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Question , Does a faster twist barrel ( 1-8) push bullets at a higher velocity than a 1-12 twist barrel. One rifle a 16 inch XBolt 223 the other a Rem Mod 7 20 inch barrel 223, both rifles using exact same load?
Haven't had a lot of experience with faster twist barrels so interested to see what people think.
Not faster velocity, but faster spin obviously, which provides greater stability at longer range
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No it shouldn't all other things being equal.
In theory if anything it should be slower as using more of the energy to rotate the projectile faster.
and by spinning it faster it should expand faster/more explosively......
Thanks for the replies, Beeman has picked up a 16 inch XBolt and is trying different loads to find a nice accurate load. I said to him that the 60 gr loads he was trying would be on the slow side ,maybe. Anyway the other day we took it out and run some loads through the Chrono plus to see how slow they were going, surprise, suprise, they were honking it.
The fastest 60 gr load went through at 2948 fps, very good, then we tried the normal old load of 55 gr Hornady with 25 grs BM 2 and they were cruising at 3103 and 3090 fps ( only had 2 left to try).
Now my 20 inch Rem Mod 7 shoots the same 55 gr Hornady load at about 2950- 3000 fps. Not sure if mine may be one of those slow barrels but that little XBolt is a grunty ,short , package .
The 20 inch barrel should be faster than the 16inch. Which one is the fast twist?
I was sort of expecting about 120 fps slower than my velocity but it's just about the other way round his rifle appears to be up to 150 faster than mine using the same loads. Very interesting stuff.
The 16 inch X boltQuote:
Originally Posted by Cigar
not necessarily....once all the powder has burnt,a longer barrel slows the projectile down...WHY 22lr is hard to keep subsonic with really short barrel....
definately a longer barrel will be faster with large amount of powder to burn....7mm mag etc...but a 223 only NEEDS something like 16-18" to have complete burn....
Maybe a smaller chamber in the fast twist (so more pressure, therefore higher velocity).
Probably easy enough to check by dropping a case fired in the Remmy into the X-bolt.
Lots of things could affect it.... The Rem probably has a looser chamber and or more freebore lowering preasure and hence velocities.
Greetings All,
I have not seen any evidence presented to suggest that a faster twist increases velocity. There are two .223 rifles in my cupboard, one 12" and one 8" twist. Velocities are about the same once barrel length is allowed for. The 26" barrel 12" twist gives about 80 fps more than the 570mm 8" twist barrel pretty much what you would expect. Differences due to other variables can be much larger. Case capacity, powder lot, chamber variables and many others all have an effect on velocity. Over the last few years I have been doing some test firing with some of my rifles, initially looking at powder lots in the 6.5 and more recently different powders and different projectiles in the .308. More tests on different powders and cases in the .223 and different case weights in the .308 are still in the blocks waiting to be shot. I am only using ADI powders and so far have found most but not all of the Hodgdon/ ADI data to be pretty good.
Will report more later. Regards Grandpamac.
My understanding of barrel twist rates are really only to do with the projectile stability not to do with velocity.
Not quite that assumes that all energy from burnt powder is instantly passed on to the projectile but realistically it has intertia and take time to accelerate similar to dropping a bullet from a high building. It doesn't instantly reach terminal velocity. Just because all the powder is burnt doesn't mean acceleration stops. The bullet will still accelerate until the force from the pressure of the xplosion is equal and opposite to the drag from the barrel and air. If you want to see this go run a few loads though quickload etc. Complete burn is not the same as max velocity. Ie why you will see 7mm08 and 6.5 creedmoors with 30 inch barrels etc for target.Quote:
Originally Posted by Micky Duck
Here’s article from Accurate Shooter on the topic Twist versus Velocities.
How Muzzle Velocity Changes with Different Barrel Twist Rates « Daily Bulletin
And here’s Frank Green's (co-owner Bartlein Barrels) comment that he posted on the Oz F Class forum re that article.
“Not only did we make all those barrels in the test but we chambered them as well. So same chamber reamer was used in all of them and the barrels where all made at the same time. If I recall correctly all of the barrels where made out of the same lot of material except for the left hand twist was out of a new lot. So about as identical as you can make them.
It's always been my understanding that twist might have a small impact on velocity but for the most part it really doesn't in the grand scheme of things.
Later, Frank
Bartlein Barrels”
It could lead to more pressure for the same load same as a bullet seated deeper in the same rifle should up pressure and therefor velocity but if you went and loaded both rifles the same pressure the 20 inch barrel should be faster (obviously some barrels are faster barrels but that's not due to twist rate. Personally I've never found such a things as too fast a twist but I think you can run into issues at really high speeds with light constructed bullets exploding mid air. A fast twist does give more versatility though in projectile selection.Quote:
Originally Posted by Mooseman
The principal factors affecting velocity variations with an identical load in different rifles are barrel length, bore diameter and chamber dimensions. Twist rate is not a factor but is required for stabilisation of various bullet weights. The standard .223 twist is 1-12" which is designed for the 55 grain bullet, 1-9" for 62 grain, 1-8" for 68-69 grain, 1-7" for 69-77 grain. You will find an overlap of performance in practice but those are the optimum rates for gyroscopic stability. I was getting sub 0.5 MOA performance from my 1-7" Ranger AR with 69 grain BTHP Sierras until Jacinda got it. My replacement 1-8" Tikka CTR gives 0.6 MOA with the same load - still good enough for 350 metre rabbits!
