Interesting finding on velocity difference between 158 grain Zero bullets.

[muddocktor]

The other day I finally got to go to the range and play a little and try out some new-to-me Zero 158 grain JHP bullets and brought along my chronograph and I also brought along some rounds loaded with some Zero 158 grain JSP bullets I had bought a year or so ago. Besides the different bullets, everything else was the same as far as powder charge and primers and both batches were loaded on the same day from the same lot of powder. I figured that since the shape of the bullets were pretty close besides the fact that one was a hollow point and the other was a soft point, but I did see a significant velocity difference. Here is what they were loaded with:

Pistol: S&W 627 Pro (4" barrel)
Bullet: Zero 158 grain JSP or 158 grain JHP
Case: assorted
Primer: CCI 550
Powder: Alliant 2400, 14.5 grains
Both were loaded and crimped in the crimp serrations

The Zero 158 grain JSP bullets averaged 1037 fps with a SD of 17. The Zero 158 grain JHP loads averaged 1114 fps with a SD of 22.

The JHP bullets averaged a good bit faster than the JSP bullets, which surprised me. The SD also was higher, but not a whole bunch more.

I also brought along my old Beretta M9 and a couple of different loads to run across the chrono too. The bullets were some Zero 147 grain JHP bullets and some MBC 124 grain coated "Small Ball" bullets. I had gotten the Zero bullets when I had ordered the 158 grain JHP bullets for kicks and giggles to try out and I had bought the Small Ball bullets the last time I had ordered from MBC. The loads for them and the results are as follows:

Pistol: Beretta M9 (4.9" barrel)
Bullet: Zero 147 grain JHP
Case: assorted
Primer: CCI 500
Powder: Longshot, 4.4 grain
Avg velocity: 889 fps
SD: 9

Bullet: MBC 124 grain Hi Tek coated "Small Ball"
Case: assorted
Primer: CCI 500
Powder:Longshot, 5.0 grains
Avg Velocity: 1061 fps
SD: 14

Both of those loads were fun to shoot, with pretty mild recoil and cycled well and grouped the cases pretty much in one area. And looking at the primers, they were not nearly as hot as the factory cases I also picked up at the range and were not remotely close to being flattened. They were some fun rounds to shoot.

Finally, I also brought along my 629-3 Classic and some light loads for it and ran them across the chrono.

Pistol: 629-3 Classic (6 1/2" barrel)
Bullet: Bayou Bullets 240 grain Hi-Tek coated SWC
Case: FC
Primer: CCI 350
Powder: Alliant Unique, 7.1 grains
Avg Velocity: 876 fps
SD: 12

These were also a pleasure to shoot and I had fun running 100 rounds of this load. They also seemed to shoot pretty clean for a Unique load also and the pistol isn't too terribly dirty.

The conclusion of all this? I had a good time playing at the range and surprisingly, it didn't rain until I was driving home. And I figured I would share a little number info on what I saw with these loads at the range with my fellow reloading friends here on the forums.

 

[Pisgah]

Honestly, I would not consider those 158 gr. figures significantly different. It's not unusual to see a less-than-80'/second shot to shot variance, and hardly more significant to see that difference in an average, unless the average includes at least several hundred rounds. In fact, they are so close that it would not surprise me at all to see the numbers reversed if you ran the same comparison again.

 

[mike campbell]

Statistically, if that data is from only 6 rounds of each, the 1037 and 1114 means are very significantly different.

Given identical primers, powder and charge weights one wonders why one is likely higher pressure than the other. Different bullet tension would be the next most logical variable.

Less likely bullet tension factor would be bullet diameter...same maker and weight, you'd expect the same diameters but maybe not. A micrometer (not calipers) would tell.

More likely tension factors would be case make and degree of crimp. Some makes will have thicker walls than others; mixed lengths can have some heavily crimped, others not at all.
Bottom line: just one of those things that would make me say "hmmmm."

 

[muddocktor]

Those were actually averages from around 14-16 rounds, not 6 or 8. I had a few I had to cull because of bad readings. And I found that the 2400 was shooting kind of dirty too, with a little unburned powder left in the cases, so I think that some unburned powder was also traveling out of the barrel too and possibly interfering with the reading. One string I shot I had to cull because over half the readings were a little more than 1/2 the expected velocity in the 600-650 ft/sec range. When I backed the chrono further out around 3 feet those went away.

