excessive velocity spread

[Bart]

Yesterday, I loaded some 6.5 Creedmoor rounds using new, out of the box Nosler cases, 142g AccuBond LD bullets, Fed 210 primers, H-4350 powder. These were for an OCW test, which showed me about what I expected except for the differences in velocity for each of the powder weight groups. I was very careful to weigh each powder charge on an electronic scale and to seat each bullet the same. I am using a Caldwell chronograph which gave no error readings. I let the barrel cool between each group.

The readings for the last four groups were as follows:
AVG - - Spread - - Std Dev.
2605 - - 41 - - - - - 20
2620 - - 49 - - - - - 19
2650 - - 61 - - - - - 26
2690 - - 83 - - - - - 32

I'm looking for help getting the velocities even. A spread of 49 is not going to be conducive to accuracy, this I know. I could not find any Fed Match primers, however, I have always understood that Fed primers were pretty even. Other than the primers, I expected spreads in the ten to fifteen range. Am I expecting too much?

Bart

 

[SJB358]

Try the same loads again with fire formed brass. Some folks have good luck with new brass but I have not.

Neck tension and a just having brass that fits the chamber seems to work better for me.

 

[elkhunternm]

What kind of groups are you getting,that is what I would pay attention too.

 

[jimbires]

how far are you going to shoot ?

 

[truck driver]

I'm no expert on this by a long shot but when dealing with my 338Wm a retired Marine told me I need to get the pressure up so it would settle down and it worked as far as wide velocity swings.
I think there was also some stock issues which I hope I have also eliminated.

 

[Dwh7271]

Agree with the fellows above. Fireformed is better IMO.
Are you dropping from an automatic charger (like the Hornady or Chargemaster)? If so, I would check to see on another scale if you're getting some slight variance there.
Then neck tension, runout etc.

 

[Bart]

SJB

I had the same thought. I just neck sized the brass and checked neck thickness. Outside trimmed to .013 + .0005 - .0. I'll try loading 10 with the same load and 10 with a different (Winchester) primer.

Elkhunternm

Groups are not that great, smallest was 2.5 inches, which at 200 yards is over 1 moa. Nowhere good enough!

Jimbries

I have in mind using this rifle at 500 yards plus. Prairie dogs are quite small at that distance.

Truck driver

As pressure (speed, load) went up, both groups and variation also went up.

dwh7271

No, using stand alone PACT electronic scale. I was very careful with the weights. I did find 10 cases that had neck thickness variation of .001 and corrected them.

To All

Thanks for your input. I stay on this forum and let you know what I find.

 

[truck driver]

Yes it will as it should. If you look at the max powder charge for the bullet weight and powder back off 1.5grs and weigh the powder charges in.2gr increments for ten charges and seat the bullets to sammi OAL then fire them over the chronograph. you should see where there is no appreciative in crease in velocity probably somewhere between loads 4-7 take the middle load and then seat the bullets in .005" depths going deeper till you find the optimum seating depth for accuracy. This how I was told to do it for best over all velocity and consistence.

 

[elkhunternm]

SJB

I had the same thought. I just neck sized the brass and checked neck thickness. Outside trimmed to .013 + .0005 - .0. I'll try loading 10 with the same load and 10 with a different (Winchester) primer.

Elkhunternm

Groups are not that great, smallest was 2.5 inches, which at 200 yards is over 1 moa. Nowhere good enough!

Jimbries

I have in mind using this rifle at 500 yards plus. Prairie dogs are quite small at that distance.

Truck driver

As pressure (speed, load) went up, both groups and variation also went up.

dwh7271

No, using stand alone PACT electronic scale. I was very careful with the weights. I did find 10 cases that had neck thickness variation of .001 and corrected them.

To All

Thanks for your input. I stay on this forum and let you know what I find.

Ok,I would try a different powder or bullet,just to see what happens. Changing the primer might help,but not by much.

Just my s.w.a.g.

 

[jimbires]

now that you cleaned up the necks and have the brass once fired with a neck size only, I'd reshoot your test to see what happens . I would not change anything . if you have another scale maybe double check your powder charges on it before pouring in the case . also watch your seating depth doesn't vary more than a couple thousandths . you want to measure this off the ogive , not the bullet tip . be sure to clean the carbon from the primer pockets .

one more thing kind of jumps out at me , how reliable is the chrony ? did you have the sky screens on ? was the sky steady or was it changing from overcast , to bright sun or the sun going behind clouds . these optical chronys can give wild velocity swings from changing light conditions . I found the best time to use one was very early morning before the sun came out . once the sun brightened up the chrony wasn't reliable .

I seem to have my best luck by using max or close to max powder charges that fill the case 95% or more . I weigh my powder charge to the kernel on a good electronic scale . I also seem to do better with less neck tension than the standard dies give . I've been using either a Lee collet die , or a redding bushing die . I run a sinclair neck expanding mandrel in the case after using my sizing die . I also have been dipping my bullet base in dry graphite just before seating . I'm starting to feel neck tension is about the main problem with high ES and SD , and have been trying to do all I can to get it under control .

 

[Bart]

now that you cleaned up the necks and have the brass once fired with a neck size only, I'd reshoot your test to see what happens . I would not change anything . if you have another scale maybe double check your powder charges on it before pouring in the case . also watch your seating depth doesn't vary more than a couple thousandths . you want to measure this off the ogive , not the bullet tip . be sure to clean the carbon from the primer pockets .

The only other scale I have is a RCBS balance beam. And, I've tested it's sensitivity against my electronic and I get much better accuracy with the electronic.

one more thing kind of jumps out at me , how reliable is the chrony ? did you have the sky screens on ? was the sky steady or was it changing from overcast , to bright sun or the sun going behind clouds . these optical chronys can give wild velocity swings from changing light conditions . I found the best time to use one was very early morning before the sun came out . once the sun brightened up the chrony wasn't reliable .

Ahah! I have absolutely no idea! It's a Caldwell that wasn't too expensive. I am actually more concerned about its consistency than absolute accuracy. That said, I wasn't aware that differing light conditions would change the reading. The day was sunny and warm, around 85 degrees with few clouds. I don't recall cloud shadows.

I seem to have my best luck by using max or close to max powder charges that fill the case 95% or more . I weigh my powder charge to the kernel on a good electronic scale . I also seem to do better with less neck tension than the standard dies give . I've been using either a Lee collet die , or a redding bushing die .

The best group I got was half grain under book max. I am using a Redding competition die with a bushing giving .002 less than case with seated bullet. However, I didn't do anything to the new cases before doing this test. Guess I just "assumed"...

I run a sinclair neck expanding mandrel in the case after using my sizing die . I also have been dipping my bullet base in dry graphite just before seating . I'm starting to feel neck tension is about the main problem with high ES and SD , and have been trying to do all I can to get it under control .

That's interesting! Have to take that under consideration. Like you said, I'll reload and run the test again. Thanks so much!

Bart

 

[jimbires]

I have a RCBS 10-10 scale . I can weigh very accurate powder charges with it , but it is slower and hard on my neck and eyes staring at the pointer . I suggest you double check your powder on your beam scale too , just to be sure your electronic scale isn't goofing up every once in awhile . if both scales weigh the same for 15 or 20 charges I'd say you've proven your scales to be accurate .

I have a few different weight bullets that I set aside to weigh on my scale . I weighed them and wrote the weights down . every time I start to load I let my scale warm up a little , then I weigh these bullets just to be sure nothing seems out of the normal .