Gunsmithing How to determine barrel diameter @ muzzle?

[BadKarma47]

Hey guys! Something that's been kind of bugging me...
Let's say you have a barrel contour that is 1.25 x 5" - straight taper to .930 @ 30". What would be the formula used to determin what the diameter of your barrel would be at say, like 27"?

There really is no practical purpose to this question other than satisfying boredom-bred curiosity from having too much time on my hands.

 

[colchester]

Re: How to determine barrel diameter @ muzzle?

Lemme take a stab at this for ya. 1.250 for 5" straight taper to .930 @ 30". So this barrel tapers from 1.250" to .930" over 25" subtract .930" from 1.250" divide the difference by 25" now you know how much taper per inch. Just pick a length say 27" subtract the 5" ( no taper ) you get 22 multiply 22 by TPI should give you the dia at 27"

 

[BadKarma47]

Re: How to determine barrel diameter @ muzzle?

30" - 5" of no taper = 25"
25" - 3" = 22" (because we are going for 27" barrel so 3" off of the 30" overall)

1.25 - .930 = .320
.320 / 25 = .0128
.0128 x 22 = <span style="font-weight: bold">.2816</span>

So I dont think that's the right formula... hmm...

maybe .0128 TPI x 3 (the 3" we chopped off) = .0384
.0384 + .930 = <span style="font-weight: bold">.9684</span>

Sound about right you think? I'm just pullin shit outta my ass now. lol Talk about a SWAG!

 

[LRI]

Re: How to determine barrel diameter @ muzzle?

Starting at the muzzle end of the barrel measure the OD.

move one inch towards the breech and measure again. Subtract the muzzle od from this number.

That's your taper per inch. Now figure how many your cutting off. Multiply that times your taper/inch and you should have your new muzzle OD.


Doing it this way works for sporter barrels and big heavy hogs as well. With a sporter you've got the heavy taper right after the cylinder. Going this route stays away from it so that your #s still work.

Hope this helped.

C.

 

[colchester]

Re: How to determine barrel diameter @ muzzle?

Sorry about I should have proved the math I think I forgot a step, subtract the total taper over 22" from the 1.250 gives you .9639 Sound right?

 

[MikeeBooshay]

Re: How to determine barrel diameter @ muzzle?

Chad's method works pretty good, since the taper is not over the whole length of the barrel, just the end you are cutting from. Don't know how ya'll ya'll do it, but I cut at least an inch from BOTH ends, due to the lapping processes, so don't figure your diameter by taking all three inches from the muzzle end.

But... I am very curious, why do you care what the diameter will be? Fitting a brake and want to know what your options are?

 

[BadKarma47]

Re: How to determine barrel diameter @ muzzle?

Partially that, but 90% boredom! lol I know, it's a waste of Hide space!

 

[USW.260]

Re: How to determine barrel diameter @ muzzle?

Cool...Just started the Taper Chapter in Machine school this week. I did a formula for tapering a barrel using the offset in the tailstock...fun stuff. Just started learning to thread last week to.