Hex Boron Nitride question

[hemiford]

How would coating the projectiles affect freebore ?

If a given charge pushes a coated bullet faster down the bore, and
peak chamber pressures are reduced due to reduced bore friction,
does it not seem that freebore could be reduced ?

Or, the charge could be increased, to maintain chamber pressure ?

 

[royinidaho]

How would coating the projectiles affect freebore ?

If a given charge pushes a coated bullet faster down the bore, and
peak chamber pressures are reduced due to reduced bore friction,
does it not seem that freebore could be reduced ?

Or, the charge could be increased, to maintain chamber pressure ?

It is my experience that HBN reduces friction which reduces pressure which reduces velocity.

I don't understand "If a given charge pushes a coated bullet faster down the bore..."

 

[hemiford]

Well then I'm totally off on that. Not sure what I was thinking.

Couldn't you still though reduce freebore, because of reduced chamber
pressure ?

Or increase charge to maintain the same chamber pressure ?

You'd think reducing bore friction would automatically increase velocity,
maybe that's what I was thinking.

Anyway, it's really the freebore issue I'm driving at.

 

[royinidaho]

Couldn't you still though reduce freebore, because of reduced chamber
pressure ?

Or increase charge to maintain the same chamber pressure ?

The effect of less friction is as the bullets slides easier pressure goes down resulting in less velocity.

Remedies are to increase powder charge to attain the same pressure thus the same velocity.

The "free bore" is a bit more involved.

Freebore can be said to be the distance from the front of the neck to where rifling starts.

To change "freebore" means to rechamber with a different throat reamer.

However, the work around is to simply seat the bullets longer. The net effect is increased effective case volume.

Increased case volume + HBN reduced friction means an even greater powder charge is possible with a significant increase in velocity.

Ya gotta sneak up on things fairly conservatively otherwise there may be some not so fun experiences.

Hope this helps.

 

[hemiford]

Roy,
So if using hBN is one way to shorten freebore, would the highly
overbore cartridges like 7rum or 30-378 benefit from it's use ?
"Benefit" meaning potentially straighter bullet contact/engraving
and therefore accuracy ?
Potentially even more velocity too.

 

[royinidaho]

Roy,
So if using hBN is one way to shorten freebore, would the highly
overbore cartridges like 7rum or 30-378 benefit from it's use ?
"Benefit" meaning potentially straighter bullet contact/engraving
and therefore accuracy ?
Potentially even more velocity too.

I run a 270 Allen Magnum which eats barrels like pigs eat corn.

It is about as overbore as ya get. When Bergers start fragmenting I went to Matrix until they started tearing the jackets off (shooing 2 foot patterns @ 300 yards with only one shot). Nothing against the bullet manufacturers but a 3 groove 8 twist barrel is pure torture.

I switched to Cutting Edge Bullets and all was restored.

Saying all of this a good bore polishing and HBN would do the same thing.

There's a fella that burned out a 270 WSM with 140 Bergers then started coating with HBN and accuracy was restored.

From all of this, I'd start out with HBN at the very beginning and run extreme velocities until she wouldn't shoot any more.

I'd say that HBN while reducing friction, allows greater velocity and longer barrel life.

"Benefit" meaning potentially straighter bullet contact/engraving
and therefore accuracy ?

I don't think it has anything to do with "straighter contact and engraving but it sure does something.

On a heavily burned throat I don't think the rifling is anywhere even from land to land.

I've ordered this stuff and will put it to good use. Watch his video. It'll convince you.

Tubb Precision Blended Boron Nitride Bullet Coating Kit

 

[hemiford]

OK well thank you much kind sir !
I'm thinking hard. I might might pester you with some more questions.
Need money.

 

[royinidaho]

Need money.

Who doesn't....:roll eyes:

Im going to to the HBN thing to a hot running 270 AM that seems to have returned to life with Cutting Edge Bullets. We'll see how that goes.

I'm also going to HBN Cutting Edge Bullets in 375 cal (377 grains) for the 375 AM. I'm thinking I'll be able to get the desired velocity with increased case life.

Shooting these big cartridges makes one need even more money....