My 7PRC Load Dev Journey

[philcox]

Finally got everything together and started the journey. Figured I'd post it for others to learn from and have a reference.

The Parts

• 20" CarbonSix 1:8 on a Tikka LA
• Primer: CCI 250
• Brass: ADG
• Powder: H1000 (as this seemed to be one that I had some of, and there was some starting data on-line)
• Projectile: 168 LRX and 160 CX
• MagnetoSpeed Chrono

My Process

• Note I am a "speed" junky and try to get as much out of a load as I can, it probably causes me a huge amount of time and resources (e.g., I do ladders and not Formidious “painless load development”), with likely real little net return, since I am only using this for hunting. However, it is what it is
• Use .3 increments and try to find a high node
• Shot 16 of each projectile
• 160 CX : 67.5 … 72
• 168 LRX: 64.3 … 68.8

Results so far

• Hornady Outfitter factory 160 CX: was 2840 fps out of my gun
  • Side note: Precision Hunter 175 ELD-X was 2775fps
• 160 CX @ 71.0g H1000 @ 2940fps
• 168 LRX @ 67.8g H1000 @ 2860fps

Next Step: See what groups

• I do 3 - 3 shot groups. Then I’ll see which groups best. I am expecting 1/2 MOA.

To be Continued …

 

[philcox]

I am a bit curious, though, as to how a 2 inch longer barrel can produce the velocity differences is documented in this article, https://hawkinsprecision.com/2022/10/24/reloading-for-7-prc/ compared to mine.

For example, I shot the Factory Precision Hunter, 175 ELDX, and it Chrono at a roughly 2775 … that article has a 22 inch barrel clocking that same factory load, at 3040! Roughly 250fps with 2” increase.

Then the H1000 velocities are significantly more at a certain grain

Really can’t do anything about it, because my barrel shoots what it shoots, but it is curious to me is that it could truly be that much slower

 

[eroksolfe]

Hey sir, tagging in here. I just built up a 7 PRC on a 22” proof prefit and terminus action. I’ve shot factory ELD-M and CX through it to this point (120 rounds). I don’t have a chrono yet but the ELDM was way slow using drops but the CX seems to be at normal speeds (~3000 fps) validated out to 1000 yards. I expected the CX to be a bit slower but the bullet don’t lie. All that to say, very interested where you end up with your testing especially since the CX was a touch inconsistent in the accuracy department.

 

[DEW0341]

Following.


Sent from my iPhone using Tapatalk

 

[Lunchbox37]

Interesting results so far... glad to see the hand rolled stuff is bumping velocities up. I just started breaking in a new 7prc Xbolt and am looking forward to reloading for it. Thanks for the leg work here!

 

[DiabeticKripple]

I used H4831sc in mine cause it’s readily available up here and I bought 16lbs of it.

I posted some pics of my groups in another thread on here. I was very unimpressed with the 160gr CX, it was over MOA all through the ladder test I did.

The 168gr LRX was much better, averaging 3/4 MOA and I got a great grouping at 65.5gr at 2950fps.

Going to the range with the 168gr LRX today to verify the load. I loaded 5 rounds of each from 64.9-66.1gr in 0.3gr increments.

Once I verify the load, I’ll load up 50 and take it to 600m to verify drops, and that’ll be my load for hunting cow elk (2 tags) out to 600m next month on the CFB Suffield military base.

 

[Lunchbox37]

... I posted some pics of my groups in another thread on here. I was very unimpressed with the 160gr CX, it was over MOA all through the ladder test I did....

Just out of curiosity, what was your seating depth or COAL with the 160gr CX bullets? On my '06 I found seating them deeper (away from the lands/jam) improved groupings.

 

[DiabeticKripple]

Just out of curiosity, what was your seating depth or COAL with the 160gr CX bullets? On my '06 I found seating them deeper (away from the lands/jam) improved groupings.

I did what I’ve done with the Barnes, 0.050” off lands.

 

[Lunchbox37]

Yea, I too found that the mono's like that jump. I landed at .060 with the .308 165gr CX for best groups

 

[philcox]

I used H4831sc in mine cause it’s readily available up here and I bought 16lbs of it.

