7mm PRC Pressure Signs?

[35WhelenAI]

Curious what IMR7828(SCC) on the "a bit quicker side" and Retumbo on the "a bit slower" side show for % burn in an 18" bbl.

 

[TxLite]

Curious what IMR7828(SCC) on the "a bit quicker side" and Retumbo on the "a bit slower" side show for % burn in an 18" bbl.

So I plugged it in a minute ago and it spit out the following based on my actual seating depth along with tweaks to the 7 Blaser Mag. Some of the data doesn’t jive, which is probably user error on my part as well as a side effect of finagling the 7 Blaser case since 7mm PRC is not on GRT yet. For instance, it lists 69gr H1000 as 105.3% case fill which I know to be untrue. So basically this is probably all useless but I find it interesting.

H1000 -

• 95% burn at 69gr and 64k psi at 105.3% case fill. Estimated velocity at 2739fps (this is 90fps faster than I achieved)
• 99.9% burn at 72gr (75k psi) and 110% case fill estimated 2888fps. I would think this is probably unachievable without getting dangerous pressure.

Retumbo

• 99.9% burn at 71.5gr and 104.5% case fill. 60k psi and estimated 2708fps at muzzle
• 100% burn rate at 72.5gr and 106% case fill. 63.5k psi and 2758fps estimated velocity.

7828ssc

• 95% burn at 65gr (GRT lusts this load at max safe pressure) and 95% case fill. 63k psi and estimated 2702fps

RL26

• 100% burn at 61.5gr with 86.8% case fill and 48k psi so plenty of room to run it up
• 100% burn at 66.5gr with 94% case fill and 64k psi. Est. Velocity of 2759fps

For shits and giggles I pulled apart a factory 175 Precision Hunter and evaluated the charge. Charge weight was 66.2gr of what looked to me like RL 26. I plugged this into GRT based on the above data but swapped the 175 Berger EH to the 175 ELDX and it spit out the following.

• 96% case fill with 100% burn rate and 67,000 psi. Estimated muzzle velocity 2788fps

The data provided is roughly 26fps faster than I experienced. So not too terrible far off. I do find it interesting that the 175eldx is estimated to run faster with less powder than the 175 eh. I would’ve guessed the opposite.

 

[z987k]

Here's the 7PRC GRT file.

https://file.io/jVdxErI2vZLL

If you get on discord, people have posted a lot of stuff that doesn't come with the software yet, including a bunch of wildcats.

 

[JjamesIII]

That was with the factory ammo. I haven’t seen any pressure signs with handloads yet. I’m using a magnetospeed v3 that has been accurate for me on other rifles. For what it’s worth, I also shot some factory ammo yesterday and did not see and sticky bolt lift like I did the first day.

Magneto speed are accurate. I’d trust the data. Maybe just steer away from that brand/lot. If they load to the saami limits vs other companies it could be problematic as the ambient temp gets hot in the summer, or if a round sits in a warm chamber pressure might get spicy with some types of powder.

 

[TxLite]

Magneto speed are accurate. I’d trust the data. Maybe just steer away from that brand/lot. If they load to the saami limits vs other companies it could be problematic as the ambient temp gets hot in the summer, or if a round sits in a warm chamber pressure might get spicy with some types of powder.

I generally don’t buy factory ammo. Unfortunately not much choice with 7 prc.

Here's the 7PRC GRT file.

https://file.io/jVdxErI2vZLL

If you get on discord, people have posted a lot of stuff that doesn't come with the software yet, including a bunch of wildcats.

You da man! Thanks

 

[35WhelenAI]

Thanks Txlite, interesting info from a curiosity standpoint on my part about the powder burn.

You could chalk up the lower velocity on your loads to different powder lots.

With case fill, different brass has different capacity, may account for some of that numerical difference.

I am only familiar with QL, is this program able to use fired case capacity measured in grains of water and perform similar calculations? That takes the element of playing with case dimensions out of it and gives an actual measurement based on what your components give.

 

[TxLite]

I am only familiar with QL, is this program able to use fired case capacity measured in grains of water and perform similar calculations? That takes the element of playing with case dimensions out of it and gives an actual measurement based on what your components give.

Never used quickload. But with Gordon’s reloading tool you can plug in case volumes. I’m fairly new to the program. I’m sure others can provide more info

 

[35WhelenAI]

Are you able to input case capacity? Or is it only done dimensionally? Then you are dealing with your exact case volume versus having to play around with it and get it close.

 

[TxLite]

Are you able to input case capacity? Or is it only done dimensionally? Then you are dealing with your exact case volume versus having to play around with it and get it close.

Case capacity, case length, cartridge length

 

[z987k]

Are you able to input case capacity? Or is it only done dimensionally? Then you are dealing with your exact case volume versus having to play around with it and get it close.

Ya, you can enter the fired or new brass case volume after entering the dimensions.

The software is free.

 

[35WhelenAI]

Understood. That's where I was going with my line of questioning. Sounds like it's a "no" on using case capacity only.

That said, Tx have you measured case capacity (grains of water I would gather) to go with the dimensions you put together or just used the dimesions to create a "default" capacity?

 

[TxLite]

That said, Tx have you measured case capacity (grains of water I would gather) to go with the dimensions you put together or just used the dimesions to create a "default" capacity?

I plugged in the case capacity listed by backfire, which admittedly is RCC brass and not Hornady so obviously there is opportunity for differences between the data.

 

[TxLite]

Ok I think I solved my pressure problem. Can’t wait to see how this goes.

 

[NevadaMike]

Ok I think I solved my pressure problem. Can’t wait to see how this goes.

View attachment 555579

I ran my ADG over the max recommended charge and there are no signs of pressure at all. You would not know they were fired if the spent primer was not there. I settled on 66.5 of H1000 shooting the Berger 180 VLD-H with a COAL of 3.3095. My precision hunter had a 2.2" 20 shot group and this latest load was under .75 with 11 rounds. I am no marksman and I am calling it good right there. Let us know how it goes for you!

 

[TxLite]

I ran my Peterson over the max recommended charge and there are no signs of pressure at all. You would not know they were fired if the spent primer was not there. I settled on 66.5 of H1000 shooting the Berger 180 VLD-H with a COAL of 3.3095. My precision hunter had a 2.2" 20 shot group and this latest load was under .75 with 11 rounds. I am no marksman and I am calling it good right there. Let us know how it goes for you!

What’s your jump look like on that? I loaded these 180’s to 3.3375 and they’re going to be jumping 65 thou.

 

[NevadaMike]

What’s your jump look like on that? I loaded these 180’s to 3.3375 and they’re going to be jumping 65 thou.

Its ADG not Peterson. My Jump is .05. Berger sent the load info for the VLD and I just followed their suggested starting points