Frustrated: Velocity Variance Huge

[Seeking_Coyotes]

No idea what is going on... Been reloading about 12 - 15 years.

Getting 100 fps velocity delta between ten rounds I shot through the chrony! This was a ladder test load that was putting five inside an inch but tonight is the first time I took out the Chrony. Sig Sauer M400 Predator AR-15, US Optics MR-10 scope, etc.

Using a Rockchucker, CFE 223, Lyman digital scale, small rifle primers. 60 grain Nosler Vmax, mixed brass. Full length sizing (always). COAL within a thousands of an inch. What the heck could be causing this...what am I missing? Hoping it could not be due to neck tension as it is something I have never done and kinda happy with my full length sizing. Can't imagine the powder measure is starting to play tricks on me?

Extremely frustrated...

 

[dmoran]

A couple possibilities:
If tumbled, possibility of media or pins trapped in the cases.
If a powder was accidentally put into a wrong container.
Electronic error (scale, chrono) or setup error
Mixed brands of brass

Suggest to reverse play each aspect, in attempt to finding the culprit.
Good Luck
Donovan

 

[dedogs]

Mixed brands of brass

+1 I would look here first although 150 fps spread seems extreme. Could also be the crony as dmoran suggested.

 

[boltfluter]

I would take said "crony" and place directly in front of truck wheel and drive over it until its good and dead. Problem solved.

Paul

 

[Homerange]

I would take said "crony" and place directly in front of truck wheel and drive over it until its good and dead. Problem solved.

Paul

And yet a pair of Cronys we set up one after the other agreed with each other within a few fps for EVERY shot.

The cause of the OP's problem is simple.....mixed brass.

 

[boltfluter]

And yet a pair of Cronys we set up one after the other agreed with each other within a few fps for EVERY shot.

The cause of the OP's problem is simple.....mixed brass.

Maybe. But could also be confirmation that both cronies are calibrated to each other but dead wrong. In my experience with chronographs, you get what you pay for.

Paul

 

[Seeking_Coyotes]

Used the chrony on some factory 300 Win. Mag ammo and seemed about 40 fps slower than the box indicated so I figured the chrony was ok. Here is the velocity data:
3027
3091
3064
2851
2965
2931
2996
2965
2902
2933
2961
2888
2966
2991
2986
2958

 

[Seeking_Coyotes]

And yet a pair of Cronys we set up one after the other agreed with each other within a few fps for EVERY shot.

The cause of the OP's problem is simple.....mixed brass.

How can mixed brass cause a huge 100 fps velocity spread?

 

[dmoran]

How can mixed brass cause a huge 100 fps velocity spread?

Capacity variance can be substantial from one brand of brass to another, which in return can create combustion/pressure variance that may also be substantial, from the variation in the powder columns.

Were you using different brands of brass?

Also your chrono data from the 300WM purchased ammo is very extreme and suspect to me of the chrono or its setup. How far from the muzzle did you have it setup?

 

[Twoboxer]

Your OP says 10 rounds of your handloads gave 100fps ES. There are 16 velocity numbers in your second post, so I guess that's the factory? If so:

Max 3091
Min 2851
ES 240
STDEV 61
Avg 2967

That's either terrible factory ammo or a terrible chrony.

 

[Ned Ludd]

If you have a fair bit of fully processed "mixed" brass, simply pick out 30 or so cases of the same brand (headstamp), then weight sort enough cases for 5 foulers and 10 shots for velocity. I would try to keep the case weights within 0.1-0.2 gr spread, if possible. This is a fairly crude test (case weight isn't always perfectly proportional to case volume); however, restricting them to a single manufacturer and weight sorting should be more than enough to make that small set of brass much more uniform in terms of case wall thickness and case volume than the "mixed" lot as a whole. So with a few minutes of your time and 15 loaded cases, you ought to get a very good idea of how a more uniform brass prep behaves in terms of velocity data with your specific load/setup.

One other issue alluded to by Paul above is in regard to the Shooting Chrony (if that's the brand you were actually using). Those instruments can work well with certain precautions, but they are very sensitive to shot placement over the sensors, as well as changes in ambient light (i.e. sun vs clouds) during the course of a shot string. If that's what you're using, I'd suggest marking the sunscreen supports in addition to proper target placement to ensure you're shooting at the appropriate height, as well as centered over the sensors. In addition, if shooting on a mixed sun/clouds day, try to get all the shots in a string off during approximately equal ambient lighting conditions. Only after that would I consider the truck tire approach .

 

[Homerange]

How can mixed brass cause a huge 100 fps velocity spread?

