Calculating barrel weight

F

Fred J

Active member
Besides the Lilja web site, where can I find the formulas for calculating finished barrel weight?
 
The weight per cubic inch of 416 stainless is listed as .28 lb. Calculate the volumes of the cylinders, add the volume of the truncated cone, subtract the volume of the bore, all in cubic inches, and multiply by .28.
 
Boyd: Thanks. I've tried several different formulas and measured them against a proven weight, and still come up ounces off. Most of these formulas will only figure to 2 decimal points. Ill keep trying is see if I can make one of them work. Who would have thought, that all that math they tried to shove into my brain during my school years would be needed now.
 
Fred J said:
Boyd: Thanks. I've tried several different formulas and measured them against a proven weight, and still come up ounces off. Most of these formulas will only figure to 2 decimal points. Ill keep trying is see if I can make one of them work. Who would have thought, that all that math they tried to shove into my brain during my school years would be needed now.
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Ounces high or low?

0.28 pounds per cubic inch is light for any steel alloy. I would tend to use 0.30 pci in order to be conservative and produce a barrel on the light side. The error caused by ignoring the rifling lands is small, but requires some compensation. If 0.30 pci strikes you as too conservative, then use 0.29 pci.

But be prepared to make an overweight barrel by using the handbook density and simplified unconservative geometry.

The forumulas you are using are as accurate as the dimensions fed to them, and that includes the density of the material used. The density of these steels is available to three decimal places; check MIL-HDBK-5 or the more recent MMPDS-01 through -04, which is essentially the same document.

0.063 pounds is 1.000 ounces, so machining a barrel "several ounces" light is a Good Idea.
 
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weigh the blank on a scale that reads in ounces and divide by the length in inches
that will tell you the weight per inch
 
Results of a quick perusal of MMPDS-04 for densities of steels:
All of the low carbon steels such as 4130. 4340, 8630, and so on: 0.283 pounds per cubic inch (pci)
Custom 450, 455, and 465: 0.28 pci
PH13-8Mo: 0.279 pci
15-5PH: 0.283 pci
17-4PH: 0.282 to 0.284 pci depending on the heat treat condition. (Seems odd, but there it is, in black and white.)
17-7PH: 0.279 pci
The austenitic "18-8" or "300 series" steels: 0.286 pci
The 250 and 280 18Ni maraging steels: 0.286 pci

When I get some time I'll pull up an AMS for 416 steel alloy to see where it falls, and whether the density is given to two or three decimal places; I'm curious. In any case, 0.29 pci is probably a safe number to use if the external dimensions of the finished barrel are held reasonably close. The diameter squared effect on cross section area adds weight quickly if the barrel is left a little fat. The cross section area of a 1 inch nominal OD barrel left 0.010 inches over increases by a little over 2% (1.01^2 ), which is about the same as the difference between using 0.28 or 0.286 pci in a calculation of weight.
 
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Thanks Jerry: That's what made me start thinking about a new calculator. ie: 4 X 5.5 = didn't come up 22 every time.
 
Jerry H said:
weigh the blank on a scale that reads in ounces and divide by the length in inches
that will tell you the weight per inch
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This would only work for a straight(unlimited) barrel. A tapered(varmint) barrel will weigh less per inch as you get closer to the muzzle due to the lessening outside diameter.
 
I believe Fred said it was a straight .875 barrel which is typical for RF

Jerry W said:
This would only work for a straight(unlimited) barrel. A tapered(varmint) barrel will weigh less per inch as you get closer to the muzzle due to the lessening outside diameter.
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Wadw::
That's what I needed. Now it looks like I need someplace else to cut weight. New or different stock might be a way to lighten it as well. Fred J
 
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