The most important aspect as I understand it no matter what size cartridge you are shooting is it's easier on the bullet as it makes first contact with the rifling to preserve the integrity of the bullet. Instead of torquing it immediately with a fast twist that is constant, the gain twist gradually increases bullet rpm as it travels down the bore.
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Gain twist barrels?
- Thread starter Mattm8725
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The most important aspect as I understand it no matter what size cartridge you are shooting is it's easier on the bullet as it makes first contact with the rifling to preserve the integrity of the bullet. Instead of torquing it immediately with a fast twist that is constant, the gain twist gradually increases bullet rpm as it travels down the bore.
I believe this is the video Frank has been referring to. Good info.
Bullet selection is what's got my attention for small game.
I'd imagine that would work out pretty horribly as you'd have a very spread bearing surface due to the length between the lands initially.
How so? Maybe only do the first 6" or so. it would be a gradual twist from almost nothing to 8. Its not like there is a hard stop where one stops and the other starts.
Im thinking like a roller coaster easing into a barrel roll twist vs starting full speed and immediately hitting a twist.
Your bullet already goes from a 0 twist to whatever in your freebore, whatever that is.
Pretty sure it takes the most force to start the bullet spinning whichbcould be the cause of erosion. the first section of lands do the most work and take the most punishment.
Im thinking like a roller coaster easing into a barrel roll twist vs starting full speed and immediately hitting a twist.
Your bullet already goes from a 0 twist to whatever in your freebore, whatever that is.
Pretty sure it takes the most force to start the bullet spinning whichbcould be the cause of erosion. the first section of lands do the most work and take the most punishment.
The gain twist is a gradual and infinitely increasing ratio twist of a sprial over distance. Theoretically you could start at 100:1 and increase the spin rate to end at 7.5:1 over the course of a given distance. That distance and type of twist rate, I'm guessing, would be limited by the tooling, work holding (clamping), programming, and pixie dust.
So, you don't really start at 100:1, then instantly change to 8:1, then instantly change to 7.5:1. That instant angular change would destroy the bullet.
Yes. Of course.
But you could determine at what point it reaches each twist rate. And from that point on keep the same rate. Like stretching half a spring.
Lets say 100:1 to 8:1 for the first 8" it would be all rates in between 100-8 in that distance.
For the next 8" an 8:1 to 7:1
And for the last 8" all 7:1
Theoretically. I have no idea how any of this works. But i did stay at a Holiday Inn once.
You would need a length a lot longer than 8" to take advantage of what you are talking about.
Maybe, maybe not. Its purely conceptual. Wonder if its possible or if anyone has ever tried it.
But thats what happens now be cause the bullet goes from 0 to full barrel twist in .02" how is forcing a bullet into exponentially less aggressive lands and over 8" 400 times more distance worse?8
100 is an arbitrary number that i used to show extreme, i doubt if it worked the number would actually be that. Don't get hung up on the number.
Not sure you're following me. There is not 8" of 100:1 and point where it goes to 8:1. Because its transition is happening over the whole 8". you are slowly ramping up to 8:1 w. Basically putting pre-spin on the bullet before it hits the desired twist rate.
It's about the bullet
The bullet is the weak link in all this, because:
1. They are mass produced in the millions with very little QC beyond the batch
2. The jackets and lead can vary in microscopic ways that we never see
The elliptical views and flight path data that is demonstrated by guys like Bryan is microscopic which that translates to variations downrange. How the bullet and barrel interact are super important.
Look at Benchrest where every micron is squeezed out of accuracy. They do a minimal twist to put a minimum pressure on the bullet. They want just enough spin to be stable. On the other hand, long range guys are not in the market for more spin, the goal is when transitioning to transonic speeds we get better stability. That has a cost, and not a positive one.
Bullet with thinner jackets or off balance lead will get deformed in ways you cannot see, well the bullet has to be fired and is now in the air. So nobody is able to look at this very well. So instead we see bullet recalls and even companies like Bartein barrels saying, send us the bullets if the barrels seems off. This is because the pressure of the twist.
When you gain twist the barrel you ease that pressure so not to deform the bullet. We are trying to marry two principles, the bench rest one of less twist and the Long range one of more twist. You are trying to ramp up the spin without throwing a wheel weight off the tire.
It's just like that, a bullet out of balance, even microscopically, will start to get worse the more it slows down. You see it as fliers, dropped shots or ones that go low. It's not quite a vertical spread issue because it's not every round, its only the rounds which might be slightly out of spec. So you see once every 10 or 20 and easily dismissed. Bad shot, weird wind, weak load, all kinds of things will give the same appearance.
That is the benefit of GT Barrels, the ease of the transition between lands and bullet and the less impact on the jacket or underlying lead.
