Freebore vs Jump

[kwak]

So we purchase a special competition reamer with a super lead in angle. Ask for .050 freebore and we jump our VLD's .025. It all sounds great at the start.

600 rounds later we now have .100 freebore and we have to chase the lands to get back to the .025 that our VLD's like.

What happens to the special lead in angle? And all the carbon and copper that builds up in the freebore? What advantage does all that freebore offer?

I do not understand, please help my understanding. Thanks

 

[Cascade Hemi]

What advantage does all that freebore offer?

There is no advantage to excessive freebore unless you use a bullet that is tolerant to jump. The reality is that if you want to use Berger VLDs you will likely have to chase the lands. Freebore is, and always has been, specific to the bullet you intend to use. If your throat erodes beyond your ability to chase the lands (assuming you want or need to chase the lands) you either have to accept the performance you have or switch to bullets that are tolerant of jump or shaped/longer to closer engage the throat.

 

[918v]

So we purchase a special competition reamer with a super lead in angle. Ask for .050 freebore and we jump our VLD's .025. It all sounds great at the start.

600 rounds later we now have .100 freebore and we have to chase the lands to get back to the .025 that our VLD's like.

What happens to the special lead in angle? And all the carbon and copper that builds up in the freebore? What advantage does all that freebore offer?

I do not understand, please help my understanding. Thanks

What happens to the special leade angle?

It erodes away.

What advantages does freebore offer?

Reduced start pressure and better primer pocket life.

And fouling needs to be removed periodically.

 

[straightshooter1]

So we purchase a special competition reamer with a super lead in angle. Ask for .050 freebore and we jump our VLD's .025. It all sounds great at the start.

600 rounds later we now have .100 freebore and we have to chase the lands to get back to the .025 that our VLD's like.

What happens to the special lead in angle? And all the carbon and copper that builds up in the freebore? What advantage does all that freebore offer?

I do not understand, please help my understanding. Thanks

Unless your loading to touch or jam the lands, you really shouldn't chase the lands, because . . .

when you say your VLD's like the .025 jump (like in the beginning), what you're really saying is that your seating depth you have when you had that .025 jump is what it likes. That seating depth is WAY more important than that jump. So, whatever seating depth you had when you set up that .025 jump that your VLD's like, you should stick to that seating depth and you'll find that even as the throat erodes and the jump becomes longer that load will still work well. Eventually the jump can be significant enough to change the pressure curve (that's usually quite significant change, like maybe .050 or .060) where you might need to adjust the seating depth a little, but the jump is really a very minor function, even for VLD's configuration.

 

[MarkyMark007]

today ppl dont chase lands anymore...

 

[Haney]

today ppl dont chase lands anymore...

Wrong .

 

[Gil P.]

Wrong .

There was an interesting article or podcast on this. I think it was by Bryan Litz.

One of the questions was: how do we develop a loading that will shoot well for the life of the barrel, without changing the seating depth or charge weight?

Iirc, the answer was to use a long jump. If you jump the bullet far enough, it will shoot the same, even when the freebore gets longer.

He was talking about jumping the bullets 60 or 80 thou and beyond, and making seating depth adjustments in large increments as a best practice.

I think this is why loaded ammo like 308 cal 175gr FGMM shoots well in almost any rifle you put it in, regardless of length of freebore.

Someone correct me if I'm wrong, my memory is a little fuzzy on this.

 

[Sig Marine]

Custom reamer...custom problems. Any time you design/order a reamer cut for a specific bullet with a specific freebore, you MUST be aware of throat erosion/increase of freebore and your bullet's ability to bridge that gap. As a general rule, throats erode at roughly .002-.004 per 100 rounds, with .003 being where mine wear, although it is not a constant rate of wear and is dependent on other factors like caliber (especially over-bores), load, rate of fire and how hot your barrel gets, etc.

When choosing a reamer, selecting a freebore and bullet (or bullets) that will work with the growth expected for the life of the barrel will help with using up the entire barrel life. Many shooters have had good success with Berger Hybrids, Sierra Match Kings and the Hornady ELD-Ms as they have proven to be jump tolerant and will work with long freebores or freebores as they erode.

 

[918v]

today ppl dont chase lands anymore...

Wow I wasn’t expecting this sudden burst of wisdom

 

[kwak]

Some people like jump, some chase the lands. The leade angle is lost with barrel wear either way. It is difficult to build a rifle for one bullet only unless you have a source to buy 4-5 thousand at a time.

If you start with .100 or more freebore sooner or later you will have too much. Then you will have no room left to to get back to the lands.