7mm mag - what's going on?

[kpk]

Having an issue and could use some insight...

I'm using all RP brass (previously fired from 2 rifles but I wasn't able to measure any differences)
CCI #34 primers - the only ones I was able to find
Nosler partition 160gr
RL-26

I ran a ladder test of 2 shots each.
68gr went into 1/2" - 68.5gr I KNOW I pulled a shot - 69gr went into 1/2"
Velocities were acceptable

So, I loaded up 10 rounds at 68.5 grains thinking it would be a good starting point. Wrong.
I shot 4 rounds into about 2.5" and velocity varied 100FPS.

I'm going to change batteries in scale and chrono.
I'm going to weight sort the brass and use stuff fired from this rifle now.

I'm hoping that maybe this rifle just really hated the 68.5 gr charge and my chrono batteries are dying.
With how hard components are to get, what else should I be looking at?

 

[Harvey_NW]

Are you using a Magnetospeed?

 

[doverpack12]

Your scale has batteries? What scale that might be the place to start along with ensuring the chrono is capable of acceptable accuracy.

you mentioned 1/2” group at 68 and 69. What distance did you shoot at? Ladder isn’t really looking at horizontal just vertical and velocity.

what are your velocities? 68 and 69 could have been blind luck/coincidence.

 

[kpk]

Your scale has batteries? What scale that might be the place to start along with ensuring the chrono is capable of acceptable accuracy.

you mentioned 1/2” group at 68 and 69. What distance did you shoot at? Ladder isn’t really looking at horizontal just vertical and velocity.

what are your velocities? 68 and 69 could have been blind luck/coincidence.

I've used a competition electronics chrono for years and I've never seen anything that seemed "off".
I also shot a bunch of 10mm loads same day and they were right on what the box stated.

The 7mm loads were "mostly" right around 2950. There were several that were WAY off.

Shot at 100 yards - just starting to get data for this rifle but something was clearly very off yesterday.

 

[Roksliding]

Are you shooting for groups with the magneto speed on? Or did I misunderstand.

 

[Rob5589]

I'd be inclined to think the charges weren't uniform. But 100 fps difference isn't going to take you from 1/2" groups to 2.5" groups at 100 yds. Double check charge weights with a scale you trust; keep working on different charges and maybe seating depths but, one thing at a time.

 

[kpk]

Are you shooting for groups with the magneto speed on? Or did I misunderstand.

I don't have a magneto speed. I have one of the old school shoot through ones - but I've never had an issue with it before.

I was shooting a ladder test just to start getting some data, but the two shots of 68gr and the two shots of 69gr (so 4 shots total) were basically dime sized and velocities were acceptable.

So, I loaded up a batch with a 68.5gr for the next day - and then everything seemed to fall apart. After 4 shots I knew something was clearly wrong. I'm going to pull the rest and start over.

 

[sneaky]

I'd try and find some different primers in the meantime. But, like has already been said, change one thing at a time.

Sent from my SM-G955U using Tapatalk

 

[kpk]

I'd try and find some different primers in the meantime. But, like has already been said, change one thing at a time.

Sent from my SM-G955U using Tapatalk

I pulled the remainder last night and checked charge weight - they were all dead on (with 2 scales)

Have you seen issues using the #34 primers? I wasn't able to find much info on them other than they are considered a magnum and most people said they were GTG.

Seems I'd have better luck finding a dinosaur bone than mag primers right now - I've been looking for a long time.

 

[Rob5589]

I pulled the remainder last night and checked charge weight - they were all dead on (with 2 scales)

Have you seen issues using the #34 primers? I wasn't able to find much info on them other than they are considered a magnum and most people said they were GTG.

Seems I'd have better luck finding a dinosaur bone than mag primers right now - I've been looking for a long time.

I don't know anything about the #34 but it is listed as a "large rifle" 7.62 primer. The shell is also harder to prevent slam fires in semi auto guns. I honestly couldn't say if that is part of your problem or not.

