Weird velocity vs powder position

[griz]

I was testing how a powder’s position in the case affects velocity. This was done by clocking strings with the powder against the primer and separate stings with the powder against the bullet. Not surprisingly the rounds affected most by this phenomenon are straight walled revolver cases with fairly fast powders that have a lot of empty room in the case. I was using 38 Special loads with a 158 grain lead bullet at velocities of around 750-800 FPS from a four inch barrel.

Most loads showed about 70 FPS gain when the powder was against the primer versus all the way forward. This made sense to me and closely matched everything I had read about it. The surprise came with Accurate Arms #2. It lost velocity when the powder was positioned against the primer. It was only about 20 FPS less, but the effect was definitely reversed.

Any ideas why? By the way this is a very consistent load that had lower extreme spreads with the gun held level for each shot compared to the up/down positioning. Does it just ignite better with the powder evenly spread?

 

[caz223]

Try titegroup.
Typically, best results are had when the case is almost full of powder.
The problem is when using fast powders and big cases, that you get this position sensitive stuff.
Search a little, this horse has been beat to death.

 

[griz]

As a matter of fact Titegroup is what started me looking at this. Hodgdon says it is supposed to be less sensitive to powder position than other powders, and it's probably true in other calibers.

But I shoot 38's in SASS and noticed the first shot from the revolvers sounded weaker than the rest. Of course starting from the holster is the worst case since the powder will be against the bullet for that shot. Clocking them showed a big difference, about 160 FPS, but this was with a load reduced quite a bit from Hodgdon's starting load. I think the fact that there is so little Titegroup in the case exagerates the problem. Indeed when compared with midrange loads it is on par with 700X and a bit better than 231. The only other powder I tried was #2 which was better. At least in this narrowly defined field.

Please don't take this as a knock on Titegroup. I started using it because it was useful for SASS. I now prefer it in several calibers because of it's consistency. I just wanted to find out how it did in forward/reward comparisons, and stumbled across this blip in the way things are "supposed" to work. In fact I'm not sure this is a valid test because the powder would almost never be right against the primer. I'll still use Titegroup, but there are probably powders better suited to the powderpuff SASS loads.

 

[Jim Watson]

That is interesting, I have not tried AA #2 in position tests.

I did compare 231 (worst), Titegroup (middle), and 700X (best) in .44-40, though. And have a supply of .38 Specials with a wider variety of powder ready for the next opportunity to fool with it.

Guess I'll have to get some Trail Boss when it comes out. It avoids the position sensitvity question by being of very low bulk density and not leaving much room to move around inside the case.

 

[caz223]

I can't remember who was telling me this, so forgive me if I can't pick an audience, but there was someone mentioning developing wads/duplex loads etc.
I think he was also trying using quilt batting/paper 'wads' trying to keep the powder from wandering around in that big 'ol .45 colt case.

Isn't there a way of deep seating the bullet, and using even less powder to reduce the position sensitivity?

I guess I just can't wrap my head around wanting to put less powder in the case to get less velocity.
I usually load 'em up to the point that they look like flamethrowers after 6 in the afternoon.

 

[griz]

I guess I just can't wrap my head around wanting to put less powder in the case to get less velocity.

Yep, that's a little different. Some of the folks who frown on the little calibers have gone to 150 grain 45 bullets, kind of button shaped, to get less recoil than a standard 38. And then we get debates on minimum velocity, but that's another story.

As far as fillers or wads, I've tried grits as a filler and it does make for a more consistent load. But it's messy to reload, requires an extra step, and smells funny when fired. I haven't used dacron much, but I still worry about it moving around in the case. In an effort to retain some semblance of authenticity, SASS requires the bullet to be seated outside the case. Somebody did make some rounds with a reccessed bullet, which I think led to the rule.

Anyway, I picked "normal" loads to avoid an underloaded bias. I think I'll try again with minimum reccomended loads and add a few powders.

Can you point me toward any other threads about this? I only found a couple where people had measured the difference regarding position, even though people in several threads said Titegroup was the least affected.

 

[HSMITH]

The worst case of position sensitivity I have run into was a bulky powder in a straight wall case, namely Blue Dot in 45 Colt. It was terrible.

I have not run into problems other than this instance though.

