CMP Modern Military AR is over weight, Questions for machinists. Calculating weight of material

mac1911

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I have a Frankenbuild going on and its a parts on hand build.

I need to make weight and the barrel I have needs to shed a lb or so.

Its a 20" A2 Hbar style barrel. I already removed the pinned and welded brake which I did not want or like. Plus addition barrel length. Im going to cut more off the muzzle end and loose another 2oz.
I still need to get down 14oz or so.
The original A2 barrel is .672" or so under the hand guards.
my barrel is .950" for 12" or so.
The actual area I think I would cut in is closer to 10"

Can any one figure out how much weight I will loose if I where to machine down the 10" area to .750"?
 
In an effort to avoid math, Is it possible to locate a barrel with similar dimensions and get the weight of it that way?
 
The math is pretty simple. Just calculate the volume of steel removed in cubic inches and look up the weight of the metal in cubic inches. Jack.

removing and calculating a cylindrical area is simple? I remember covering this in calc 3 and diff eq's but I like the total math avoidance strategy... ;)
 
The math is pretty simple. Just calculate the volume of steel removed in cubic inches and look up the weight of the metal in cubic inches. Jack.
math is not simple for me....
If I did it right I think if I went from .950" to .750" Maybe loose 12oz
 
Understood. Then weigh the barrel as is , remove the metal and weigh it again. Go half way the first time. Jack.
more my speed but trying to vut machine time down....I dont have a lot of time to get out and get it done... i also cant afford a new barrel.....
 
Calculate volume using the outer barrel diameter (radius) using 3.14(r)(r)h
Then calculate volume of cylinder with your planned diameter.
Subtract the second from the first and then multiply by steel density (4.6 oz/cubic inch)
ETA: result is weight removed
 
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Google. I bet there is a calculator for that.

Otherwise, consult your machinery handbook. If you dont have one of those, get one, or you are no machinist at all.
 
Google. I bet there is a calculator for that.

Otherwise, consult your machinery handbook. If you dont have one of those, get one, or you are no machinist at all.
im no machinist but im pretty good at using tools to get what i need done.
I have been looking at thrift stores and libraries for older (free) books though
 
math is not simple for me....
If I did it right I think if I went from .950" to .750" Maybe loose 12oz
... steel density (4.6 oz/cubic inch)

Basically, OP, based on the above, you'd be removing about 1/4 cubic inch of steel per inch (length) of barrel you reduce from .95" to .75" OD. So that's about 1.22oz per inch length you reduce.
 
removing and calculating a cylindrical area is simple? I remember covering this in calc 3 and diff eq's but I like the total math avoidance strategy... ;)

Its WAY before calc 3, its simple geometry. Area of the circle times the height is the area of a cylinder - Radius squared X Pi (~3.1415) X Height. If its a barrel, calculate the same using the bore radius and subtract that from the total to get the actual volume of that length of barrel. There will be a sleight error because of the rifling making the bore not a perfect cylinder but its relatively negligible.
 
whats calc3? just for the record my daughter is smarter than me when it comes to math and most school stuff....I forgot a lot..
 
As a suggestion, don't hurt yourself. You won't learn to run a lathe in 10 minutes. Have someone do it for you. Jack.
I have a good concept on what Im doing, bit type, turning speeds, feed rates will all be factored in before I chuck up a cutter and start spinning and cut'n.
Unless someone wants to do the work for free Im going to take the offer up on the use of their tools. Im sure we can get it done.

I might even turn this barrel into a hexagon just because. The barrel is a inexpensive AR barrel and it has its share of rounds down range so Im not worried about how it looks. Just want to shave about 1lb off it if I can do it safely

Heck I was thinking of buying some harbor frieght end mill bits and a one of these!
it does not have to be pretty boys. If I get frustrated I might just hit it with the grinder!
<iframe src="
View: https://player.vimeo.com/video/125809277
" width="640" height="360" frameborder="0" allowfullscreen></iframe>
 
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save your money - That x-y table is complete junk.

My lathe (7 x 12) isn't really big enough to turn it or else I'd offer - you don't need to pass it through the chuck for what you want so just about any lathe will work as long as it has a long enough bed.

If you aren't joking about cutting a hex - you could use my micro mill. Would take a while but would be better than a grinder.
 
save your money - That x-y table is complete junk.

My lathe (7 x 12) isn't really big enough to turn it or else I'd offer - you don't need to pass it through the chuck for what you want so just about any lathe will work as long as it has a long enough bed.

If you aren't joking about cutting a hex - you could use my micro mill. Would take a while but would be better than a grinder.
yeah I would probably step up and at least buy Grizzly?
maybe someday I will have space!
 
Its WAY before calc 3, its simple geometry. Area of the circle times the height is the area of a cylinder - Radius squared X Pi (~3.1415) X Height. If its a barrel, calculate the same using the bore radius and subtract that from the total to get the actual volume of that length of barrel. There will be a sleight error because of the rifling making the bore not a perfect cylinder but its relatively negligible.

