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View Full Version : Billet AR Lower for $109????


ElvenSoul
10-18-2009, 12:48 AM
http://www.centerfiresystems.com/ARLOWER-MACH.aspx

I was looking for some toys for one of my other rifles when I saw this. Previously the cheapest I had ever seen a billet lower go for was $249.

NSR500
10-18-2009, 1:18 AM
Difference is in the material. Seems like the more expensive ones are 7075.

badhabit90
10-18-2009, 1:24 AM
hmmm....seem okay. allthough it doesnt tell you if it is heat treated or not??

ke6guj
10-18-2009, 1:40 AM
maker appears to be www.tnwfirearms.com
you could call them and ask what material it is made out of.

NSR500
10-18-2009, 7:15 AM
hmmm....seem okay. allthough it doesnt tell you if it is heat treated or not??

ARs don't need heat treatment, they just benefit from hard anodizing.

badhabit90
10-18-2009, 10:33 AM
ARs don't need heat treatment, they just benefit from hard anodizing.
billet aluminum is rather soft i thought. ive had billet wheels and man those things bend easy....perhaps it already treated before its machined??:confused:

ke6guj
10-18-2009, 12:49 PM
ARs don't need heat treatment, they just benefit from hard anodizing.standard AR made from forgings are usually made from 7075T6, T6 noting the level of heat treatment..

NSR500
10-18-2009, 1:03 PM
standard AR made from forgings are usually made from 7075T6, T6 noting the level of heat treatment..

But it is not a post processing heat treatment like an AK or anything, right?

ke6guj
10-18-2009, 1:19 PM
not that I know of. If it is heat treated before machining, as long as the machining doesn't overheat the item and destroy the temper, then it shouldn't need tobe re-treated.

NSR500
10-18-2009, 1:41 PM
Did a little research and found this:

http://www.substech.com/dokuwiki/lib/exe/fetch.php?cache=cache&w=364&h=700&media=aluminum_temper_designation.gif

Although I still think with the AR, the heat treatment is before the machining. Otherwise 80% lowers would have to be heat treated in addition to being hard anodized.

THT
10-18-2009, 1:46 PM
Just spitballing here but why would you heat treat then machine? You'd be subjecting your work tools to cutting through harder material and you'd also be wearing down the case (hardened surface). The risk you run with heat treating post-machining is warping the material.

eaglemike
10-18-2009, 1:56 PM
Just spitballing here but why would you heat treat then machine? You'd be subjecting your work tools to cutting through harder material and you'd also be wearing down the case (hardened surface). The risk you run with heat treating post-machining is warping the material.
7075 machines VERY nicely in the T6, T651, T6511 condition. It's also almost 50 percent stronger than 6061. 6061 is also gummy, so I'd always choose 7075 over 6061, unless it needs to be welded. Hard anodize is a good finish for 7075, as it's a little less corrosion resistant than 6061.

"Billet" and forging strength from the same alloy is very comparable in this application. Find out which alloy the things are made from, 6061 or 7075. You want 7075.

all the best,
Mike

Joe788
10-19-2009, 9:54 AM
Both forged and billet receivers (and virtually ANYTHING else made from aluminum) are all heat treated long before any cutting tool touches them.

Sicarius
10-19-2009, 11:42 AM
But in all honestly... 6k or 7k series AL... is it really need for a lower. Does it really effect anything? Either will work fine and with all tolerances being equal, you won't notice a thing. Upper will be different since the carrier rides on it but the lower could be practically made out of delrin and be fine IMO.
Kevin

reidnez
10-19-2009, 12:32 PM
Holy tensile strength, Batman! when did this become a metallurgy forum? :)

SlowArrow
10-19-2009, 12:50 PM
Heating the these lowers after machining would cause some amount of distortion......not the best way to manufacture them accurately. I found a nice Billet Lower from J&R in Livermore for under $200 made by C3 Defense (it was even their "enhanced" lower). Not sure of the material they used, but it was a pretty nice unit that I couldn't past up.

hkdad
10-19-2009, 12:58 PM
But in all honestly... 6k or 7k series AL... is it really need for a lower. Does it really effect anything? Either will work fine and with all tolerances being equal, you won't notice a thing. Upper will be different since the carrier rides on it but the lower could be practically made out of delrin and be fine IMO.
Kevin

that's what i was thinking too. most weekend warriors here on this board who shoots at paper targets once a week or maybe less needs something battle proven. :rolleyes: i might consider this lower next time i'm planning to build another AR. i think with $109 you can't go wrong with this one. ;)

coop44
10-19-2009, 2:25 PM
that's what i was thinking too. most weekend warriors here on this board who shoots at paper targets once a week or maybe less needs something battle proven. :rolleyes: i might consider this lower next time i'm planning to build another AR. i think with $109 you can't go wrong with this one. ;)

Absolutely lowers are not subject to much stress at all. The beauty of the design. As long as all the holes are in more or less the right places, it will work. I have considered machining one from lucite, just haven't had the time. Always thought it would make a cool display. Yes, I would be tempted to shoot it. It would probably work, for a limited time.

eaglemike
10-19-2009, 2:58 PM
I'm going to disagree with those that say "why not use the cheaper 6061."

