Unexplained velocity variation - help!

[elwaine]

I'm laddering my loads in a .22-250 rifle that I've had for 2 years. It already shoots below 1" at 200 yds (no bragg... no bull, but please do not tell me to leave things be as they are - that will not be helpful). I recently bought a CED M2 chronometer and decided to ladder the loads to make sure that I'm reloading in a velocity plateau zone.

The velocity results were surprising: in the lower and mid range of gun powder charges - each charge individually weighed on an accurate scale - the velocity varied as much as 200 or more ft/sec with the same weight of gun powder. I used Berger bullets and loaded 4 cartridges with the same charge, then increased the charge by 0.2gr and loaded another 4 cartriges, etc.

As an example, 34.2 grains of Varget resulted in the following velocities - 3203 ft/sec, 3422 ft/sec, 3232 ft/sec and 3282 ft/sec. Similar results were obtained at all loads from 29.6 grains of gun powder to 34 grains. From 34.2 grains to 36.0 grains, velocity variation was less than 50 ft/sec - and usually within 20 - 30 ft/sec.

My shooting buddy - using a similar rifle and the same bullets and gun powder... and the same range of charges, never exceeded a variation of greater than 50 ft/sec.

I rechecked my scale... pulled bullets are re-weighed charges in other cartridges that I loaded to check my accuracy and consistency. I checked my scale against my bddies scale to check its accuracy. I remeasured the seating depth on unfired re-loads as well as the overall cartridge length, etc.. I could find no explanation for the odd velocity variation that I encountered. My charge weights did not vary more than 0.1 gr. Overall cartridge length did not vary by more than a few 100 thousandths of an inch. I cannot understand why I encountered such extreme variations in velocity.

Any ideas or suggestions?

[Yithian]

How old is your powder. Not just age but where was it stored etc.
I think vibrations can cause a separation in the powder kernels. Smaller particulates burn faster.

I saw an article someplace where a guy ran his Win748 thru a set of sieves. The smaller powder ran all the way thru to the bottom tray. The bottom powder burned with a higher presure and faster. All the layers of powder also yielded better results in bullet velocity consistency.

Maybe any long term storage on a shelf someplace like near a speaker, or the other side of a wall from a woofer, can result in the powder separating into layers by size?

It's the best guess I have. (shrug)

[B.L.E.]

Variations in neck tension and/or crimp can cause velocity variations.

[Scorch]

It could be a dozen things. Primers, powder, neck tension, load density, distance from the lands. full-length resized vs neck sized, and the list goes on. Try a different powder or different primers and repeat the test.

[csmsss]

Have you verified the accuracy and repeatability of your chronometer? Try a batch (or two or three, even) of factory rounds and see whether you see consistent velocity readings with them or whether you observe the same sort of variations?

[bcrash15]

Have you verified the accuracy and repeatability of your chronometer? Try a batch (or two or three, even) of factory rounds and see whether you see consistent velocity readings with them or whether you observe the same sort of variations?

My first thought as well. Verify the velocity readings with another chronometer and make sure everything jives.

[elwaine]

Thanks guys. Good suggestions all.

As far as the age of the powder, I buy it in 8 lb. containers and go through 8 lbs every 7 to 8 months, so I'd guess the powder is about 4 months old (4 months in my possession, anyway). When I ordered it from Powder Valley, they were out of stock (this was before the election when all of us were sure that our reloading supplies would vanish when the new crowd took over Washington). So I assume it was fresh stock when they shipped it to me.

The powder looks good - no fine grains mixed in with the extruded rods.

Primers all came from the same box. Primers are just a few months old (CCI 200)

Variations in the distance from lands is an excellent thought - excellent, because I thought of it also :) - but that should only happen if there are variations in bullet seating depth - and I double checked that. My seating depth is constant to within a few hundred thousandths of an inch.

Variation in neck tightness may make some difference, but my hunting buddy and I tested that about a year ago on his chronometer and we could find no consistent velocity changes attributable to the ranges in neck tightness that we experience using our dies - certainly nothing in the 200 ft/sec range (for our powder, bullets and cases).

I do not mix batches of shells. I keep careful records and label all my containers. So I did not mix and match cases. They were all from the same batch - all worked the same... etc..

Many thanks for your suggestions. I remain puzzled. I may have to try a different powder and repeat the measurements, as suggested.

[wpcexpert]

Verify the velocity readings with another chronometer and make sure everything jives

I'f you are getting velocity spikes, the only way to check that is to put the crono's one directly behind the other.

[brewman]

Are you loading all the same brand cases that weigh the same?

Apparently internal dimensions can vary considerably between brands and even production batches from the same manufacturer affecting case volume and hence start pressure.