BTW, I'm not trying to be overly scientific with this or trying to make some competition ammo or anything. I'm just out having fun and putting rounds on target. And sharing some info here, as many times I see people post up stuff here and assume some velocity for their load with no scientific basis to establish real world results. I think that next time I play with these I will use Accurate #9 instead of 2400 for my powder, as I've found it burns more completely than 2400. And I will bring my Rossi 92 to compare the ammo betwen a short barrel pistol and a 20" barrel rifle.

 

[forestswin]

How far was the chrono from the muzzle for the data you are keeping?
3 feet?
Or 3 feet more from initial placement of say 10 feet?

 

[muddocktor]

Yeah, 3 feet from the original placement, which was around 10 feet or so.

 

[forestswin]

I agree, it's fun to get out and play at the range

I'm trying to get out later this afternoon

I really don't think you're getting too much velocity differences.

I haven't really researched the topics much....but your 2 bullets do have different sectional densities and different ballistic coefficients

How long are the 2 bullets?
If same COL
Is one seated deeper in case than the other?

 

[Will2]

I expect the HP would be longer than the SP. If so, and you used the same COL, then the HP would have a smaller volume for the powder. This would increase velocity slightly...

Wil

 

[BB57]

The Zero 158 grain JSP bullets averaged 1037 fps with a SD of 17. The Zero 158 grain JHP loads averaged 1114 fps with a SD of 22.
The JHP bullets averaged a good bit faster than the JSP bullets, which surprised me. The SD also was higher, but not a whole bunch more.

Statistically, if that data is from only 6 rounds of each, the 1037 and 1114 means are very significantly different.
Given identical primers, powder and charge weights one wonders why one is likely higher pressure than the other. Different bullet tension would be the next most logical variable.
Less likely bullet tension factor would be bullet diameter...same maker and weight, you'd expect the same diameters but maybe not. A micrometer (not calipers) would tell.
More likely tension factors would be case make and degree of crimp. Some makes will have thicker walls than others; mixed lengths can have some heavily crimped, others not at all.
Bottom line: just one of those things that would make me say "hmmmm."

I don’t put much confidence into 5-6 shot sample sizes, but the OP used 14-16 rounds. With that sample and SDs of 17 and 22 respectively, 1,037 fps is significantly lower than 1,114 fps.
Generally speaking with an average velocity of 1,037 fps and a SD of 17, you’d expect 67 of the rounds fired from a 100 round box to have a velocity within +/- 1 SD. In this case, between 1,020 fps and 1,054 fps. About 95 of the rounds from a 100 round box would fall between 1,003 fps and 1,071 fps, and essentially all of the rounds in the box would call between 986 fps and 1,088 fps. In short the expected extreme spread is +/- 3 SD, or 6 SD in total (17 fps x 6 = 102 fps extreme spread).
Similarly, for the 1,114 fps load with the SD of 22, you’d expect 67 of the rounds fired from a 100 round box to have a velocity within +/- 1 SD. In this case, between 1,092 fps and 1,136 fps. About 95 of the rounds from a 100 round box would fall between 1,070 fps and 1,158 fps, and essentially all of the rounds in the box would call between 1,048 fps and 1,180 fps. The expected extreme spread is again +/- 3 SD, or 6 SD in total (22 fps x 6 = 132 fps extreme spread).
There is an overlap of 40 fps in the 3rd SD between the fastest JSP rounds and the slowest JHP rounds, but that represents only about 2% of the total rounds fired.
The JHPs are significantly faster, at least at a 95% confidence level.
----
It’s hard to say exactly why, but there are some easily identifiable suspects, even if exactly the same powder charger, crimp, etc was used with both loads.
The hollow point displaces some lead, which has to go somewhere if both bullets still weigh 158 grains.
If the nose profile is the same, then the weight displaced from the hollow point ends up being in the base of the bullet, where it not only reduces the case volume under the bullet (if the same OAL is used) but also increases the bearing surface of the bullet, and both of those will increase the pressure while the rifling engraves the bullet. The longer bearing surface would also very slightly increase friction in the bore, but would also very slightly reducing the amount of gas that gets past the bullet in the throat and in the barrel, so it’s a bit of a wash after the initial pressure effects the charge ignites until it’s fully engraved in the rifling in the barrel.

