7 PRC & 140 GR bullets?

[southpa]

Typical cup and core 7mm 140s like to be seated near if not barely touching the lands, such as a 140g Nosler ballistic tip, accubond, Berger vld hunting, Sierra tipped game king. So, if you order a reamer ground with shorter freebore and order a 7mm Unithroater , you could custom throat for the heavier longer bullets.

Many of us have been using this method for decades. When the intersection of the bullet shank/boat tail, sits around .020 above the shoulder neck junction, you get the accuracy that is on par for a benchrest rifle.

The accuracy of the 140s at 3200 fps+ at 600 yards can be amazing, and they flatten deer at that distance. However, hunting in the open Plains `where a calm wind is 15 mph, you need all the B.C. you can get. I also shoot 162,168, and 175s in my 7mm's.

Southpa, hope this makes sense to you now.

The current trend is to order the fastest twist, and shoot the heaviest bullet even for short range, even for 300 and under-yard hunting.

I'm pretty sure I fully understand it. I'm pretty sure you're basically saying what I said. The 140 bergers are too short to run in a saami length 7prc. I don't understand why you'd order a short throated reamer to run berger 140s but then use a unithroater to then run heavies.
If you're going to run a short throated 7prc what's the point? Why not just chamber in a 7RM with more case capacity and a reamer that most any smith carries...

 

[VinceMule]

I don't understand why you'd order a short throated reamer to run berger 140s but then use a unithroater to then run heavies.

The heavier bullets would be in a different barrel or another gun. I run 7 Mags with std short .110 length throats, and .211 length throats for heavy bullets. The longer throat sure changes how pressure builds for the 180s.

The 7 mag and 7 PRC have practically the same case capacity, but the PRC has better ergonomics.

 

[Varmint Hunter]

I am really excited to see what my new 7stw will do this fall with the whitetails.
I am going to use the same 140g Nosler CT's that I am running in my 7RM at 3250fps. My STW is pushing them to 3535fps.

On the shoulder or behind, the 7STW is devastating on whitetails. I never used the 140g Nosler but I'm sure that it will work great at the velocities a 7STW can generate.

 

[southpa]

The heavier bullets would be in a different barrel or another gun. I run 7 Mags with std short .110 length throats, and .211 length throats for heavy bullets. The longer throat sure changes how pressure builds for the 180s.

The 7 mag and 7 PRC have practically the same case capacity, but the PRC has better ergonomics.

So what are you recommending to the OP is to buy a special short throat reamer for the PRC to run 140 bergers. Then buy/build two barrels/rifles and have one chambered in saami and the other in the reamer he has made. So he can run 2 different barrels when he wants to shoot 140s and or heavies.....

 

[Phil Rizzo]

You know what, that's a REAL good idea now that you mention it.
For a 7mm sicko like me especially.
I'm thinking Public Relations Cartridge for the 140-150's and the Sherman Mega for 180-190. Standby.

7ss stays put with 160's though.

 

[VinceMule]

Speed freeks love the 140s. Sierra 140s shoot very well jumping, but they are not high velocity bullets as they will detonate on shoulders.

I am very anal on accuracy first, this is why I stress matching the freebore to the intended bullet to be used. Most of these 7mm will shoot sub 3/8" groups, and often much less. Also, the bullet will LOVE a particular distance from the lands for best accuracy, and when you can not maintain that distance over time and wear, accuracy will degrade.

Also, a guy wanting to shoot 140s may want to consider matching the twist rate to the bullet. Years ago, I wanted to shoot the 140s at warp speed to maximize the point blank range and create tremendous internal damage on the deer. I build a 7 STW with a Pac Nor three groove 11 twist. I shot the 140g Nosler C/T bullet at 3700 fps into groups the size of a pencil eraser. The reamer used had zero freebore for this 7 STW. Big Kansas deer, near and far died in their tracks, with one exception of a 360 lb buck shot at 580 yards, he took three steps and fell over. That big buck had a tremendous rack, but he was so old, he did not have brow tines.

Bullets will only take so much rotational torque before the base of the bullet will deform during obturation, which creates flyers... another can of worms that leads you to slow "most accurate" loads.

The goal is to shoot 3/8" and smaller three-shot groups that repeat time after time. When you achieve these tiny groups, a 600 yard shot will be easy, in as far as the gun's capability.

 

[VinceMule]

Speed freeks, 7 STW and 28 Nosler, very short freebore reamer, consider the 120g Nosler ballistic tip(very tough bullet) and the 120g Barnes TTSX with R#22 and IMR 7828 with a wide accuracy node running from 3750-3900 fps on a 26", 9Twist barrel. These two bullets were the most accurate bullets I have ever fired in my 7 STW's with sub 1" groups being the norm at 300 yards with high powered glass, 8-32 Black Diamond is what I ran. Deer folded up in their tracks.

 

[southpa]

Speed freeks love the 140s. Sierra 140s shoot very well jumping, but they are not high velocity bullets as they will detonate on shoulders.

I am very anal on accuracy first, this is why I stress matching the freebore to the intended bullet to be used. Most of these 7mm will shoot sub 3/8" groups, and often much less. Also, the bullet will LOVE a particular distance from the lands for best accuracy, and when you can not maintain that distance over time and wear, accuracy will degrade.

