.223 Rem, Rifling Twist Rate, and Velocity

[clowdis]

I shoot long range competition and am trying to find the "better mousetrap" for a long range .223 rifle. The standard twist for most people trying this is 7" with 85-90 grain bullets. Last year I used a 6.5 twist and the 95 grain Sierra with good accuracy, but the 85 to 90 grain bullets would shed jackets occasionally making them unusable in that barrel even though the accuracy and speed were both acceptable. So this year I decided to try something different. I got a 7.5 twist barrel thinking that maybe I could get good accuracy at maybe a higher speed if I got the same bullet rpm's, about 290,000 rpm. As it turned out I got neither. I got accuracy at a lower velocity and when I tried to push it over 2850 fps I got too much pressure. I could get 2930ish with the 6.5 twist barrel with good accuracy. This all seems to be bassackwards to me. The slower twist barrel should have shot better at a higher speed but the fast twist barrel shoots better at the higher speed! Any ideas?

 

[Liven The Dream]

The Guy's in Central Oregon are shooting Palma Rifles in 1-7 Brux Barrel and Hornady 88 gr.with a long throat.
They picked those 88's up at 11 cents back a ways .
Putting up some nice scores.

 

[jelenko]

For accuracy in the 1/2 MOA range, I haven't noticed better accuracy per se with higher velocities. I.e., I wouldn't expect a slower twist barrel to shoot bullets more accurately at higher velocities.

Again, for groups in the 1/2 MOA range, I've found the 'node' to be near the same velocity in barrels of different twists but same length and chamber.

 

[Forum Boss]

With the same chambering/caliber we have seen different barrels have max velocity difference of up to 125 FPS.

Point is, you could get a different 1:7"-twist or 1:7.5"-twist barrel that would be FASTER than your 1:6.5" barrel, not slower. It just depends on the barrel. Additionally, some barrels will speed up as they wear in...

 

[Laurie]

Twist rate has a tiny effect on potential MVs. Bryan Litz's Applied Ballistics outfit nailed that myth a long time ago. Imparting rotational motion to the bullet requires a minute percentage of the powder charge's energy compared to moving it from rest to 2,800 fps plus velocity over 30-inches of movement and engraving it in the rifling, so a change of an inch in pitch rate on its own might change MVs by single figures. As @Forum Boss says, internal barrel dimensions variations have far more to do with available MVs within usable pressures.

I rebarreled a Savage 12 LRPV to 223 with a 7.5-inch pitch Bartlein many years ago when I knew no better, only a 26-inch barrel Palma profile, as a knockabout range rifle. It shot the now discontinued 90gn Berger LRBT very well indeed at modest MVs at shorter distances, mainly 300 yards. I never shot it at 600 yards or longer, but I'm pretty sure it would have disappointed. In theory, it shouldn't have shot well at all at any distance - Berger's stability calculator gives it a mere 1.27 Sg under my range conditions.

 

[Laurie]

Additionally, some barrels will speed up as they wear in...

This is a factor that seems to have come out of the relative blue in only the last few years and affects some makes of cut-rifled barrels markedly, increasing pressures too in some cases. I know many experienced shooters who refuse to believe in it, but recently reran some 223 test loads after several hundred rounds down the barrel.

Benchmark 30-inch 7-twist
Lapua brass / old PMC SRM
Sierra 77gn MK seated out longer than SAAMI to suit a chamber with ~150 thou' FB
MVs measured on Labradar.

H. VarGet top test load of 25gn with c. 90 rounds through the barrel: 2,935 fps
H. VarGet as before with several hundred rounds down barrel: 3,000 fps

H4895 top test load 24.4gn with c. 120 rounds through the barrel: 2,975 fps
H4895 as before with several hundred rounds down the barrel: 3,015 fps

Unfortunately, the VarGet powder lot was different for the second run, so some of the increase may be due to that.

The H4895 was the same lot in both sessions, so only the barrel round-count had changed. Ambient range conditions were close enough between sessions to be discounted.

 

[Ned Ludd]

I shoot long range competition and am trying to find the "better mousetrap" for a long range .223 rifle. The standard twist for most people trying this is 7" with 85-90 grain bullets. Last year I used a 6.5 twist and the 95 grain Sierra with good accuracy, but the 85 to 90 grain bullets would shed jackets occasionally making them unusable in that barrel even though the accuracy and speed were both acceptable. So this year I decided to try something different. I got a 7.5 twist barrel thinking that maybe I could get good accuracy at maybe a higher speed if I got the same bullet rpm's, about 290,000 rpm. As it turned out I got neither. I got accuracy at a lower velocity and when I tried to push it over 2850 fps I got too much pressure. I could get 2930ish with the 6.5 twist barrel with good accuracy. This all seems to be bassackwards to me. The slower twist barrel should have shot better at a higher speed but the fast twist barrel shoots better at the higher speed! Any ideas?

