7mm PRC Build barrel?

[GAHunterJim]

I'm assembling parts for my next DIY pre-fit build in 7mm PRC and I can't decide on barrel length, the action will be Defiance Ruckus and the barrel a Proof Carbon. I really think I should get a 22" barrel as I intend to use a suppressor but I can't get away from the idea of a 24" barrel, 22" just seems too short for a 7mm "Magnum". If it weren't for the suppressor, I'd go 24" for sure. I'm not entirely worried about the velocity loss but I don't want to give up too much but this is a hunting rifle so it has to be handy.

 

[Sevens]

Mine is 20". A 24" barrel seems way long after having a 20" barrel.

 

[GAHunterJim]

I have a 20" on my 308 with a Harvester EVO suppressor at 6" and it's just about perfect. I just completed a 6.5 CM with a 24" and I just submitted paperwork for another EVO, I've tried it with the suppressor from the 308 and it's a bit long but ok. The suppressor is rated to 300 WM mag capacity/burn rate and the 7mm PRC is about 90% of that, just don't want to push my luck. The can should make up for some of the lost barrel length. I know the right answer is 22" but I can't help my fondness for longer barrels.

 

[wind gypsy]

The suppressor is rated to 300 WM mag capacity/burn rate and the 7mm PRC is about 90% of that, just don't want to push my luck.

Always wondered how they figure these out. TBACs cartridge max lengths don't always make sense from a case size to bore area ratio standpoint. For example, they say 26 nosler can go 18" but 300 PRC needs 20". The 26 nosler is a bigger case with a smaller bore and a close enough SAAMI max pressure, yet you can go shorter with it?

7 PRC : 300 wm case capacity ratio is almost identical to 0.284 : 0.308 bore area.

 

[GAHunterJim]

I would agree, that does not make much sense. You would think a 308 bore would accommodate a shorter barrel than a similar capacity 284.

 

[Alex Genereux]

If I built a 7prc I would go 20"

 

[5811]

I watched this video in another thread and it inspired me to go 20"

 

[sjvcon]

Always a trade off. I am going to build one with a 24", but a lot of people say that the shorter barrels don't give away that much and are so much easier to carry. Hard to know. I guess when you have carried a 26 with a brake forever, anything shorter seems short ... which might be a good thing.

 

[Alex Genereux]

I should say the reason I would go 20” is because I am now 100% shooting with a suppressor. I have an ultra 7 may get an ultra 5 in the future. I don’t even own a gun that isn’t threaded so I can put the thunder beast break on it.

 

[Wapiti1]

Always wondered how they figure these out. TBACs cartridge max lengths don't always make sense from a case size to bore area ratio standpoint. For example, they say 26 nosler can go 18" but 300 PRC needs 20". The 26 nosler is a bigger case with a smaller bore and a close enough SAAMI max pressure, yet you can go shorter with it?

7 PRC : 300 wm case capacity ratio is almost identical to 0.284 : 0.308 bore area.

It's a pressure verse bore relationship. Pressure is per square inch, larger bore means more square inches that pressure acts on. The same concept is used for sizing hydraulic cylinders. For a given pressure, a larger cylinder has a larger area the pressure acts on and can push harder after you do the math to convert to pounds force.

As and example with rough numbers: At 60ksi, the .264 exerts 3240 pounds of force. At 60 ksi, the .308 exerts 4440 pounds of force. The .308 bore can push 1200 pounds harder. It doesn't matter how long it pushes due to case volume. It only matters if that push exceeds the yield strength of the can at any point in the pressure curve.
Now, back to the OP's post. I don't want to derail the topic.

If it were me, I would go 20" if the can will handle it. The can itself negates some barrel length loss velocity wise since it still allows the expanding gases to act on the bullet. i.e. you don't lose the same velocity as just cutting the barrel. At 20", you'll be at a rough 26" barrel length which is manageable for me. At 22, you get out to a 28" plus barrel which is long and more and more unbalanced.

Jeremy

 

[Team4LongGun]

20-22"

 

[wind gypsy]

It's a pressure verse bore relationship. Pressure is per square inch, larger bore means more square inches that pressure acts on. The same concept is used for sizing hydraulic cylinders. For a given pressure, a larger cylinder has a larger area the pressure acts on and can push harder after you do the math to convert to pounds force.

As and example with rough numbers: At 60ksi, the .264 exerts 3240 pounds of force. At 60 ksi, the .308 exerts 4440 pounds of force. The .308 bore can push 1200 pounds harder. It doesn't matter how long it pushes due to case volume. It only matters if that push exceeds the yield strength of the can at any point in the pressure curve.
Now, back to the OP's post. I don't want to derail the topic.

If it were me, I would go 20" if the can will handle it. The can itself negates some barrel length loss velocity wise since it still allows the expanding gases to act on the bullet. i.e. you don't lose the same velocity as just cutting the barrel. At 20", you'll be at a rough 26" barrel length which is manageable for me. At 22, you get out to a 28" plus barrel which is long and more and more unbalanced.

Jeremy

Thanks Jeremy, that makes a lot of sense.

 

[TxLite]

I think 20” is probably the sweet spot. I have an 18” that is very handy with a suppressor but I think 20” would be better for a more complete powder burn.

 

[762 ULTRAMAGA]

I'm assembling parts for my next DIY pre-fit build in 7mm PRC and I can't decide on barrel length, the action will be Defiance Ruckus and the barrel a Proof Carbon. I really think I should get a 22" barrel as I intend to use a suppressor but I can't get away from the idea of a 24" barrel, 22" just seems too short for a 7mm "Magnum". If it weren't for the suppressor, I'd go 24" for sure. I'm not entirely worried about the velocity loss but I don't want to give up too much but this is a hunting rifle so it has to be handy.

I spent one season hunting suppressed with a 24" 30 Nos, that's all it took to realize the downside of long barrels with cans on the end.
I shoot and hunt long range almost exclusively, and my longest barrel now is 19"

 

[GAHunterJim]

I spent one season hunting suppressed with a 24" 30 Nos, that's all it took to realize the downside of long barrels with cans on the end.
I shoot and hunt long range almost exclusively, and my longest barrel now is 19"

You must have quality cans, can't imagine how they hold together but then again, I'm new to suppressed shooting.

 

[762 ULTRAMAGA]

You must have quality cans, can't imagine how they hold together but then again, I'm new to suppressed shooting.

Yeah I only buy cans rated up to 300 RUM without barrel length restrictions.

 

[Kolt45]

Mine is 20". A 24" barrel seems way long after having a 20" barrel.

What velocity are you getting with the 20? I've got a brux 20in 7 prc in the works. Curious what I'll be seeing

 

[todd458]

Disregard box. Scope is vx-6 velocity is 2877

 

[GAHunterJim]

2877 with 162 ELD-X

 

[sjvcon]

My kid is building one right now ... he's been carrying a 26" for so long he is staying with that (even though I told him to go 22"). We'll see what he gets for velocity and I'll post it. I am interested how much different it will be. What is normal? About 50-75fps per inch?