There is stress in the lower, and I'm pretty sure most people don't realize that. Every time the gun is fired, the bolt cycles against the buffer and spring. The stress it takes to compress the spring is applied to 2 small pins. If you want a lower that will last forever, why not do it right? I learned that from some old guys when I started in a machine shop. 7075 isn't that much more expensive than 6061. It's likely only $5 difference in material for a "billet" lower, for about a 50% increase in strength. If 6061 was "good enough" don't you think the "mil-spec" lowers would be 6061?

I've had similar conversations about this material comparison using suspension linkage parts on motorcycles. There's some pic's on advrider of a guy riding a wee-strom that had the 6061 links (eBay el cheapo's) fail out in the middle of a ride. Don't be that guy.

I could make one of out lucite, sure. I wouldn't shoot it. It'd be a pretty display model though.

all the best,
Mike

Sicarius
10-19-2009, 3:57 PM
Don't get me wrong, 7K is really nice but I don't see anything wrong with 6K series AL. My sun devil(6k) is working just fine for my weekend warriorness with my pinned 10 round non FA toy. I wouldn't let the series sway me from purchasing a nice product. I don't know everything but I have yet to hear of a lower breaking/failing from normal use without the ammo being the culprit. I have had 7k series AL fail on me(non gun related). Yes it is more rigid but it also is much more brittle...
Kevin

hkdad
10-19-2009, 4:01 PM
do they ship to cali?

SoCalRandy
10-19-2009, 5:06 PM
That is definetly a really good price.... For only about $60 more you can get one of these Mega billet lowers from Rainier...

http://www.rainierarms.com/?page=shop/detail&product_id=1539

I saw these Mega lowers last weekend at T&A Armory (really cool shop and nice guys over there) and they are awesome! I ended up ordering one from Rainier though because of the great price.

coop44
10-20-2009, 8:28 AM
I'm going to disagree with those that say "why not use the cheaper 6061."

There is stress in the lower, and I'm pretty sure most people don't realize that. Every time the gun is fired, the bolt cycles against the buffer and spring. The stress it takes to compress the spring is applied to 2 small pins. If you want a lower that will last forever, why not do it right? I learned that from some old guys when I started in a machine shop. 7075 isn't that much more expensive than 6061. It's likely only $5 difference in material for a "billet" lower, for about a 50% increase in strength. If 6061 was "good enough" don't you think the "mil-spec" lowers would be 6061?

I've had similar conversations about this material comparison using suspension linkage parts on motorcycles. There's some pic's on advrider of a guy riding a wee-strom that had the 6061 links (eBay el cheapo's) fail out in the middle of a ride. Don't be that guy.

I could make one of out lucite, sure. I wouldn't shoot it. It'd be a pretty display model though.

all the best,
Mike

OK mike, which of the forging companies use 6061? we can just avoid them.

my mind wanders into the "what if" realm occasionally, the lucite would be a cool display, but, no better than a cutaway would, for training or display. (Unless you put in bushings for the fcg pins)

I have considered a lower built around the sideplate idea, ala 1919, thank you john browning. Or folded like an AK. Just mental exercises, nothing practical, it would be far too costly an time consuming.

zchen
10-20-2009, 8:56 AM
I'm only aware of Sun Devil Lowers using 6061, they do claim they use the highest strength of 6061 however.

THT
10-20-2009, 8:58 AM
I'm only aware of Sun Devil Lowers using 6061, they do claim they use the highest strength of 6061 however.

But isn't 6061 the same regardless of source? I mean, it has to have a certain mix of elements to be classified as 6061, right?

zchen
10-20-2009, 9:13 AM
But isn't 6061 the same regardless of source? I mean, it has to have a certain mix of elements to be classified as 6061, right?

Correct. But there are still different strength level of 6061 depending on the temperature treatment.

