Do you guys think that an aluminum screw 1/4-28 1/2" is strong enough for the pistol grip? I'm building a lightweight rifle.

Sure, I would think so....so long as the screw threads in enough to get a good bite.

For only $8 this seems like a better idea:

https://www.vsevenweaponsystems.com/titanium-grip-screw/

I bought several of those screws, I concur!

Well I'm ordering those titanium screws too, but I'm asking about aluminum because it's lighter, although not as strong.

You should torture test one and get back to us, FOR SCIENCE!

Im no expert, these are my thoughts.

I would think that a 1/4" aluminum screw would be sufficiently strong for securely attaching the pistol grip to an ar15 lower. The way the grip interfaces with the lower was done well by design, it removes the potential of putting a shear load on the bolt. Impacting the grip from the side would put large percentages of the force on the upper tabs of the grip and the lower receiver itself but not much on the bolt. Impact on the bottom front of the grip towards the buttstock would probably put the most force on the grip screw as the mounting surface at the top rear of the grip becomes a pivot point and the grip itself becomes the lever. The bolt is still resisting destruction through tensile strength in that scenario. I googled to try and find tensile strength at yield for an aluminum 1/4 28 bolt but got tired of searching. So i calculated it.

Formula
ASTM specs

Using formula (yield min x stress area of the specific diameter = yield strength)

ASTM F468 UNS A96061 machined has a Minimum yield strength of 45,000psi

A 1/4 28 bolt has a stress area of 0.0364

45,000 x 0.0364 = 1,638 lbs

As far as the bolt length, that will depend on the grip you are using as some of them have more material than others at the mounting location. The first 6 threads do all the holding, after that the fastener will fail before the treads will.


With a 1/4-28 bolt 6 threads is about 0.214" so as long as 1/4" of the bolt is threaded into the lower you should be good to go.

With statements like, "i think" and "should" people always tend to lean towards, "definitely" and "absolutely". Titanium has a far superior yield strength and is certainly overkill for the application but provides cheap insurance for those that don't like to innovate.

Hope this helps.

How much weight can you save by changing grip screw

It seems silly,  but it does indeed all add up. A decade in the avionics industry showed me just how far the reach is to shave ounces.

Not much lol. The real question is how much weight can you save by analyzing every single component on the rifle, implementing new materials, and removing unnecessary redundancies? The answer to that is a lot.

Certainly worth taking into consideration. I'm not up to speed on the potential for galling or corrosion between anodized 7075 and whatever alloy screw is threaded into it.

Sounds like a bit of overkill for a plastic lower.  Have you tried glue?  

Why not?  Your buffer tube is aluminum threaded into aluminum.  A lot of aftermarket barrel nuts are aluminum threaded onto aluminum.

Superglue won't hold.  The right epoxy would.

This.

I run the Magpul K2 grip on all my rifles and I really like the screw that comes with it. I am not sure if it is aluminum, but it threads in well and does the job. I always put a few drops of oil on it in case it does turn out to be made our of aluminum and it makes threading it in that much easier.

Pics of steel buffer tubes, pls.  

There is some discussion about this in the Lightweight Parts List with WEIGHTS (AR-15) thread IIRC. Not sure how far back, but for what you want to do, that thread is a goldmine.

Yes an aluminium screw is going to be more than sufficient as a grip screw.  Not a lot of force is honestly applied to the screw and the tighter the fit of your grip sliding on to the lower the even better you are.  The screw honestly just holds the grip in place against the safety detent spring.
What I would be concerned about it driving it in and out if you have to. I would avoid a slot cut screw and opt for an Allen or torx head screw and at minimum a Phillips to lessen to likeliness of boogering up the screw.

I would expect the aluminum screw to be more susceptible to galling than the Ti on Al combination.

This. If you do this, put some grease on the threads for sure.

If you think about it the giant tab the grip slides over takes the brunt of any shear stress. The screws just there to prevent the grip from sliding off. Look how thin the plastic is that the screw seats against. That would break before an aluminum screw head....probably

Also take into account that your whole gun is a lot lighter. therefore less stress on the bolt all together. Either way, your plastic is going to break well before the screw.

Yes aluminum screws are plenty strong even for a normal weight gun!  I use them in all of my builds because I purchased a bag of 50 screws!  I can mail you a couple if you want to try them out!   Let me know.

The std. aluminum, pan-head phillips machine screws at local hardware stores are pretty soft crap...  That said, with a snug fitting grip, yeah - pretty much there to keep from sliding as noted above.

I don’t know how much I’d worry about galling given anodizing on the lower, but sure, put some anti-sieze on the screw threads and use the correct Keps lockwasher...be fine.

If you're going for the light weight of an aluminum grip screw, I'd think you're also going for a lighter lower than aluminum...  My poly lower has threaded brass inserts for that sort of thing.  No aluminum-on-aluminum crime to worry about.

Quick article on galling.
They don't mention silicon or graphite lubes
Wonder if they work?

https://www.boltdepot.com/fastener-information/materials-and-grades/thread-galling.aspx

Steel buffer tube

I have to agree with this...in fact, got me to thinking, I am going to look up the galvanic index of zinc coated steel and SS vs aluminum today when I get to work.  The two most common fasteners for attaching grips.

When installing a grip, I take my time when starting the threads.

77

Personally I'd be more concerned with the bolt shearing if you ever have to back it out.

But I'm also one who's swapped grips on my ARs at least a half dozen times each. So much I even ruined a polymer lower when half the threads came out last time I tried to swap grips.

You are over tightening your grip screw.

My first thought.

I would not use an alum screw on any of my AR’s, but I don’t know that it would not work.
I don’t think ½” is long enough and would use a regular length screw.

It does work and 1/2" is plenty long enough.

The most stress in a .223 rifle the AR pistol grip will take would be during bayonet work or grenade launching.  Even in grenade launching or using a Can Cannon, the buttstock should take most of it.  And sadly, I'm not aware of any ranges in my area w/ a bayonet dummy.