Lija 1:7 30cal

[TXAoudadKlr]

Was surfing through various barrel makers website's and scrolled on to Lija's Calibers and twist rates. In doing that I took notice to the 1:7 3 groove.

I've been looking at a 1:8 for a planned 300WM/30 Nosler. Anyways just kind of curious about the viability of a 1:7

 

[TXAoudadKlr]

Nada?

 

[HARPERC]

I'm not sure there is another .30 in my future, but if there is 1-7" will be what I choose.

 

[jebel]

I think it all comes down to what bullets you want to shoot. If you wanted to launch the .308 Hammer Hunter in 227 grains from a 300 WSM, you might want something a bit faster than 1:8, though 1:7.5 would be plenty. There aren't many bullets in .308 that would like a twist faster than 1:8, but there are some. And, of course, likely to be more. Depends on your personal preferences.

 

[jebel]

I would add, there may be shooters who want a stability factor significantly higher than traditional figures, perhaps for ELR. 1:7 may well make sense there for quite a number of bullets.

 

[NEMTHunter]

Mine finishes @ 1:7.5 Kind of with I would have gone down to a 1:7 twist. But for the bullets made currently a 7.5 will be more then enough. My next one will be a 1:7 5R though. There comes a point when all you do is over spin the bullet.

Also depending on how fast you shoot the bullet a tight twist could have a adverse affect. Why? The bullet might have to much forward momentum depending on the bearing surface (not enough), type of twist, Or to thin of jacket for the bullet to properly grip the rifling. What this will do is smear the bullet down the bore and give you bad results even though you have the right twist for the bullet.

Think on it like this. Say you have a bullet thats stable at 2800 fps and hits the target point first. But as you pick up speed and get closer or above 3000 fps you loose stability. What is causing this? Since we know more speed means more RPM of the bullet and that increases stability. I have a theory what as speed picks up it becomes unstable.

Some of it could be the fact the bullet is not able to grip the bore as needed so it is pushing through the rifling. TO move force pushing the bullet into a tight twist for it to be able to grip the rifling. A short bearing surface from light engraving pressure or a super short bearing surface. A thin jacket I feel could do the same thing. Unless the bullet hits and grips you will have trouble and speed will keep that from taking place.

Just some thoughts I have had.

 

[TXAoudadKlr]

Another site there's a discussion on groove count and effects on bullets from tight twist barrels....I would lean towards a 5r myself now.

I do like speed but I'm wanting to move back to heavy for caliber bullets. Have the big Hammer solid, 230-250gr Hornady bullets soon a 245gr Berger a 1:8 or faster looks to be on my horizon.

 

[RockyMtnMT]

Mine finishes @ 1:7.5 Kind of with I would have gone down to a 1:7 twist. But for the bullets made currently a 7.5 will be more then enough. My next one will be a 1:7 5R though. There comes a point when all you do is over spin the bullet.

Also depending on how fast you shoot the bullet a tight twist could have a adverse affect. Why? The bullet might have to much forward momentum depending on the bearing surface (not enough), type of twist, Or to thin of jacket for the bullet to properly grip the rifling. What this will do is smear the bullet down the bore and give you bad results even though you have the right twist for the bullet.

Think on it like this. Say you have a bullet thats stable at 2800 fps and hits the target point first. But as you pick up speed and get closer or above 3000 fps you loose stability. What is causing this? Since we know more speed means more RPM of the bullet and that increases stability. I have a theory what as speed picks up it becomes unstable.

Some of it could be the fact the bullet is not able to grip the bore as needed so it is pushing through the rifling. TO move force pushing the bullet into a tight twist for it to be able to grip the rifling. A short bearing surface from light engraving pressure or a super short bearing surface. A thin jacket I feel could do the same thing. Unless the bullet hits and grips you will have trouble and speed will keep that from taking place.

Just some thoughts I have had.