There was a post by Sun devil at ar15.com regarding the issue



"well guys, thought maybe we should respond to this one. some of you are stating that the 6061 alloy is inferior to the 7075, and that this is a big issue for you. there are several types of 6061 aluminum. we use 6061-T651. its the strongest of the 6061 and actually has a greater elongation than any 7075 of the same thickness. what does that mean? it means the material will have some give to it before it snaps, meaning less brittle. 6061-t651 has a elongation of 10% where as 7075 only has an elongation anywhere between 3-10% on the same thickness of material. it also has a tensile strength of 42,00 psi. there are several types of 7075 that have that same tensile strength. do you know what type of 7075 your lower is? are you sure your lower is made with the strongest 7075 available? i can tell you its not because the price you would pay would be substancually higher for your lower.

we here at Sun Devil Mfg do use the 6061 for several reasons. conturary to what has been posted, its actually a lot more corrosion resistance than 7075. it also holds an anodize better than 7075. we hard anodize are lowers making the anodize thicker. 6061 is cheaper and its easier to machine. we dont use forged molds like all other lowers. some people are claiming that a forged lower is stronger than our billet lower. what happens when something is forged. 2 parts are pressed together at extreme pressure which causes the molicules to align, creating a stronger product than say a cast part. now how do we get our blocks of aluminum? they're not from a cast block thats for sure. when we buy a bar of stock aluminum, say 12 ft long, we get it in our desired dimensions. how do the metal companies get those dimensions? they press the metal to the desired size, just like a forge. all the strength of a forged product is there. now that we have a forged brick 8" in length we can start our machining process. this means we dont have to rely on the 3 or so main companies that supply all the other lower manufactures w/ their molds.

of course our products are a bit more expensive by a couple bucks, but i can guarentee you that you will not find another lower that has been built and has been looked over for any imperfections, quite like our lowers. attention to perfection is key here at Sun Devil. we also have the tension screw mod on our lowers. this takes out all the slop that comes from the mating of the upper and lower. our lowers are all within mil-spec. they will fit any mill spec upper as will our uppers fit any mi-spec lower. not only do we offer just flat black receiver's, but we also anodize sets in green, blue, gold, maroon, pink, purple, and we can also coat our receivers in our Devil Coat (Np3 nickel-teflon).

we really do appreciate those that use our products and continue to give the rave reviews of them. we know that you are the real advertisement of our products and we thank you."

hotwls13
10-20-2009, 9:42 AM
+1 I have a Sun Devil and while I haven't done any strength testing, the quality is superb!

eaglemike
10-20-2009, 9:57 AM
OK mike, which of the forging companies use 6061? we can just avoid them.

my mind wanders into the "what if" realm occasionally, the lucite would be a cool display, but, no better than a cutaway would, for training or display. (Unless you put in bushings for the fcg pins)

I have considered a lower built around the sideplate idea, ala 1919, thank you john browning. Or folded like an AK. Just mental exercises, nothing practical, it would be far too costly an time consuming.
All the forged lowers I've seen are 7075. I've hardness tested several lowers and uppers. Results indicate tensile strength is above 70KSI, which is a lot stronger than ANY 6062.

There is some misleading information in the post from Sun Devil quoted above. Specifically - they talk about elongation before failure. The 6061 will fail before the 7075 starts to yield. All the lowers I've seen are hard anodized - they seem to imply they are the only ones doing this, making the anodize thicker. Yes, hard is thicker than soft - but again, lowers are typically hard ano'd. You'll notice they don't mention tensile strength of 7075, or the yield of either alloy.

all the best,
Mike

Joe788
10-20-2009, 10:10 AM
This topic cracks me up. Lots of people that are just repeating stuff they read on the interweb. The post from Sun Devil is really shocking. Just reading that makes me not want to buy any of their product. I really hope the guy was BSing, and that he doesn't actually believe what he was saying.

The truest words spoken in this entire topic:

"Either will work fine and with all tolerances being equal, you won't notice a thing."

ar15barrels
10-20-2009, 9:59 PM
There is stress in the lower, and I'm pretty sure most people don't realize that. Every time the gun is fired, the bolt cycles against the buffer and spring. The stress it takes to compress the spring is applied to 2 small pins. If you want a lower that will last forever, why not do it right?

