6 UM or 6-7PRC?

[BNORTH7]

I crossed the 4k line when playing with some 87 AH hammers and RL26. Was over 3800 with the 90HHT and RL26.

I would like to hear more about your build and how you like the performance of the 6-7. I’m gathering supplies to build my own. I would like to run something in the 80gr range and shoot for 4k.

 

[GoatPackr]

I would like to hear more about your build and how you like the performance of the 6-7. I’m gathering supplies to build my own. I would like to run something in the 80gr range and shoot for 4k.

Send me a pm and I'll give you my #
I definitely think you can get 4k with the right bullet and barrel length. I did

 

[BNORTH7]

Send me a pm and I'll give you my #
I definitely think you can get 4k with the right bullet and barrel length. I did

Unfortunately I’m still new and can send a PM yet. Not sure if you can send me one

 

[GoatPackr]

Sent you my #

 

[RogerPa]

It really isn't that much more powder. I didn't want the extra screwing around and cost of custom dies. Normally I'd jump right at the 6UM but was trying to keep the price down on this one.
It'll be slinging a 90 grn HHT from a 26" 1:7 barrel so it won't be slow. If I don't like it I can always order another barrel and change it.

Kris75

GoatPackr,
I’ve finally taken delivery of my own 6-7 PRC, and early tests have been very promising! One question I have I thought perhaps you’d have the answer for is trim length? The few fire-formed rounds that came along with the rifle from UM are all in the 2.263 to 2.265 range. The book trim number for the “7 PRC” is 2.275,and my first 40 fire-formed cases are all in that 2.275 to 2.277 range. (I did not trim them after neck sizing & fire-forming.) I know you’ve been shooting this cartridge for awhile now, and appreciate your input.
Thanks, RogerPa

 

[GoatPackr]

@RogerPa

I asked UM the same question when I was starting on mine. Blaine told me to fire form all my brass and pick the shortest one and run with it. Pretty simple way of doing things and it's worked for me.

 

[RogerPa]

@RogerPa

I asked UM the same question when I was starting on mine. Blaine told me to fire form all my brass and pick the shortest one and run with it. Pretty simple way of doing things and it's worked for me.

Thank you! Couldn’t be simpler than that! I much appreciate your insight & experience.

 

[OldTracks]

Lots of good info!

 

[knorthcutt222]

Built a 6-7 over the weekend. UM got me the reamer specs and JGS made the reamer. Took a Bergara crest 7prc and spun up a Shilen 1:8 22" long. Fire forming with n570. With 70gr and a Hornady 80gr eldvt I'm getting 3330. Seems kinda slow. I'm going to drop the charge weight down to 65gr and fire form my ADG brass and then start looking for speed.

 

[huntnful]

Built a 6-7 over the weekend. UM got me the reamer specs and JGS made the reamer. Took a Bergara crest 7prc and spun up a Shilen 1:8 22" long. Fire forming with n570. With 70gr and a Hornady 80gr eldvt I'm getting 3330. Seems kinda slow. I'm going to drop the charge weight down to 65gr and fire form my ADG brass and then start looking for speed.

Is it an improved shoulder design?

If you’re legit just fire forming, I’d be doing it with a less destructive powder and lower charge weight for sure.

You probably just weren’t reaching pressure with N570 and that specific bullet is the reason for the slower speeds also.

 

[knorthcutt222]

Is it an improved shoulder design?

If you’re legit just fire forming, I’d be doing it with a less destructive powder and lower charge weight for sure.

You probably just weren’t reaching pressure with N570 and that specific bullet is the reason for the slower speeds also.

Not a improved shoulder. Just a straight neck down of 7prc to 6mm. Used a 243 wssm die to neck it down. Worked like a charm. What powder do you think would be better for fire forming?

 

[GoatPackr]

Not a improved shoulder. Just a straight neck down of 7prc to 6mm. Used a 243 wssm die to neck it down. Worked like a charm. What powder do you think would be better for fire forming?

I've got a UM biult 6-7 PRC and fire formed with N565.

My 26" barrel is slinging 90 HHT at 3560 fps with 71 gr N570.
I'm not even at full pressure.

Very flat shooting. We were shooting little water bottles at 545 yards this winter and dialing 1.9 Mils.

 

[huntnful]

Not an improved shoulder. Just a straight neck down of 7prc to 6mm. Used a 243 wssm die to neck it down. Worked like a charm. What powder do you think would be better for fire forming?

