7mm PRC

6brshooter said:

So, what was different in your reloading between first and 2nd rd of testing? Or are we gonna chalk it up to barrel? On 2nd rd, did you do more than 3 rd groups/velocity strings?

You kind of conflated those. Initial load work showed promise, even bragged on best group youd ever shot. Wandered about retumbo and QL prediction and opined about saving components. Sorry you weren't clear about that. If you would have said "computer predictions can be useful if you don't know where to start," I'd have agreed with you. It just sounded weird with your initial load work and best group ever comment.

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Nothing was different. Same lot of brass, same primer, same trim length, same powder charge, & same bullet / seating depth etc…

I left the barrel uncleaned, and repeated the test. No I did not retest shot strings greater than three. My reason for that is because if the load I’m retesting doesn’t repeat why shoot more.

(Barrel was cleaned during 1st test and 5 fouling shots were fired on the paper, followed by a 8-10minute cool down.

Normal I shoot x1 shot string of three till
I find something that shows promise. If it shows good ES/SD with acceptable accuracy .5” or better, then I load up another three shoot paper again, and what I’m looking for is consistent ES/SD, similar group size or better, and same point of aim/same point of impact. If the second group repeats, then I load up 6 more retest everything I said above, & if it checks out okay I’ll then test at distance.

Sorry if I wasn’t clear @6brshooter

Range report:

Berger 190g LRHT
66g H1000 (x3 shot group)
66.50g H1000 (x5 shot group)

Believe I found a solid node here, but still need to confirm that it can repeat itself. Plan to load up 66g, 66.2g, & 66.4g and see if I can repeat similar groups. Muzzle velocity was hovering 2950 +/- 12fps with very acceptable ES. For this being a hunting rifle, I’m extremely pleased thus far.

Thought I would share my load for my MPA Matrix Pro II 7PRC 26”

185 RDF loaded .03 off lands.
Hornady Brass
Remington 9 1/2M
VV N570- 68.7gn
MV 2940fps
ES 19
SD 7
The group was 5 shot and measured at .172” after removing the .284” projectile diameter.

I have since shot 700 of this combo out to 1250 yards and it has been the most consistent load in any rifle I've ever shot. Daily still get 1/3 inch 5 shot groups when I recheck for various temps. N570 has proven to not really give me issues with temps… 110 degrees down to 17 degrees in the past year of shooting. Something I was not expecting…

to follow-up on my post on p16

I dropped down to 67.5 (Hornady book max) H1000 and now that the barrel has 75 down it, i'm seeing right at 2900 with SD single digit, so that's where she'll stay. Whorenady brass seems to tolerate that charge. it's at 3.310 abotu 0.03" off lands. It's harder to shoot well than my 15# ring, especially with teh Ultra 7 (come on TBAC, send that Magnus S RR!), but I still think it's probably a 0.75 MOA gun for 10 shots, which is fine for a rifle intended for maximum range 800 yards or so.

I tried retumbo and got no better speeds and almost same pressure at same charge. 69 grains RUINED the Whorenady cases with one shot, I think abotu 67 grains would be max for RETUMBO adn teh 180.

secondofangle2 said:

to follow-up on my post on p16

I dropped down to 67.5 (Hornady book max) H1000 and now that the barrel has 75 down it, i'm seeing right at 2900 with SD single digit, so that's where she'll stay. Whorenady brass seems to tolerate that charge. it's at 3.310 abotu 0.03" off lands. It's harder to shoot well than my 15# ring, especially with teh Ultra 7 (come on TBAC, send that Magnus S RR!), but I still think it's probably a 0.75 MOA gun for 10 shots, which is fine for a rifle intended for maximum range 800 yards or so.

I tried retumbo and got no better speeds and almost same pressure at same charge. 69 grains RUINED the Whorenady cases with one shot, I think abotu 67 grains would be max for RETUMBO adn teh 180.

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With only 75 rounds on your barrel, you should see velocity speed up 50fps or so.

they started at 2875 so I'm half way there

I cool every 3-4 shots for 5-10 min with high volume RYOBI blower, which probably lengthens the break-in time; plus this is not a large sample test

secondofangle2 said:

they started at 2875 so I'm half way there

I cool every 3-4 shots for 5-10 min with high volume RYOBI blower, which probably lengthens the break-in time; plus this is not a large sample test

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Mine really started to stabilize around 150 rounds, and velocity gained was around 50fps. I bet you'll be close to 2925ish.

Love my 7mm prc rifle from fierce

I am building a 7 PRC now and I always start by buying my own reamer with custom freebore for the bullet I am going to be primarily shooting. This way I can always chamber up another barrel later.

I am planning on shooting the 190gr A-Tip primarily or exclusively. Anyone have the ideal measurements for base to ogive or simply OAL for the A-Tip on a 7 PRC? I am used to keeping the bullet bearing surface ahead of where donuts form, but I would love to hear if others are doing this or not also.

What I am ultimately trying to do here is answer the reamer manufacturer's question of how much Freebore I want on the reamer which I'll provide to my gunsmith for chambering.

b2948kevin said:

I am building a 7 PRC now and I always start by buying my own reamer with custom freebore for the bullet I am going to be primarily shooting. This way I can always chamber up another barrel later.

I am planning on shooting the 190gr A-Tip primarily or exclusively. Anyone have the ideal measurements for base to ogive or simply OAL for the A-Tip on a 7 PRC? I am used to keeping the bullet bearing surface ahead of where donuts form, but I would love to hear if others are doing this or not also.

What I am ultimately trying to do here is answer the reamer manufacturer's question of how much Freebore I want on the reamer which I'll provide to my gunsmith for chambering.

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I had this done for my 7 PRC hunting rifle I have posted above, however I did not provide my own reamer, all I did was make note on my build sheet that I requested the chambering job to allow enough free bore for the Berger 190g LRHT’s.

With that being said, I could get that info from my smith if you’d like me to. Also I believe the A-Tips are longer than the Berger’s so they won’t be the same.

Your best bet is to load up a dummy round and send it to Manson Reimers, and they will design the reamer around that.

If you’ve never done it before, and you go trying to measure this and that and map it onto a known reamer drawing you’re gonna have a high chance of screwing it up. Costly mistake.

The other thing is, you could always use a standard reamer and have your gunsmith extend the free bore. You can always extend the free bore of a standard chamber, but you can’t shorten the free bore if extra is built into the reamer.

It’s not a really big deal, but that reamer is basically a one trick pony And you can start out with the best of intentions about those 190s and wind up changing your mind after you’ve shot a bunch of them and are working on your second barrel