 

[Sharps Shooter]

Griz,
Yeah, I've noticed some tremendous velocity swings using 158 grain bullets and HS-6 or Unique powder out of my wifes little LadySmith. I figured it had to do with powder position in the case and I've meant to try some dacron fiber pillow stuffing for a filler. I've used a wisp of dacron fiber in .44 Magnum cases with Unique powder and it seemed to work well. The truth is though, I never shot the .44 Magnum loads over a chronograph to determine just how well it worked. I've never used Titegroup either.
You've got me to thinking. I believe I'll go downstairs and load up a few .38 Specials with HS-6 and a dacron fiber filler and give them a try this weekend. Like I said - I meant to anyway. I'll let you know how it turns out.

 

[caz223]

OMG, .45 colt and blue dot cowboy loads!!!!
ROFL
I think I tried like 12 or 13 grains of blue dot and a 250 lead bullet.
I loaded up like 250 of 'em in my infinite wisdom, and went to the range.
I shot 50 of 'em, and my gun looked like it had been dipped in a bucket filled with molten tar, then tied to a string and dropped down a chimney for a week in mid-winter.
I had a light colored shirt, and I was covered in black specks all over, my face, my hair, my arms, etc.
BAD.
What a mess.
Then I still had to shoot the other 200.
It took a while to clean the gun, and I bet I never do THAT again.....

 

[Sharps Shooter]

Experimenting With Filler

Okay, I got out and did a little experimenting this morning with some .38 Special loads. I was using 158 grain SWCs and my revolver has a 4†barrel. I used 2 different powders – HS-6 and Tite-Group. I didn’t use filler with any of the Tite-Group loads, as it is not suppose to be position sensitive, but with half of the HS-6 loads, I used .1grs (a wisp) of polyester fiberfill batting to keep the powder against the primer. I also experimented using the same brand of brass (Winchester-Western) for half the loads and mixing brands for the other half. I fired ten shot strings of each load. The lowest standard deviation was 13.4 fps using HS-6 with filler and all W-W brass, which is kind of what I expected. But that load didn’t beat the Tite-Group load with all W-W brass and a standard deviation of only 16.9 fps by much. What did surprise me, was using filler obviously boosted pressures in those HS-6 loads by quite a bit. Without the filler in the HS-6 loads, velocity averaged 781.0 fps, but by adding just .1grs filler, keeping the powder against the primer, average velocity was boosted to 889.2 fps – over a 100fps gain.

6.0 grs. HS-6
.1 grs filler
WW Brass
Avg. Vel. = 889.2 fps
Std. Dev. = 13.4 fps

6.0 grs. HS-6
.1 grs filler
Mixed Brass
Avg. Vel. = 859.7 fps
Std. Dev. = 25.0 fps

6.0 grs. HS-6
No filler
WW Brass
Avg. Vel. = 781.0 fps
Std. Dev. = 39.4 fps

3.8 grs. Tite-Group
No filler
Mixed Brass
Avg. Vel. = 736.7 fps
Std. Dev. = 22.3 fps

3.8 grs. Tite-Group
No filler
WW Brass
Avg. Vel. = 765.9 fps
Std. Dev. = 16.9 fps

I also fired 5 shots with a 2†snubby using HS-6 powder, filler, and all WW brass. Average velocity was 792.0 fps and standard deviation was 18.0 fps.

 

[caz223]

Thanks, Sharps Shooter.
For putting numbers on what everyone suspected.
The velocity gains from HS-6 using filler are indeed impressive.

 

[griz]

Another thank you Sharp Shooter for the useful info. Did you try moving the powder charge any (muzzle down/up before firing) on any of the no-filler loads? I ask because I'm begining to suspect that some of the confirmations of Titegroup's claim of insensitivity to position position do not involve any difference in powder position. This may be semantics but to me that would justify a claim of consistency, but not any powder position advantage.

Thanks again, Griz

 

[Sharps Shooter]

You're welcome guys.
No, I didn't think about verifying whether or not TiteGroup is position sensitive. I should have done that. Because of the routine I followed, I suspect the TiteGroup was in about the same position for every round - lieing right in the bottom of the case. I was sitting, and after firing each round, I would lay the revolver on my bench long enough to write down the chronograph reading, then pick the revolver back up and fire another round.
I'm not sure a polyester fiber filler is the way to go either. My gun was pretty sooted up when I got through yesterday and adding a filler really slows down the loading process. I'll probably keep working with TiteGroup and no filler for a while. I'd like to find a consistent load that gives decent velocity. Besides, I have nearly a pound of TiteGroup left - at 3.5 to 4.0 grains per load, it's going to take a while to use it up.