I posted some pics of my groups in another thread on here. I was very unimpressed with the 160gr CX, it was over MOA all through the ladder test I did.

The 168gr LRX was much better, averaging 3/4 MOA and I got a great grouping at 65.5gr at 2950fps.

Going to the range with the 168gr LRX today to verify the load. I loaded 5 rounds of each from 64.9-66.1gr in 0.3gr increments.

Once I verify the load, I’ll load up 50 and take it to 600m to verify drops, and that’ll be my load for hunting cow elk (2 tags) out to 600m next month on the CFB Suffield military base.

What length barrel you shooting? I have some H4831SC that I may try as well. I really want the LRX to be the better group, so hopefully it turns out that way. Keep me updated on your results.

 

[DiabeticKripple]

What length barrel you shooting? I have some H4831SC that I may try as well. I really want the LRX to be the better group, so hopefully it turns out that way. Keep me updated on your results.

24" IBI Carbon Hunter

I had issues with the rifle yesterday, front action screw came loose and groups were very odd.

1st shot bullseye, 2nd shot 4" high, 3rd shot bullseye. Ended up shooting all the loads for velocity measurements and will revisit next week.

 

[philcox]

Finally got to Grouping today. I tested 2 loads that I had found "nodes" on in a ladder test:
- 168 LRX, 68.1g H1000 COAL 3.20
- 160 CX, 71.1g H1000 COAL 3.29

I shot 3 shot groups. Let barrel cool to touch in between each group. Same setup for rest etc. I shot in this order:

1. 3 Factory 160 CX - Chrono with MagnetoSpeed to see what they were at, AND to heat up the barrel so my hand loads could be as "similar conditions" as possible - Note the Factory 160 CX: 2869, 2853, 2845 ... so essentially 2855 out of my rifle
2. 3 Hand load 160 CX: Shot 1 & 2 were .099 MOA, 3rd shot turned it into a 1.265 MOA group
3. 3 HL 168 LRX: 1.785 MOA
4. 3 Factory CX: Shot 1 & 2 .290 MOA, 3rd took it to 1.091 MOA
5. 3 HL CX: Shot 1 & 2 .216 MOA, 3rd took it to .622 MOA (I am noticing a trend here, not sure of ammo/rifle or shooter getting lazy on #3)
6. 3 HL LRX: 1.722 MOA (confirms first group)
7. 3 HL CX: At this point, I knew the CX was the load for this rifle until I can get some diff powder to try with the LRX, because I WANTED the LRX to win. Slapped the MS Chrono back on and: 3010, 2974, 3011 ... Avg ~3000

So at this point, since I want to bear hunt with it, I am going to stick with the 160CX. I will load up another 100 and do some more shooting and chrono to get better data, and to see if the 1,2, then 3 issue is a shooter or rifle issue.

Primary Load: 160 CX @ 71.1g H1000 and COAL 3.29, ~3000 fps out of a 20" Carbon Six barrel.

Now to Zero with that load, as you can see my impact and POA were consistently off.

 

[philcox]

To follow up here. I posted this to another thread ...

I think the "your groups are too small" is going to make me cry. I am working up an 168 LRX and 160 CX loads in my new PRC. With this 20, I am about 140 down the barrel. I finally got everything for the 160 CX, and went out and shot a "20 group" this AM. As the MOA expansion chart shows, I was happy, then ultimately determined "this load is not going to work". When I shot #14 I was like "I think I pulled this", but remembering the podcast comments, thought, finish the 20 and find out. It likely was not ...

Next step is to follow Formidilosus recommendation to drop 1g and see if it does the trick. If not, try another powder ...

I get my LRX components Thursday, and will do my 20 round with that. If it works, I'll use that vice spend more time on the 160 CX. However, I did a 10 shot group with the LRX earlier, and that did marginally better. We'll see if I got the "worst" in that 10, or if this new 20 exposes even more problems.

 

[doc holiday13]

To follow up here. I posted this to another thread ...

I think the "your groups are too small" is going to make me cry. I am working up an 168 LRX and 160 CX loads in my new PRC. With this 20, I am about 140 down the barrel. I finally got everything for the 160 CX, and went out and shot a "20 group" this AM. As the MOA expansion chart shows, I was happy, then ultimately determined "this load is not going to work". When I shot #14 I was like "I think I pulled this", but remembering the podcast comments, thought, finish the 20 and find out. It likely was not ...

