What Material Is Used for Standard AR Lower Parts

[DMW1116]

I’m gathering parts for a project and there is a bewildering array of lower parts available. Many are aluminum, some are titanium. I’d like to possibly substitute some parts but don’t want to downgrade in materials.

What materials are used in standard lower parts? Specifically I’m thinking of the castle nut, end plate, safety selector, bolt catch, magazine release, and pivot and takedown pins.

If they are not aluminum, does using aluminum cause issues with durability? If staking the end plate to hold the castle nut, is the dimpling less effective? Would pivot and takedown pins wear out?

 

[NIGHTLORD40K]

Standard would be steel for those you mentioned. The nuts and pins are machined, end plates stamped, and the rest usually MIM at this point.

I would NOT want aluminum for any of these applications. Ti offers a tiny weight savings for a significant cost increase.

Barrel choice will have the most effect on overall rifle weight, followed by the chosen sighting system.

I dont personally think TI is worth the cost for the small lower bits. Better to get simple and strong, inexpensive steel for these and spend the savings on a better trigger, bolt, barrel, and optics, IMO.

 

[DMW1116]

My intent is to build a 300 BO. However I have a similar 5.56 also. I wanted to primarily make the controls a different color for immediate recognition. All the different color parts I’ve seen are anodized aluminum. I can find other ways to do it if changing materials isn’t a good idea.

 

[mcb]

Stay with standard parts and have someone Cerakote the exposed parts in whatever color you want to denote your 300 BO.

 

[NIGHTLORD40K]

My intent is to build a 300 BO. However I have a similar 5.56 also. I wanted to primarily make the controls a different color for immediate recognition. All the different color parts I’ve seen are anodized aluminum. I can find other ways to do it if changing materials isn’t a good idea.

Stainless?
https://saltwaterarms.com/product/s...teel-lower-parts-kit-5-56-assemblers-special/
This kit even has the EZ-Pull pins and the price is right.

They have stainless end plates and nuts too.

 

[powermad]

I use BCM's Lower parts kit if I need a trigger and grip.
If it's just the bits then I use CMMG's kit.

I like the Radian Talon selector and have it in everything, they have several colors.
I use a Geissele Maritime bolt catch as well.
The endplate and such should come with the extension tube.
Take a couple of minutes and stake the castle nut, every time I don't they seem to rattle loose.

 

[InTheSwamp]

I usually default to Aero or BCM for those parts.

 

[DMW1116]

Stainless?
https://saltwaterarms.com/product/s...teel-lower-parts-kit-5-56-assemblers-special/
This kit even has the EZ-Pull pins and the price is right.

They have stainless end plates and nuts too.

You have my attention. Have you used them?

 

[NIGHTLORD40K]

You have my attention. Have you used them?

Haha, no I just found them after thinking about your thread question- but Im going to order a set anyway and use it for another of my upcoming builds.

EDIT: Drats! They appear to be on backorder. Ill have to call them tomorrow to see if and when they expect to get more.

 

[lysanderxiii]

I’m gathering parts for a project and there is a bewildering array of lower parts available. Many are aluminum, some are titanium. I’d like to possibly substitute some parts but don’t want to downgrade in materials.

What materials are used in standard lower parts? Specifically I’m thinking of the castle nut, end plate, safety selector, bolt catch, magazine release, and pivot and takedown pins.

If they are not aluminum, does using aluminum cause issues with durability? If staking the end plate to hold the castle nut, is the dimpling less effective? Would pivot and takedown pins wear out?

The only aluminum parts in an AR-15 lower are the receiver extension, trigger guard, buffer body and the magazine release button, besides the lower itself.