The bullet is the weak link in all this, because:
1. They are mass produced in the millions with very little QC beyond the batch
2. The jackets and lead can vary in microscopic ways that we never see
The elliptical views and flight path data that is demonstrated by guys like Bryan is microscopic which that translates to variations downrange. How the bullet and barrel interact are super important.
Look at Benchrest where every micron is squeezed out of accuracy. They do a minimal twist to put a minimum pressure on the bullet. They want just enough spin to be stable. On the other hand, long range guys are not in the market for more spin, the goal is when transitioning to transonic speeds we get better stability. That has a cost, and not a positive one.
Bullet with thinner jackets or off balance lead will get deformed in ways you cannot see, well the bullet has to be fired and is now in the air. So nobody is able to look at this very well. So instead we see bullet recalls and even companies like Bartein barrels saying, send us the bullets if the barrels seems off. This is because the pressure of the twist.
When you gain twist the barrel you ease that pressure so not to deform the bullet. We are trying to marry two principles, the bench rest one of less twist and the Long range one of more twist. You are trying to ramp up the spin without throwing a wheel weight off the tire.
It's just like that, a bullet out of balance, even microscopically, will start to get worse the more it slows down. You see it as fliers, dropped shots or ones that go low. It's not quite a vertical spread issue because it's not every round, its only the rounds which might be slightly out of spec. So you see once every 10 or 20 and easily dismissed. Bad shot, weird wind, weak load, all kinds of things will give the same appearance.
That is the benefit of GT Barrels, the ease of the transition between lands and bullet and the less impact on the jacket or underlying lead.
I do understand what you saying. I averaged your 100:1 for 8" and it looks something like this:
1:88.5
1:77
1:65.5
1:54
1:42.5
1:31
1:19.5
1:8
The very gradual engraving of the rifling now becomes very aggressive after the first 8" and that does not have a positive effect on the bullet.
But all those are less aggressive. How does it become any more aggressive than a standard 8:1 barrel? Either way your arriving at 8:1, the rest of the barrel is standard. It's how your delivering it there. Current rifles are basically ∞:1 and slam into 8:1 in a distance of .02" off the jump. I dont see how imparting some spin on the bullet over a greater distance easing into an 8:1 is a bad thing or more aggressive.
@Lowlight im sold on GT. But to take this a step further. bullet quality considered. what point in the barrel puts the most stress on the bullet? My guess is the first few inches that the bullet goes from zero spin and pressure against the lands have to overcome the inertia and mass of the bullet in order to impart spin. What If the design of the barrel mitigated this stress with pre-spin. Something like an extremely slow twist rate for a few inches to get the bullet started before hitting final twist rate?
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It's two separate issues. A fast twist from the start imparts stress on the bullet like you are referring to which can cause jacket/core integrity issues. Running a overly conservative twist at the chamber end (much more conservative than the norm) into that same fast, aggressive twist causes a different problem. The bullet is already engraved by the rifling and then suddenly has to transition into the much faster rifling causing the bearing surface to deform which will not be conducive to long range accuracy.
So after reading this I called bugholes and just ordered a left twist 8.25 to 7.5 gain barrel in M24 to be finished at 28". I want to be able to run the 107 sierras Im currently running in my 6br but also have the option of the higher bc 110 smk. Will the end gain of the 7.5 give me enough spin to run the 110 smk. I have run them in a straight 7.75 twist creed before but they were going a little faster.
Makes sense. You don't think the barrel length is enough to swage it into a stable form? Is what you say also theoretical or has this been tested?
Isn't the issue of gain twist and bullet deformation fundamentally about slowing the rate of RPM acceleration? If so, then that becomes intertwined with what cartridge you are running, what bullet, how fast of a powder you are using, and of course barrel twist rate.
Bullets don't slam into the lands at full speed, they continue to accelerate as they move out of the case and down the bore. Quick examples...
6mm Dasher typical Varget load with a 105gr bullet. At 1" of travel the bullet is going 770 fps, at 2" 1250 fps, 5" 1900 fps, etc
300 WM with a 230gr bullet and H1000. At 1" of travel bullet is 620 fps, 2" 988 fps, 5" 1650 fps etc.
Assuming the 6mm runs an 8 twist and the 300WM runs a 10 twist, the 6mm is ramping up in RPM acceleration much, much faster. Yet most of the 1000 yard benchrest world records with 6mm's are shot with standard 8 twist barrels so obviously it's not destroying bullets.
Perhaps some bullets are more vulnerable to damage than others? Bigger bullets with larger diameter take more torque to accelerate to RPM? How would you quantify what cartridges need or would benefit from gain twist barrels?
Bullets don't slam into the lands at full speed, they continue to accelerate as they move out of the case and down the bore. Quick examples...
