Wide range in velocityin my 38 load

[westczek]

Looking for a little advice. I just got a chronoghaph and discovered there is about a 40 fps range in my 38 special load. This is shooting my 6" barreled 686 revolver. Bullets chrono'd 792 to 834 fps.

I'm using 158 grn lead round nose bullet with 4 grns of Unique. I'm loading on a Hornaday LNL. I've been wieghing every tenth charge with a Lyman mechanical balance.

My 9mm load using 147 grn jacketed bullets and W231 showed similar range of velocity out of my CZ75.

any thoughts?

 

[steveno]

sounds normal to me

 

[Ignatz]

Nothing wrong with that. Different powders show tighter or larger spreads. Are you using mixed brass?

 

[RDub]

I'm assuming you are using a powder measure of some kind and not weighing every charge..
UNIQUE has relatively large flakes which makes consistent drops within 0.1 tenth of a grain unlikely.. Usually its more like 0.2 or 0.3 grs.

Even when you weigh every charge you are going to get a velocity spread of some kind. There are just too many variables involved to expect every shot to clock exactly the same.

 

[Wyo]

I spent two years chronographing various powders and bullets in the 38 Special. Unique usually showed good accuracy with 158 gr. lead bullets, but the numbers were inconsistent, sometimes approaching variations of up to 75 fps. The most consistent powder I found, by far, was Bullseye. Velocity variations were very small with all bullet weights tried, sometimes in the 10 fps range. Some folks will tell you they don't like Bullseye for various reasons and I make no comment on that one way or the other. But I can tell you it's the most consistent stuff out there.

 

[ArchAngelCD]

Those numbers sound just about right for Unique in a .38 Special. I don't see a problem here. Did you think your ammo shot at exactly the same velocity before you bought a Chrono to see what you are really getting?

 

[westczek]

Thanks for the responses. It's nice to know that the spread isn't as bad as I imagined.

I didn't expect every cartridge to have the same velocity, I just expected less of a difference. I started reloading last year and this was my first time using the chronograph.

I'm not using mixed brass. I have my revolver cut for moonclips which means I need to stick with either Remington, Federal or Starline brass. The batch I was using today was all Remington.

 

[ddixie884]

4grs is a very low density load with Unique, I think it would be more consistent with a heavier charge. JMHO.

 

[handgunner356]

If that is your max spread then your standard deviation is probably something like 20, which is quite good. Any load I come up with that stays in the 20 or less SD range usually prints very good and is better than most factory loads you'll ever check.

 

[Titegroups]

Always have wondered how accurate and repeatable a chronograph actually is. We all would like to think they are perfect, but I doubt that's the case.

 

[Steve C]

Shoot some factory loads over your chronograph as a standard and you will see similar range and deviation. While the chronograph's are not an exacting measurement every time their published accuracy is generally 99.5% so on a 800 fps load a maximum of +/- 4 fps could be attributed to the chronograph

 

[Skip Sackett]

Not always the case but................

4grs is a very low density load with Unique, I think it would be more consistent with a heavier charge. JMHO.

This is probably the best information in the thread. 4gr of Unique is too light of a load with a 158gr bullet to be consistent. Not only that, I'm gonna guess that you get a bunch of smoke and unburnt powder in your barrel too. Just a guess though.

I don't use a lot of Unique. One fellow I shot against in a plate competition used it though and he said that he found all of the bad things associated with Unique went away at 4.5gr.

What do you use your moon-clipped M686 for? I would guess you had it modified for some kind of competition. Just wondering what kind. If you want a lighter round for faster follow up shots, maybe a different powder would be better.

As for a chronograph, good on you for getting one. They are the only tool most of us hobbyists have to check our work. If you can get the SD down to single digits you are doing exceptional. Other loads shoot fine with 20fps SDs. 40fps isn't a big spread, or ES. If your chronograph doesn't give you the SD you can find it in most spreadsheet programs. Microsoft Excel or Works, Openoffice has one for free.

I have a sheet all set up that has those functions. I just plug my rounds into it and is shows the other numbers automatically.

Hope this helps!

 

[epj]

4grs is a very low density load with Unique, I think it would be more consistent with a heavier charge. JMHO.

+1, and likely burn cleaner as well.

 

[westczek]

The loads are a little smokey, and it did get a little tougher to load rounds as I went. I did load on the low side of the loading data for Unique.

I shoot USPSA matches and I need to make the minor power factor required. I'm just starting out with revolver, so minor is fine. Leave major for the guys with the 625s.

These loads were just making minor, so I really do need to go to a heavier load, but not much. I need the slow side to stay above 800 fps to be safe.

I like the heavier bullets for knocking down heavier steal poppers. I switched to revolver from production.

 

[goldenlight]

I load 4.4 gr. of Unique in 357 magnum cases. I've been using the same loads for decades.

I chronographed them so long ago, I can't remember the data well enough to quote numbers.

But your numbers sound about the same as what I was getting. I was surprised at the velocity variation, considering how good my accuracy is.

Unique has fairly large flakes, so it doesn't meter as accurately from most power measures as well as some other powders.

I use Unique, because I started with it over 30 years ago, and I can load 8 different kinds of pistol and revolver ammunition, using the same powder.

If you are getting good accuracy, I wouldn't obsess about your chronograph numbers too much.

 

[Vulcan Bob]

Dont forget a firm crimp. I use some light Unique loads for some of my older guns and use a medium roll crimp to aid ignition. This may help with shot to shot deviation a bit, but as already stated what you now have is not unusual.

 

[westczek]

I'm really glad everyone could put this velocity question into the proper prespective for me.

I did use a roll crimp and accuracy is good. I put my numbers into a spread sheet and calculated the standard deviation, came out at just over 14.

I love my new toy, I think I could really geek out with this chronograph.

 

[ChuckS1]

Unique is best when NOT lightly loaded. I like firm crimps too and have found that the upper half to upper third of the loads shoot the best and the cleanest.