If it helps any, you are not alone. There have been quite a number of folks in the last few years that have tried to set up a .223 Rem rifle with the intention of using it with "heavies" in F-TR matches. What many have found is that if you're not dealing with bullet jacket failure, it's poor brass life. If it's not poor brass life, it might be poor precision, or any one of a number of other issues that preclude successful use of the setup for its intended purpose.

Here are a few things I've learned over the years from my own experiments and those of others about how to get a .223 Rem to shoot with heavy (88-95 gr) bullets. First and foremost is dealing with the jacket failure issue. In an F-TR match, even one bullet failing to make it to the target means you will likely not end up on the podium. Bullet jacket failures are generally caused by excessive friction. The heat from friction can actually be sufficient to heat the surface of the lead core underneath the jacket and cause molten or vaporized lead to spew out of any crack or pinhole in the jacket it can find, leading to what are known as "comet tails" on the target (https://forum.accurateshooter.com/threads/comet-tails.3972620/).

As friction is the primary cause of this phenomena, it is easy to understand how long barrel length (i.e. 28" to 30"+) can exacerbate the issue. Excessive twist rates can also promote this issue (i.e. RPM values over 300K). What was not obvious, to me at least, is that the "tightness" of the bore plays a critical role in this process. To make a long story short, shooters running heavies in the .223 Rem have found that by using a 0.219"/0.224" bore and groove configuration instead of the tighter 0.218"/0.224" bore/groove configuration makes some of the other "undesirable" features in a barrel prone to causing jacket failures go away, such as using excessive twist rates. FWIW - Bartlein makes 0.219"/0.224 barrels. As it turns out, going to the 0.219" bore will allow the use of twist rates as fast as 6.5-twist, without fear of the jacket failure issues associated with 0.218" bore barrels. Also, some types of rifling, such as 5R, may be a little easier on bullet jackets, but the real key to mitigating jacket failures is using a 0.219" bore barrel.

A second major consideration in getting a .223 Rem to work with heavies is high pressure and poor brass life. The kind of velocities we would like to achieve with 88-95 gr bullets from a 28" to 30" barrel will sometimes result in operating pressures well in excess of the 55K psi SAAMI max. For example, I used H4895 under Berger 90 VLDs for years to achieve velocity in the 2840-2850 fps range, which is a very good precision node for a 30" barrel. Long story short, 3 to 4 firings and Lapua brass is done when run at predicted pressures (QuickLoad) of slightly over 57K psi. On some pieces, the primer pockets will enlarge to the point of being useless after only one or two firings.

There are various methods to deal with this issue. One is simply to accept the poor brass life. However, with the current scarcity of reloading components such as Lapua brass, that is not always a viable plan. Switching to a different powder such as Varget will typically net you about 25 fps less velocity in a tuned load than H4895, but with the added benefit of lower pressure and potentially better brass life. There are certainly other powders that are worth investigation as far as lowering pressure. However, it is not so easy to get around the physics of velocity and pressure. Another approach would be to use a brand of brass that is thicker/stronger in the case-head/webbing region. Brands of .223 Rem brass such as Lake City and Starline seem to be better capable of withstanding high pressure than Lapua. But that advantage doesn't come without a cost. More specifically, if you choose to go with a different brand of brass that may have slightly greater structural integrity, be prepared to spend a great deal more time uniforming the flash-holes, and sorting cases for uniform case/neck wall thickness. Even with the extra effort, other brands of brass have not reliably provided the precision I am accustomed to getting from Lapua brass.

The bottom line is that we're really asking a LOT of the small .223 Rem cartridge when attempting to push heavies at high velocities out of long barrels. Using a 0.219" bore barrel is a good starting point, preferably with 5R rifling and a twist rate that is just barely sufficient to achieve a gyroscopic stability coefficient (Sg) of very close to 1.5. That usually means no faster than about 6.7-twist, which is sufficient to generate the Sg necessary to achieve the full BC of the bullet in many regions across the country (i.e. altitudes), without going too far. AFAIK, a 6.7-twist is sufficient to fully stabilize the longest (heaviest) .224" lead core bullet currently available, i.e. the 95 SMK, at most elevations/temperatures above 1000 ft/65 degrees or so. Those shooting on the beach in winter may still be giving up a bit of the intrinsic bullet BC, but it should still work just fine. A final note is that some bullets simply have tougher jackets than others. I have never [yet] caused a jacket failure using a Sierra 90 or 95 gr bullet, even in barrels that have routinely caused jacket failures with bullets from other manufacturers.

