probablyGonna be expensive to save ounces for sure

Look up aero thunder ranch lower
You could mill that area out and lose some ounces.

Carbon handguard and if they make it a carbon pistol grip

Titanium parts and pins

Wilson combats minimalist stock or something like it from carbon fiber would help I’m sure

Smaller Barrel profile and go with a shorter barrel pinned and welded if you need a muzzle device. Although losing the muzzle device would save weight as well.

This is the way.

Start with this link to AR parts weight database. This will give you a good idea on how to save weight. Just weigh your easily replaceable parts and find where to shave weight. If your rifle is functioning fine right now I wouldn't mess with the BC, Buffer, buffer spring.

I've been looking at the POF Prescott Rogue in 6.5CM that weighs 7 lbs. That's a very nice weight for a spot and stalk hog rifle.

Get rid of the heavy handguard and go with a old military style split handguard. Way lighter.z

Add in the delta ring, end cap and heat shields and there are lots of rails that are lighter.

Start with a lighter barrel and light accessories (grip, stock, hand guard, sights/scope/mount.

Leaving the buffer, BCG and spring matched to the gas port is how you maintain reliability. It’s a system that works well but the weight is needed.

Care to name a few?

BCM KMR was about as light as I thought they’d get until i saw a Troy carbon fiber. Now there’s plenty out there that weigh less than the shipping box.

Maybe this will help
https://www.pewpewtactical.com/lightest-ar-15-handguards-roundup/

https://www.ar15.com/forums/ar-15/Weight_of_different_hanguards_/19-432157/

I have forgone my original KMR hand guards and now have been using Midwest Industries. They aren’t as light but the are stronger and cost less.

I have also used MagPul SL hand guards when I needed a little extra length and didn’t want to lose the front sight tower or needed the lightest weight possible. With everything I stick on a gun and in it, I’m averaging around 8 lbs but that includes lights and a loaded mag.

I chased the lightest AR dream a long time ago and while I start as light as I can, they never get close to my Kimber Montana bolt guns.

A standard handguard with the two piece heat shield compares favorably to all but the lightest handguards and coming within 3 ounces or less of them. Prices go up a lot with the lightest of hanguards and they appear fragile.

It’s an ounces makes pound game and a rail gives greater benefits than the stock M4 hand guards but only you can decide if it’s worth it or not.

Don't find I need the rails my self.

carbon wrapped barrel?

It's a lot easier to start with one of these.

https://www.gunbroker.com/item/938438131

about 3 pounds.

Switch to 16" pencil bbl, adj gas bock/tube and light weight stock.

Presto done

I changed out the tube handguard rr predator pursuit yesterday with a slim handguard with top rail only, took 12 ounces off the weight

This.............as in all of it.

But ASSUMING is not borderline under-gassed, or is some version of a 5.56, if you go to a lighter BCG, you are ALWAYS well advised to use an adjustable gas block (AGB). Period.

Best place to shed weight is barrel, stock, rail......................

The BCG is best left to last & lighter BCG's are best suited to a play gun with generally than normal power loads to speed shot recovery.

YMMV

MM

Barrel, stock and handguard. I'd never go to a poly lower, but if one did, that would be a good way to lose some more weight. I know some guys at a club I go to in Washington that have some really lightweights. They run lightweight BCG's, but they don't seem to be as reliable. Its kind of cool how light you can go with one of these, but if it's not reliable, it's no bueno to me..

^^^^

Not enough to be gained to make it worth doing.

To get light, you have to start light. The BCG alone isn't enough to do it. I have one light weight (not crazy) gun and it's for shooting really fast. It's got a LWBCG but it's also got a skinny barrel, light forearm, light stock, etc.

I also have a fairly light .300BO that looks exactly like the hoser but it's got a full mass operating system because I hunt with it. The weight saved in parts allowed me to scope and suppress it and still have reasonable overall weight.

This conundrum makes me smile. The M16A1 became the Army standard rifle in '69 and it's unloaded weight was 6.4 pounds...with a 20" barrel. My opinion is that someone fixed something that weren't broke.

My A2 is 6.5 pounds and it feels like a toy sometimes..

M16A2 as issued is 7 lbs 8 oz naked.

That's good to know. Check out how much the Colt sporter target model weighs..

Weight is only one metric, functionality is another.