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I know the AR556 has a 1/8 barrel twist rate and that will help stabilize larger weight bullets, but to what extent. I was reading an article about a 77 grain bullet that recommended a barrel with a 1/7 twist, so it got me wondering what bullet weights are ideally suited for the 1/8 twist the Ruger has.
 

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"The Real Deal"
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I know the AR556 has a 1/8 barrel twist rate and that will help stabilize larger weight bullets, but to what extent. I was reading an article about a 77 grain bullet that recommended a barrel with a 1/7 twist, so it got me wondering what bullet weights are ideally suited for the 1/8 twist the Ruger has.
Most of the 1n8 16" barrels I use normally like the 69, 75 or 77 grain in my reloads. The 55 and 62 only produced 2 moa or 3 in some cases. The other produced under 1moa. Their is exceptions to this rule, but thats the research I have personally fielded.
 

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I shoot 62gr green tips along with 69 and 75 grain OTM. 62gr is about as low as I want to go with my 18" 1:8 223 wylde barrel, but if someone gave me a can of 55gr for free, I'd shoot it. Why not.

62gr is good enough to make gallon containers filled with water explode violently at 200yds. It makes me smile. I have not tried the 69 grain yet but 75gr is very accurate. My shooting is not good enough to really say how much better, but I do notice considerably better groups with the 75gr
 

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A good buddy has an 18" 1/8 SS AR-15, and I shot a one hole group using Australian .223 at 100 yards, the grain weight was 69 grain if I remember right. It was factory. Further he had some other 69 grain of different brands that would not compete with that Australian .223.
 

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I know the AR556 has a 1/8 barrel twist rate and that will help stabilize larger weight bullets, but to what extent. I was reading an article about a 77 grain bullet that recommended a barrel with a 1/7 twist, so it got me wondering what bullet weights are ideally suited for the 1/8 twist the Ruger has.
The bigger issue in stabilization is the bullet length - that's why you can't get a consistent answer by bullet weight, since a boat-tail bullet will be longer for a given weight than a flat-base bullet.

Also, it depends a lot on what number you use to call a bullet "stabilized"; a bullet can be just barely stabilized (used to be common for target rifles) but that means that under certain conditions, the bullet won't be stabilized by that twist. It used to be considered a problem to "over-stabilize" a bullet, but modern bullets are uniform enough (usually!) to be accurate when spun "too fast".

The best way to find out is to load up a small number of rounds with that bullet and fire them at a targets 100 and 200 yards away. Poor stabilization will show up as a significantly greater spread (in MOA) at 200 yard than at 100 yards.


Jim
 

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I have an MPR with about 500 rounds through it. I have yet to find a good 55gr. bullet that will shoot around the 1" mark. Am I asking too much from this rifle? People I shoot with own Colts with a 1 in 7 twist and they don't seem to have the accuracy issues I have with the 55 grainers.
 

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My .223/5.56 Gunsite Scout and .223 American both have 1:8 twists and both handle 55 gr Sierra soft point boat tails very well.
 

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I would take those charts with a large grain of salt. A barrel with a 1:8 twist rate is quite versatile and should be able to shoot just about anything except perhaps very lightly jacketed and low mass varmint rounds, and tracer rounds. Basically anything from 55 grain (or a bit lighter) up to rounds with projectiles too long to fit into an AR magazine.

As to what grain weight projectile will be most accurate in any barrel, I think this must be determined by trial and error. I know one owner of an AR with a 16" 1:7 twist barrel who claims that his carbine shoots 55 grain projectiles more accurately than heavier ones, although this is probably an exception.

Another consideration is the range at which you plan to shoot. Some long projectiles might be adequately stabilized by a barrel of a given twist rate at short to medium ranges, but lose accuracy at long ranges.
 

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I would take those charts with a large grain of salt. A barrel with a 1:8 twist rate is quite versatile and should be able to shoot just about anything except perhaps very lightly jacketed and low mass varmint rounds, and tracer rounds. Basically anything from 55 grain (or a bit lighter) up to rounds with projectiles too long to fit into an AR magazine.

As to what grain weight projectile will be most accurate in any barrel, I think this must be determined by trial and error. I know one owner of an AR with a 16" 1:7 twist barrel who claims that his carbine shoots 55 grain projectiles more accurately than heavier ones, although this is probably an exception.

Another consideration is the range at which you plan to shoot. Some long projectiles might be adequately stabilized by a barrel of a given twist rate at short to medium ranges, but lose accuracy at long ranges.
Very solid reply, and I totally agree with, and what I have personally seen, and I have had alot of trigger time on the ar rifles, as well as reloaded thousands of rounds for them.

Two entriely the same rifles may like different rounds. I have seen it. Their is no one all be all, many variables have to be considered. Just to add to the discussion barrel length and velocity of the round also play Into the equation. I had a 24" dpms barreled 1n9 twist. It did not like 55 grainers. I perferred the 75 bthp, most likely due to added velocity for the longer barrel. It was frustrating since I wanted to shoot 55's in it. I have a 1n9 10.5 that only likes 69 to 77 for 1" groups. I have many 20" barreled a2's that are 1n9 that love the 55 grainer in the 3000 fps range. I do have a mini 14 target 1n9 that loves the 40 grain vmax at 3600 or faster. It all depends on testing with what your shooting. Some rounds and speeds and bullet types just don't like some rifles, factory or custom.

