- Thread starter stevenh
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77 grain SMK is the best for that twist rate. 1/7 tends not to like lighter bullets in regards to accuracy.
I run 77gr and 75gr bullets in my 18" 1:7 twist SPR rifle. However, both of my 16" 1:7 M4 clone carbines seem to group better with 60gr, 62gr, 68gr, and 69gr bullets. One of my rifles is a standard chrome lined 1:7 twist M4 contour barrel, and it shoots the 60gr, 62gr (SS109), and the 69gr bullets with surprising accuracy. The other carbine has a stainless match grade 16" 1:7 medium contour barrel, and it will hit very consistently out to 600 yards with PPU 68gr Match ammo. It shoots the 62gr bullets quite well too. Your results may vary, as it seems rifles (much like women) can be finicky, fickle, and fierce. Grab a few boxes of the heavier bullets (60gr and up) and do some load testing.
I have had really good luck from Private Partizan's 68gr match ammo. Unfortunately, availability as with all ammunition these days can be an issue.
Good luck,
Tman
I have had really good luck from Private Partizan's 68gr match ammo. Unfortunately, availability as with all ammunition these days can be an issue.
Good luck,
Tman
I have seen nothing that would remotely suggest the 1/7 twist tends not to like lighter bullets in regards to accuracy. Also, I shoot 52 to 80 grain loadings from my match conditioned 1/7 .223 chambered AR and the surprise is I can get results with the 80's rivaling the 52's. There are reasons to shoot light bullets as there are reasons to shoot heavy ones. At distance, it's the bullets b.c. that becomes important for accuracy and a high b.c. bullet will require a fast twist to stabilize it. The bottom line is the 1/7 is a very versatile twist that does not appear to give up anything, appraised from target grouping, when shooting low b.c. bullets within their distance domain, while slower twists do give up the ability to shoot bullets made for LR. They simply won't stabilize them.
OP,
You have a rifle that is effective on the E sized target out to about 600 meters when matched with proper ammunition. Match grade loadings in the 75-77 grain arena will be nose-on at such distance; and therefore, if you can correctly counter for wind and weather effects and your basic marksmanship knowledge and skill is up to par you too should get good hits on the E sized target out to about 600 meters.
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Bingo. I only shoot from 55s to 77s in my DCM gun (20" White Oak 1/7 barrel), but it has shot lights out with everything I've fed it.
SterlingShooter's sig line says "Distinguished Rifleman #1769", so seems like he would know what he is talking about.
It was just my personal experience. Admittedly I have not shot match grade light grain bullets out of the 1/7 twist. When shooting non match 55 grain bullets in the 1/7 they group much larger than if shot out of a 1/9 twist. The reason is the imperfections of the bullet are exaggerated by the faster spin rate.
The bottom line is if you shoot near flawless bullets in the 1/7 twist barrel you probably won't see much difference in the accuracy from one weight to another. However if you shoot flawed bullets the faster twist rate will exacerbate the flaws.
Really? The sole purpose of the spin imparted on the bullet is to keep it stable. The factors that describe external ballistics to not indicate bullet imperfections are exaggerated by the faster spin rate. That is a misconception.
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Spinning a bullet faster will degrade accuracy slightly. Since that's the case, it is optimal to shoot the slowest twist you can for a given bullet.
What that means is that *all else equal*, you're better off with a 1/10 or 1/12 with a 52 grain bullet. It does not mean a 1/7 won't shoot a 52 or that it prefers heavy bullets. Heavy bullets are also less accurate when spun faster - in fact, more so than light bullets (they are more sensitive to imbalance than lighter bullets, very roughly speaking). It just happens to be that we have no choice but to spin them or they won't stabilize.
So it's a misconception that faster twists like heavy bullets. A more accurate way to put it is that no bullet likes being spun any faster than it has to be, and heavy bullets need more spinning.
