Does twist rate effect velocity

[Shane Lindsey]

Greetings,
I have a 270 Win with a 26" 1:8 twist Hart barrel on it.
I have loaded the Matrix 165s and getting lower velocities than I thought I would get based on what I have read others have gotten with similar setups. I am getting pressure signs lower than what I would have expected.
Have tried H4831sc only so far.
Win case
CCI 200
Matrix 165 gr VLD
Seated .016" out of lands (best accuracy)
Velocity 2640 FPS at sea level in CA

So does twist rate effect velocity? Pressure?

Any powder suggestions that may increase velocity without spiking pressure?

Shane

 

[stanley52]

Yes it certainly can affect velocity and pressure. To what extent, I cannot tell you, but I do know it does.

 

[J E Custom]

Greetings,
I have a 270 Win with a 26" 1:8 twist Hart barrel on it.
I have loaded the Matrix 165s and getting lower velocities than I thought I would get based on what I have read others have gotten with similar setups. I am getting pressure signs lower than what I would have expected.
Have tried H4831sc only so far.
Win case
CCI 200
Matrix 165 gr VLD
Seated .016" out of lands (best accuracy)
Velocity 2640 FPS at sea level in CA

So does twist rate effect velocity? Pressure?

Any powder suggestions that may increase velocity without spiking pressure?

Shane

Rotating the bullet requires energy. the faster your rifling twist rate is, theoretically the slower
velocity will be and higher the pressure.

The smooth bore will get you the fastest velocity But you will lose accuracy in small (.50 cal down)
bullets.

The difference is not much, but it is there.

The really fast barrels normally have twist rates of 1 in 14 or 1 in 15.

Simple physics

J E CUSTOM

 

[Edd]

So does twist rate effect velocity? Pressure?

Any powder suggestions that may increase velocity without spiking pressure?

According to Bryan Litz, twist rate has an insignificant on effect velocity.

For a bullet that heavy, I would use H1000.

 

[Lefty7mmstw]

Twist rate has to have some effect on pressures generated with a given charge/bullet combo; as JE said it's simple physics that it takes effort to spin the bullet.

On the other hand; my 10" twist 7stw is significantly slower than my 9" twist sendero was with the same box of ammo. I had a couple of hundred 140's loaded with rl25... The old rifle was at 3400 fps; the new rifle is just under 3300 fps. It does have a 24" bbl. compared with the old rifle's 26" bbl. though. Given the bbl. length difference I'd say another grain of powder would likely level the playing field.

 

[Edd]

Twist rate has to have some effect on pressures generated with a given charge/bullet combo; as JE said it's simple physics that it takes effort to spin the bullet.

That's the same thing Bryan said. He also said the amount of energy it takes to spin the bullet is insignificant. His data was based on a 12" twist vs an 8" twist.

 

[Shane Lindsey]

I may give some other powders a look.

I have gotten some good advice from some folks on here over the years and that is what got me to do this 270. Some of them are running numbers that are in the 2830 fps and above range (some are more but running AIs). I think this is with a little longer barrels also but not significantly longer than the 26 inches I have.

I am sure their elevation is helping a little also.

 

[amce]

There is of course a difference - basic physics. But it's negligible. Check out this preview chapter from Bryan Litz's latest book:

http://appliedballisticsllc.com/Articles/MAiLRS_preview.pdf


Cheers

 

[scottishkat]

I have always found H4831 to shoot slow in my 270. I have switched to VV N560. Started at about 50gr with 160 NPT. What is your powder charge for H4831? I had good velocity with AA4350 and the 160 partitions as well. I was getting right at 2700 from my 24" accumark and the 160 NPT with both powders. H1000 should be a great choice.

I am not familiar with the matrix bullet but I can't imagine it has a longer bearing surface than the NPT.

Good luck and shoot straight.

Bob

 

[Shane Lindsey]

I am only at 55.5 gr with H4831sc. The Matrix 165gr has a shorter bearing surface than the partition. I used that load data to start, but couldn't get as much before the pressure started.
I will also try some H1000 when I get around to it. Have quite afew pills with the 4831 right now. I am getting good vertical data at range (1/2 MOA) or better. I am pleased with the accuracy of the load and as it sits have 1698fps at 800 yds. Matrix states that is sufficient for bullet performance so I may leave it alone after all. Really wanted to try and get more velocity though.

Is the N560 temp sensitive? I live in the Ca and don't get temp changes like at thise elk elevations.

 

[budlight]

I used 7828 ssc & AA magpro with magnum rifle primers with my 270 win 29 inch barrel shooting 169.5 VLD's

I did not have H1000 or another possible choice would have been reloader 25 or even the new RL 33


I have heard that increasing twist drops velocity. But I think it also has to do with barrel type, number of grooves (Lands)

I have an AR 20 inch stainless Match 1:9 and a 20 inch chrome lined 1:7 The same ammo chronos 40 fps slower in the 1:7

 

[den]

I was thinking rl 25 also might need to drop tube it but it is supposed to work well for the 30-06 and the 280 with heavy bullets