EDIT: ** Sorry I see you already covered this, I should learn to read better**

[sadsack]

Elwaine: One other thing you might check is your case lube process. If you're getting more or less lube in the necks it can cause this. I wouldn't think a 200 fps difference, but its something to look at.

[elwaine]

Have you verified the accuracy and repeatability of your chronometer? Try a batch (or two or three, even) of factory rounds and see whether you see consistent velocity readings with them or whether you observe the same sort of variations?

I though of that, too. But it doesn't explain the tight velocity readings that my buddy recorded on the same chronometer. Sorry if I wasn't clear - and apologize for that. We shared the same chronometer, alternating every 10 rounds, for a total of 66 fired rounds each. I should have included these charts before also:

My results .22-250, Savage model 12 LRPV - Berger 60gr HP - Varget 29.6 - 36 gr
http://www.thefiringline.com/forums/attachment.php?attachmentid=41265&stc=1&d=1232590478

My buddy's results.22-250, Savage model 12 LRPV - Berger 60gr HP - Varget 29.6 - 36 gr
http://www.thefiringline.com/forums/attachment.php?attachmentid=41266&stc=1&d=1232590478

Case lube... you guys are good! But in this instance, the cases were all necked only and no case lube was used (same is true of my buddy's cases).

[P-990]

elwaine,

If I had to guess, I'd say it's your rifle (barrel) combined with the powder not responding well at the lower pressure levels. You said that the ES tightened as you climbed the charge weights, no? Makes sense; more consistent fill, better pressure, better ignition. I've also heard and read that some lightly compressed loads will show better consistency than loads with airspace in the case.

Of course, you also high-light why I don't bother weigh all of my charges. I've seen the 50-fps +/- variation enough times to not get too troubled. Stick with what works, really really. Out to 600 yards, I've had good luck with some .223 loads that get thrown charges and carefully seated bullets. At longer ranges, I'd probably start figuring out how to get the ES down as low as possible. But that's a different ballgame (not mine).

[elwaine]

Of course, you also high-light why I don't bother weigh all of my charges. I've seen the 50-fps +/- variation enough times to not get too troubled. Stick with what works, really really. Out to 600 yards, I've had good luck with some .223 loads that get thrown charges and carefully seated bullets. At longer ranges, I'd probably start figuring out how to get the ES down as low as possible. But that's a different ballgame (not mine).

600 yards is as far as I shoot as well, and my accuracy is pretty good out to that range (except when it's windy).

I was having no difficulty what so ever until a friendly old fellow at a gun club I just joined gave me several really good pointers - and if he stopped there, I'd be OK. But then he suggested I ladder the loads...

Theory is theory - but what works, works. So I'm going back to my 34.7 gr target load. Even though it's on the steep part of the slope and not within a plateau, I hit my target using it.

You guys are always great to chat with and to learn from... Thanks again for your help.

[elwaine]

:o I'm embarrassed to tell you guys this, but 75% of the cause of the "slow" bullets" was due to copper fouling. Fouling is the one thing none of us thought of. - Live and learn.

I always clean my rifle after each 20 rounds fired. (I put over 1,200 rounds through the bore so far). But I've learned the hard way that the cleaners I use - regular Shooter's Choice and Butch's - are not very good at removing copper. Although, I can tell you that Butch's removes more copper than Shooter's Choice.

I was perplexed over the problem of the "slow bullets" that we've been discussing. I remember reading an article about a gun smith who restored the accuracy in some rifles simply by giving them a thorough cleaning. So, on a whim, I bought a bottle Shooter's Choice Copper Remover (no one around here carries Sweet's... but I've just ordered some on line). It reeks of ammonia, but it sure did a job on removing copper.

I went through several dozen swabs before they came out white instead of blue. Back at the range, a repeat run of laddered rounds resulted in an increase in velocity of approximately 150 ft/sec. That left a spread of only about 50 ft/sec between my rifle and my buddy's. Fine tuning the seating depth closed that gap to about 20 ft/sec. +/- 5 ft/sec..

[MacGille]

Very nice, methodical investigation. I am impressed by the care and knowledge you show in reloading. Happy shooting.:)

[FrankenMauser]

Thanks for the update. It makes me want to scrub my .220 Swift even more.

I just can't figure out how to do it. I may have to go to a friend's garage...

I have some of the Xtreme Copper Killer, and holy crap does that stuff have some serious chemicals in it! I nearly had to visit the emergency room the first time I attempted to use it, and I hadn't even gotten a patch wet. Because of where I live, I have absolutely no means of providing enough ventilation to do a proper copper stripping.

Again, thanks for the heads up. I'll have to find another place where I can restore the Swift to its proper glory.