Next step is to follow Formidilosus recommendation to drop 1g and see if it does the trick. If not, try another powder ...

I get my LRX components Thursday, and will do my 20 round with that. If it works, I'll use that vice spend more time on the 160 CX. However, I did a 10 shot group with the LRX earlier, and that did marginally better. We'll see if I got the "worst" in that 10, or if this new 20 exposes even more problems.

View attachment 626736

View attachment 626737

don't be afraid to change your seating depth

 

[donrleonard]

To follow up here. I posted this to another thread ...

I think the "your groups are too small" is going to make me cry. I am working up an 168 LRX and 160 CX loads in my new PRC. With this 20, I am about 140 down the barrel. I finally got everything for the 160 CX, and went out and shot a "20 group" this AM. As the MOA expansion chart shows, I was happy, then ultimately determined "this load is not going to work". When I shot #14 I was like "I think I pulled this", but remembering the podcast comments, thought, finish the 20 and find out. It likely was not ...

Next step is to follow Formidilosus recommendation to drop 1g and see if it does the trick. If not, try another powder ...

I get my LRX components Thursday, and will do my 20 round with that. If it works, I'll use that vice spend more time on the 160 CX. However, I did a 10 shot group with the LRX earlier, and that did marginally better. We'll see if I got the "worst" in that 10, or if this new 20 exposes even more problems.

View attachment 626736

View attachment 626737

thanks for posting your journey. I’m on a similar one. I’m stuck with factory ammo for now, so I’m hoping you are able to make the 160CX behave.

 

[doc holiday13]

I wasn't planning on doing 7prc dev just yet but I happened into some components.

I didn't do full accuracy but it seems the gun isn't unhappy at
berger 180 hybrid
70g of h1000.
adg new brass
215 primer
2915fps

 

[philcox]

Based on all the info that I have consumed over the past 3 weeks from @Formidilosus and the Hornady “your groups are too small” podcats, I have determined that I need a 1.5 MOA rifle. Since this is basically a “semi-custom”, seems that should be a reasonable expectation. I had chased my tail on ladders, depths, etc. for about 200 rounds. I flushed it all and embraced the “painless load dev” process Form discusses.

Since I don’t have a 1000y range, I have split Forms process on 1/2 and if I can get a 1.5 MOA group from a 10 shot group. I’ll take that to a longer range. Until then, not wasting the time or resources.

I tried 168 LRX with H4831SC. Tried at 66.5 (was about 3050fps), got a 3+ MOA group of 10 … bumped it down to 65.5 (2950). Decided to do 2 groups of 5 (my mag holds 5, so that could be a real scenario on a hunt. I shoot until they are down). First group (yesterday) of 5 printed 1.01MOA, I was excited! Took rifle out today to do the other 5 (similar conditions). 1st shot was about 1.5” from center of yesterdays group … fail. I shot another just to see if there was a scope (poi) shift … nope. Shot 2 hit back in “yesterdays” group of 5. I stopped and packed up my goods. I had shot the 168 with H1000 a few weeks ago, and 3 shot groups were at 1.7MOA. So 2 powders, 2 loads each, neither worked sufficiently, so the 168 LRX is a scratch with this barrel. am onto the 160 CX.

If the CX does not work, I will try the 180 ELDM, to see if it will group. That would mean I can’t use this rifle in California. If the CX and Factory ELDM don’t cut it, I will send the barrel back to CarbonSix.

I’ll update as I progress. I am about 230 rounds down the barrel.

 

[doc holiday13]

t, I will send the barrel back to CarbonSix.

I’ll update as I progress. I am about 230 rounds down the barrel.

I've heard carbon six is hit or miss.
do you know what your Freeborn is?
how much are your bullets jumping before they hit the rifling?
have you played at all with bullet seating depth?

generally once you have found a speed node you'll want to stick to it and play with seating depth to see how much jump the bullets want to take

 

[Thomsisaac]

Following. Looks to be a nice build.

 

[philcox]

Moving this to this thread https://rokslide.com/forums/threads...-load-dev-and-shoot2hunt.335590/#post-3362166