We have been dealing with this in @HARPERC 's 6.5 Ultracat. The long bullet that we designed for the 6" twist shot great until we reached 3300 fps. Lost stability. We first thought we were slipping in the rifling so we caught one to examine the bullet engraving. No slipping, nice clean engraving. The dynamic stability looks to be the culprit. The faster the bullet is going the more force is exerted on it causing it to tumble. The longer a bullet gets for caliber the more prevalent the problem gets.

Only downside to faster than needed twist that we have seen is that it causes more torque on the rifle, making it more difficult to shoot.

 

[TXAoudadKlr]

I was reading a piece on Left hand twist being better being that it torques into you rather than away

 

[NEMTHunter]

We have been dealing with this in @HARPERC 's 6.5 Ultracat. The long bullet that we designed for the 6" twist shot great until we reached 3300 fps. Lost stability. We first thought we were slipping in the rifling so we caught one to examine the bullet engraving. No slipping, nice clean engraving. The dynamic stability looks to be the culprit. The faster the bullet is going the more force is exerted on it causing it to tumble. The longer a bullet gets for caliber the more prevalent the problem gets.

Only downside to faster than needed twist that we have seen is that it causes more torque on the rifle, making it more difficult to shoot.

Good information Steve! Hope you all get it ironed out! Is there any chance that a slimmer as in higher caliber Ogive would let the bullet to slip through the air better so less drag and in turn less chance of a tumble? Do you feel that the pressure of the air against the Ogive could be causing the base to past the nose up?

 

[HARPERC]

....I was reading a piece on Left hand twist being better being that it torques into you rather than away....

To my way of thinking it seems the right hand torques up and into my face. Never shot a left hand twist, but it would seem to torque down, and away from the cheek weld, for a right hand shooter?

 

[RockyMtnMT]

Good information Steve! Hope you all get it ironed out! Is there any chance that a slimmer as in higher caliber Ogive would let the bullet to slip through the air better so less drag and in turn less chance of a tumble? Do you feel that the pressure of the air against the Ogive could be causing the base to past the nose up?

Too bad I'm not a rocket scientist. The way I understand the pressure it is the pressure from running above the sound barrier that causes the instability not the air. Could be wrong here but it is different than the drag of air under the sound barrier. It's the pressure wave that concentrates closer to the tip the fasterthe bullet is moving.

Also it seems that the higher density the bullet material is the less It is effected by this.

So far we have only tried bullets with a 1.5mm hollow point. Would be interesting to try the same bullets with no hollow point.

 

[HARPERC]

.....Too bad I'm not a rocket scientist..........So far we have only tried bullets with a 1.5mm hollow point. Would be interesting to try the same bullets with no hollow point...........

I think even rocket scientist are mostly trial, and error. Or maybe they just aren't good working in teams...Then there is the subject of O rings, maybe they needed a Montana kid to work out the cold weather kinks!

 

[NEMTHunter]

Too bad I'm not a rocket scientist. The way I understand the pressure it is the pressure from running above the sound barrier that causes the instability not the air. Could be wrong here but it is different than the drag of air under the sound barrier. It's the pressure wave that concentrates closer to the tip the fasterthe bullet is moving.

Also it seems that the higher density the bullet material is the less It is effected by this.

So far we have only tried bullets with a 1.5mm hollow point. Would be interesting to try the same bullets with no hollow point.

I get you. and Think I know why you say that. But that lingo could just go right over my head. You are trying to keep it as a hunting bullet. That would be very neat if you could get it to work. I bet the bigger end is also causing some drag. I need to do more reading on this kind of thing. It very intriguing.

On some research I have done about Meplats or pointed tips is a fine point has more drag then a very small meplat. And a interesting thing is the faster the projectile the or aircraft or anything that hits mach 5 or faster. We are not hitting mach 5 that would be 5580 FPS. But still wonder if it could play a part with a bullet? They also say they is no set size to the meplat, but thats it designed for the given nose length.

Copy and paste. Not me!!---- Coincidentally, the shape of the nose of an axisymmetric projectile that gives it the least possible aerodynamic drag at hypersonic speeds always has a meplat, the diameter of which depends on the length of the nose