Reply With QuoteNice animal Bleeb! Is that a 7x7? My eyes lie to me sometimes.
I think David addressed the Tenon size. But here is some data on the bolt head.Originally Posted by Chris_in_Idaho
The 7mm PRC is a long action cartridge with a .532 rim. The WSM's and the 9/16" Bolt Head are for short actions and have the .532" diameter rim. The 9/16" bolt head requires a firing pin that is 1/8" longer than the standard firing pin in a short action with the standard 7/16" Bolt head. The standard BH length for a long action is 1/2" and would need to find an additional .062" somewhere. All LA calibers in my recollection where made with this length Bolthead including the .532 Magnums.
The 338 Lapua (.588 rim diameter) and the ultra mags(.534 rim diameter)may have a different BH length. I can't recall.
Hope this helps lead you to the conclusion you are after.
Is there any particular reason having the 9/16 Bolt head is important?
The Dunning-Kruger effect is alive and well.
Nice animal Bleeb! Is that a 7x7? My eyes lie to me sometimes.
The Dunning-Kruger effect is alive and well.
The 7 PRC and the 300 WSM both have a much larger internal case diameter than a belted magnum, which I believe could contribute to higher bolt thrust. Larger internal surface area for the pressure to push against the bolt head. I have wondered if that's why Savage gave the WSMs extra thick locking lugs, and if so, if they gave them to the 7prc as well.
The WSM’s are considerably larger, at .555” as the parent case is the 404 Jeffereys, vs the 7mm PRC @ 532” with the 375 Ruger serving as the foundation. So being we know it’s Small Shank, I doubt it’s using anything else beefed up.
Interesting that they're using the small shank. All 375 Rugers and 300 PRC's that I've seen have been large shanks (same case diameter as the 7mm PRC as they're all derived from the 375 Ruger case). I have a 116 in 375 Ruger and a 110 in 300 PRC and they are both large shank. Also, they only have the 1/2" locking lugs, not the 9/16" like the WSM's and RUM's. My 375 Ruger appears to be a regular 116 action with no special mods to it. My 110 300 PRC on the other hand, appears to be built on the same action as the 338 Lapuas, as it has the enclosed receiver top and 8-40 screw holes.
Well they aren’t exactly the same loading. Look at the picture. And bullet weight makes a huge impact. Remember physics: it takes an equal amount of force pushing on the Lugs as it does to propel a heavier projectile forward. The 7mmPRC has a 175gr projectile as heaviest. The 300PRC has a 212gr projectile as its heaviest. That is quite a difference.
Although they came from the same Parent Case, there is no contest on capacity. The 300PRC dwarfs the 7mm!
I'm well aware of the differences in the case lengths, as well as the bullets they use. I was merely referring to the case diameter. Heck, the 6.5 PRC's I've seen have been large shanks as well. All I said was given what I've seen, it's interesting that the 7mm's are small shanks.Well they aren’t exactly the same loading. Look at the picture. And bullet weight makes a huge impact. Remember physics: it takes an equal amount of force pushing on the Lugs as it does to propel a heavier projectile forward. The 7mmPRC has a 175gr projectile as heaviest. The 300PRC has a 212gr projectile as its heaviest. That is quite a difference.
Although they came from the same Parent Case, there is no contest on capacity. The 300PRC dwarfs the 7mm!
Yes it did. As dead as those taken with my 340 Weatherby. Thanks.
And 7mm RemMag
Not exactly. The force imparted on the bullet and other ejected particles and gasses is going to be roughly equal to the force imparted on the rifle as recoil, but that's not the same as the force on the locking lugs.
The pressure of the expanding gasses in the case is applied equally against all of the internal surface area of the case. The larger the internal diameter of the case, the harder the case head presses against the bolt face. However that doesn't mean more net recoil because the larger case has more surface area pressing forward (shoulder, body taper) as well. Recoil is going to be affected by the difference between the net forward surface area and the net rear surface area, and this difference is the bore diameter.
Imagine you have a long skinny case and a short fat case with the same bore diameter, capacity, pressure, etc. The fat case will put far more force against the bolt face, and also against the shoulder in the opposite direction. The skinny case will put less force against the bolt face and the shoulder. Their net force (recoil) will be the same because the bore diameter is the same, but the fat case is trying harder to split the chamber front from rear.