There are injection molded plastic lowers handling the stress just fine. ;)

eaglemike
10-20-2009, 10:15 PM
There are injection molded plastic lowers handling the stress just fine. ;)
Randall, would that be your lower of choice? :)

I know of occasional cracks showing up in the carbon versions. I don't know about the injection molded versions. I would not choose one. I wouldn't have thought that would be your style, but whatever (tongue in cheek here). ;) Sometimes polymers are affected by various chemicals, or other environmental issues. (as you know :) ) Lots of cracked plastic laying around..... :)

I usually only buy a specific bar shape and alloy in a few hundred pounds at a time. Memory says the price difference between 7075 and 6061 is about $1.25/lb for extruded. Cold finished has a larger price difference, but market conditions are interesting right now. Imported 6061 is usually pretty cheap, maybe $1 or so per lb cheaper. Aluminum is about .1 lb per cubic inch, so the math is easy.

all the best,
Mike

ar15barrels
10-20-2009, 10:30 PM
Randall, would that be your lower of choice? :)

I have one, but for the most part, I only use lowers made from 7075 forgings.

The carbon lowers are injection molded too.
They just have a lot of carbon fibers in the mix.

How about a billet lower made from laminated HDPE :eek:

http://www.weaponeer.net/forum/forum_posts.asp?TID=8035&PN=1&TPN=3

Joe788
10-21-2009, 8:04 AM
Randall, would that be your lower of choice? :)

I know of occasional cracks showing up in the carbon versions. I don't know about the injection molded versions. I would not choose one. I wouldn't have thought that would be your style, but whatever (tongue in cheek here). ;) Sometimes polymers are affected by various chemicals, or other environmental issues. (as you know :) ) Lots of cracked plastic laying around..... :)

I usually only buy a specific bar shape and alloy in a few hundred pounds at a time. Memory says the price difference between 7075 and 6061 is about $1.25/lb for extruded. Cold finished has a larger price difference, but market conditions are interesting right now. Imported 6061 is usually pretty cheap, maybe $1 or so per lb cheaper. Aluminum is about .1 lb per cubic inch, so the math is easy.

all the best,
Mike

In July and August, 6061-T6 flat bar was $1.60/lb, while 7075-T6 was $4.00/lb.

Now, 6061-T6 is about 2.00/lb, while 7075 is $4.60-$5.30/lb.

I remember the good old days, when 7075 was only about 50% more than 6061.

eaglemike
10-21-2009, 8:46 AM
In July and August, 6061-T6 flat bar was $1.60/lb, while 7075-T6 was $4.00/lb.

Now, 6061-T6 is about 2.00/lb, while 7075 is $4.60-$5.30/lb.

I remember the good old days, when 7075 was only about 50% more than 6061.
I've been able to buy extruded 7075 for about $2.75 to $3.00. Cold finished is about the price you quoted. I paid $1.55/lb yesterday for extruded round 2.5" (4 bars), a little over 280 lbs. 6061 flat bar is close to the same. Scrap prices are still down.

ar15barrels
10-21-2009, 9:11 AM
I've been able to buy extruded 7075 for about $2.75 to $3.00. Cold finished is about the price you quoted. I paid $1.55/lb yesterday for extruded round 2.5" (4 bars), a little over 280 lbs. 6061 flat bar is close to the same. Scrap prices are still down.

I was talking to the guy I get my bolt knobs from.
The bolt knobs are made from 7/8" round bar.
He said there's something like 25 cents in material for 6061, but closer to $1 for 7075.
I could not believe that 7075 was THAT much more expensive.
Maybe he's buying it from McMaster...

Joe788
10-21-2009, 10:18 AM
I've been able to buy extruded 7075 for about $2.75 to $3.00. Cold finished is about the price you quoted. I paid $1.55/lb yesterday for extruded round 2.5" (4 bars), a little over 280 lbs. 6061 flat bar is close to the same. Scrap prices are still down.

Where did you find those prices? Even buying a mill run of extruded 7075 right now will only get down to $3.30/lb for full length bars. $3.00/lb a month ago. I haven't seen anything close to $1.55/lb on 6061 for awhile, and we buy 1000lbs or more every week or two.

eaglemike
10-21-2009, 1:43 PM
Where did you find those prices? Even buying a mill run of extruded 7075 right now will only get down to $3.30/lb for full length bars. $3.00/lb a month ago. I haven't seen anything close to $1.55/lb on 6061 for awhile, and we buy 1000lbs or more every week or two.
Fry Steel, they usually have the best prices. Sometimes Jorgensen is a little better, or has more stock selection. Fry sells import and domestic, sometimes harder to get domestic. I buy a lot of 17-4, price on that didn't drop as much as the aluminum did last year.

Randall, I don't know how they are finishing the bolt knobs, 2011 machines really nice, still has decent mechanical properties.

ar15barrels
10-21-2009, 2:11 PM
Randall, I don't know how they are finishing the bolt knobs, 2011 machines really nice, still has decent mechanical properties.

Type 2 anodized.