Barrel contour smothe vs stepped for accuracy

[johnmventers398]

Hi folks.

Ive done serches on here and on google and have come up blank.

So my question is in relation to the profile if a blank.

Im re barreling a rifle and have a new mod for it which is a reflex stile.

What i would like to know is if i was to have the barrel full diameter to the point where the mod needs to be and then have an abrupt step down to internal dimensions is this likly to cause a harmonic nightmare? Am i better off with a smooth and continuous taper from chamber to crown?

I have a supplier here in the uk who makes barrels to order and any contour before stress relief so im not worried about the barrel shifting on me.

I eegerly anticipate the discussion.

John


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[Mulligan]

John,
Reach out to forum member Boyd Allen @BoydAllen
I believe he described to me in great detail some testing he has done along the same lines with good success.

CW

 

[JEFFPPC]

We reinvent the wheel. Popcorn please.

 

[F Class John]

Only because I'm really curious to read what people have to say, am I correct in that the OP is asking if anyone has tapered a barrel so it looks like this or some facsimile and what the results were?

 

[Dos XX]

Like a Mauser barrel?

 

[jackieschmidt]

Last year, I took a good shooting HV profile 6PPC Barrel and machined 4 equal steps in it. I was careful to take light cuts, avoid any chatter and use plenty of coolant.

As best I can tell, it shot exactly the same as before.

 

[Dusty Stevens]

Talk to your local tinkering gunsmith and ask him how the steps would slug. Im sure he will give you an earfull of thoughts to ponder

 

[D-4297]

Talk to your local tinkering gunsmith and ask him how the steps would slug. Im sure he will give you an earfull of thoughts to ponder

Guess most people who haven't done a lot of tubular machining don't grasp that machining on the outside diameter of a tube can also change the inside diameters of said tube . Or cause "waves" in the I.D's.

 

[Dusty Stevens]

Guess most people who haven't done a lot of tubular machining don't grasp that machining on the outside diameter of a tube can also change the inside diameters of said tube . Or cause "waves" in the I.D's.

It WILL change the inside especially on a barrel. This is why rimfire BR barrels are straight now with no taper or steps, not even much for a tenon

 

[Think4Self]

It WILL change the inside especially on a barrel. This is why rimfire BR barrels are straight now with no taper or steps, not even much for a tenon

I've always thought the wild fluting on some of the barrels looked cool, but I stay away because I wasn't sure about this.

 

[TylerFromMS]

Guess most people who haven't done a lot of tubular machining don't grasp that machining on the outside diameter of a tube can also change the inside diameters of said tube . Or cause "waves" in the I.D's.

How? Is it relieving stresses where it’s machined or is stress being transferred deeper into the material or something along those lines? I’ve done zero machining so I’m trying to wrap my head around it.

 

[D-4297]

Two things occur when you machine a rifle barrel , or any "Tube" for that matter . First ; you are cutting material from the O.D. , and that changes the stress load on that surface . Second , No matter how much coolant is run on the cut , you will still develop heat , which will be transferred through the barrel , and it will affect the internal I.D. , causing both enlarging of the I.D. in certain areas , as well as reducing the I.D. . Understand that this change of I.D. may only be measured in tenths . Or Ten Thousandths , or even less , or it can go the other way , and enlarge a thousandth , or more . It depends on the quality of the material , machining practices used , and other variables . The main reason quality barrels are stress relieved after machining is completed , and lapping is done . Think I got all that in the right order .

 

[TylerFromMS]

@D-4297 Thanks! That’s a bunch of good information.

 

[NZ_Fclass]

I've always thought the wild fluting on some of the barrels looked cool, but I stay away because I wasn't sure about this.

Just look at the winners in F-Class and Benchrest. See the steps or fluting? No. There's your answer.

 

[darkangel_r2]

It WILL change the inside especially on a barrel. This is why rimfire BR barrels are straight now with no taper or steps, not even much for a tenon

A reverse taper section at the muzzle matching the largest diameter on the chamber end for an inch or two is starting to sound like a better and better idea. Not only would the extra mass at the muzzle work to improve the consistency of the harmonic profile it would also keep the crown tight.

