Irregular velocities with 7prc loads

[Johrichal]

I recently built a lightweight 7prc and started trying to work up a load. I am running into some odd velocities and wanted to see if anyone has experienced anything similar.

I am using ADG brass, h1000 powder federal gold medal match large rifle magnum primers and have tried 175 eld-x and 180 ELD-M bullets velocities are measured on a Garmin zero chrono

During my load work ups I am struggling to find any nodes at all and my velocities jump around a lot there have been 2 charge weights that gave decent which were 66.6grns and 67.5 grns after my initial testing I loaded 5 rounds of 66.6, 66.4 and 66.8 grns, the 66.6 grn group gave me an average velocity of 2815fps with and SD in the teens, 66.4 grns was an average of 2790 with a SD in the 20's and 66.8 had an average of 2754 with an SD in the 20's.

That's just an example and I've been seeing similar results across all charge weights if I load up 5 rounds at least 2 of them are 50-200fps different than the rest and it's had me pretty confused.

The other day I tried a few different primers with a load of 67.5grs and was kinda shocked. I loaded 5 rounds each with gold medal match magnums and Remington lrm primers the federals had an SD of 28 the Remington's had an SD of 9. I also loaded 2 rounds at the same charge with white river standard large rifle primers and the SD from those was 1.6, I know 2 shots is not a significant source of data but still definitely worth exploring more.

So it would seem that my rifle doesn't like the powder/primer combo I've been using and just wanted to see if anyone else has ran into something similar with this cartridge.

Just as a note so far every group I've shot with this rifle has been under 1" at 100yds but I haven't got it out to farther distances yet

 

[FireFlyFishing]

So you're grouping under 1" and you think this isn't the right combo?

 

[ShtrRdy]

Is the brass new/ unfired?

 

[MagnumManiac]

I have one question; what seating depth testing have you done, if any at all?

Cheers.

 

[Johrichal]

@FireFlyFishing - I'm happy with the groups at 100yds but I do a lot of long range shooting (1000+ yards) and at that distance 100fps variances in velocity make a significant difference

@ShtrRdy - brass is all fire formed using low end charges 2 times, on 4th or fifth load on most of them now.

@MagnumManiac - not much in the way of seating depth testing yet I've shot some at .020 and some at .030 off the lands so far. I usually try to find a load with consistent velocities before I do much with seating depth but it's on my list of things to try.

 

[MagnumManiac]

If you are having sporadic velocities, it may be ignition problems caused by low pressure loads. Slow powders like H1000 need high pressure to burn efficiently and effectively. Anything below this can cause wide start pressure, which effects max pressure levels.

Cheers.

 

[Johrichal]

I was wondering if it might be something like that, I started seeing ejector marks at 68.5gr and didn't push it any further, are you suggesting seating the bullet farther to take up more case capacity? The federal gold medal primers seem to be very hot maybe I'll try working up a little higher with the Remingtond

 

[Rflshootr]

If you have a decent supply of the Remington primers, I would do more testing with those. Remington's have a lower brisance then Federals. Meaning, the term "brisance" it represents the speed/rate at which a primers releases it's full energy. I think of it describing not power, or heat, but speed.
Sometimes with slower powders, the "longer burn" will produce more consistent results.
While you're at it, just to be sure, I'd strip the bolt and clean it internally just to make sure it doesn't have any anything to make the firing pin fall inconsistent.

 

[Tiny Tim]

How much interference fit between bullet and neck? have you ever tried crimping? How are you measuring your charges? A lot of variables unaddressed.

Sounds like you are a relatively experienced reloader, so maybe focusing on a load with the other primer types may be your answer.

 

[MagnumManiac]

I concur, try both standard and magnum primers. Often, a standard primer works best.
I cannot help specifically with the 7PRC, but in many of my magnum cartridges, which I have dozens, start pressure is important, you can crimp, which boosts start pressure considerably, seat close to the rifling, this also works even though you have increased case capacity.
You can use solid copper bullets, or you can use a different powder.
It is obvious something isn't meshing with your loads,

Cheers.

 

[Paulstarr]

The best thing I can suggest is stop using SD and use the extreme spead,ES.you may be happy with the results at 100yds if the ES of your 5 shots is over 20/25 fps the results at 1000yds will be dismal.

 

[Rpr]

Try BR2 s

 

[letzhunt]

I know it may be asking if you have a pet unicorn but if you have access to any Reloder 26. That's a powder to try. Also, as suggested, give a Barnes LRX or other solid copper a try. Not saying it's a powder issue or a bullet issue but it may be a powder and bullet COMBO issue. The factory Barnes load uses RL26 and the 160 LRX. It shot so well in my rifle I stopped toying with loads. I have pretty much duplicated and exceeded their load with their fired brass and the combo mentioned. But I bought a $h!! Ton of factory Barnes for fear they will have to pull a Hornady and switch powders and it will change their loads ..... a lot!

 

[Dmagna]

Sounds like you are under pressure