Decreasing velocity question

[Star1pup]

I ran some loads over my Chrony today using my 1894C in .357.  It seemed that each shot fired showed a decrease in velocity.  By the time I fired 5 rounds it was significant.  It is really hot here.  Could it be that the barrel is getting hot?

I'm loading 11.5 gr Blue Dot behind a Hornady 125 gr HP-XTP.  I don't have my book here with the data, but the first shot was something like 1,850 and then it started down.  It was in the mid-1,700s after 5 shots.

[DWTim]

The higher ambient temperature would likely increase velocity. It's normal for loads to vary by a certain percentage. Just about any reloading manual will tell you that their velocity figures are an average, and loading data which only quotes the highest velocity of the lot is disingenuous. A variance of 100 feet-per wouldn't be unusual with my .357s, but then again, I only shoot them out of short-barrel hanguns.

Any other signs that something is wrong? Bad brass? Unusual report? Just guessing here, buy maybe the bullets are jumping the cases under recoil? :?

[CyberSniper]

I developed the opinion that blue dot was not a good powder to use in hot weather years ago.
I don't know if they have changed anything about it over the years, since I haven't
used it in a long time.

[Star1pup]

DWTim:  It was all new brass and everything, including the report seemed fine.  The first round was 1,852 and the second was 1,875.  Then it dropped to 1,791 and 1,716.  I let the rifle sit for a while.  It was still warm when I shot the final round at 1,747 so it did take it up a bit.

I realize that this is a short gun, but I would like to develop a decent round that would make a fairly good group at 100 yards.  Maybe I'm asking too much.

CyberSniper:  I was using Blue Dot because it was recommended by Alliant.  They also recommended 2400 so maybe I should try that.

[CyberSniper]

You might want to try Hodgdon H-110 also, or Winchester 296.
Those two are very similar to each other.

[DWTim]

Well, so much for guessin' I don't think 1800 is too much ask from that gun at all!

I'm surprised to hear this about Blue Dot. Perhaps I should avoid it, since it looks like it would be an awful nice powder for my 45 LCs. I use Unique, and that seems to be temperature-sensitive as well.

[CyberSniper]

We used to see pressure spikes with Blue Dot in hot weather.
I've never had trouble with Unique, but then maybe that's because I
never used real heavy loads with Unique.

[dubber123]

Is it possible that there was oil or some other type of lube in the bore that was getting cleaned out as you shot?  I have shot loads out of my 50-70 contender pistol that varied 100 fps.  but I also have one that varies less than 10.  Same bullet, different powders.  2400 is faster than H-110, and may work well with your lighter bullets with hot loads.  It doesn't burn clean with lighter loads though, and if you don't shoot it at high enough pressure, it will likely dirty up your action with unburned powder.

[Sixgun]

The things that you are seeing, shooting over your chrony, is the reason to own a chrony.

I have found that when working up a load, one essentiol step is to run them over a chrony.  a high extreme spread will kill accurracy.  It can all change with a different powder, bullet, or a primer.  Cases in a 357 don't seem to be as critical.

One time a friend, who didn't handload, shot his 30-06 over my chrony.  He got an extreme spread of over 150 fps from some Remington ammo he thought was pretty good.  He did get flyers but always figured it was him and not the ammo.  After that session, he decided to try some of my handloads.  I loaded up some medium loads for him and he got severe case seperations and we found out his headspace was extra long.  It worked fine with new brass but when I loaded those cases once more, they seperated.  He got the rifle fixed and now it shoots good groups with the origional ammo.

For a 357 some of the powders that I get really good results with are:

Bullseye for cast bullets.  5 gr for any weight from 125 to 170 gr bullets will give 1400 to 1100 fps with great accuracy
Unique for medium loads.  8.5 gr under a 125 gr jacketed bullet will give 1650 fps and good accuracy from a 20 inch barrel.
H110 and W296 are good
Lil'gun.  16 gr with a 190 gr cast bullet will give 1900 fps and knock down 200 meter rams really good.  20 inch barrel.

These are just a few that I like and they were all developed with my guns using a chrony.

Sixgun

[Bullseye]

Now I have a different opinion and think that this a good reason not to own a Chrony.  I find a load that has the accuracy i want which I have always been able to do without a Chrony and keep from beating myself up and worrying about things like this that I would find with a Chrony.  I am an Engineer and have that cursed technical and worrying mind that thinks way to much over small details and little things like this would drive me nuts!