Longer barrel, slower speed? HS-6 .38 Spl.

K

Kframe

New member
I've been working up some loads in .38 S&W Special, using three bullets.
All are cast lead from Acme Bullet Company, 125 grain TC-RN, a coated 158 grain SWC and a Keith style 158 grain RN-FP. All sized .358

Going from my resources, I've been trying 6.3 grains of Hodgdon HS-6, with a magnum primer, in the 158 grain loads; 7.3 grains HS-6 in the 125 grain load.

Today, over the chronograph, I got the following averages.

125 grain TC-RN
M64 2"
838.0 fps avg

M15 4"
991.2 fps avg

M14 6"
979.5 fps avg

158 grain coated SWC
M64 2"
771.7

M15 4"
843.3

M14 6"
853.8

158 grain "Keith"
M64 2"
802.8

M15 4"
884.6

M14 6"
867.8

So, in the 125 grain and the "Keith" 158, my 4" M15 shot about 20 fps faster than my 6" M14. Now this could just be due to tolerance of these two particular revolvers, and I certainly could run some through many other 4 and 6 inchers, but as fun as that sounds I don't think I'm going to do that right this second. The coated 158 did go 10 fps faster out of the M14, so that may contradict the other findings.

My thought is *perhaps* the chosen powder charge is used up by about 4 inches and if I use more HS-6 or switch to something a little slower I may see increased gains from the longer barrel.
And that's my question, am I on the right track?

I am not looking to make any wrist-wrenching Keith loads, but I would like to get in the 950-975 fps range out of the M15 with the 158's, and a bit over 1000 in the M14.

38%20Cal%20125%20FP-230x230.JPG

I have an older version that has a round nose, not this flat one.
In fact, maybe it was a Lasercast slug, the lube was red, not blue.

Copy%20of%20C%2038%20158%20SWC-230x230.JPG


38Cal158RNFP3-230x230.JPG
 
Not unusual. I primarily load and shoot rifles and it is very common to see 25-50 fps differences between barrels of equal length. I've seen as much as 130 fps difference and seen 20"and 22" barrels shoot faster than 24" barrels with the same ammo.

Note where the 4" Smith 686 is consistently 75-100 fps faster than the 6" Python in these tests with the same ammo.

http://www.ballisticsbytheinch.com/357mag.html

I can't say for sure with the handguns, but with rifles a faster powder won't help. It is primarily differences in the tolerances in the chamber and barrel.
 
I'll have to check the gaps again, but IIRC they're around .003-.005.

I guess it sounds like statistically they're within the margin of error of each other and the velocity difference can't be pinned down to that two inch barrel difference...

The cases showed no obvious pressure signs (not that that mean much in a straight pistol cartridge) and extraction was easy, so I think I am going to up the powder charge before the next trip to the range.
 
Similar results

I've done chrono tests with 3 model 686's; 3", 4", & 8-3/8". I've gotten similar results. Between barrel friction and the barrel/cylinder gap, your lesser powered rounds can yield lower velocities in longer barrels. It happens.

IMO, in the 38 caliber range, there are diminishing returns once bbl lengths exceed 4". With a larger caliber (44), it's probably around 5". Of course, this is with "mainstream" ammo. If you're loading big giant rounds with tons of slow powder, your longer barrels will come through with more velocity.

My long barreled magnums are safe queens these days. The above phenomenon is one of the reasons why, among others.
 
The industry has long talked about "fast" vs "slow" barrels, without being able to find the secret measurement as to why.
For revolvers, you have the cylinder's throat ID, the cylinder gap, the forcing cone, the actual groove diameter, the bullet's actual OD after seating and crimp, standard statistical variation in averages for a small sample size, and some other variables I can't think of, I am sure.
 
Now this could just be due to tolerance of these two particular revolvers,...The coated 158 did go 10 fps faster out of the M14, so that may contradict the other findings.
Click to expand...
And that's my question, am I on the right track?
Click to expand...

The industry has long talked about "fast" vs "slow" barrels, without being able to find the secret measurement as to why.
Click to expand...

Powder position is a big deal in 38 special and 357 with certain powders
Click to expand...

All this, and more.

I think you are on the right track if you think its just one revolver shoots a little faster than the other. I think you are on the wrong track if you consider a 10fps difference to be in any way significant.

The reason the industry isn't able to find the "secret measurement" is simply because there isn't one. Its the total combination of ALL factors, and its different with each individual gun, and ammo.

I've seen a 100fps difference using the same ammo between 3 guns of the same (nominal) barrel length. That's beyond the common difference, but not unheard of.

I've seen shorter barrel gun clock higher speed than longer barrel ones. Again, not common, but it does sometimes happen.

Don't obsess over a handful of fps. It simply just wastes your time and effort.
 
Don't obsess over a handful of fps. It simply just wastes your time and effort.
Click to expand...

I just wanted to repeat and emphasize this answer, since some variation of it is what I am constantly telling people who contact BBTI about fairly minor variations in performance between one ammo and another.

Shot placement is much more important. Reliability of a particular ammo in your gun is much more important. Having some ammo (or components) rather than none is much more important. Don't get caught up in trivial concerns.

Jim
 
Thanks guys.
Given the small number of rounds I sent over the chrony to get the averages, plus the fact that I only used one 4" and one 6" revolver, I don't believe I've got a data set that shows much more than that all the bullets exited the muzzle. ;)

I do want to run a little warmer, so I'm going to continue to work up the HS-6 a few more tenths.

I also have a pound of U.Clays and am looking forward to playing with that some more. I used U.Clays about a dozen years ago in some light loads and was unimpressed by the leftover unburnt/charred powder and wide SD and ES numbers. Since then though I've read that UC is one of the powders that tends to burn cleaner closer to max pressures. So it's worth another look.
 
Well, the clear solution, is to do a decent size test, say 50 rounds, with your 6" barrel.

Then get hacksaw, and turn it into a 4" barrel and compare the results.

To be properly thorough, you would then need to cut it down to 2" and repeat.

:D

Or you could just not worry about it.......:D
 
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