Heavy bullets require faster twists even though it makes them less accurate. This is a good trade off at long range where ballistic performance is quite a bit more important than intrinsic precision. At short range benchrest matches, you'll see small stubby bullets spun at slow rates. 1/18 or 1/20 for a .30 BR is not uncommon, and they use 110ish grain bullets. But to them, intrinsic accuracy is all important - ballistics mean nothing.
All in all, this is a small effect, and is mitigated largely by using good bullets. But that's how it works.
What that means is that *all else equal*, you're better off with a 1/10 or 1/12 with a 52 grain bullet. It does not mean a 1/7 won't shoot a 52 or that it prefers heavy bullets. Heavy bullets are also less accurate when spun faster - in fact, more so than light bullets (they are more sensitive to imbalance than lighter bullets, very roughly speaking). It just happens to be that we have no choice but to spin them or they won't stabilize.
So it's a misconception that faster twists like heavy bullets. A more accurate way to put it is that no bullet likes being spun any faster than it has to be, and heavy bullets need more spinning.
Heavy bullets require faster twists even though it makes them less accurate. This is a good trade off at long range where ballistic performance is quite a bit more important than intrinsic precision. At short range benchrest matches, you'll see small stubby bullets spun at slow rates. 1/18 or 1/20 for a .30 BR is not uncommon, and they use 110ish grain bullets. But to them, intrinsic accuracy is all important - ballistics mean nothing.
All in all, this is a small effect, and is mitigated largely by using good bullets. But that's how it works.
optimum twist rate is a formula used when shooting large projectiles out of ship guns and such. it is used to make sure that the projectile lands on its nose and explodes. an over spun projectile will tent to nose up and not detonate as reliably. this is where this jargen comes from. one twist rate is not inherently more accurate than another. but not enough twist is very inaccurate. too much twist can also tear bullets apart in the air. if you want to shoot as heavey bullets out of a carbine barrel it probly better be a 1 in 7 though. i like the 77 smk i shoot it out of a 26 inch 1 in 9 barrel though 2850 fps it is flatter to 800 than my 308.
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What you just said is false. If something is physically unbalanced it will be more unstable the faster it is spun. Think of a ceiling fan that is not ballanced. You can run it on low or medium but put it on high speed and it wobbles badly.
Here are some words on the subject from the world's best barrel maker.
You've picked an article that has absolutely nothing to do with this topic. Bullets going through his barrel sideways in his scenario indicate an eroded throat, jump distortion, or bad bullets. A better way to think of a spinning bullet is a children's top or a football not a ceiling fan. It's clear you don't know much of anything about external ballistics. You have picked up gobbledygook which you have misinterpreted.
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It wasn't from an article. It was from a thread on Sniper's Hide a year ago pertaining to twist rate. You obviously didn't read what he said or couldn't comprehend it.
Here's what I comprehend, you're in over your head. It started with your first post here on a topic you have no experience with.
Here are the facts that matter: Any defective bullet will not be as accurate as one which is not defective regardless of spin. At some point, drag will slow the bullet down and it will eventually fly erratically and tumble no matter what the muzzle velocity, bullet b.c. or twist. Velocity, spin, and attitude will get any bullet to a greater distance nose-on. The twist rate must satisfy the necessary applications. If you need to shoot an M856 tracer or a 77 , a 1 in 7 twist will stabilize these, as well as any other factory loaded .223 round, while a slower twist will not stabilize the 77 or even a 62 to any meaningful distance. Now with these facts, and knowing that the 1 in 7 will shoot any weight bullet with accuracy better than what Gomer can muster, it's as moot as it is academic that a slower twist may shoot a some bullet profiles better than could a faster twist at short range. Choosing the slower twist limits distance capability. The bottom line is you get the twist needed to shoot the sort of bullet demanded by the unknown or known distance target scenario. The fast twist no doubt satisfies more field scenarios than the slow twist.
Reality check:
M16A1, 20 inch 1/12 barrel shoots M193 effectively to about 300 meters.
M4, 14.5 inch 1/7 barrel shoots M193, M855, M856, and Mk. 262. Mk. 262 is effective using BDC function to about 600 meters.
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