Why do we get fanatical over barrel alignment?

[dnellans]

Has that ever been proven? I was taught to seat into the lands ever so slightly. If its touching how can it get misaligned? Everyone screams jump, yet no one wants a long throat. why go to the trouble to make a perfect bore chamber alignment if you are going to hold the bullet back so it can have enough room to enter the bore at an angle? It makes no sence to me, but them no one ever accused me of being the sharpest pencil in the pack.

Non-benchrest shooters have plenty of reasons to not jam bullets which is why jump is talked about so much, but none of them are trying to achieve the best absolute precision.

I've also wondered if there are any benchrest or f-class shooters who jump regularly or if its pretty much accepted that "the best" accuracy is going to come at some varient of touch to jam?

 

[tobnpr]

What i don't get is after you/gunsmith jump through all these hoops and get a perfectly aligned camber that hits the bore of the barrel just right why would you load ammo with jump?

Anyone that does OCW-type load development, knows that we look for a "node"; and the same experimentation applies when it comes to bullet jump. It's the final step in load development. Sometimes jamming, sometimes "kissing", sometimes a mile jump- provides best accuracy. I do it just like Berger recommends.

VLD - Making it Shoot

VLD bullets are designed with a secant ogive. Berger VLD bullets are consistently and exceptionally capable of putting game down quickly

bergerbullets.com

 

[LVLAaron]

What i don't get is after you/gunsmith jump through all these hoops and get a perfectly aligned camber

Because I'm not lazy, and I can.

Even if you are jamming, do you want your bullet jammed crooked, or straight?

 

[dnellans]

Because I'm not lazy, and I can.

Even if you are jamming, do you want your bullet jammed crooked, or straight?

You're missing his point... He's asking why you wouldn't jam, to support the bullet in your nicely aligned throat.

 

[dnellans]

Anyone that does OCW-type load development, knows that we look for a "node"; and the same experimentation applies when it comes to bullet jump. It's the final step in load development. Sometimes jamming, sometimes "kissing", sometimes a mile jump- provides best accuracy. I do it just like Berger recommends.

VLD - Making it Shoot

VLD bullets are designed with a secant ogive. Berger VLD bullets are consistently and exceptionally capable of putting game down quickly

bergerbullets.com

I'm not buying it... I want to hear from someone who is shooting benchrest f-class at a nationally competitive level who is doing so with a 140k jump a "mile". I could be wrong, but I don't think thats happening.

 

[LVLAaron]

There are some. I wont name names but berger hybrids are generally as fine at 100+ jump as they are 10.

 

[X Count]

Amongst the team I was involved in everyone ranged from about .025 out to .015 in and any combination in between. This is even with the same bullet. I haven't seen on heard anyone getting BETTER accuracy further out but it may not get any worse further out either. You see your major wins or losses in that first .040 range and then its just jumping.

My preference is to see if the gun will shoot jammed first. I feel it gives the bullet a uniform engagement into the lands , ignition and pressure are only building against the rifling (not neck tension and then the rifling), may be more tolerant to neck tension variations, helps seat new brass against the bolt for proper fire forming, earlier gas seal at the bullet expands the case into the chamber quicker and reduces gas bypass forward of the bullet or backwards past the neck. I had a chamber that I was running .100+ jump with .005" neck clearance and on some cases the gas was actually bumping my shoulder back .010" . . . . .. that's not good!!!

In saying the above I've seen guns give just as good accuracy with jump so it comes down to what you prefer and what the gun prefers.

 

[gunsandgunsmithing]

IME, just about every bbl I've ever had shot best between .010 off and .010 into the lands. I can't think of a single exception to that, in any caliber. I will say that, IM E, the 30's seem to like more jam that the 22's, 6's 6.5' or the 7mm's, though. It think starting pressures with available powders for a given capacity are affected by seating depth and neck tension. To a lesser degree with the latter but that can depend on if it's jammed relatively hard or not. Less neck tension won't allow as much jam as heavy.

Again, this is IME but I've been around a lot of different stuff over the years and the only time I use a lot of jump is if mag length stops me. I do think there are different accuracy requirements for different games and I also think that both ways can work to a degree that satisfies most people's requirements.

As with tuners, I think tune repeats and that you can skip over sweet spots unless you are very methodical and that not every cartridge combination has the same spacing between "nodes."

Ultimately, just do what gives you winning results. If you're not winning with your method, try something else. Lol!

 

[sdean]

I hope everyone is jamming their 180 hybrids next match I shoot.

 

[Clark]

The math still works 65 years later, bullet tilt matters:
scroll down in link

Indicating Barrels to chamber

This is a .338 edge chamber, the end of the free bore is about 3.174" from the back of the barrel. Then you have the even longer stuff like the 33/37XC. Edit: video is gone, no more youtube

forum.accurateshooter.com

Chamber tilt matters a lot less.
I cut the tennon off a Rem700 take off barrel in 2012, and without cutting off the burr, I inserted a 7mmRM reamer. The reamer wobbled 0.0070" all the way to head space.

As a joke, I took it along on a range trip and sighted it in.
It shot better than some premium new 7mmRM rifle barrels I dialed in with an Interapid 0.0001" test indicator.


What does it all mean?
a) Loading ammo is a recurring task that human instinct would minimize.
b) Dialing in rifle barrels in a non recurring task that human instinct would invest a premium effort.

Our instincts failed us.