Spot on. The pressure curve keeps driving the bullet faster until it runs out of puff. Area under the pressure curve over time vs resistance. Combustion doesn't drop to zero the moment combustion finishes.Quote:
Originally Posted by Stocky
Here's a QuickLOAD analysis of a 223 loaded with a 40 gr V-Max at ADI's max recommended load. I just plucked this from ADI, it's not my pet 223 load, although its close to it.
Attachment 165090
The graph on the bottom left shows the pressure curve in red and the velocity in blue. The Chamber Pressure curve peaks after 1.28"/0.3 ms bullet travel and begins to fall but the Velocity continues to accelerate until the projectile exits the barrel.
Also of interest is the Amount Of Propellant Burnt is 91.3% indicating some powder being burnt after the projectile exits the barrel ie some wasted powder.
If running the same analysis with a 22" barrel instead of 24" the Chamber Pressure remains the same, Muzzle Velocity drops to 3435 fps, Amount Of Propellant Burnt inside barrel 90.46%, Barrel Time drops from ~0.95 ms to ~0.9 ms.
Greetings Zimmer and All,Quote:
Originally Posted by zimmer
There we have it. Twist makes no practical difference to velocity. Hard data should triumph over theory every time, especially theory not based on fact.
I saw an ad the other day for a Winchester rifle in .223. It had a 1 in 11" twist and was touted as being compatible with 55 grain projectiles. This is pure pandering to the ignorant. Both my 1 in 12" and 1 in 8" twist .223 rifles shoot the 55 grain projectiles equally as well and I expect that most will have the same experience. Perhaps the fast twist may shred some really tender projectiles but the thing that the 1 in 11" twist won't do is stabilise most of the high BC projectiles. Rant ended. Curmudgeon back in box.
Regards Grandpamac.
And some of these longer more modern projectiles are tending to show that extra twist helps with BC as shown by Byran Litz Testing of the Accubond long range projectiles.Quote:
Originally Posted by gundoc
No two 'identical' barrels produce the same velocity either, further skewing any results. Or rather it could be almost impossible to make identical barrels. I reckon this question could only be answered by a manufacturer using statistics from thousands of testfires...
Something i (if i were them) would never release. The moment it became known that there was a 50ft per second advantage having 1/7 twist on any model, the 1/8 would be chopped liver and hard to sell:D
Confusing the term "fast or slow twist" as also being directly related/connected to speed.
Yes never identical but they can get damn close. Matches guys often by multiple barrels and own there own reamer and can reuse load data from previous iterations to damn near the same results saving redoing load development. So if Bartlien does a test and limits variation even more by using a reamer sequentially limiting difference and pulling barrels from the same batch of steel and cutting them sequentially I'd say they are a pretty good authority to say that it's insignificant.Quote:
Originally Posted by T.FOYE
I definitely think we can conclude that the difference in the to rifles mentioned in the original post is not significantly impacted by the twist rates and is more likely a result of different batchs of powder, bore diameter, tighter chamber, faulty chromo or incorrect validation of speed.
Twist has nothing to do with velocity it is purely to stabilise the projectile, decide which projectile you want to shoot and the twist that will stabilise it
in a .223 up to 60gr 12" 69gr 9" 70-80 gr 8' 90gr 7". I had two 6mmBR's Barnard actions 30" True flite barrels chambered with the same reamer same load
one was 70fps slower than the other
It is the length of the projectile that determines the twist not the weight, The rotational speed of a fast twist can rip a light weight varmint bullet to pieces even in a .223.
All valid points except I wouldn't put true flite in the same repeatability league as Bartlien being buttoned vs cut and unless the barrels were made sequentially the more wear on the rifling button could partially explain any variation as could minute differences in chamber depth.Quote:
Originally Posted by shooternz
But regardless the point is moot in regards to question asked as twist rate doesn't effect velocity in any significant manner.
Does it effect wear and total life of the barrel? I know that's not the OP of the thread but i'm looking at replacing my barrel which is 1/8 with a 1/7.5 or 7 to be able to stabilise the longer projectiles
I don't think anyone could definitively say for sure. But I doubt it would be much if it didQuote:
Originally Posted by T.FOYE
There's a book by Bryan Litz that covers this (and other things) called "Modern advancements in long range shooting"
Apparently yes there is 5ft/sec in it. In both theoretical and practical testing.
I guess that it now turns into a question about which brands of projectile can handle being sent at 2800fts+ without flying apart...
