Thin cut-rifled barrels and long strings of fire

[Ledzep]

Hello,

How well do quality (Krieger, Bartlein, Brux, etc.) cut-rifled barrels of thinner profiles (.600-.700 at the muzzle) hold up over long(er) strings of fire (10-30 rounds)?

I've seen quite a few rifles with thinner barrels that last about 3-4 shots before they open up from sub-MOA to about 2-3 MOA. However, all of those were factory guns with (I assume) cheap factory button-rifled barrels. I'm curious to see a lightweight sporter contour precision barrel's 10-round group.

The rifle this will go on is a bit of mix of target practice and hunting. Mostly my go-to rifle for everything, and it would be nice to be able to shoot 20 rounds without having to wait 20 minutes every 5 shots. At the same time, if I can shave off excess weight, I will.

 

[bohem]

Re: Thin cut-rifled barrels and long strings of fire

I've personally taken a Kreiger contour that was 0.57" @ 26" from the bolt face and shot strings of 6mm Remington Imp. that had it hot enough to discolor the paint on the barrel. At 1kyd it was still hammering pounding a 10" disc like a screen door in a hurricane. We burned up 50rd in <20mins with it. For grins we cut 5 into ~1/2" from 100yd at the end.

The owner put the rifle back in the case and the foam melted to the barrel.

A good barrel will shoot no matter how you slice it. I've seen/shot several "beanfield rifle" barrels that are so hot you can't resolve 2MOA targets from 500yd without someone blowing in front of the optic to reduce barrel mirage but the rifle was still hitting the movers when we shot at them.

 

[Unknown]

Re: Thin cut-rifled barrels and long strings of fire

I imagine that the construction of these barrels will effect barrel accuracy. I'm referring to some companies (like Alexander Arms) who are now producing lightweight fluted barrels. I would be keenly interested to find out if anyone knows how these lightweight fluted barrels perform when they warm up.

 

[sinister]

Re: Thin cut-rifled barrels and long strings of fire

Barrel life can generally be measured at the throat as heat advances wear in the form of smoothing, then cracking of the steel in the bore.

In general terms a cut-rifled barrel should last longest, followed by a hammer-forged or buttoned barrel. Alloys and stress relief will also make a difference. Stainless will generally produce a more accurate barrel in the beginning (as the alloy is softer and more machinable), but as the barrel wears accuracy can drop like falling off a cliff, while chro-moly alloys typically show a gradual decline.

You'll pay more for a harder stainless barrel as they're typically tougher on rifling tools.

Heavier bullets will also shorten life given an identical barrel shooting lighter bullets (it takes longer for a heavier bullet to leave a barrel than a lighter one, given identical powder charges -- exposing the throat to higher heat for longer).

A custom barrel blank is generally made to a higher standard under more careful surveillance than a mass-produced barrel made on a hammer-forging machine. Hammer-forged barrel machines are typically designed to put out high numbers of good barrels cheaply and quickly. Proper stress relief can help prevent zero shifts as metal expands and contracts.

As they say in manufacturing you can get good, fast, and cheap -- pick two.

 

[Ledzep]

Re: Thin cut-rifled barrels and long strings of fire

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">I've personally taken a Kreiger contour that was 0.57" @ 26" from the bolt face and shot strings of 6mm Remington Imp. that had it hot enough to discolor the paint on the barrel. At 1kyd it was still hammering pounding a 10" disc like a screen door in a hurricane. We burned up 50rd in <20mins with it. For grins we cut 5 into ~1/2" from 100yd at the end.

The owner put the rifle back in the case and the foam melted to the barrel.

A good barrel will shoot no matter how you slice it. I've seen/shot several "beanfield rifle" barrels that are so hot you can't resolve 2MOA targets from 500yd without someone blowing in front of the optic to reduce barrel mirage but the rifle was still hitting the movers when we shot at them. </div></div>

That is very confidence-inspiring. Thank you gentlemen for the replies. I'm curious to hear more people's experiences and opinions-- Good and bad, I'm trying to get a solid feel on the subject before I put money down.

 

[DJ 480]

Re: Thin cut-rifled barrels and long strings of fire

I would like to hear more as well seems the old school of thought has always been you need a thicker barrel to maintain accuracy the more rounds you shoot..which has to ring true somewhat or why would majority of the guns you see have heavier contours..except for rifles where weight is a concern..IE(hunting or walking rifles)

 

[bmt]

Re: Thin cut-rifled barrels and long strings of fire

FWIW:

I shot a PacNor Number 3 contour 308 sporter (a custom, but essentially a sporter) at Thunder Ranch, High Angle. The tube is 0.625 at the muzzle.

After shooting 50 rounds at various targets (600 to 900 yards, improvised position, high winds, unknown distances) I moved onto the 950 yard target.

Clint Smith gave me some DOPE and Wind Readings based upon his experience with the target.

First Round Hit.

No luck in this shot--Clint had about 10,000 rounds of Spotting this location with 308s. I just held an squeezed--barely able to take credit for the shot (but I will).

So, yeah, thin hot barrels can still shoot.

BMT

 

[Frank Green]

Re: Thin cut-rifled barrels and long strings of fire

The more stress free the barrel blank and the straighter the barrel blank and the more uniform the twist and bore sizes the more forgiving the barrel is going to be. No way around it. Cut rifling doesn't induce any stress into the blank. Cut rifling produces a way more uniform twist than button rifling and this is not just me being biased towards cut because I work here either. Button rifling is basically a cold swagging type process. It does not remove the material but displaces the material. This leads to the bore being work hardened and one of the main reasons it effects the barrel life to be shorter on a button barrel besides the quality of the steel and heat treat etc.... Also during the rifling process the button has the twist built into it. Any hard spots or soft spots in the steel and this can have an effect of slowing down and then the button could speed back up again. If this happens you end up with a non uniform twist. Some button rifled barrel makers are trying/doing things to help guide the twist of the button to produce a more uniform twist.

Button barrels can make great barrels and have more than proven themselves but I don't feel they are as consistent from one to the next.

It's an old saying that a heavier contour barrel will shoot better over longer strings of fire than a lighter one. I agree with this only to an extent for the reasons listed above.

My current med. palma contour which has a .820 muzzle at 30" finish will shoot as good or better than any HV contour barrel or straight blank. The gun will shoot flat .2's and consistently has shot sub 1/3moa at 1k.

Later, Frank
Bartlein Barrels