So I do not believe the practice of well I have a 1n9 so this is the round I need, or I have a 1n7 and this is what I need. Their is more science to it than that. Its better to get several different factory rounds and test them under the same circumstances, then you will know. You can do this, then experiment with powders, speeds to get the desired result if you reload. Thats the best advice.
 

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pblanc, Tacky:
I agree with both of you: every carbine is different. The chart was basically a "rule of thumb" as a starting point. Even .223 FMJBT rounds from different manufacturers will provide differing results.

My two Mini-14s are 1:10 and 1:9 (1:10 has an 18" barrel, 1:9 has a 16" barrel). I prefer 55gr M193 (or PMC Bronze .223 55gr) for both, for my purposes: no need for me to single out specific ammo for a specific Mini. Then again, I don't hunt or shoot paper (just plink coffee creamer jars out to about 75 yards, usually unsupported or with a bi-pod or rest in the prone position). Pretty close to 100% hits at that range from either Mini - even from a rather impatient Mr. Magoo shooter (me). Perhaps I'm suffering from the bigotry of low expectations, but that is good enough for a man-sized target at 300 yards, should the unthinkable ever happen.

Without getting too technical, it isn't really the weight of the bullet but the length that is important. But since almost all ammo is listed by weight rather than bullet length, weight is a handy reference we use. Generally speaking, the heavier the weight, the longer the bullet...The length of the barrel also has a vote.
 

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It used to be considered a problem to "over-stabilize" a bullet, but modern bullets are uniform enough (usually!) to be accurate when spun "too fast".
That's pretty much the correct explanation. Modern bullets are indeed far more uniform and concentric than in the past and high spin rates are tolerated very well.
 

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pblanc, Tacky:
I agree with both of you: every carbine is different. The chart was basically a "rule of thumb" as a starting point. Even .223 FMJBT rounds from different manufacturers will provide differing results.

My two Mini-14s are 1:10 and 1:9 (1:10 has an 18" barrel, 1:9 has a 16" barrel). I prefer 55gr M193 (or PMC Bronze .223 55gr) for both, for my purposes: no need for me to single out specific ammo for a specific Mini. Then again, I don't hunt or shoot paper (just plink coffee creamer jars out to about 75 yards, usually unsupported or with a bi-pod or rest in the prone position). Pretty close to 100% hits at that range from either Mini - even from a rather impatient Mr. Magoo shooter (me). Perhaps I'm suffering from the bigotry of low expectations, but that is good enough for a man-sized target at 300 yards, should the unthinkable ever happen.

Without getting too technical, it isn't really the weight of the bullet but the length that is important. But since almost all ammo is listed by weight rather than bullet length, weight is a handy reference we use. Generally speaking, the heavier the weight, the longer the bullet...The length of the barrel also has a vote.
RJF!

Don't think I was bashing the chart you posted, I wasn't in any regard, all information is knowledge, and helps some understand things. I also agree about the length and weight principle, just didn't want to get too technical. Its funny how much science is needed to determine whats the best for what you have, and desire to do with it. I am always amazed at how much difference powders make, bullet length, weight, design, heck even muzzle device, barrel material, and many other variables like weather and humidity. I still get those yathzee moments when something unexpected happens positive or negative in some cases.

My most recent was with my barrett 50bmg. I was shooting m33 ball ammo and not getting any good groups. I then tried several different bullets in reloads the barnes tsx, tax x in 647 grains with us869 ball powder, better but not grreat. Then the 750 amax with us 869 still same results. Swapped to h50bmg powder and the 750 amax and 6 shots under 1.75" at 200 yards. Yathzee. So it took alot of testing and development, but the trip was worth the destination.

Had a similiar occurrence with the 25-45 and a 117 grain round nose bullet. No data available so started testing with powders i used on hand for 223 rem. H4895 worked great for me with a 75 grain 223 rem reload, submoa. So i used it to develop my 117 grain 25-45 round. Worked it up by .5 grain increments, found the sweet spot at 19.5, 21.5 and 23 grains. All, that time was checking for stress cracks on the brass, popped primers, etc. Did the same with 338 federal umtil I found the best combination. Here is my 50 bmg first the factory ammo, then my reload.
 

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Tacky, that is very impressive!

And, no offense taken from your previous post, nor from pblanc's. That chart is understandably a generalization/simplification of a very complex equation with multiple variables, but good as a start point - particularly for non-reloaders like myself.
 

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I love playing with loads until you find the right combination. I know that not everyone reloads and they are left with factory shooting fodder. I reload using Nolser, Sierra and Hornady bullets and several different powders. Most of my rifles are a 1:9 twist with a couple of exceptions so I load with the 1:9 in mind. The chase is as much fun as the shooting itself. At least in my humble opinion.

kwg
 

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Tacky, that is very impressive!

And, no offense taken from your previous post, nor from pblanc's. That chart is understandably a generalization/simplification of a very complex equation with multiple variables, but good as a start point - particularly for non-reloaders like myself.
:thumbsup:

Yes I was really surprised with the 50. Its a tough round to load for, maybe 6 bullets and only 2 powders available for it, so im just glad I found the combination with the limited amount of components available.

I love playing with loads until you find the right combination. I know that not everyone reloads and they are left with factory shooting fodder. I reload using Nolser, Sierra and Hornady bullets and several different powders. Most of my rifles are a 1:9 twist with a couple of exceptions so I load with the 1:9 in mind. The chase is as much fun as the shooting itself. At least in my humble opinion.

kwg
It can be frustrating though when you cannot find the right combination. But it is a great adventure, and love when a plan comes togather.;)
 
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