 

[Ray123]

Yep, machining steps on the OD will likely cause ID variations...especially in button rifled barrels where more pressure is exerted outward to from the button rifling process..this stress will be relieved slightly by machining the OD, which opens the bore...
Proven 35 yrs ago...when 22 LR competition was going strong ...one of the leading rimfire gunsmiths in the competitive rimfire shooting , as explained in Precision Shooting, was using a lead lap and could feel when the barrel bore became loose where ANY OD machining took place...He also was ringing a barrel, like a tuning fork, and would select an accurate barrel by the tone... that seemd out there but you could not argue with his success, at picking winning barrels. Even the 2 gas block set screws that push up on the bore that hold the gas block in place will slightly produce a smaller bore diameter on one side of the bore with upward screw pressure on the OD.... alot of AR accuracy shooters prefer clamp on over set screw gas blocks....that's why both are offered, and why I sometimes use them.

 

[Hengehold]

Hi folks.

Ive done serches on here and on google and have come up blank.

So my question is in relation to the profile if a blank.

Im re barreling a rifle and have a new mod for it which is a reflex stile.

What i would like to know is if i was to have the barrel full diameter to the point where the mod needs to be and then have an abrupt step down to internal dimensions is this likly to cause a harmonic nightmare? Am i better off with a smooth and continuous taper from chamber to crown?

I have a supplier here in the uk who makes barrels to order and any contour before stress relief so im not worried about the barrel shifting on me.

I eegerly anticipate the discussion.

John


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The short answer is Yes, a stepped profile rather than a gradual taper can perform well. If you look at the AR-15 barrel profile that ALL service rifle shooters use to compete in CMP and NRA highpower rifle competition, you will find the following dimensions to be used with great accuracy out of an AR-15 platform (sub MOA at 600yds).

-20” length overall
-1” dia for something like the first 16 inches.
-.750” (this is appropriate. I don’t know the exact number off hand) dia from 16” to 20”

The transition from 1” to .750” is an immediate and abrupt step. The x-ring at 600 yds is 1” MOA and guys can shoot 50%-75% of their shots in the x-ring when shooting prone with a sling. Obviously there is plenty of user error there so the platform is capable of sub MOA.

hope this helps.

 

[Hengehold]

A reverse taper section at the muzzle matching the largest diameter on the chamber end for an inch or two is starting to sound like a better and better idea. Not only would the extra mass at the muzzle work to improve the consistency of the harmonic profile it would also keep the crown tight.

I believe Anschutz rimfire barrels match your description. Larger diameter at muzzle than the back & middle section of the barrel.

 

[D-4297]

Want to repeat a very important point to this whole issue . Regardless of when machining is done on a barrel , if it is not stressed relieved and then , "Lapped" as a final process , you will have deviations in the I.D. No matter which directions the barrel or taper is cut .

 

[jelenko]

The short answer is Yes, a stepped profile rather than a gradual taper can perform well. If you look at the AR-15 barrel profile that ALL service rifle shooters use to compete in CMP and NRA highpower rifle competition, you will find the following dimensions to be used with great accuracy out of an AR-15 platform (sub MOA at 600yds).

-20” length overall
-1” dia for something like the first 16 inches.
-.750” (this is appropriate. I don’t know the exact number off hand) dia from 16” to 20”

The transition from 1” to .750” is an immediate and abrupt step. The x-ring at 600 yds is 1” MOA and guys can shoot 50%-75% of their shots in the x-ring when shooting prone with a sling. Obviously there is plenty of user error there so the platform is capable of sub MOA.

hope this helps.

To add to this.
The 20" service rifle barrel drops from the .750" to something less. The barrel is .750 for ~ 2".

The barrels used on a 'spacegun' start at the same 1", drop straight down to either .936, .875 or .750, for about 2", then drop several hundreds straight down to the end of the barre.

All that said, for this type of competition, 1/2 MOA groups are fabulous - i.e., not looking for differences in the tenths.