Finally arriving at the OPs questions, going with a 7.5-twist barrel is really not going to be a good option. You cannot typically push the heavies fast enough to reliably overcome the decrease in BC caused by such a large deficiency in Sg. At that point, you would be better off using a lighter (shorter) bullet with a lower BC, but one that you could fully realize with the slower 7.5-twist barrel. Giving up too much BC with a lower twist rate is not the answer. As to why you had the results you had with the slower twist and faster twist barrels, I'm going to agree with others that have commented above that you may simply be experiencing barrel-to-barrel differences. It could be something as simple as non-uniform bore diameter between the two barrels, or something else, such as how the chambers were cut, etc. Much as we would like to, it is not always possible to know why certain behaviors are observed from certain barrels, at least, without more extensive barrel analysis that the average shooter may not have the equipment to carry out. Rather than trying to understand why those barrels did not work, I would suggest that you may have better luck choosing a specific barrel configuration that has the best chance of generating the results you would like to see. Were I in need of any more .224" barrels at this point in time, they would be Bartlein 5R, 0.219"/0.224", 6.7-twist barrels at a 30" finish length. Yes, those barrels would represent a custom order, and take a long time if you ordered them directly from Bartlein. However, you could probably get one a little faster by ordering through a reputable Bartlein vendor such as Bugholes (aka Southern Precision). I would then take whatever those barrels gave me in terms of a final tuned load. In other words, I would not be pushing the developed load any harder than necessary in terms of pressure/velocity. Frankly, the gains in terms of reduced wind deflection to be had from increasing bullet velocity by less than about 50-75 fps, or by increasing the twist rate by 0.25 or so are too small to reliably provide a noticeable increase in performance.

 

[Laurie]

If it helps any, you are not alone. There have been quite a number of folks in the last few years that have tried to set up a .223 Rem rifle with the intention of using it with "heavies" in F-TR matches. What many have found is that if you're not dealing with bullet jacket failure, it's poor brass life. If it's not poor brass life, it might be poor precision, or any one of a number of other issues that preclude successful use of the setup for its intended purpose.

Yup, I don't know why we bother. Actually, I wouldn't today if I were to re-enter F-TR competition seriously, but fun shooting in club matches is a different matter.

 

[clowdis]

Thanks to those that have posted above, all good information. Again, it isn't that the barrel won't shoot, I'm getting great accuracy with the ELDM and N140 at 2840fps. It's just that I was hoping for the same accuracy at a higher velocity, but I've been around long enough to know that you don't always get what expect. At 580 rounds I don't think it's going to speed up much. As a shooter and wind coach on the USNRT I am not sure that the .223 will ever be equal to or better than the .308 with the 155 bullet at 1,000 yards even though a couple of shooters are doing well with it. I did see the Sierra Cup lost at Atterbury last month when a shooter switched from his .308 to his .223 halfway through because of not enough .308 ammo. But a .223 with cheaper bullets and less powder is a fun consideration for local and state matches and I do believe that at the 600 yd. line the .223 may have a bit of an advantage for sling shooters if it's tuned right. So I think I'll just do as suggested, take my good accuracy at 2840fps and be happy with it. Again, thanks for all the advice.

 

[jelenko]

If it helps any, you are not alone. There have been quite a number of folks in the last few years that have tried to set up a .223 Rem rifle with the intention of using it with "heavies" in F-TR matches. What many have found is that if you're not dealing with bullet jacket failure, it's poor brass life. If it's not poor brass life, it might be poor precision, or any one of a number of other issues that preclude successful use of the setup for its intended purpose.

Here are a few things I've learned over the years from my own experiments and those of others about how to get a .223 Rem to shoot with heavy (88-95 gr) bullets. First and foremost is dealing with the jacket failure issue. In an F-TR match, even one bullet failing to make it to the target means you will likely not end up on the podium. Bullet jacket failures are generally caused by excessive friction. The heat from friction can actually be sufficient to heat the surface of the lead core underneath the jacket and cause molten or vaporized lead to spew out of any crack or pinhole in the jacket it can find, leading to what are known as "comet tails" on the target (https://forum.accurateshooter.com/threads/comet-tails.3972620/).

