What is the lifetime of an 80% AR 15 lower?

Brian the gunner · September 10, 2014, 10:25 AM

Brian Pfleuger · September 10, 2014, 10:28 AM

I'm quite certain I must not understand the question.

There's no "lifetime" difference between a (properly finished) 80% lower and any other lower of the same quality.

Panfisher · September 10, 2014, 02:10 PM

If you keep it as an 80% lower it should last forever.

IF you finish it out correctly it should be the same as any other AR lower made of similar materials i.e. aluminum, poly etc.

BarryLee · September 10, 2014, 02:17 PM

I believe 80% is a brand.

http://www.80percentarms.com/

Brian Pfleuger · September 10, 2014, 03:19 PM

Ahhhhh... that makes more sense.

Panfisher · September 10, 2014, 03:38 PM

Well son of a gun, never heard of that 80% brand before. Still injecting facts into a conversation sort of kills the mood.

Technosavant · September 10, 2014, 05:01 PM

AR lowers don't get that much stress. Any of them should last as long as any other of similar materials provided there aren't defects hiding in the metal. The few lowers I've heard of breaking were cheap polymer ones that had the receiver extension snap off at the rear takedown pin. The better poly ones seem to not have that issue.

I've not heard of any aluminum (forged or billet) lower breaking due to use.

Mobuck · September 10, 2014, 08:01 PM

My poorly informed opinion is that pin holes which are bare aluminum may wear faster than holes which have been anodized or otherwise surface treated/hardened.

tirod · September 10, 2014, 08:43 PM

To be precise, the lifetime of an 80% lower is measured in hours of labor it takes to turn it into a 100% lower. At which point it starts the clock over when you shoot the first round out of it.

As for the bare aluminum being softer than anodizing, one of the curious facts of materials science is that when two dissimilar materials are wearing against each other, the harder surface wears faster. It's caused by the softer one embedding grit it it and acting as an abrasive.

For the round steel trigger pins to interact with the holes, they have to move, an in particular, rotate, which isn't as likely as the retailers and fan boys of KNS pins would like to make it out.

Put a witness mark on yours and see.

Ritz · September 11, 2014, 07:03 PM

6061-T6...meh. That's effectively all they sell since you need to wait 3 months to get the "available" 7075-T6 parts. 6061-T6 is a pain in the ass to mill.

I'd pass. There are other shops selling 7075-T6 for the same price as the 80% 6061 parts that have product in stock all the time.

I would expect the lower to effectively outlive the owner unless it's abused. The same goes for polymer lowers. As someone else pointed out, they're just not subjected to a lot of stress.

Mobuck · September 11, 2014, 09:37 PM

"As for the bare aluminum being softer than anodizing, one of the curious facts of materials science is that when two dissimilar materials are wearing against each other, the harder surface wears faster. It's caused by the softer one embedding grit it it and acting as an abrasive."
And that's why crankshafts wear out while crank bearings stay good as new, right?

tirod · September 12, 2014, 08:35 AM

No, it's why rubber seals wear grooves in the crank and a new one doesn't fix the leak. You have to install the seal at a different depth or sleeve the bearing surface.

As for bearings to journal faces, there isn't supposes to be any contact at all - the oil pump floats the crank on a thin film. Pump dirty oil between them and then the bearings start taking a lot of abuse.

The point is that drilling the holes in an 80% lower has more to do with pin fit than the pins spinning or beating the hole larger in the lower. Again - mark the pins and see for yourself. They don't spin, it's a marketing myth started when someone got overly concerned about their $10,000 machine gun lower and shooting thousands of rounds with it at shows and demonstrations.

Shoot thousands of rounds of full auto during a weekend and see what yours do.

September 10, 2014, 10:25 AM	#1
Brian the gunner Member Join Date: September 25, 2013 Location: Bahía de Banderas,Méxic Posts: 81	What is the lifetime of an 80% AR 15 lower?