True I was probably overthinking it.
 
im no machinist but im pretty good at using tools to get what i need done.
I have been looking at thrift stores and libraries for older (free) books though
You won't find a free Machinery's Handbook
1) They are not inexpensive
2) Any machinist will never part with their copy
But, yes, the formula for volume of a cylinder is in there, as is steel density
 
im no machinist but im pretty good at using tools to get what i need done.
I have been looking at thrift stores and libraries for older (free) books though

May have come off a bit harsh there, not really my intention.

Be safe. Not knowing you, your skillset, or what your final plans are, i feel someone should pipe up with that statement. A gun doesn’t take too much modification to turn into a hand grenade. Don’t mean to discourage, just make sure you have considred that.
 
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May have come off a bit harsh there, not really my intention.

Be safe. Not knowing you, your skillset, or what your final plans are, i feel someone should pipe up with that statement. A gun doesn’t take too much modification to turn into a hand grenade. Don’t mean to discourage, just make sure you have considred that.
Absolutely , same here i see folks doing brake jobs in thier driveways and think the same thing
This is where I Ido look for help.
Things like
A. Are there certain cutting methods that are more prone to damage or weakening the barrel.
B. At what point do I need to worry about heat and how it impacts metal hardness?
Like I said I might also just buy a nice file and file some flats on 4 sides taking about .100" off each side. ?
Take me a while but i do have a lot of time when Im home to do stuff like file metal.

maybe after I dig out of the debt hanging on me at the mo ment I will start looking for tools?
 
I have a good concept on what Im doing, bit type, turning speeds, feed rates will all be factored in before I chuck up a cutter and start spinning and cut'n.
Unless someone wants to do the work for free Im going to take the offer up on the use of their tools. Im sure we can get it done.

I might even turn this barrel into a hexagon just because. The barrel is a inexpensive AR barrel and it has its share of rounds down range so Im not worried about how it looks. Just want to shave about 1lb off it if I can do it safely

Heck I was thinking of buying some harbor frieght end mill bits and a one of these!
it does not have to be pretty boys. If I get frustrated I might just hit it with the grinder!
<iframe src="
View: https://player.vimeo.com/video/125809277


" width="640" height="360" frameborder="0" allowfullscreen></iframe>



You don't chuck up a cutter or else you'll end up with an upper cut that makes you upchuck.


As for speeds and feeds, sight and sound are critical. Slow spindle speed, light cuts ( .01-.03 depth maybe ) , supported with a live center in the tailstock. Using oil as a lube will smoke alot, but if you can , you can also use compressed air.

Always wear safety glasses!

No long hair, jewelry, gloves , long sleeves. Dont leave the key in the chuck either.
 
You don't chuck up a cutter or else you'll end up with an upper cut that makes you upchuck.


As for speeds and feeds, sight and sound are critical. Slow spindle speed, light cuts ( .01-.03 depth maybe ) , supported with a live center in the tailstock. Using oil as a lube will smoke alot, but if you can , you can also use compressed air.

Always wear safety glasses!

No long hair, jewelry, gloves , long sleeves. Dont leave the key in the chuck either.

Right,
basically This is what I want to do for about 10-11" length and im not trying to get the right angles to touch. I actually would like to have the end results with either 2 or 4 flats and try to retain the round edge/corners just for looks
maybe if time allows do something for looks on the barrel forward of the gas block. Matbe just quick flats or even hex?
this video shows the end result im looking for not if its the right or wrong way

View: https://www.youtube.com/watch?v=in2NeZa4NoM
 
Absolutely , same here i see folks doing brake jobs in thier driveways and think the same thing
This is where I Ido look for help.
Things like
A. Are there certain cutting methods that are more prone to damage or weakening the barrel.
B. At what point do I need to worry about heat and how it impacts metal hardness?
Like I said I might also just buy a nice file and file some flats on 4 sides taking about .100" off each side. ?
Take me a while but i do have a lot of time when Im home to do stuff like file metal.

maybe after I dig out of the debt hanging on me at the mo ment I will start looking for tools?

Both A and B are kind of the same question, and the answer is, it depends. It is all about heat. Your cutting method, and how it is executed determine the heat added to your work and the way it is added. The effect of that heat on any given part can have several effects, the severity of those effects largely determined by the material in question. The main effects you are concerned with (simplified) are the strength of the material, and distortion of the part you are working on.

Long story short, don’t “take a grinder to it”. You could grind it, if you took light cuts and kept the part cool. However you do it, apply this same idea. Take your time, and keep it cool.

Honestly, not knowing what your final plans are, I would be most concerned about you removing any material at or near the chamber. Without strong working knowledge of the physics involved there, you should absolutely make no modifications in this area. Information on barrel contours is available on some manufacturer’s websites. That is a good place to start for some parameters on the rest of the barrel.
 
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