 

[B Nettesheim]

The math still works 65 years later, bullet tilt matters:
scroll down in link

Indicating Barrels to chamber

This is a .338 edge chamber, the end of the free bore is about 3.174" from the back of the barrel. Then you have the even longer stuff like the 33/37XC. Edit: video is gone, no more youtube

forum.accurateshooter.com

Chamber tilt matters a lot less.
I cut the tennon off a Rem700 take off barrel in 2012, and without cutting off the burr, I inserted a 7mmRM reamer. The reamer wobbled 0.0070" all the way to head space.

As a joke, I took it along on a range trip and sighted it in.
It shot better than some premium new 7mmRM rifle barrels I dialed in with an Interapid 0.0001" test indicator.


What does it all mean?
a) Loading ammo is a recurring task that human instinct would minimize.
b) Dialing in rifle barrels in a non recurring task that human instinct would invest a premium effort.

Our instincts failed us.

My instincts tell me to dial them in

 

[X Count]

And what about loaded round runout? It's not uncommon for ammo to shoot well with .003 or more runout. That's 15x more error than what most would say a barrel NEEDS to be dialed in to be able to shoot well.

 

[LVLAaron]

And what about loaded round runout? It's not uncommon for ammo to shoot well with .003 or more runout. That's 15x more error than what most would say a barrel NEEDS to be dialed in to be able to shoot well.

If you could make perfect rounds, you would right?

That's why we align chambers, if nothing else, because we can.

Pretty simple.

 

[INTJ]

Has that ever been proven? I was taught to seat into the lands ever so slightly. If its touching how can it get misaligned? Everyone screams jump, yet no one wants a long throat. why go to the trouble to make a perfect bore chamber alignment if you are going to hold the bullet back so it can have enough room to enter the bore at an angle? It makes no sence to me, but them no one ever accused me of being the sharpest pencil in the pack.

This is why. These are jammed .021. And I fussed a lot getting the throat straight before I cut the chamber.

 

[LVLAaron]

not familiar with LR BR - how big is the 10 ring? 1 moa?

 

[INTJ]

I have been able to get okay groups from my LRBR rifles with bullets jumped .020". The smallest HG group every shot at 1000 yds (a 2.6" something) was shot with bullets with a .030" jump--IIRC. However, most of the time I--and many of my fellow competitors--have found that jam works best.

However, I don't even test hunting rifles with jam. Why?

1. Too much jam will leave a bullet in the chamber

2. A small jam can be fussy, requiring constant chasing of the lands. Most of us test LRBR loads before every match and adjust as required. That usually isn't done with hunting rifles. Generally, the more the jump the less sensitive the load is to throat erosion

3. If your loading practices are decent, then your bullets are straight regardless of how much jump you need. And if you bullets are loaded crooked, then regardless of jump or jam there will be an alignment issue. In fact, a jump would likely allow the bullet to straighten out more before engaging the rifling than a jam. A crooked jammed bullet starts out crooked.

 

[INTJ]

not familiar with LR BR - how big is the 10 ring? 1 moa?

7" 10-Ring. I have seen 3" posted for the X ring, but I have measured it at less than that. (I just measured again. It's 2 7/8") The groups above are 10-shots at 1000 yds, a 3.855 and a 4.3 something.

 

[ebb]

Aaron i totally get having a perfect chamber matched dead center to the bore i just don't get why you would do that then seat the bullet so far back that it has a chance to enter the rifling sideways. Obviously it can't enter the rifling sideways but the further away from the start of the rifling the more chance for error. yes INTJ ive dumped a trigger full of powder and it sucks, even though a hunting rifle I some times think I need that extra bit of help and just can't resist.

 

[LVLAaron]

Aaron i totally get having a perfect chamber matched dead center to the bore i just don't get why you would do that then seat the bullet so far back that it has a chance to enter the rifling sideways. Obviously it can't enter the rifling sideways but the further away from the start of the rifling the more chance for error. yes INTJ ive dumped a trigger full of powder and it sucks, even though a hunting rifle I some times think I need that extra bit of help and just can't resist.

I guess, because a 1/4 minute gun that I can remove loaded rounds from and not chase lands is more than enough for my sport.

 

[tobnpr]

Aaron i totally get having a perfect chamber matched dead center to the bore i just don't get why you would do that then seat the bullet so far back that it has a chance to enter the rifling sideways. Obviously it can't enter the rifling sideways but the further away from the start of the rifling the more chance for error. yes INTJ ive dumped a trigger full of powder and it sucks, even though a hunting rifle I some times think I need that extra bit of help and just can't resist.

I'm with ya. This is an interesting topic for discussion.
Found this article in Rifleshooter, and has interesting results, even if anecdotally.

Bullet Runout - How It Affects Accuracy - RifleShooter

A simple test of sorting ammo and a shooting session at the range will show how bullet runout can affect the accuracy of your rifles.

www.rifleshootermag.com

He found that ammo with heavy bullet runout performed as well as those with mimimal to none- with an occasional flyer. Still, quite puzzling. If 80% of the time, non-concentric rounds shoot just as accurately- how does one explain the 20% that result in a flier?

I found the results of my tests conclusive but also perplexing. Clearly, sorting for tight concentricity helps eliminate fliers. According to these simple tests, it appears 80 percent of bullets exhibiting poor concentricity still group well, with only about one out of five actually resulting in a flier. But that’s enough for me to keep sorting my ammo for concentricity.

The above one would carry more weight with me if it had been conducted from a rigid rest instead of freehand off a bipod. Better yet, rigidly held test barrel to eliminate any possibility of shooter influence.
At the end of the day, it's likely another "it depends" variable with no definitive answer.