Hammer - 4620 or 8620 casting
Trigger - 8620 casting
Bolt catch - 8520 casting or 8620 MIM
Retainer, buffer - 4130, 4140, or 4340 bar
Safety selector - 8620 casting
Magazine catch shaft - 1018, 1118, or 1215 bar
Magazine catch plate - 1018 bar or 8620 MIM
Pin, takedown and Pin, pivot - 8620 bar
Pin, hammer and trigger - 4130 or 4140 bar
Dent, safety - 1117 bar
Trigger guard plunger - 303 stainless steel
Detent, pivot and takedown - 1012 through 1018, 1212, 1213, 1215, or 1113 bar
Springs, hammer, safety and ejector, - music wire
Springs, disconnect, bolt catch, trigger guard, takedown, trigger, magazine catch, buffer retainer, action - stainless steel
Pins, tubular, slotted - 1070 through 1095

 

[Pat Riot]

Another way of differentiating guns would be the color of the stock, grip and forend. Also, you could color match the mags to the stock, like as in Magpul polymer mags. Black for .5.56 and FDE or ODG for .300 BO or vice versa.

 

[DMW1116]

The other part of my plan was to use P-Mags for one or the other and different mags for the other caliber. I've been using GI metal magazines so far, so using a P-Mag would be a noticeable difference. I think maybe just a magazine release button in red or orange would be sufficient, plus the different magazines. If all goes as planned, it will be my only adjustable stock as well, along with having a different grip from the A2 grip I have now. The handguard will also be a different length from my 5.56 upper.

Here's a question I should have asked at the beginning. Am I overreacting to the possibility of mixing things up? Can a 300 BO chamber in a 5.56 barrel enough to actually fire?

 

[bearcreek]

Here's a question I should have asked at the beginning. Am I overreacting to the possibility of mixing things up? Can a 300 BO chamber in a 5.56 barrel enough to actually fire?

It's tough or impossible to do with most 300 BO ammo, but it has happened. Just buy a couple cans of Krylon and paint each rifle a different color. Or, pay attention to which ammo you're putting in the rifle.

 

[LiveLife]

Here's a question I should have asked at the beginning. Am I overreacting to the possibility of mixing things up? Can a 300 BO chamber in a 5.56 barrel enough to actually fire?

Have you considered 350 Legend (9x43mm)?

You can use cheaper 9mm bullets with no chance of accidentally chambering in 5.56 barrel.

 

[mcb]

I am not saying the 300 BO in a 556 thing cannot result is a bad situation but its not that hard to avoid. I have two 556 guns and three 300 BO. They are all black and I have never had an issue mixing them up. Just because they are all black they are such dramatically different configurations it would be nearly impossible to mistake one for the other. I have dedicated 300 BO magazines (I have subsonic loads that will only feed from 300BO magazines) and dedicated 556 magazines. In addition my two favorite 300 blackout loads will not chamber in a 556 gun not matter how hard you try. The bullets are long enough they go solid on the powder charge well before the bolt get any where close to closing.

 

[DMW1116]

Have you considered 350 Legend (9x43mm)?

You can use cheaper 9mm bullets with no chance of accidentally chambering in 5.56 barrel.

I have not. Thats a good idea. That precludes my current barrel maker of choice, as they don't make one in that chambering, but I'll dig into things and see what I can find.

 

[Varminterror]

Can a 300 BO chamber in a 5.56 barrel enough to actually fire?

Yes. They can, and it does happen, for the ONLY reason that it can fit. Almost all other cartridges are designed to NOT fit into the wrong chamber whenever a destructive mismatch of dimensions is possible. If JD had blown out the shoulder to prevent chambering of 300blk into 223/5.56 chambers, thousands of rifles would not have exploded between now and then.

Human processes such as color coding are not infallible. I can’t close a 308win round into my 270win rifle - and there’s good reason for that. Color coding certain parts may HELP prevent a human mistake, but it’s simply not a guarantee. It’s a manageable risk, an acceptable risk for many folks, but it remains an unpreventable risk.

 

[LiveLife]

I have not. Thats a good idea

I too went the way of .223 and expanded to .300 BLK due to using same bolt/magazine with simple swap of upper but cost of .308 bullets is a factor and lower cost of 9mm for 350 Legend is quite appealing.