As friction is the primary cause of this phenomena, it is easy to understand how long barrel length (i.e. 28" to 30"+) can exacerbate the issue. Excessive twist rates can also promote this issue (i.e. RPM values over 300K). What was not obvious, to me at least, is that the "tightness" of the bore plays a critical role in this process. To make a long story short, shooters running heavies in the .223 Rem have found that by using a 0.219"/0.224" bore and groove configuration instead of the tighter 0.218"/0.224" bore/groove configuration makes some of the other "undesirable" features in a barrel prone to causing jacket failures go away, such as using excessive twist rates. FWIW - Bartlein makes 0.219"/0.224 barrels. As it turns out, going to the 0.219" bore will allow the use of twist rates as fast as 6.5-twist, without fear of the jacket failure issues associated with 0.218" bore barrels. Also, some types of rifling, such as 5R, may be a little easier on bullet jackets, but the real key to mitigating jacket failures is using a 0.219" bore barrel.

A second major consideration in getting a .223 Rem to work with heavies is high pressure and poor brass life. The kind of velocities we would like to achieve with 88-95 gr bullets from a 28" to 30" barrel will sometimes result in operating pressures well in excess of the 55K psi SAAMI max. For example, I used H4895 under Berger 90 VLDs for years to achieve velocity in the 2840-2850 fps range, which is a very good precision node for a 30" barrel. Long story short, 3 to 4 firings and Lapua brass is done when run at predicted pressures (QuickLoad) of slightly over 57K psi. On some pieces, the primer pockets will enlarge to the point of being useless after only one or two firings.

There are various methods to deal with this issue. One is simply to accept the poor brass life. However, with the current scarcity of reloading components such as Lapua brass, that is not always a viable plan. Switching to a different powder such as Varget will typically net you about 25 fps less velocity in a tuned load than H4895, but with the added benefit of lower pressure and potentially better brass life. There are certainly other powders that are worth investigation as far as lowering pressure. However, it is not so easy to get around the physics of velocity and pressure. Another approach would be to use a brand of brass that is thicker/stronger in the case-head/webbing region. Brands of .223 Rem brass such as Lake City and Starline seem to be better capable of withstanding high pressure than Lapua. But that advantage doesn't come without a cost. More specifically, if you choose to go with a different brand of brass that may have slightly greater structural integrity, be prepared to spend a great deal more time uniforming the flash-holes, and sorting cases for uniform case/neck wall thickness. Even with the extra effort, other brands of brass have not reliably provided the precision I am accustomed to getting from Lapua brass.

The bottom line is that we're really asking a LOT of the small .223 Rem cartridge when attempting to push heavies at high velocities out of long barrels. Using a 0.219" bore barrel is a good starting point, preferably with 5R rifling and a twist rate that is just barely sufficient to achieve a gyroscopic stability coefficient (Sg) of very close to 1.5. That usually means no faster than about 6.7-twist, which is sufficient to generate the Sg necessary to achieve the full BC of the bullet in many regions across the country (i.e. altitudes), without going too far. AFAIK, a 6.7-twist is sufficient to fully stabilize the longest (heaviest) .224" lead core bullet currently available, i.e. the 95 SMK, at most elevations/temperatures above 1000 ft/65 degrees or so. Those shooting on the beach in winter may still be giving up a bit of the intrinsic bullet BC, but it should still work just fine. A final note is that some bullets simply have tougher jackets than others. I have never [yet] caused a jacket failure using a Sierra 90 or 95 gr bullet, even in barrels that have routinely caused jacket failures with bullets from other manufacturers.

Finally arriving at the OPs questions, going with a 7.5-twist barrel is really not going to be a good option. You cannot typically push the heavies fast enough to reliably overcome the decrease in BC caused by such a large deficiency in Sg. At that point, you would be better off using a lighter (shorter) bullet with a lower BC, but one that you could fully realize with the slower 7.5-twist barrel. Giving up too much BC with a lower twist rate is not the answer. As to why you had the results you had with the slower twist and faster twist barrels, I'm going to agree with others that have commented above that you may simply be experiencing barrel-to-barrel differences. It could be something as simple as non-uniform bore diameter between the two barrels, or something else, such as how the chambers were cut, etc. Much as we would like to, it is not always possible to know why certain behaviors are observed from certain barrels, at least, without more extensive barrel analysis that the average shooter may not have the equipment to carry out. Rather than trying to understand why those barrels did not work, I would suggest that you may have better luck choosing a specific barrel configuration that has the best chance of generating the results you would like to see. Were I in need of any more .224" barrels at this point in time, they would be Bartlein 5R, 0.219"/0.224", 6.7-twist barrels at a 30" finish length. Yes, those barrels would represent a custom order, and take a long time if you ordered them directly from Bartlein. However, you could probably get one a little faster by ordering through a reputable Bartlein vendor such as Bugholes (aka Southern Precision). I would then take whatever those barrels gave me in terms of a final tuned load. In other words, I would not be pushing the developed load any harder than necessary in terms of pressure/velocity. Frankly, the gains in terms of reduced wind deflection to be had from increasing bullet velocity by less than about 50-75 fps, or by increasing the twist rate by 0.25 or so are too small to reliably provide a noticeable increase in performance.

