Usually on the giving end of advice...need help

[Bang4theBuck]

As far as neck thickness/ clearance, I've never worried one iota about it as long as I can put a bullet into the neck on a fired case without a seater die and it's not sloppy either... If you can get to just looser than a slip fit you should be good.

I can get a bullet to seat back into the case, but it takes a little bit of push. It doesn't just slide right in. And ironically, it isn't the exact same amount of effort on each one either.

 

[Harry Knutz]

The plot thickens!

The bullets seat like butter....no issues. My loaded outside case neck dimension is .274" with the Petersen Brass. As stated above, my neck is reamed at .276", netting a .002" clearance fit. Might be low.

The lapua brass that got over-turned measures .0115 to .012.
The Petersen that is unturned measures .0155 to .016" both measured with a ball-end micrometer.

Seems possible that I am at opposite ends of the spectrum here with neck thickness. One problem is, if I turn much off of my petersen brass, the die is not going to act upon it sufficiently, using the expander ball If I go without using the expander ball it might be fine.

What are the reamer specs for the neck? Can you drop a bullet into the fired case?

 

[Lefty7mmstw]

I can get a bullet to seat back into the case, but it takes a little bit of push. It doesn't just slide right in. And ironically, it isn't the exact same amount of effort on each one either.

I'd guess that's a good part of your issue right there... fix that with a really mild skim turn... I've even heard of some guys using steel wool to tune their casings for even release, but I haven't ventured there, as I don't have the patience for that and I'll probably garf it up.

 

[Bang4theBuck]

What dimensional clearance am I targeting between chamber neck dimension and loaded cartridge outside neck dimension?

I currently have .002"

 

[Petey308]

If you can't easily drop a bullet into the neck of a fired case, that's a problem. It means the case isn't opening fully to release the bullet completely upon firing. That'll mean pressures will spike and be inconsistent.

If it's not a carbon ring causing the necks not to expand fully, it's a tight chamber and you'll need to turn your brass for proper clearance. Once you can drop a bullet easily through the neck of a fired case, you should be good.

 

[Lefty7mmstw]

What dimensional clearance am I targeting between chamber neck dimension and loaded cartridge outside neck dimension?

I currently have .002"

with my 7rum I had to go to .315" seated bullet/ .320 fired casing for enough neck clearance... just measured one as I just went for what Petey said...

 

[Samesaw]

So, I built a custom 6x284 with a 26' carbon barrel. The rifle is showing lots of promise on the accuracy front with the reloads, but I am getting velocity spreads that are well outside the norm as compared to all of my other reloads. I have tried 3 different bullets, and two different batches of brass. Looking for the "smoking gun' reason why the spreads are so high.
Started with Lapua 6.5x284 brass necked down to 6x284, then neck turned. While I was trying to just skim turn them, I managed to reduce the neck thickness to .011". After firing, the necks had expanded around .010" over the loaded outside dimension. Assuming that was my problem with velocity consistency, I canned that brass and bought new petersen brass and necked it down to 6x284. Still I am getting some very high extreme spreads (40-65 fps).
I am using RL26, BR2 primers and I've shot Berger Hunting Hybrids, Hornady ELDX and Hammer hunters. All with the same high extreme spreads. I've meticulously checked and rechecked my powder weights, checked all the necks for concentricity, verified good primer seating, etc.

I am wondering if this charge of powder and primer combo are a little incompatible? Woukd moving up to a magnum primer help? Is this common woth the first firing of a necked down case to be this way?

Thoughts?

1) those aren't extreme velocity spreads

2) try moving away from small primers

3) shooting altitude, humidity and weather temperature will affect velocity spreads

4)

 

[Bang4theBuck]

1) those aren't extreme velocity spreads

2) try moving away from small primers

3) shooting altitude, humidity and weather temperature will affect velocity spreads

4)

I'm not sure we're looking at the same thing.

Extreme spreads in the 45 to 60 FPS range are terrible. I don't have a single rifle that I reload for that is even half of that.

Not sure what you mean by small primers. There are large rifle primers.

Altitude, and humidity are external ballistic factors, and have little to no affect on muzzle velocities. Temperature only affects muzzle velocity as it relates to powder temp sensitivity and in some extreme cases, primer performance.

 

[Petey308]

shooting altitude, humidity and weather temperature will affect velocity spreads

That only affects external ballistics as far as point of impact.

Temperature wouldn't cause big velocity swings like that in one sitting. It would case the averages from one day, one month, etc to another to vary, sure.

Humidity in regards to moisture content in the powder can vary lot to lot (batch to batch) performance but in one outing, it wouldn't affect ES if all the ammo was loaded at the same time and same keg of powder.

 

[Dean2]

With the steps you have taken so far, my bet is powder is your issue. You also have a large number of variables that are well outside optimal ranges. I would start with 25 new brass, .003 neck tension, .004 min clearance on once fired brass. Bullets seated at least .04 off the lands. Work up a test load in batches of 5 per powder weight. Try a faster temp stable powder from Hodgdon that gives you at least a 95% case fill, same bullets, CCI 250 mag primers. My bet is you will find the ES tightens up a lot.

 

[Hugnot]

I don't think 40-65 fps spreads (about 2%) are that extreme for a large capacity to small bore case like the 6mm-284. Searching for a combo that might reduce spreads, try a magnum primer.

Different primers produce different energy levels.

https://arxiv.org/ftp/arxiv/papers/1203/1203.2701.pdf

The graph, fig 2, gives an indication of primer strength.

For large capacity to bore size using slow burning powders, I like Fed 215's & CCI 250's (LRP).

RL 26 is touted as having Alliant's EI technology that states the deterrents are imbedded or infused into powder grains rather than coating the grains with deterrents. This feature might require a hotter primer than the much less dense, deterrent coated H1000. The imbedded or infused deterrents are claimed to provide a more sustained energy or pressure increase to provide higher velocities.

As mentioned above ^^, try another powder, I have seen some H4831SC and VN 165 available online. Either that, try a magnum primer like CCI250 or Fed 215 primers. Loads using H1000 & CCI 200's gave extremely low velocity spreads & great accuracy in my 6.5-06. Possibly, you might be able to scrounge up some H1000. All my VN 165 loads use standard LRP's and have low velocity spreads.

Turning necks and maintaining neck tension are important^^. Having a nice slip fit of bullet into fired brass would indicate enough neck/chamber clearance, like .004. I turn my 6mm necks to .268.

 

[Bang4theBuck]

I neck turned 30 pcs of brass. The result is .005" of clearance between outside loaded case neck dimension and inside throat dimension. I am going to load a couple strings with the same powder primer combo I've been loading to see if that was the only problem.

Then I'm going to change the primer, for a couple strings. Then a few woth H1000.

 

[Petey308]

I neck turned 30 pcs of brass. The result is .005" of clearance between outside loaded case neck dimension and inside throat dimension. I am going to load a couple strings with the same powder primer combo I've been loading to see if that was the only problem.

Then I'm going to change the primer, for a couple strings. Then a few woth H1000.

Good luck

 

[Dean2]

I neck turned 30 pcs of brass. The result is .005" of clearance between outside loaded case neck dimension and inside throat dimension. I am going to load a couple strings with the same powder primer combo I've been loading to see if that was the only problem.

Then I'm going to change the primer, for a couple strings. Then a few woth H1000.

Be interested to hear how that comes out. Just changing one variable at a time will help isolate cause but I honestly dont think neck thickness, and neck tension/clearance is going to be the factor that cures this. Be very interesting however if it does. Look fwd to hearing how it goes.