I have not worked extensively with the 110SMKs.. However, they are very long and it could be that a 7.5 twist is right on the ragged edge. I can't say for sure.. However, it could be a contributing factor..
Any Disadvantages to Faster Twist?
- Thread starter Phil3
- Start date
shoot4fun
Gold $$ Contributor
Your area, at least from the location you have in your profile, puts you about the same elevation as me. The big difference I would assume is your humidity and temperature range. My take on twist is that I want to be at a stability factor that doesn't degrade the BC of my bullets and allows them to be stable all the way to my target, whether that be 300 or 1,200 yards. I prefer 7.5 twist 6mm barrels for the 105 class bullets but think an 8 twist will handle virtually any 6.5 bullet out there. For 22 centerfires I shoot the heavy (75 or heavier) in at minimum 7.7 twist and in some cases prefer a full 7 twist. There is a point where you're asking some bullets to do things they aren't good at and over-spinning is not a good thing.
It was cold and very humid that day. Well cold for Mississippi. About 50 degrees. And almost 0 elevation
My first exposure to fast twist 223's was last year when I purchased a Tikka T3X (8" twist) so I'm not expert on fast twists.
However I did learn that my rifle shot 55 grain bullets better (groups) with lower powder charges than higher charges and even better with heavier bullets, i.e. 60 grain bullets.
However I did learn that my rifle shot 55 grain bullets better (groups) with lower powder charges than higher charges and even better with heavier bullets, i.e. 60 grain bullets.
This is pretty simple, The faster the twist, the greater magnification in any differences between individual bullets when trying to put them all in the exact same spot.
Not much of an issue if you’re shooting absolutely perfect,uniform bullets.
I.E. always shoot the slowest twist to stabilize the slug at the required distance.
Not much of an issue if you’re shooting absolutely perfect,uniform bullets.
I.E. always shoot the slowest twist to stabilize the slug at the required distance.
Ned Ludd
Silver $$ Contributor
Several years ago, Bryan Litz' recommendation was to use a twist rate that gave a minimum gyroscopic stability coefficient of 1.4 (or greater) in order to obtain the full intrinsic BC of a given bullet. Not that long ago, he changed that to suggest using a twist rate sufficient to achieve an Sg of 1.5 (or greater). In other words, he advocated using a slightly faster twist than had been previously recommended, even though nothing else had changed (i.e. with components). He has also provided evidence that overspinning a bullet could actually to some extent help to overcome other possible deficiencies or design flaws such as dynamic instability. So there are some instances in which spinning a bullet slightly faster than necessary can be advantageous.
I have run 40 gr .224 bullets out of a 7-twist barrel, and 155 gr .308 bullets out of an 8-twist barrel. They shoot just fine. It's easy to state that running a faster twist than necessary can amplify all sorts of potential imbalance issues that might be present in a bullet, and it's almost certainly true. Nonetheless, if you can't shoot the difference, it might as well not exist. Unless you're a BR shooter printing groups in the 0.1s, having a slightly faster than necessary twist rate is not going to hurt you at all. By the same token, having a slightly slower than optimal twist rate may not hurt you either. I would say that being within half an inch of the optimal twist rate either way is fine for most applications. For example, if the "optimal" twist for a given bullet/cartridge is 10.0, chances are pretty good that using anywhere from a 10.5- to a 9.5 twist barrel is not going to hurt you. Using a twist rate slightly too slow will theoretically result in a slight loss of BC; using a twist rate slightly too fast may not quite as accurate.
Like many things, the key here is moderation. You don't need an uber-fast twist rate relative to a bullet's length, it's not going to buy you anything. Likewise, an uber-slow twist rate will generate stability problems if it's too slow...also undesirable.
I have run 40 gr .224 bullets out of a 7-twist barrel, and 155 gr .308 bullets out of an 8-twist barrel. They shoot just fine. It's easy to state that running a faster twist than necessary can amplify all sorts of potential imbalance issues that might be present in a bullet, and it's almost certainly true. Nonetheless, if you can't shoot the difference, it might as well not exist. Unless you're a BR shooter printing groups in the 0.1s, having a slightly faster than necessary twist rate is not going to hurt you at all. By the same token, having a slightly slower than optimal twist rate may not hurt you either. I would say that being within half an inch of the optimal twist rate either way is fine for most applications. For example, if the "optimal" twist for a given bullet/cartridge is 10.0, chances are pretty good that using anywhere from a 10.5- to a 9.5 twist barrel is not going to hurt you. Using a twist rate slightly too slow will theoretically result in a slight loss of BC; using a twist rate slightly too fast may not quite as accurate.
Like many things, the key here is moderation. You don't need an uber-fast twist rate relative to a bullet's length, it's not going to buy you anything. Likewise, an uber-slow twist rate will generate stability problems if it's too slow...also undesirable.
I worked up a short range load with 80gr Berger FB in a 243win with 8" twist. Did the load development in the winter, well below freezing temp, and the bullets shot crazy amazing.
Then after the winter when the temp was above freezing, once the barrel got nice and warm about 20% of the bullets blew up.
The groups at 100 meters were 2x bigger than in the freezing winter, but all bullets made it to the 100 meter targets. But when shooting them at 200 meters I could not get 5 in a row to stick. At least 1 bullet from each 5 shot groups never made it to the 200 meter targets, and made a cracking sound.
I now use this load in the winter only, and for the warmer weather I slowed it down by 300 fps.
Then after the winter when the temp was above freezing, once the barrel got nice and warm about 20% of the bullets blew up.
The groups at 100 meters were 2x bigger than in the freezing winter, but all bullets made it to the 100 meter targets. But when shooting them at 200 meters I could not get 5 in a row to stick. At least 1 bullet from each 5 shot groups never made it to the 200 meter targets, and made a cracking sound.
