Extremely extreme spread!

[Handsome Rob]

I've got a question:
Can crimping a rifle case cause HUGE velocity differences?

I loaded up a bunch of .308 the other day. 165gn Sierra Gamekings over 42gn of 3031.
The only thing is, I messed up & ran them all through a Lee FCD by mistake.
I ran them all through a chrono yesterday & had the weirdest velocities. I was expecting speeds around the 2400 fps area.
What I got was velocities from 1347 to 1986!!
The only thing I know I did wrong was the crimp. Every charge was measured & weighed individually to +/- 0.1gn. Every round was measured for length to within 0.001"

The only variable I can see is the crimp.
I tested the chrono with some factory loads in .223 & they were right on spec.
I'm having a hard time figuring this out.

[Lumber_Jack]

I can't see where crimp would cause a decrease in velocity, and especially carrying velocity. Excessive crimp can cause high pressure signs and potential problems.

[Handsome Rob]

Any idea what could cause the extremely low overall velocity?

[Lowpower]

What does the brass look like? Any blackened necks?

 

Next, what gun? Bolt? Gas? Barrel length? 42 gr = like 2700 fps and aound 60K PSI depending on barrel length and that's pushing the charge a bit.

 

Any noticeable differences in recoil? 

 

Got any .308 factory loads you can compare everything with?  I normally use Varget @ 43.1 gr at 2515 fps.

.

[Handsome Rob]

Savage Hog Hunter, bolt action, 18" barrel.
Brass looks perfect, no sooting around the neck, primers look good. No obvious signs of over pressure.
I don't have any factory ammo to compare to I'm afraid.
Recoil felt about right (muzzle break) but I could feel the differences, shot to shot.

[Raoul]

What kind of powder measure?

[Handsome Rob]

RCBS, but trickled & individually weighed.

[samson7x]

Different batch of powder?  I know that can cause some degree of variance, but I doubt it would lead to your results.  Just throwing it out there.

[Handsome Rob]

Someone else has mentioned that I may have a contaminated or 'off' pound of powder.
Unfortunately I'll never know that now as I used up the last of it with these loads.

As soon as midway delivers some more bullets I'll try a different powder & chrono that too.
I really wish I'd chrono'd all the others I put together with this powder & didn't crimp.

My honest second thought was possibly I'd messed something up reaming out the primer pockets of the Lake City brass, but the primers all seated nicely & none blew out or acted oddly at all.

[cj0e]

1. What kind of chrono?

 

2. How far is it from the muzzle?

 

The IMR load data imr3031 shows for a 165gn Hornady SP pill, 41.6gn is the top end load - out of a 24" barrel. If it's a light sensitive chrono, with your load and an 18" barrel with a brake I'd wager your sensors are being spoofed by excessive flash. This could also explain why your .223 loads are reading normally as well as your erratic readings on the .308.

 

I'd probably back down on the charge as well, if you think the bottle was "off". Granted, I'm a novice reloader, and generally excessively cautious.

[gregintenn]

I'd be suspect of your chronograph. I don't believe there's any way whatsoever that a crimp could cause what you've described.

 

I do not own a chronograph, but the only difference I've noticed when crimping is a slight edge in accuracy with some loads.

 

I've never seen a significant point of impact change between crimped and non crimped loads that were otherwise similar.

 

Were you shooting a target? Where were your bullets hitting? Were you getting a decent group?

[EssOne]

robtatoo, I'd do two things before shooting any more of those cartridges.  

 

First, run a check of your scale to make sure it's giving correct weights. Weighing a new bullet of a known weight will give you a good idea if it's off or not, or you can borrow a buddy's scale to verify yours with.

 

Second, go to your powder cabinet and make darn sure you loaded the powder you think you loaded. A good friend of mine blew up a beautiful custom '98 Mauser by grabbing Olin 296 pistol powder instead of Olin 760, which had similar markings. They were side by side on the shelf and he didn't know what he'd done wrong until we broke down one of the crumpled rounds in the magazine and compared the powder granules in it with the two powders. There was no doubt about it - he put 55 grains of pistol powder in the case and blew the rifle to kingdom come. FWIW, I always used two scales to hand measure loads, one to constantly verify the other, and I ran "bullet checks" like I described fairly often too. With a high pressure round like the .308 or.270 I pour myself an extra measure of  careful . Hope this helps.

[Handsome Rob]

Definitely the correct powder. I only had 3 different powders on hand (4189, 4895 & 3031) and I only ever take them out of the case one at a time to save mixups on my bench.

It was a 'Chrony' type chrono, tripod mounted, roughly 2' from the muzzle (it's not mine & I didn't want to either accidentally shoot it or keep calling for a cold range after every shot!)

One of the guys on the line (a serious F-class shooter) also tested the chrono & verified it to be on the money.

I know it's an odd thought, but if I'm over pressure (on closer inspection, my primers are slightly flattened, but none are pierced or falling out & my brass isn't extruded into the extractor) could that cause a velocity loss over normal???

I've been researching (Googling) all day & I've learned that badly over pressure could cause that, but I wouldn't imagine less than half a grain would be THAT significant, surely(?)

Interestingly, the Lyman 49th book lists 42gn as the maximum (although in a 24" bbl)
Would barrel length alter chamber pressure to that extent?

