Aluminum vs. Steel Picatinny Rails

[Brewer]

OK, just for fun, I did the math on a 1000 yard target. if you use the coefficient of expansion for aluminum figures that were just given, and that expansion were (because of the base being mounted in say 4 locations) in only one direction (worst case scenario here) you could get as much as a whopping 3.6" of deviation at 1000 yards.

having said that, it should be relatively consistent, so your bullets should all land in the same area.

so. it probably doesn't matter.

 

[Timber338]

OK, just for fun, I did the math on a 1000 yard target. if you use the coefficient of expansion for aluminum figures that were just given, and that expansion were (because of the base being mounted in say 4 locations) in only one direction (worst case scenario here) you could get as much as a whopping 3.6" of deviation at 1000 yards.

having said that, it should be relatively consistent, so your bullets should all land in the same area.

so. it probably doesn't matter.

Pretty cool ... just curious, when you were running the numbers, did you assume the rifle was put together at room temp (72 degF) and then assume a worst case delta for a hunting situation on a cold morning, some like 20 degF? So about a 52 degF delta to generate expansion values?

 

[Brewer]

so that was worst case. site rifle in at 30 degrees F and shoot at 120 degrees F. so 90 degrees between site in and shoot.

so I figured the expansion all in one direction, but more likely, it would be more even, some forward, some back some up (probably none down) so realistically, you might see a 1" shift in POI.

 

[Goss]

OK, just for fun, I did the math on a 1000 yard target. if you use the coefficient of expansion for aluminum figures that were just given, and that expansion were (because of the base being mounted in say 4 locations) in only one direction (worst case scenario here) you could get as much as a whopping 3.6" of deviation at 1000 yards.

having said that, it should be relatively consistent, so your bullets should all land in the same area.

so. it probably doesn't matter.

Thanks.
I guess I'm more concerned about the rail getting loose over time due to the different changes in movement.
I'll dig around the shop and see what I can find. If I can come up with a 400 series stainless bar, then I'll go that route. If not, then I know I have some 7075 on hand from an AR project.
Thanks to all who posted.
Goss

 

[Timber338]

That's good stuff. I don't think there is anything wrong with using steel for whatever the reasons may be. I do like applying some good engineering to mathematically prove why any particular setup may or may not work. You cannot argue with the numbers. I'm sure we could spend a whole lot of time working on a model to be very accurate.... but I'll just use the numbers you just came up with and then settle for the results out in the field to save some time.

 

[Timber338]

Thanks.
I guess I'm more concerned about the rail getting loose over time due to the different changes in movement.
I'll dig around the shop and see what I can find. If I can come up with a 400 series stainless bar, then I'll go that route. If not, then I know I have some 7075 on hand from an AR project.
Thanks to all who posted.
Goss

Something tells me you are pretty darn good at making your own parts. That makes the whole project a lot more fun.

 

[brentc]

Thanks.
I guess I'm more concerned about the rail getting loose over time due to the different changes in movement.
I'll dig around the shop and see what I can find. If I can come up with a 400 series stainless bar, then I'll go that route. If not, then I know I have some 7075 on hand from an AR project.
Thanks to all who posted.
Goss

Your concerns can be cured with some blue loc tite and proper torque. You won't have any problems.

 

[Brewer]

yep, that's what its all about right. its where the bullet actually lands!

Gross, this is a good point about stuff working lose over time as well. especially if you do a lot of hunting in cold weather and it goes in and out of a warm truck our house and then shoot in summer and winter.

there is another issues that we could really drag this thing out if we wanted to. and that is corrosion due electron transfer related to dissimilar metals! I suppose though this would only be valid for Titanium and Stainless because they are left uncoated. but then they are super duper resistant to corrosion and oxidization. But if you coat them, then nothing to worry about.

and I am not doing the math on this one because: 1. I have already used too much office time today on LRH, and 2. because I really don't know how to calculate it anyway.

Hey Sully, send this to your wife if she gets a spare minute. I'll even buy you another round of that chocolate milk!

 

[Brewer]

Your concerns can be cured with some blue loc tite and proper torque. You won't have any problems.

Dammmit, you are taking all the fun out of this discussion!

 

[Goss]

Dammmit, you are taking all the fun out of this discussion!

Or silver soldering in a stainless rail milled at 20moa .
I'll bolt it in. Not quite so dang permanent that way.

 

[Brewer]

Or silver soldering in a stainless rail milled at 20moa .
I'll bolt it in. Not quite so dang permanent that way.

you use a ball end mill to do the bottom of the rail?

 

[Goss]

you use a ball end mill to do the bottom of the rail?

Umm, no.
I'll machine out a shallow (.03) slot for the rail to fit in on the receiver, then drill and tap down the rail into the slot. Easy when your making the rail. Just mill to match.

 

[Brewer]

so if I have you right, you are flattening the top of your receiver off for a better fit? or making a tongue and grove type deal.

 

[Goss]

so if I have you right, you are flattening the top of your receiver off for a better fit? or making a tongue and grove type deal.

I'll flatten. Think of it as a shallow keyway.