I now use this load in the winter only, and for the warmer weather I slowed it down by 300 fps.
shoot4fun
Gold $$ Contributor
Two cases with same brand of bullets that have total opposite results:
A friend, now departed, wanted to go for a 1,000 yard plus prairie dog. He decided on a 22-6mm using a Brux 7T barrel. His load (I forget powder charge now) was topped off with the 80 grain Amax. We shot this combo at least 100 rounds during break-in and load development and, as he was anal, the barrel was kept spotlessly clean. With high hopes, the perfect day for a long shot on the TX Panhandle arrived and shooting began. Imagine our surprise when bullet number 37 blew up just about 20 yards downrange. You could see the puff. A few patches and he tried again but had the same result. I accounted it to a fairly large altitude change and big change in weather conditions. The rifle was put away and, to my knowledge, never fired again until a new 6.5-284 barrel was spun on the action. We will never know now as to the actual cause.
Second case, I took an AR15 SBR with suppressor to WY for a PD shoot. This rifle has a 7T 5R barrel of 14.5" so I really should have been shooting heavier bullets than the factory ammo with 40 grain varmint bullets. I found myself second guessing as the difference in ASL was over 5,000' elevation. The round count for that rifle totaled over 900 in 2 1/2 days of shooting. It was never cleaned (not even a bore snake) during the whole time. The last PD had no more clue what him it than the first and there was never any type malfunction, especially not one of those little pills blowing up until they PDH (prairie dog hide).
Point is, experts would have said the 7T was "perfect" for the 80 grain and way too fast for the fragile 40 grain varmint bullet. Just as you have to pass Obamacare to see what's in it you have to pull the trigger to see what will happen.
A friend, now departed, wanted to go for a 1,000 yard plus prairie dog. He decided on a 22-6mm using a Brux 7T barrel. His load (I forget powder charge now) was topped off with the 80 grain Amax. We shot this combo at least 100 rounds during break-in and load development and, as he was anal, the barrel was kept spotlessly clean. With high hopes, the perfect day for a long shot on the TX Panhandle arrived and shooting began. Imagine our surprise when bullet number 37 blew up just about 20 yards downrange. You could see the puff. A few patches and he tried again but had the same result. I accounted it to a fairly large altitude change and big change in weather conditions. The rifle was put away and, to my knowledge, never fired again until a new 6.5-284 barrel was spun on the action. We will never know now as to the actual cause.
Second case, I took an AR15 SBR with suppressor to WY for a PD shoot. This rifle has a 7T 5R barrel of 14.5" so I really should have been shooting heavier bullets than the factory ammo with 40 grain varmint bullets. I found myself second guessing as the difference in ASL was over 5,000' elevation. The round count for that rifle totaled over 900 in 2 1/2 days of shooting. It was never cleaned (not even a bore snake) during the whole time. The last PD had no more clue what him it than the first and there was never any type malfunction, especially not one of those little pills blowing up until they PDH (prairie dog hide).
Point is, experts would have said the 7T was "perfect" for the 80 grain and way too fast for the fragile 40 grain varmint bullet. Just as you have to pass Obamacare to see what's in it you have to pull the trigger to see what will happen.
I've heard a few posters suggest that elevation can make a difference in bullet stabilization. Is there a direct correlation (meaning higher elevation equals less stable, or vice versa)? My 1:10 .223 stabilizes the 69gr Lapua Scenar L beautifully at 2,500 feet, but that bullet weight is probably pushing the limits of a 1:10 twist. Not sure what to expect when I move to 500 feet with higher humidity.
Go to the Berger Twist Rate Caculator where one of the variables you input is the altitude/elevation where you are shooting at and you will see that it does make a difference.
http://www.bergerbullets.com/twist-rate-calculator/
A couple folks reported their 22" 7.62 NATO service rifle good barrels would not shoot M852's 168 Sierra's fast enough from 1:12 twist barrels to remain stable at 600' thru 1000 yards but ok at 6000' altitude at 1000 yds. Those with 1:10 twists had no problems in both environments. 24" barrels with either twist had no problems with M852 ammo with good barrels.
Good barrels are those with .3079" groove and less than 2500 rounds through them
Looks like bore-rider monos might tighten things up bit. However, its been said that 8-10 shots shooting monos right after cap-n-core bullets are needed to get an accurate sample...
good call on your part. I have a 6BR used only for varmint shooting (that's all I shoot really) inside 500 yds. Gunsmith said a 14 twist is the ticket, and he was correct. It shoots 58g -75g all with very good accuracy. Surprised it stabilized 75's but it does.I am glad I erred on the side of slow twists, given the explanations provided. On a 6mmBR barrel I was ordering, I saw so many advocating for the 1:8 barrel, as it could shoot everything, but Berger said my 65 and 68 grain flat based target bullets needed about 1:14 and 1:13 twist respectively. I went with 1:13. At 3,300 fps (estimating velocity will be around that), bullet rpm with an 8 twist barrel would be 297,000.If 1:13 is sufficient, that is about 183,000 rpm, a heck of a lot slower. Spinning a bullet, even a light one, up to nearly 300,000 rpm in a bit over .001 second could certainly cause some torque in the barrel.
Phil
Murray Brook
Silver $$ Contributor
According to the Berger T R Calculator an SG of 1.5 gives complete stabality. Anything under and BC is compromised. At what point above an SG of 1.5 does damage occur to accuracy. In other words would an SG of 1.8 or 1.9 be bad for accuracy. At what # does the twist rate become to fast for the bullet. TKS
Yeah I scrapped that load. Didn’t work. Now using Bart’s hammers and couldn’t be happier
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