[Handsome Rob]

Oddly (again) Sierra bullets reloading data calls for a max load of 40.6gn of 3031 for the same bullet.

This confusion is why I put off reloading for so long! I'm dreading having to start 'proper' reloading once I get my 6.5x55 target gun built!
Neck turning, seating depth, jump-to-lands measurements.... It's honestly pretty freaking intimidating!

[cj0e]

Definitely the correct powder. I only had 3 different powders on hand (4189, 4895 & 3031) and I only ever take them out of the case one at a time to save mixups on my bench.

It was a 'Chrony' type chrono, tripod mounted, roughly 2' from the muzzle (it's not mine & I didn't want to either accidentally shoot it or keep calling for a cold range after every shot!)

One of the guys on the line (a serious F-class shooter) also tested the chrono & verified it to be on the money.

I know it's an odd thought, but if I'm over pressure (on closer inspection, my primers are slightly flattened, but none are pierced or falling out & my brass isn't extruded into the extractor) could that cause a velocity loss over normal???

I've been researching (Googling) all day & I've learned that badly over pressure could cause that, but I wouldn't imagine less than half a grain would be THAT significant, surely(?)

Interestingly, the Lyman 49th book lists 42gn as the maximum (although in a 24" bbl)
Would barrel length alter chamber pressure to that extent?

 

 

Barrel length will cause more unburnt powder to flash, 3031 is slow burning - that high load, with that shorter barrel - and only 2' away from the chronograph. I'd put money down that you had muzzle flash interfering with the chrono. I've seen the same thing with a buddy of mine's Chrony brand chronograph. We were shooting .223 out of my 10.5" ar pistol, couldn't get reliable reads. Moved the chrono out, much more reliable (though higher pucker factor for sure! I didn't want to buy a new chronograph either!)

[deadeye111]

Barrel length will cause more unburnt powder to flash, 3031 is slow burning - that high load, with that shorter barrel - and only 2' away from the chronograph. I'd put money down that you had muzzle flash interfering with the chrono. I've seen the same thing with a buddy of mine's Chrony brand chronograph. We were shooting .223 out of my 10.5" ar pistol, couldn't get reliable reads. Moved the chrono out, much more reliable (though higher pucker factor for sure! I didn't want to buy a new chronograph either!)

The Oehler 33 that I own is set up approximately 10' from muzzle per manufacturer's instructions. Check your manual if you have one and set up accordingly. Muzzle blast and powder still burning possibly causing erroneous readings as mentioned already. Edited April 3, 2015 by deadeye111

[EssOne]

I honestly don't know what your problem is, neighbor, but the chronograph is the weakest link in your chain, so I think my next step would be to go out with some proven loads and fire them over it just like before. If it gives erratic velocities on the known loads, then the chrono is probably your answer. I don't think I'd fire any more of the suspect loads without pulling the bullets and checking the powder charges again, just to be safe.

 

I have a 6.5x55 sporter I built and have loaded for it quite a bit over the years. None of the things you are worried about are problems. You'll love it. My favorite load is a 120 grain Nosler Ballistic Tip at 3,050 fps. Here are a few photos of it. It is a Mark X Whitworth Mauser action with a 24" medium weight Shilen barrel in a nice piece of Northern California English Walnut.

 

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[Handsome Rob]

Ohhh myyy....

Unfortunately, mine we'll be way more utilitarian.
Like this...

[EssOne]

You'll love it. Have a ball. My best loads were with IMR 4064 and IMR 4350 FWIW. Remington brass and Federal match primers.

[Clod Stomper]

Barrel length will cause more unburnt powder to flash, 3031 is slow burning - that high load, with that shorter barrel - and only 2' away from the chronograph. I'd put money down that you had muzzle flash interfering with the chrono. I've seen the same thing with a buddy of mine's Chrony brand chronograph. We were shooting .223 out of my 10.5" ar pistol, couldn't get reliable reads. Moved the chrono out, much more reliable (though higher pucker factor for sure! I didn't want to buy a new chronograph either!)

This would be my guess as well.

I once got readings of 3000+ fps from a snub .38 SPL. Yep, I was too close. Or I possibly stumbled upon the magic load that bridges the gap between handgun and rifle.

[z0mbies fear me]

According to my "Chrony" manual the minimum distance from the muzzle of a non-magnum rifle to chronograph is 10 feet.

[samson7x]

I agree with the others.  I think your chrono placement was way too close.  I place mine 10' away from muzzle and have never had any problems. 

[Trekbike]

Yep I agree with the distance being too close. I had a similar issue on some pistol rounds and once I moved back some, everything settled down with the velocity.

[gregintenn]

I honestly don't know what your problem is, neighbor, but the chronograph is the weakest link in your chain, so I think my next step would be to go out with some proven loads and fire them over it just like before. If it gives erratic velocities on the known loads, then the chrono is probably your answer. I don't think I'd fire any more of the suspect loads without pulling the bullets and checking the powder charges again, just to be safe.

 

I have a 6.5x55 sporter I built and have loaded for it quite a bit over the years. None of the things you are worried about are problems. You'll love it. My favorite load is a 120 grain Nosler Ballistic Tip at 3,050 fps. Here are a few photos of it. It is a Mark X Whitworth Mauser action with a 24" medium weight Shilen barrel in a nice piece of Northern California English Walnut.

 

Get that thing checkered and you'll have a jewel for sure! I love it.