Explain How 7 PRC Has Tighter Tolerances VS 7 MM Rem Mag, without bashing any company

[Cholla]

I keep reading and hearing how the 7 PRC was designed from the ground up with tighter SAAMI tolerances, so therefore it is easier to get better accuracy from non-custom guns and factory ammo. I assumed the tolerances would be evident on the SAAMI drawings, but with my limited knowledge, I do not see these tighter specifications. Can someone please enlighten me?

I see that the shoulder is a different angle and what is preferred these days. I see the case neck is longer. I see the throat is longer. I don't see anything else being tighter. Please explain what I am missing without bashing any company and complaining about media hype. I honestly want to know.

 

[Mikecr]

I see no tolerance difference.
Clearances are also same.
Was it suggested somewhere that the 7PRC was tighter than -the 7RM?

 

[PopNFresh]

maybe someone was taking about belted magnum headspacing?
that's a can of worms sometimes

 

[Cholla]

Yes, I have listened to podcasts and read on various websites that the tolerances on the 7 PRC are tighter so that bullet alignment with the bore is more precise and there is a smaller window of accepted chamber tolerances. As I was listening (I drive long distances) I was expecting to be able to see the differences in the SAAMI drawings. I get that the SAAMI spec for the 7 PRC twist is faster to stabilize longer bullets. The whole point of calling it PRC was because it is a precision rifle cartridge.

 

[PopNFresh]

alignment would be more of a shoulder angle and body taper issue wouldn't it?
maybe it was poorly explained.
as I don't want to repeat a poor attempt maybe a link with some ideas

Modern Cartridge Design: Why New Rifle Cartridges Are Superior to the Classics

Modern Cartridge Design has revolutionized how we build cartridges, leading to hunting and competition rounds that outperform the classics.

www.outdoorlife.com

 

[chav0_12]

I think head spacing off of the shoulder instead of the belt is an advantage by itself that would lead to "tighter tolerances" but I'm not sure there are other tolerances that are being accounted for. I like straighter bodies and sharper shoulders so the PRC speaks more to me than the Rem Mag in every way. I got rid of my last belted magnum more than a decade ago and I don't see myself going back with the new available cartridges.

 

[Cholla]

alignment would be more of a shoulder angle and body taper issue wouldn't it?
maybe it was poorly explained.
as I don't want to repeat a poor attempt maybe a link with some ideas

Modern Cartridge Design: Why New Rifle Cartridges Are Superior to the Classics

Modern Cartridge Design has revolutionized how we build cartridges, leading to hunting and competition rounds that outperform the classics.

www.outdoorlife.com

Thank you. This explains it well.

 

[MagnumManiac]

There are no tighter tolerances with SAAMI, and or, factory chambering. It is purely hype and marketing.
Shoulder angle, essentially a cone, makes ZERO difference to how concentric it sits in its collective taper, if you believe this, then you do not understand engineering principles.
Also, headspace, and how it is derived, has little to do with accuracy, and it has been noted and proven that a belt is conducive to fine accuracy where the shoulder moves to fill the chamber prior to max pressure being reached…too many believe what is said by nuff nuffs in gun rag publications that read HYPE from companies that are PAYING them to market their products.

Cheers.

 

[Justice1327]

I personally think it's because Hornady worked with specific manufacturers on the firearm side, and they kept their tolerances tighter.

 

[Opa-lopa]

I keep reading and hearing how the 7 PRC was designed from the ground up with tighter SAAMI tolerances, so therefore it is easier to get better accuracy from non-custom guns and factory ammo. I assumed the tolerances would be evident on the SAAMI drawings, but with my limited knowledge, I do not see these tighter specifications. Can someone please enlighten me?

I see that the shoulder is a different angle and what is preferred these days. I see the case neck is longer. I see the throat is longer. I don't see anything else being tighter. Please explain what I am missing without bashing any company and complaining about media hype. I honestly want to know.

View attachment 527709

View attachment 527710

I keep reading and hearing how the 7 PRC was designed from the ground up with tighter SAAMI tolerances, so therefore it is easier to get better accuracy from non-custom guns and factory ammo. I assumed the tolerances would be evident on the SAAMI drawings, but with my limited knowledge, I do not see these tighter specifications. Can someone please enlighten me?

I see that the shoulder is a different angle and what is preferred these days. I see the case neck is longer. I see the throat is longer. I don't see anything else being tighter. Please explain what I am missing without bashing any company and complaining about media hype. I honestly want to know.

View attachment 527709

View attachment 527710

It's all about the diameter control of the throat. The 7mm PRC has a cylindrical throat of .2846, while the 7mmRem mag has essentially the same diameter but a 3 deg taper. That mean the Rem throat is 0.006" larger just in front of the case mouth, allowing the bullet to tip relative to the bore centerline as it releases from the case.

 

[joelpend]

It's all about the diameter control of the throat. The 7mm PRC has a cylindrical throat of .2846, while the 7mmRem mag has essentially the same diameter but a 3 deg taper. That mean the Rem throat is 0.006" larger just in front of the case mouth, allowing the bullet to tip relative to the bore centerline as it releases from the case.

Respectfully, this is not correct. You have freebore diameter, freebore length and throat angle when talking chambers. The freebore diameter is virtually the same on both and the 3 deg throat on the RM is steeper than 1 1/2 deg on the PRC which means the bullet ogive will touch sooner. The freebore is quite a bit longer on the PRC because it was designed to shoot long heavy bullets. The beltless case is an advantage but that is not what was promoted. Marketeers are good at hyping their products especially some companies as has been noted many times on this forum.

 

[skibbyshot]

The John Snow article linked above is awesome. Anyone interested in this topic should read it.

 

[VinceMule]

It's all about the diameter control of the throat. The 7mm PRC has a cylindrical throat of .2846, while the 7mmRem mag has essentially the same diameter but a 3 deg taper. That mean the Rem throat is 0.006" larger just in front of the case mouth, allowing the bullet to tip relative to the bore centerline as it releases from the case.

Joelpend is correct. The throat dia in the above print is .2845 for the 7 Rem Mag, My JGS print is the same. Standard 7 Rem mag Chambers have a short throat .110 which has worked very well for us up to the 168g and even the 175g Nosler LRAB with tiny groups 3/8" and less being the goal. A throat length in the 7 Mag of .210 with a 1.5 Degree leade angle is a beautiful thing with the 180s. I have never seen a 180g Berger seated in a standard throat of a 7 Mag, hindered by the powder column.

The Concern has always been that when the bullet is seated past the shoulder/neck junction in the brass a doughnut that has formed may pinch the bullet creating a pressure spike resulting in flyers which would never happen in new brass. My brass firings in the 7 Rem mag are usually around 5-7 or so, and I have never seen doughnuts form in Remington brass.

It is amazing the number of people that shoot 120g-150g in the 7 Rem Mag, and I wonder if this trend will follow through with the
7 PRC as many prefer the speed. So, are the 7 PRC shooters being forced to shoot 175g-180's in factory ammo?

Rifle Ammunition - Hornady Manufacturing, Inc

Hand inspected ammunition to ensure consistency and quality throughout the process.

www.hornady.com

On Re-barrel projects, a question in my mind is if the lack of taper in the 7 PRC will leade to feed rail alterations on actions that were previously chambered in 7 Rem Mags? This same thing has happened in actions converting from 7 Mag to 28 Nosler due to the lack of taper in the case where an Ultra Mag action is better suited.

 

[73driver]

So are you claiming that factory ammo in off the shelf rifles that the PRC is no more accurate than the RemMag?