Is a 1 in 7 twist too fast for a 7mm prc

[TacosGigante]

Thinking about spinning up a 7mm prc barrel for long range target shooting in the 22-26 inch range. Will at least start by using factory ammo in the 170-180 grain range. PVA is out of 1 in 8 barrels currently and I am wondering is a 1 in 7 would be too fast. According to the berger calculator it is good to go, but some other calculators say it will be over-stabalized. Of course, I don't think Bryan Litz believes in over-stabalization, so who am I to question it?

That said, what do you all think?

 

[7mmShooter]

The 7 PRC won’t have enough velocity to overspin a 170gr+ projectile. You’ll be fine

 

[JR1200W3]

Stability is one end of the spectrum. RPMs is the other.

How many RPMs will it be going? How many RPMs before bullets start blowing up? The formula to calculate RPMs is:

MV(12÷ twist rate)60=RPMs

2900(12÷7)60=298K RPMs

Borderline. Especially if you're thinking of 180ELDMs or 190 ATIPs

Bullet weight doesn't factor into the formula except for speed.

 

[lash]

It’s totally overkill imo. Why do you want such a fast twist? I’m curious.

 

[TacosGigante]

It’s totally overkill imo. Why do you want such a fast twist? I’m curious.

Only availability. I’m agnostic on twist rate so long as it works.

 

[waveslayer]

Shoot some heavies

 

[TacosGigante]

Stability is one end of the spectrum. RPMs is the other.

How many RPMs will it be going? How many RPMs before bullets start blowing up? The formula to calculate RPMs is:

MV(12÷ twist rate)60=RPMs

2900(12÷7)60=298K RPMs

Borderline. Especially if you're thinking of 180ELDMs or 190 ATIPs

Bullet weight doesn't factor into the formula except for speed.

Thanks. This is very helpful and 1 in 7 is really close to the line.

 

[JR1200W3]

Thanks. This is very helpful and 1 in 7 is really close to the line.

Conventional wisdom is 290K as an upper limit

 

[surgeon260]

There are other downsides to over twisting, like adding unnecessary torque to the rifle and making it subjectively more difficult to shoot.

 

[lennyo3034]

I have a 1-8 and have blown up 180 ELDms.

 

[caberslash]

Specs are there for a reason.

Even a 1:9 will stabilise 180 ELDM's

 

[TacosGigante]

Ok, you all convinced me not to fly too close to the sun. 1 in 8 it is.

 

[TacosGigante]

To put an end to the story, turns out PVA had some 1-8 Carbon barrels, so I placed an order for a 26" barrel. Looking forward to shooting it!

 

[Top O' Texas]

7 will be fine for every mono, but as stated before it's about rpm's.

 

[sambo3006]

7 will be fine for every mono, but as stated before it's about rpm's.

Yep. That is the reason I changed my upcoming .264 Win mag build from a 1 in 7" twist to a 1 in 7.5" twist barrel (Bartlein). I want to shoot some high BC monos which require fast twist, but I also want to shoot the 140 gr ELDM. 3100 fps should put me just under 300,000 RPM.

 

[secondofangle2]

I would never make a compromise building an expensive rifle because of an availability issue

Seven is too fast. It can be harder to get it to shoot good that’s why benchrest shooters never use fast twists. It can be a benefit on the far end past a mile for stability, but you’re probably not using it there. And yes, the torque can make it harder to shoot, and jacketed bullets may come apart and any internal center of mass variability will make your groups open up