Range Report Different twist rates affect velocity?

[LSOSGT1109]

Will different twist rates affect velocity? In a Remington 12 twist I'm shooting a 155 Scenar over 43.5 grains of RL-15 at an average of 2650 fps. If I shoot that same load out of a 10 twist Savage how can I expect the faster twist to affect the velocity?

 

[JC Steel]

Re: Different twist rates affect velocity?

might be slower velocity with a faster twist barrel. I have also seen a little more velocity with less grooves.

 

[Rob01]

Re: Different twist rates affect velocity?

The twist won't effect it but there are many other things that might. I wouldn't expect two different barrels to shoot the same even if they were built identically. One way to find out, go out and shoot it.

 

[SingleShot85]

Re: Different twist rates affect velocity?

It is my experience that you will get a much higher velocity with the savage over the remy, but its not because of the twist rate. Just something about savage barrels.

 

[Jeff in TX]

Re: Different twist rates affect velocity?

Twist rates will have a very small affect on velocity. Not enough that you’re not going to see dramatic changes from one twist rate to the next, nor is this really something that you can calculate.

Assuming you’re shooting the same bullet & load, the two primary factors for velocity change in different barrels are inside bore diameter and barrel length. A tighter bore diameter will produce higher pressure and thus higher velocities. A longer barrel allows for more powder to burn thus increasing velocity.

My GAP .308 has a 22” rock barrel with an 11.27” 5R twist and a .298 bore diameter. My velocity is 50 fps faster than my buddy’s 26” Rem factory .308 barrel.

As a side note I lost approx 225 fps when I had my Rock barrel cut back from 26” to 22”.

Hope it helps.

 

[LSOSGT1109]

Re: Different twist rates affect velocity?

Thanks guys! I took the Savage out the other day and intended to Chrono the load but the freakin battery in my Chrono was dead! I haven't been able to get back out to the range yet. I was bored at work last night and was wondering what kind of velocity differences I could expect and I knew some of the fine folks on here could give me an idea!

 

[Greg Langelius *]

Re: Different twist rates affect velocity?

My crystal ball is cloudy. Always.

How a round comes out the muzzle is governed by a lot of things, many of which are randomly variable.

For the most part, there isn't even any way to collect the actual numbers associated with many of those variables. We can get a handle on the main ones and our calcs can make some ballpark predictions, but beyond that, your guess is as good as mine.

Believing we can calculate such outcomes with precision is simian conceit at its best.

Greg

 

[Fred_C_Dobbs]

Re: Different twist rates affect velocity?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KSP446</div><div class="ubbcode-body">Thanks guys! I took the Savage out the other day and intended to Chrono the load but the freakin battery in my Chrono was dead!...</div></div>
The more crap you carry to the range, the more you need a possibles box. One of the things I carry in mine is a spare 9v battery. In fact, I remove the battery when I break down the chrono and store it in the possibles box, along with the fresh battery. And chrono batteries have been known to run down in the middle of a critical session.

I also carry binder clips and keep a small piece of an old shower curtain in the bottom of my range bag. Eventually, you'll encounter a situation when the sun shines straight down on the chrono's sensors and prevents them detecting the shadow of the passing bullet. You can hang the small piece of shower curtain off your diffuser's rods with the binder clips and make an improvised sunshade.

^^^ Binder Clips ^^^

 

[Greg Langelius *]

Re: Different twist rates affect velocity?

I have used paper targets and masking tape as an improvised sun shade. I try not to turn them into a sail when the wind picks up.

These days, I just leave the crono home. I can get enough info from my dope values to input them into the Pejsa Spreadsheet, and get ballpark velocity info.

Once you get to know your rifles and loads, most of this stuff becomes pretty intuitive. For example, most of my rifles, zeroed at 100yd, will reach 1000yd with between 25 and 35MOA of elevation. The .260 does it with right around 28-30MOA. A Pejsa Spreadsheet will print me out a stock chart with elevations and wind values at regular increments all the way out to subsonic distance.

Greg