So, in my way of thinking, a fatter case needs a stronger recoil lug.
Hence my curiosity about the 7 PRC.
I get what you are trying to express, however it really doesn’t need to be overthought. Heavy projectile at higher speeds is going to cause much more backward thrust on the lugs than a lighter projectile or at lower speeds. Have you ever fired say a 30-06 with a 150gr vs a 220gr? The difference in recoil is quite noticeable. And the bolt head/Action lugs, Action Screws & Recoil lug are all being exposed to very same force difference. Right? So, yes… exactly.
What you are talking about is only evident in a larger diameter case with a higher powder charge. Given if there two cases which are the same length but one is 1.5x wider, & they both have equal powder charge, the larger diameter case will exhibit lower pressure. Thus lower projectile velocity & subsequently less energy applied to the lugs & all all other parts.
I assumed the surface area of the case exhausted some of the the thrust and the smaller area of the case head reduced it as well. PSI means surface area effects the amount of force applied.
The Dunning-Kruger effect is alive and well.
Force applied to the bolt face, and then the lugs, is related to recoil, but, not exactly. The force on the bolt is due only to the chamber pressure applied over the area of the bolt face. So, for the same chamber pressure a larger dia base means more force on the bolt.
There is also the rate at which the force is applied, but, that gets a bit complicated for these discussions. As long as you are in the elastic range of the material it only affects fatigue failure.
Recoil is determined by the acceleration of the mass of powder and bullet down the barrel. Again, related to chamber pressure, but, not a simple relationship.
You can have a max chamber pressure with a small bullet traveling fast and a lower chamber pressure with a heavier bullet traveling not so fast. The heavier bullet can have a higher recoil than the smaller, faster bullet, even at a lower chamber pressure.
Note: last portion of this was wrong so I deleted it.
Yes it is a 7x7. Pretty crazy......
This is what I was thinking but you said it more eloquently than I could have. Although the PRC’s are different lengths, and have different powder charges, and bullet sizes, they’re all the same case diameter and operate at the same MAP of 65k psi. So the bolt thrust should be the same with all 3 of them.
Well, yes & no. It doesn’t quite work nice & neat like that. Cartridge PSI is a factor, but not the only part. A more powerful cartridge is forcing the bolt back with more power. The recoil we feel is the same thing the bolt & lugs are taking the force of. If the three were the same, the recoil would be same between all three. And it certainly is not!
Edit: I understand there is all kinds of math & who’s it’s & what’s it involved…. But it remains a fact that a more powerful cartridge cause more stress on the firearm. Including the Lugs. The Pressure, weight of projectile & diameter of the case/bolt face are all intertwined in this. But I was just trying to keep it simple. Which it is.
Oh yeah, and as for the math: Bolt Thrust equals the cartridge pressure X the Area of the Case Head. However, as has been said, it’s not so simple as that.
The complex part is it happens over time. Integrating the area under the pressure curve gives the total, but, recoil feels different if that force is applied over a shorter or longer period of time.
As I said, my 375 Ruger and 300 PRC both have 1/2” locking lugs, so apparently the savage engineers thought that was plenty for that size cartridge. And the 375 has a lot more recoil than any of the PRC’s, I have the eyebrow scar to prove it lol. I still find it strange that every other PRC (including the 6.5) and 375 Ruger I’ve seen in a Savage had the large shank, yet the 7mm is a small shank. Just weird some of the things Savage does.
So then, if more recoil contributes to more force on the bolt lugs, does a muzzle brake that reduces felt recoil, also reduce the force applied to the bolt lugs?
Not in gross terms. When looking at the rifle as a 'system' there is a balance of forces from the bullet and ejected gasses. Since some of those gasses go to the rear the net linear force to the rear is reduced.
When looking at the chamber/barrel interior as a 'system' it still sees the same pressure curve.
BUT..the gasses ejected at the muzzle may present more 'resistance' to the bullet and gas path that could raise the chamber pressure slightly (kinda like the bullet resistance function in the internal ballistics programs). I've not looked at the analysis for that. I recall a section of the Army Internal Ballistics documentation that dealt with muzzle brakes. May have to look that up.
This was an interesting discussion. But I fear it’s become a runaway tangent. LOL! Good talk guys.
Makes sense. Thanks.
Posting Permissions
Bookmarks