6mm Dasher typical Varget load with a 105gr bullet. At 1" of travel the bullet is going 770 fps, at 2" 1250 fps, 5" 1900 fps, etc
300 WM with a 230gr bullet and H1000. At 1" of travel bullet is 620 fps, 2" 988 fps, 5" 1650 fps etc.
Assuming the 6mm runs an 8 twist and the 300WM runs a 10 twist, the 6mm is ramping up in RPM acceleration much, much faster. Yet most of the 1000 yard benchrest world records with 6mm's are shot with standard 8 twist barrels so obviously it's not destroying bullets.
Perhaps some bullets are more vulnerable to damage than others? Bigger bullets with larger diameter take more torque to accelerate to RPM? How would you quantify what cartridges need or would benefit from gain twist barrels?
You are not adding rifling by the faster twist, its all the same
The bullet is not laying extra rifling on itself using GT doesn't work that way and with a conservative twist like the 3/4 gain we are using it's a gradual increase but not extra rifling it's still the same
Some barrels are already a gain by how they rifle them, button cut barrels can have a gain or loss based on the consistency of the steel it's not perfect, a 10 twist barrel may not be a perfect 10 twist, but very few (Nobody) checks the actual twist rate, they just assume, it's a 10, can be a 10.1, can by a 9.9, it depends how it was done
The bullet is not laying extra rifling on itself using GT doesn't work that way and with a conservative twist like the 3/4 gain we are using it's a gradual increase but not extra rifling it's still the same
Some barrels are already a gain by how they rifle them, button cut barrels can have a gain or loss based on the consistency of the steel it's not perfect, a 10 twist barrel may not be a perfect 10 twist, but very few (Nobody) checks the actual twist rate, they just assume, it's a 10, can be a 10.1, can by a 9.9, it depends how it was done
The damage done by fast twist standard rifling is usually seen in stuff like 6mm by the bullet coming apart before it reaches the target
Dave Tooley posted pictures of the bullets leaking lead cause by damage to the jacket
I have had 6mm rounds come apart in a grey cloud about 200 yards downrange they disintegrate
Dave Tooley posted pictures of the bullets leaking lead cause by damage to the jacket
I have had 6mm rounds come apart in a grey cloud about 200 yards downrange they disintegrate
So the advantage of running a 8.25-7.5 instead of a 8 in say a 6br would be possibly being able to run a little more powder because of less pressure
Even though the gain twist itself would go from 1:100 to 1:8 over the course of 8 inches, the actual change in helix angle is not crazy - at 1:100 twist in 308 caliber the helix angle is 1.1 degrees, compared to 13.6 degrees at 1:8 twist.
This corresponds to a 2-caliber-long (0.616in) groove being offset front to back by 0.012in at the beginning and 0.149in at the end, or a change in angular offset from 4.5 degrees to 55 degrees. Again, this isn’t small, but doesn’t seem too crazy either.
This corresponds to a 2-caliber-long (0.616in) groove being offset front to back by 0.012in at the beginning and 0.149in at the end, or a change in angular offset from 4.5 degrees to 55 degrees. Again, this isn’t small, but doesn’t seem too crazy either.
I thought they established there is no effect on pressure. Maybe you could bump up the powder because the bullet could handle more velocity.
I'm building a 20BRA with a Bartlein 1/8.5 to 1/8 twist to shoot the Berger 55gr 204 bullets. This twist is what Bartlein recommened because I wanted to try a gain twist on this caliber. Hopefully I can get bullets to target without making comet tails and grey clouds.
I think that is where my 6mm GT is ... like 8.25 to 7.75 or something I would have to go back and look it up
So it was a few years ago but do you still feel a 10-8 is the go to for something like a 308. I'm looking to take advantage of a good deal and have been missing a nice 308 in the safe
has anyone tried a 300 prc in a left hand 10 to 8 twist? I am apprehensively waiting for mine. 10 to 8.125” .
Who suggested that gain rate? I’ve never used anything more than 3/4” gain
That quote may be a little out of date (c. 2018). I run a 3/4 GTLH barrel on my Valkyrie, and that's what MHS recommended.
Hi,
Ok, so after reading a couple posts about what you are looking to do..I HAVE to ask a few questions.
1. What is your intended purpose of this build?
2. What are you looking to gain with such long barrel on the 300PRC?
3. You exit twist is right in the middle ground of jacketed/monos. Depending on jacket it could be too fast at PRC MVs, depending on monos it could not be fast enough at PRC MVs...
