7mm PRC

[07Guardian]

On 6/15/2023 at 1:56 PM, azcouesandelk said:

Picked up a Christensen Ridgeline FFT a few months ago. Shooting factory ammo (Hornaday Match 180 ELD-M) and have been very pleased with it.  Through the chrono I’m getting 2860 fps and have been getting 1/2 MOA 5 shot groups at 100 and 200. Have only shot at rocks at longer distances so far but hitting what I’m aiming at out to 700. 

Little late on seeing this thread.  I put a 24" proof barrel on a Tikka action and I'm getting slightly less speed than this with Hornady 180 match ammo.  2848 avg on the Labrador.   About 30 fps more from precision hunter 175s.  This is after 130 rounds.  A FAR cry from the 2975 and 3000fps Hornady claims they got from a 24" test barrel!   I just got some ADG brass with hopes of better performance with hand loads.  Anyone on the fence on the caliber expecting 3000fps or more might want to wait till more real world #s are proven.  I really love the new rifle ...... just love it more when I'm not looking at the chrono 😀

[MMACFIVE]

On 6/16/2023 at 5:54 PM, yotebuster said:

Should be a law that 22” barrels need to go on short or medium actions.  I’m getting 2900 out of 195’s with a 22” 7mm Sherman Max.  Just don’t see how a long action cartridge with a lighter bullet is doing 50fps less. 

Its not clear how an action length affects velocity?

I believe the 7 SM has very slightly less case capacity then the 7 PRC, but very close. The differences could simple be that any particular chambering will have variances from rifle to rifle. 

If I were betting, I'd bet its because he is shooting factory and you are shooting reloads above 65K psi. 

 

[452b264]

In my experience that is normal for almost all factory ammo, its 75 to 150 fps slower then claimed. This is one reason I started reloading a long time ago.

[PRDATR]

9 minutes ago, 452b264 said:

In my experience that is normal for almost all factory ammo, its 75 to 150 fps slower then claimed. This is one reason I started reloading a long time ago.

I've run a lot of factory and handloads through my Ohler 35P and velocities were never far off taking into adjustments for barrel length. In my experience, reloaders (and women) always expect "more".

[yotebuster]

8 hours ago, MMACFIVE said:

It’s not clear how an action length affects velocity?

Shorter action can allow longer barrel length with same OAL of rifle.  

[452b264]

4 hours ago, PRDATR said:

I've run a lot of factory and handloads through my Ohler 35P and velocities were never far off taking into adjustments for barrel length. In my experience, reloaders (and women) always expect "more".

Did you post that before or after that quart of S 7?

 

[cannonball]

Im not a reloader. But I do have a 7 PRC on the way...

 

Given an equivalent barrel length, jump to land measurement, and pressure... how much affect does the cartridge length affect anything if at all assuming full powder burn out of both (7 saum/7prc)? Does 64k behind the same projectile result in pretty much the same velocity regardless of the distance from the primer to the base of the bullet?

[yotebuster]

9 hours ago, cannonball said:

Im not a reloader. But I do have a 7 PRC on the way...

 

Given an equivalent barrel length, jump to land measurement, and pressure... how much affect does the cartridge length affect anything if at all assuming full powder burn out of both (7 saum/7prc)? Does 64k behind the same projectile result in pretty much the same velocity regardless of the distance from the primer to the base of the bullet?

The difference is actually in the barrel length.  The downfall to a long barrel is OAL of the rifle.  Shorter action = longer barrel.  Shorter actions are generally stiffer as well.   But yes you are correct apples to apples if they both have the same length barrel and all things are same they should be similar.  

[MMACFIVE]

On 8/21/2023 at 7:19 PM, yotebuster said:

Shorter action can allow longer barrel length with same OAL of rifle.  

Gotcha…that’s why you used a 22” as your barrel datum…

[MMACFIVE]

On 8/21/2023 at 8:45 PM, cannonball said:

Im not a reloader. But I do have a 7 PRC on the way...

 

Given an equivalent barrel length, jump to land measurement, and pressure... how much affect does the cartridge length affect anything if at all assuming full powder burn out of both (7 saum/7prc)? Does 64k behind the same projectile result in pretty much the same velocity regardless of the distance from the primer to the base of the bullet?

 Cartridge length may not have an affect in velocity but case capacity does. In your example the PRC has about 76 gr of usable case capacity with a 185 gr bullet vs about 63 gr for the SAUM with the same 185 gr bullet. 
 

Velocity follows capacity if loaded to the same psi. The additional 20% of case volume for the PRC will give it approximately 5% more velocity than the SAUM ( nearly 150 fps) if loaded to the same psi with the same barrel length.  
 

Action length has about zero to do with it.  In other words if I take a barrel off of a gun with a short action and screw it onto a long action I will get the exact same velocity. 
 

As an example the short fat 28 Nosler has about the same case capacity as the long skinny 7mm STW and they have about the same velocities.  
 

In the same cartridge the velocity will change as you seat the bullet deeper.