It's entirely possible your chrono was being wonky. That wouldn't explain the groups opening up so much, however.

I'd start from scratch with a completely clean barrel. Try to eliminate all the variables that are in your control.

 

[Rky Mtn Farmer]

If your using an electronic scale I would check it on a traditional balance scale. I got so frustrated with my scale going crazy and being sometimes up to 2gr off, that I bought an A&D EJ-123. It goes down to the .02 gr on accuracy. When I talked with the company selling the scale I found out that other electronics will effect the accuracy of a scale, like your cell phone or fluorescent lighting. Ended up changing my lights to LED and keeping all other electronic in the other room when I am weighing charges. I have come to the conclusion that reloading for accuracy is a rabbit hole that never ends.

I don’t think this would explain the variation in the fps, but I would suggest you also give your barrel a really good cleaning and get all the copper out. Copper build up is a common killer of accuracy. That way you eliminate another variable.

 

[doverpack12]

What were your velocities for 68 and 69 grain shots. And your 68.5 grain shots of the ladder.
if those are not the same then 68 and 69 hitting in a small group was meaningless.

 

[brad407210]

60 grains tends to be the point you move into magnum primers, if you're in MN and were shooting in cold weather that probably doesn't help the ignition either. Weird things can happen if you're on the low end of ignition, I don't know the technical reasons behind this, but if you can't find any magnum primers try the test again and keep the shells in your pocket to warm them up then chamber one at a time and do the test. If the load works when warm and acts funny when it's cold you probably need hotter primers.

 

[PowellSixO]

I’d say you need a magnum primer.

 

[Sandstrom]

I pulled the remainder last night and checked charge weight - they were all dead on (with 2 scales)

Have you seen issues using the #34 primers? I wasn't able to find much info on them other than they are considered a magnum and most people said they were GTG.

Seems I'd have better luck finding a dinosaur bone than mag primers right now - I've been looking for a long time.

I am just outside of the twin city, where are you located in MN? I have some magnum primers you can have. Shoot me a pm if you are interested.

Ryan

 

[kpk]

60 grains tends to be the point you move into magnum primers, if you're in MN and were shooting in cold weather that probably doesn't help the ignition either. Weird things can happen if you're on the low end of ignition, I don't know the technical reasons behind this, but if you can't find any magnum primers try the test again and keep the shells in your pocket to warm them up then chamber one at a time and do the test. If the load works when warm and acts funny when it's cold you probably need hotter primers.

I was under the impression the 34s were a magnum mix - but maybe they're on the weak end of the spectrum?

First day I shot was 55 degrees.
Second day was closer to 30 - and they sat in my car for about an hour and a half before shooting.

 

[LaHunter]

I've used a competition electronics chrono for years and I've never seen anything that seemed "off".
I also shot a bunch of 10mm loads same day and they were right on what the box stated.

The 7mm loads were "mostly" right around 2950. There were several that were WAY off.

Shot at 100 yards - just starting to get data for this rifle but something was clearly very off yesterday.

At 68 & 69 grains of RL-26 in a 7mm rem mag, I would expect your mv to be faster than 2950. What is your barrel length and twist rate? I would suspect the non magnum primers could be an issue.
Typically, a true ladder test is best done at ranges of 400+ yards and 600+ is even better.

 

[kpk]

Figure I should update this. I met up with a guy from the hide and did some primer trading. I'm now using federal match magnums.

I shot again this past Sunday and consistently got 3050 with 70 grains of RL-26. No pressure signs and half inch groups. It's a new tikka and in tikka fashion seems a bit slow but plenty accurate.

 

[Phineas]

Did the recoil feel different? I’ve gotten wildly inaccurate numbers from my standard chrono because the light wasn’t right, or the battery was low. If they’re hitting in the same place at 100:yards, they’re not 1000 FPS different,