4. What benefits do you see in using such heavy projectile in the 300PRC?
Sincerely,
Theis
It’s old and it comes from some one who did it with a 308 not a magnum, remember when i said you can try it, that usually means nobody has any info to confirm it
i dont really gain the 30 cal because i tend to stick with a 10 twist for most of mine, that works well.
my 300NM are both 10 twist, my pro is a 9 twist
the downside will be the velocity, but it might work, 30 calls are resilient
Pitfalls of a necro post i suspect, most do hover around 3/4 most of mine are too only special purpose barrels are greater
i dont really gain the 30 cal because i tend to stick with a 10 twist for most of mine, that works well.
my 300NM are both 10 twist, my pro is a 9 twist
the downside will be the velocity, but it might work, 30 calls are resilient
Pitfalls of a necro post i suspect, most do hover around 3/4 most of mine are too only special purpose barrels are greater
What is the heaviest bullet you run in your Norma? I have one coming in a 1-8.3 but it's going to be set up to run Berger 245's or the 250 A-tip and I'm at sea level.
Hi,
May I ask why you would want to run such heavies in the 300NM?
The 300NM IMO is better suited for 210gr class projectiles to be pushed a little faster than trying to use heaviest projectile you can find for it.
Sincerely,
Theis
230s
the 8s haven’t been working for many but good luck, hopefully you’ll find a balance with it, they dont seem to like the speed.
10s do this, 5 shots at gunsite with 230s from my Norma
the 8s haven’t been working for many but good luck, hopefully you’ll find a balance with it, they dont seem to like the speed.
10s do this, 5 shots at gunsite with 230s from my Norma
I have been running some 215s too they work also, Spark has a nice 215 load i was using
this was my Norma with 215s i believe, 1425 on the IPSC plate
this was my Norma with 215s i believe, 1425 on the IPSC plate
Respectfully, this is against the grain from what I have seen lately. The 215's and 230's were the "best" bullets available when the Norma was released, and heavier bullets in the last year are superior in bc. Seeing many running these weight bullets with N570 at 2950 fps and above. If I was a building a Win Mag or PRC maybe I would keep the weights in the 215-230 range but I see plenty of shooters using the heavies in those as well with good results.
Pretty sure the 250 A-tip overtakes the 215 or 230 Berger at longer ranges.
250s going over 2900?
That seems awfully Hot, my last 230 load was 2990 and hot as hell. my GAP Remington build could not handle the heat. too light an action on that guy, which is why I built up my AWSM to a Norma.
I guess if there are no signs, but that seems pretty stout
That seems awfully Hot, my last 230 load was 2990 and hot as hell. my GAP Remington build could not handle the heat. too light an action on that guy, which is why I built up my AWSM to a Norma.
I guess if there are no signs, but that seems pretty stout
Uknown Munitions loaded ammo. This is loaded with H1000 and I have a box of 50 loaded with N570. Haven't verified speed or pressure as I'm still waiting on the finished rifle. Hopefully I'll be testing mid-January. Honestly I would be happy with anything around 2900 with this bullet.
$119.99 – $229.99
| Quantity |
|
DESCRIPTION
| CALIBER | 300 NORMA MAGNUM |
| BULLET | 250 HORNADY A-TIP |
| BRASS | ADG |
| POWDER | HODGDON H1000 |
| PRIMER | FEDERAL 215 MATCH |
| VELOCITY | 3000 F/S |
| G1 / G7 | .878 / .444 |
| COAL | 3.700″ |
| REC. TWIST | 8 |
| QUANTITY | 20/50 |
Hi,
@nick338
Please let me know when you get to testing because I would like to compare data as in same location, same range, etc.
Ballistic wise there is just no way I see those heavies can out perform say a 210gr monolithic from Badlands Precision with the speed they are able to be pushed and spun.
I have a new LH GT arriving any day now myself for new 300NM.
Sincerely,
Theis
@nick338
Please let me know when you get to testing because I would like to compare data as in same location, same range, etc.
Ballistic wise there is just no way I see those heavies can out perform say a 210gr monolithic from Badlands Precision with the speed they are able to be pushed and spun.
I have a new LH GT arriving any day now myself for new 300NM.
Sincerely,
Theis
Will do. I have a box of Berger loaded ammo with 215's that I will be using to get the rifle on paper but that will be the last of anything that light. Never been a big fan of solids as I remember Frank testing some a few years back and not having great results and also not advising going back and forth between jacketed and solids. I haven't spent much time researching them recently but I'm sure they have advanced considerably since then.
Wouldn't I need a faster than normal twist for solids as well? I understand bullet consistency wins at ELR but I don't want to be limited to just solids.
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No way those numbers are right
reciting crap off a box is suspect at best have you shot those and gotten those numbers
Like I said my H1000 load with 230 is 2990 and hot as hell, my Remington XL action could not handle it
reciting crap off a box is suspect at best have you shot those and gotten those numbers
Like I said my H1000 load with 230 is 2990 and hot as hell, my Remington XL action could not handle it
Agreed and I told him I was skeptical when I ordered it but he insisted that N570 is the magic powder for Norma/Lapua cases so I picked up 50 rds to try.
Mine is on a BAT action.