Also, a guy wanting to shoot 140s may want to consider matching the twist rate to the bullet. Years ago, I wanted to shoot the 140s at warp speed to maximize the point blank range and create tremendous internal damage on the deer. I build a 7 STW with a Pac Nor three groove 11 twist. I shot the 140g Nosler C/T bullet at 3700 fps into groups the size of a pencil eraser. The reamer used had zero freebore for this 7 STW. Big Kansas deer, near and far died in their tracks, with one exception of a 360 lb buck shot at 580 yards, he took three steps and fell over. That big buck had a tremendous rack, but he was so old, he did not have brow tines.

Bullets will only take so much rotational torque before the base of the bullet will deform during obturation, which creates flyers... another can of worms that leads you to slow "most accurate" loads.

The goal is to shoot 3/8" and smaller three-shot groups that repeat time after time. When you achieve these tiny groups, a 600 yard shot will be easy, in as far as the gun's capability.

So what are you recommending to the OP is to buy a special short throat reamer for the PRC to run 140 bergers. Then buy/build two barrels/rifles and have one chambered in saami and the other in the reamer he has made. So he can run 2 different barrels when he wants to shoot 140s and or heavies.....

 

[VinceMule]

Yes. Set the reamer design up for 140s, and order a unithroater for use with that same reamer for 180s. This is all in the pursuit of accuracy in the extreme. Paramount to use different twist rates between the 140 and 180, but I have had very, very good accuracy with 9 twists with 140s, not quite as fast as a three groove 11 twist. The 11 twists did not spike pressures like the 9 twist did, in zero freebore reamers. The 9 twists had a very different bore dia also than the 11 twist, Pac Nor vs Hart.

I have had tremendous speed/accuracy out of the Pac Nor three groove in 257 Weatherby and 7 stw. Pac Nor uses a gunsmith that really knows what he is doing. Pac Nor probably has 2000 reamers in stock, second only to Douglas. Land Height in the Pac Nors is very different than other barrel makers and do not exhibit the pressure spike that other barrels do when the bullets obturate in the lands.

The trend is to use the fastest twist available, longest throat, and heaviest bullet, which shooting in the wind at a distance demands.

Impact velocity is one heck of a thing, know your ballistics, and be realistic about the distance you shoot.

 

[southpa]

Yes. Set the reamer design up for 140s, and order a unithroater for use with that same reamer for 180s. This is all in the pursuit of accuracy in the extreme. Paramount to use different twist rates between the 140 and 180, but I have had very, very good accuracy with 9 twists with 140s, not quite as fast as a three groove 11 twist. The 11 twists did not spike pressures like the 9 twist did, in zero freebore reamers. The 9 twists had a very different bore dia also than the 11 twist, Pac Nor vs Hart.

I have had tremendous speed/accuracy out of the Pac Nor three groove in 257 Weatherby and 7 stw. Pac Nor uses a gunsmith that really knows what he is doing. Pac Nor probably has 2000 reamers in stock, second only to Douglas. Land Height in the Pac Nors is very different than other barrel makers and do not exhibit the pressure spike that other barrels do when the bullets obturate in the lands.

The trend is to use the fastest twist available, longest throat, and heaviest bullet, which shooting in the wind at a distance demands.

Impact velocity is one heck of a thing, know your ballistics, and be realistic about the distance you shoot.

Interesting. Seems like it's defeating the purpose of the 7prc. But hey, you do you. I certainly don't see the purpose of doing this but thats the beauty of building these rifles. You build what you want. If you want to backstep the chamber/throat design of the 7prc to shoot small bullets more power to ya. But logic tells me that if the 7prc and 7RM are "almost identical" capacities than building a custom short throat 7prc reamer is pointless. Like I said before, just run a saami 7rm chamber and basically outrun the 7prc with any bullet, large or small.

I don't mean any distaste towards you at all Vince. I appreciate the info you've offered. We're basically finding out that you more than likely cannot run 140 bergers in a standard 7prc. That's kind of what I'm looking for as the OP asked about them

 

[Varmint Hunter]

Who has run 140s in a SAMMI chamber and how much bullet shank remained in contact with the case neck? The 162s work perfectly so I'm assuming that a 140 wouldn't be all that bad.

 

[Phil Rizzo]

Geeeez I'm going to be looking for a 10tw

 

[VinceMule]

No worries Southpa, we sometimes do the non logical things for no darn good reason other than for the speed, and the belief that Speed creates a tremendous temporary wound cavity inside the deer, Hee Hee!

We shoot the 140g berger vld hunting in 7/08s, and the bullet kills quickly, with the bullet completely fragging the insides of the deer with a shotgun type of effect. My niece shot a really big buck in Missouri a couple of years ago with a Rem 700 in 7/08 with the 140g Berger vld hunting. She had no range finder and just held over for the buck at 420 yards, right at dusk. She hit low in the brisket, just under the heart, and bullet fragments went through the heart. They found him the next morning after he ran 75 yards or so.

Whether you can get these VLD bullets to shoot accurately jumping a country mile is sometimes a guess, and we have got lucky on some....it is trial and error as you very well know. I just would not want those particular Bergers ran at 3250-3300 fps., opting for a 140g Accubond or even a ballistic tip. I have had some decent luck with VLD bullets jumping that have more bearing surface, but I like to tip my odds with a reamer that matches the intended bullet.

It is interesting to run different ballistic charts to see where the various trade offs in B.C. actually start to pay off. Impact velocity is of paramount importance.

The 7 STW or 28 Noslers with the 120s is much flatter shooting than the 220 Swift, and is as flat shooting as the 257 Weatherby 10T, zero freebore shooting the 100g at 3850.

 

[cape cove]

A great bullet that I use in my 7mm Weatherby mag is the 145 Barnes LRX. I keep it at 3345 ft/sec, great accuracy and performance.