September 10, 2014, 10:28 AM	#2
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	I'm quite certain I must not understand the question. There's no "lifetime" difference between a (properly finished) 80% lower and any other lower of the same quality. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

September 10, 2014, 02:17 PM	#4
BarryLee Senior Member Join Date: July 29, 2010 Location: The ATL (OTP) Posts: 3,946	I believe 80% is a brand. http://www.80percentarms.com/ __________________ A major source of objection to a free economy is precisely that it ... gives people what they want instead of what a particular group thinks they ought to want. Underlying most arguments against the free market is a lack of belief in freedom itself. - Milton Friedman

September 10, 2014, 03:19 PM	#5
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	Ahhhhh... that makes more sense. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

September 10, 2014, 02:10 PM	#3
Panfisher Senior Member Join Date: July 30, 2010 Location: Missouri Posts: 1,337	If you keep it as an 80% lower it should last forever. IF you finish it out correctly it should be the same as any other AR lower made of similar materials i.e. aluminum, poly etc.

September 10, 2014, 03:38 PM	#6
Panfisher Senior Member Join Date: July 30, 2010 Location: Missouri Posts: 1,337	Well son of a gun, never heard of that 80% brand before. Still injecting facts into a conversation sort of kills the mood.

September 10, 2014, 05:01 PM	#7
Technosavant Senior Member Join Date: May 29, 2007 Location: St. Louis, MO area Posts: 4,040	AR lowers don't get that much stress. Any of them should last as long as any other of similar materials provided there aren't defects hiding in the metal. The few lowers I've heard of breaking were cheap polymer ones that had the receiver extension snap off at the rear takedown pin. The better poly ones seem to not have that issue. I've not heard of any aluminum (forged or billet) lower breaking due to use.

September 10, 2014, 08:01 PM	#8
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	My poorly informed opinion is that pin holes which are bare aluminum may wear faster than holes which have been anodized or otherwise surface treated/hardened.

September 10, 2014, 08:43 PM	#9
tirod Junior member Join Date: January 21, 2009 Posts: 1,672	To be precise, the lifetime of an 80% lower is measured in hours of labor it takes to turn it into a 100% lower. At which point it starts the clock over when you shoot the first round out of it. As for the bare aluminum being softer than anodizing, one of the curious facts of materials science is that when two dissimilar materials are wearing against each other, the harder surface wears faster. It's caused by the softer one embedding grit it it and acting as an abrasive. For the round steel trigger pins to interact with the holes, they have to move, an in particular, rotate, which isn't as likely as the retailers and fan boys of KNS pins would like to make it out. Put a witness mark on yours and see.

September 11, 2014, 07:03 PM	#10
Ritz Senior Member Join Date: January 18, 2013 Location: Virginia Posts: 283	6061-T6...meh. That's effectively all they sell since you need to wait 3 months to get the "available" 7075-T6 parts. 6061-T6 is a pain in the ass to mill. I'd pass. There are other shops selling 7075-T6 for the same price as the 80% 6061 parts that have product in stock all the time. I would expect the lower to effectively outlive the owner unless it's abused. The same goes for polymer lowers. As someone else pointed out, they're just not subjected to a lot of stress.

September 11, 2014, 09:37 PM	#11
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	"As for the bare aluminum being softer than anodizing, one of the curious facts of materials science is that when two dissimilar materials are wearing against each other, the harder surface wears faster. It's caused by the softer one embedding grit it it and acting as an abrasive." And that's why crankshafts wear out while crank bearings stay good as new, right?

September 12, 2014, 08:35 AM	#12
tirod Junior member Join Date: January 21, 2009 Posts: 1,672	No, it's why rubber seals wear grooves in the crank and a new one doesn't fix the leak. You have to install the seal at a different depth or sleeve the bearing surface. As for bearings to journal faces, there isn't supposes to be any contact at all - the oil pump floats the crank on a thin film. Pump dirty oil between them and then the bearings start taking a lot of abuse. The point is that drilling the holes in an 80% lower has more to do with pin fit than the pins spinning or beating the hole larger in the lower. Again - mark the pins and see for yourself. They don't spin, it's a marketing myth started when someone got overly concerned about their $10,000 machine gun lower and shooting thousands of rounds with it at shows and demonstrations. Shoot thousands of rounds of full auto during a weekend and see what yours do.