Well you don’t really have to fire form then. I would just shoot the bullet/powder the barrel is intended for and start getting info. Just know you’ll likely have to drop .5-1gr. from what you saw with virgin brass after it’s been fired.

 

[knorthcutt222]

I've got a UM biult 6-7 PRC and fire formed with N565.

My 26" barrel is slinging 90 HHT at 3560 fps with 71 gr N570.
I'm not even at full pressure.

Very flat shooting. We were shooting little water bottles at 545 yards this winter and dialing 1.9 Mils.

Any particular reason to fire form with 565?

 

[RogerPa]

I was hoping we’d see a thread unique to the 6-7 PRC. This one has grown to 13 pages and 250+ posts. Is it time?

 

[Ryan Avery]

I was hoping we’d see a thread unique to the 6-7 PRC. This one has grown to 13 pages and 250+ posts. Is it time?

Start one

 

[GoatPackr]

Any particular reason to fire form with 565?

No. I fire formed with it and 108s. Then tried N565 with the 90HHT but wasn't happy. N570 was much better.
The 108s didn't like the 26" 7 twist when it got several rounds on it with higher speeds.

 

[knorthcutt222]

No. I fire formed with it and 108s. Then tried N565 with the 90HHT but wasn't happy. N570 was much better.
The 108s didn't like the 26" 7 twist when it got several rounds on it with higher speeds.

I gotcha. I'm still necking down brass, waiting on my jug of 570 to get here. Got my brothers barrel in the lathe ready for the reamer

 

[rifletuner]

So is there a consensus on the 6-7PRC yet? Some of the posts from 12 months or so back were alluding to the 6-7PRC maybe being too much of a good thing. But there doesnt seem to be to many reports since then. Just wondering if the 6-7PRCs under development settled down okay? Or did it all turn out as failed experiments?

I have been going around in circles trying to come up with a hot 6mm option. I had a 6-284 over 25 years back and was a bit "meh" about it back then. But I do think I am a much better reloader now, so would be better placed to get the best out of it if I had one today.

I am in Australia, so getting a 6UM chamber and dies etc is probably not a viable option. I have looked at potentially a 6-284, 6-6.5PRC, 6-300SAUM, 6WSM and 6-7PRC. Any of these mostly unmodified cases would be relatively easy as I can use a FLS neck bushing die and ream out a Wilson inline seater die, so loading for the round is pretty easily sorted. That just leaves getting a chamber reamed.

Worst case I might need to buy a reamer to get the chamber I want. But then if I go that route, maybe its not a much bigger undertaking to just get a UM reamer and die set and be done with it.

 

[Axlrod]

So is there a consensus on the 6-7PRC yet? Some of the posts from 12 months or so back were alluding to the 6-7PRC maybe being too much of a good thing. But there doesnt seem to be to many reports since then. Just wondering if the 6-7PRCs under development settled down okay? Or did it all turn out as failed experiments?

I have been going around in circles trying to come up with a hot 6mm option. I had a 6-284 over 25 years back and was a bit "meh" about it back then. But I do think I am a much better reloader now, so would be better placed to get the best out of it if I had one today.

I am in Australia, so getting a 6UM chamber and dies etc is probably not a viable option. I have looked at potentially a 6-284, 6-6.5PRC, 6-300SAUM, 6WSM and 6-7PRC. Any of these mostly unmodified cases would be relatively easy as I can use a FLS neck bushing die and ream out a Wilson inline seater die, so loading for the round is pretty easily sorted. That just leaves getting a chamber reamed.

Worst case I might need to buy a reamer to get the chamber I want. But then if I go that route, maybe its not a much bigger undertaking to just get a UM reamer and die set and be done with it.

I have had a 6-7PRC for just over a year now.. What I like about it is, you can use off the shelf 7PRC bushing dies and Inline dies (with a 6mm seat stem). There is very good brass available in 7PRC ADG, with Lapua also going to be making 7PRC brass at some point in the future.

I had Unknow Munitions build this one, and when the barrel is gone, I will have them chamber another. The only change I will make, is the reamer they have is a bit tight on neck clearance. Using ADG brass i have to turn the necks. It's not a big deal to turn necks, but I will have them order me a new reamer with more neck clearance so I don't have to turn them next time.