 

[Ray123]

I just purchased a 6 twist, for experimental purposes. Not necessarily long range, but mag fed 95s are possible in AR 15, already accomplished in a 7 twist but too slow twist for the velocity. But also light bullets for purposeful fragmentation possibilities.

 

[gme]

So the .223 Palma gun is a tough nut to crack, having built a number of them here's my findings/solutions so far. 1:7 twist .218 bore 30" has been the standard and has worked well. Recently I started experimenting with 6.8 twist cut rifled barrels made for us by Benchmark, the bore is a bit looser, about .2185, they are showing good promise and I'd like to see more of them in use. I had been using a reamer based on Bob Gills design and it's worked well with the 80ELDM and the B90, I recently designed a reamer with some differences, basically a shallower lead angle (.75 degree vs 1.5 degree) and a slightly shorter freebore (because of the shallow lead angle) right away we noted a drop in pressure, it seems to work very well with several different bullets (B85.5, B90 and S90). Velocities that seems to work best are slower than most people are running, some where around 2800-2850 is where theses things want to shoot, but on paper those speeds are as good or better than a .308/155 in the wind. All that said, while the .223 has lots going for it, I still think the .308/155 is the easy button. Lots more to learn

 

[Brians356]

@Ned Ludd et al,

I used to shoot a lot of moly bullets, and still do some. Wouldn't moly somewhat mitigate the friction heat problem dicussed here? I know our moly detractors are many, but the immutable laws of physics cut both ways.
-

 

[clowdis]

I tried moly coating some bullets and it didn't help with the jackets blowing up. I was told by a Hornady tech that the ELDM was designed for a max rpm of 290,000. I was spinning them at 319,000 rpm in my 6.5 twist barrel so it was just a case of me exceeding the design limits of the bullet. That was one of the thoughts behind me trying the 7.5 twist barrel, to keep the same speed and accuracy but at a lower rpm.

 

[watercam]

Try backing off your velocity a tad. Much easier on the bullets and 2780 fps has worked for me with Sierra 90s, Hornady 88s and JLK 90s. All jumped 0.040" - 0.045".
Have had no issues reaching 1K when I do my part.

 

[David Milisock]

I tried moly coating some bullets and it didn't help with the jackets blowing up. I was told by a Hornady tech that the ELDM was designed for a max rpm of 290,000. I was spinning them at 319,000 rpm in my 6.5 twist barrel so it was just a case of me exceeding the design limits of the bullet. That was one of the thoughts behind me trying the 7.5 twist barrel, to keep the same speed and accuracy but at a lower rpm.

A rotational velocity if 290,000 RPM is 4,833 RPS (rotations per second), a 7.5 twist is 1.6 rotations per foot. 3,000 FPS in a 7.5 twist will produce 4,800 RPS.

An 8 twist will produce 4,800 RPS at 3,200 FPS.

I don't know what rotation you need to stabilize but here's the math.

 

[Brians356]

I tried moly coating some bullets and it didn't help with the jackets blowing up. I was told by a Hornady tech that the ELDM was designed for a max rpm of 290,000. I was spinning them at 319,000 rpm in my 6.5 twist barrel so it was just a case of me exceeding the design limits of the bullet. That was one of the thoughts behind me trying the 7.5 twist barrel, to keep the same speed and accuracy but at a lower rpm.

So that wasn't friction/heat melting the core. I wonder how often that actually happens.
-

 

[clowdis]

A rotational velocity if 290,000 RPM is 4,833 RPS (rotations per second), a 7.5 twist is 1.6 rotations per foot. 3,000 FPS in a 7.5 twist will produce 4,800 RPS.

An 8 twist will produce 4,800 RPS at 3,200 FPS.

I don't know what rotation you need to stabilize but here's the math.

Or 12/twist X Velocity X 60=RPM

 

[jelenko]

Just to clarify RPM = (12/twist rate) X Velocity X 60. Without the parentheses it could be read as dividing 12 by twist, velocity and 60.

 

[wbm]

trying to find the "better mousetrap"

6MM