You don't state your load in grains of powder.........if it's been based on brass with a larger volumetric capacity and loaded into brass with a smaller capacity you can indeed see some crazy things. What does the primer pressure signs tell you from loads you've fired ?

This reminds me of when I was working up a 222 50gr load and changed the projectile from FB to BT, no other changes BUT shorter COAL to fit the mag with the longer BT pill. Pressures went through the roof JUST from seating the bullet deeper. The load wasn't even max either but it shows how sensitive results can be with small changes to the recipe. Close to max, wilder results are possible/probable.

 

[Zero333]

For argument sake, lets say the mixed brass all has the exact same internal capacity.

Different brands of brass have different metallurgical chemistry and different hardness characteristics, therefore they expand at different rates building pressure differently.

 

[fgregorio]

Is the chrony placed more than 10 feet ahead of the muzzle? This exact issue happened to me before.
All I did was to place the chrony at more than 10 feet ahead of the muzzle and the issue was gone. Are its batteries fresh?
If it groups on target, the chrony placement needs to be checked for muzzle blast interference.

 

[Mozella]

I've tested quite a bit of CFE-223 both in my .223 and my 6mm BR Norma. With the .223 ammo I had a lot of "pop-bang" type hang fires. In other words, there was a delay between when the primer went off and the charge went off. Not a long delay, but long enough to hear the difference. I also had a few complete failures where the round didn't go off at all. This was with CCI 400 and BR-4 primers. I switched to the CCI 450 magnum primers and the problem was instantly solved. Not only is the CFE-223 now reliable for me, it's also very accurate.

Of course this may not be your problem, but inconstant ignition of the CFE-223 very fine ball powder could very well give you those mysterious variations in velocity. Have you tried the CCI 450 primers?

 

[Texas10]

I see your numbers trend downward. Interesting.
I'm going to go with electronic errors, like Donovan wrote. Battery, electronics heating up, distance from muzzle. Have you talked to the Mfg of the chrono? Is there a calibration process for your chrono?

Is there such a thing as a ladder test where you expect consistent velocities?

If it were me, I'd go with Mozilla's advice and start over with a magnum primer (since you're using a ball powder), and some new LC brass.

 

[Richard Coody]

No idea what is going on... Been reloading about 12 - 15 years.

Getting 100 fps velocity delta between ten rounds I shot through the chrony! This was a ladder test load that was putting five inside an inch but tonight is the first time I took out the Chrony. Sig Sauer M400 Predator AR-15, US Optics MR-10 scope, etc.

Using a Rockchucker, CFE 223, Lyman digital scale, small rifle primers. 60 grain Nosler Vmax, mixed brass. Full length sizing (always). COAL within a thousands of an inch. What the heck could be causing this...what am I missing? Hoping it could not be due to neck tension as it is something I have never done and kinda happy with my full length sizing. Can't imagine the powder measure is starting to play tricks on me?

Extremely frustrated...

If you are.happy with your groups then why worry about it.

If you want to try to improve your ES then i would start with your brass.

Mixed brass:

I suspect they also have all been fired mixed times. Each time they are fired they become more.work hardened. If they have all been reloaded different times the they will all have different neck tension. Some find crimping useful in this scenario. Another method is annealing.

Different cases have different case volumes. Sort by manufacturer. Can even take that one step further and weigh sort them.

I prefer full length sizing and with an AR it is necessary.

Powder charging:

That scale is not very accurate. To reduce ES accurate powder charges will get you the greatest reduction in your ES

 

[DRNewcomb]

I don't know about your chronograph. I use a CED M2 chronograph and alway approach load testing with a bit of trepidation. Is it bright or overcast? Windy? What time of day? Where do the shadows fall? I sometimes carry bits of construction paper and tape to block the direct sunlight from striking the sensors. The more powerful the load the farther from the muzzle it has to be set up. All these factors affect the performance of the CED. So, my first thought would be to look at the chronograph.

 

[Toolbreaker]

Could it be a rifle issue with bolt cycle-time varying, allowing pressure to build differently between shots? I'm not familiar with AR's, so just thinking out loud here.

Myself, I'd probably purchase a box of quality target ammo & run through it with your current chronograph setup. If the velocities settle down fairly consistent through the 20 rounds of factory ammo, then that takes the rifle & chrony out of the equation. Afterward, you have 20 pieces of brass that should be in the ballpark of each other to work your handloads with while looking for the culprit.

 

[Jackal2016]

I agree with what others have posted regarding the mixed brass as the cause of the variance. The normal golden rule of reloading, if any component change, ...work the load up from square one. And mixed brass is certainly a component change, Best to sort that brass and work up a load for each brand of brass. Or the brand you have the most of.