Watched some 147 gr XTP load development with quite acceptable accuracy and recently even down to 124 gr FMJ work up. With RMR 147 gr JHP/MPR, I am even thinking about replacing 9mm PCC for home defense duty with cheaper 124 gr FMJ practice rounds.

 

[DMW1116]

350 Legend is a new caliber for me. I don't know much about it other than it uses 9mm diameter (0.355") bullets and is straight walled. Can the brass be formed from 223/5.56 brass? Is a different bolt or magazine required? Standard gas blocks, buffers, and springs are compatible with the larger cartridge?

Me and my Canik have an unhealthy affinity for 147 grain RMR Heavy Match Winners.

 

[mcb]

350 Legend is a new caliber for me. I don't know much about it other than it uses 9mm diameter (0.355") bullets and is straight walled. Can the brass be formed from 223/5.56 brass? Is a different bolt or magazine required? Standard gas blocks, buffers, and springs are compatible with the larger cartridge?

Me and my Canik have an unhealthy affinity for 147 grain RMR Heavy Match Winners.

Some will argue that 350 Legend uses .357 diameter bullets. Both .355 & .357 are technically inside the SAAMI spec for the cartridge (bullet diameter per SAAMI is .357 +.000/-.003. Winchesters Ammunition (creator of the cartridge) claims it is a .357 caliber cartridge.

350 Legend brass cannot be formed from 223/556. It uses the same diameter rim but the 350 Legend is a rebated case and the body of the case just ahead of the extractor groove is larger in diameter than the rim. 223/556 the body just ahead of the extractor groove is basically the same diameter as the rim.

But since it uses the same rim diameter a standard bolt and bolt carrier works fine with 350 Legend.

350 Legend requires a 350 legend specific magazine, due to the straight wall that would run into the ridge in a standard 556 magazine that typically traps a 556 round at the shoulder.

It should use standard gas blocks, buffers and springs assuming the barrel you buys has the correct gas port size drilled in it. As usually selecting a heavier buffer or a different recoil spring might tweak the cycling more to your liking.

TL;DR: 350 legend requires only a 350 Legend specific barrel and magazine. Everything else can be standard 556 parts.

 

[DustyGmt]

You could color fill your lower selector markings or logo with blue or something, and the 5.56 red? That would be quick, pretty permanent differentiation. I color filled my selector markings white/safe, red/fire. If I was in your boat I'd do white/safe, blue/fire or yellow/fire

 

[citizenconn]

Here's a question I should have asked at the beginning. Am I overreacting to the possibility of mixing things up? Can a 300 BO chamber in a 5.56 barrel enough to actually fire?

Yes it can chamber in a 5.56 and there have been a lot of accidents with it. You can find videos on youtube that range from embarrassing to catastrophic.

Are you overreacting? I've shot thousands of rounds of both and it has never been a problem, but I always make sure to double check my ammo if I am firing both on the same day. Its very easy to tell the difference between .223/5.56 and .300 BLK ammo as opposed to say the difference between .223/5.56 and .22 Nosler.

I have a few dozen ARs in well over a dozen chamberings and it is easier to get the caliber of the guns mixed up than the ammo for me. I've seen guys differentiate with different color mags, grips, castle nuts and other small parts. If the chambering of the barrel is not easy to see at a glance I will mark the gun in some way so it is easy to tell.

A combination of whatever makes you confident it will not happen is your best bet.

 

[Nodakdad]

I have a number of calibers , I bought ejection port covers etched with the caliber, don't have to worry about what it is now.

 

[Varminterror]

I have a number of calibers , I bought ejection port covers etched with the caliber, don't have to worry about what it is now.

You still have to worry about it, you just have a human-dependent procedure to reduce opportunity for error. Not so different than color coding mag release buttons and mags, putting rubber bands around rifles and mags, scribing with paint pens/markers, etc.

 

[LoonWulf]

I like all the ideas for minimizing the chances of putting a 300aac into a .223/556 chamber. I do agree tho that they at best make it LESS likely to happen....Just like stop lights make accidents less likely to happen.