 

[S&WIowegan]

I agree with the posters above who suggest the JHP bullet is longer and would tend to increase velocity(all else being equal). Powders like 2400 and Accurate #9 perform best with full case loads. Reduced loads don't fully burn and leave powder granules. I experienced the same thing 20+ years ago.

I'll share another lesson I got shooting 9mm handloads using mixed brass. I was getting 4 to 6" groups at 15 yds. off bags with my Beretta M9. I got much better groups using only one brand of brass....doesn't matter what brand as long as they are the same. Try it...doesn't cost you.

Have fun.

 

[rwsmith]

Am I reading something wrong...

Aren't all of those velocities low for that load???? 14.5 grains of 2400 with a 158 gr jacketed should be going about 1200 ft/sec or better???

 

[fredj338]

Same weight bulllets, the JHP will have a slightly longer bearing surface. IT doesn't take much to up pressures & increase vel a little bit.

 

[ameridaddy]

I expect the HP would be longer than the SP. If so, and you used the same COL, then the HP would have a smaller volume for the powder. This would increase velocity slightly...

Wil

Bingo! We have a winnah!

 

[muddocktor]

I just took a few pics of the Zero bullets to post here. Looking at them, the distance from the base of the bullet to the crimp groove/serrations is very nearly the same on both bullets, so case volume differences with the bullets in the loaded condition are minimal, but might help account for the differences in velocity. The JHP bullet is longer, .650 inches versus .635 inches for the JSP bullet. Both bullets show a diameter of .357 according to my dial calipers. I'm thinking the velocity differences between them might also be tied into the bullet configuration above the crimp groove more than anything else, but that is just a guess. BTW, with revolver loads, I load to the crimp groove and not OAL.

Here are the pics. The JSP bullet is the one in the middle and the JHP bullets are on each side of it.



RW, the velocities might seem low at first glance, but you are comparing apples and pears as far as barrel length goes. My 627 Pro has a 4" barrel. Looking at the Alliant site, they are showing a max load of 14.8 grains of 2400 for 1265 fps, but that is with a 10" barrel. That 6" of extra barrel length can account for the different velocities.

 

[muddocktor]

Next time I do some experimenting with them I will use just 1 brand of cases, S&WIowegan. That is a good point you brought up and takes another variable out. I have some brand new Starline brass sitting in a box I can put into service when I do the next round of playing with Accurate #9 instead of 2400.

 

[hdwhit]

muddocktor wrote:
The Zero 158 grain JSP bullets averaged 1037 fps ... 158 grain JHP loads averaged 1114 fps....

Did you weigh the bullets before loading them to verify that they were both the same weight?

Just because they are both in the 158 grain class doesn't mean they both weighed exactly 158.0 grains and if one type was even a couple grains heavier than the other, that would be sufficient to explain the difference.

 

[muddocktor]

No, I did not weigh them before. But I just grabbed a sample bullet from each box and weighed them on my powder scale. And in both samples, they each weighed 158.4 grains. I'm sure if I grabbed 10 of each I would see some variation, but from that simple grab-n-weigh I am satisfied that they are essentially the same weight.

 

[Twoboxer]

Not to beat a dead horse . . . well, it is fun I guess . . . in addition to the JHP being longer I'd guess your seating plug might hit the JHP higher on the ogive. At least it looks that way from your photos.

That would seat the JHP even deeper.

 

[muddocktor]

Not to beat a dead horse . . . well, it is fun I guess . . . in addition to the JHP being longer I'd guess your seating plug might hit the JHP higher on the ogive. At least it looks that way from your photos.

That would seat the JHP even deeper.

I set the seating plug for the bullet I'm loading. In other words, I adjust it to set the bullet to where the crimp is applied in the crimp groove/cannelure on whichever bullet I am loading. I've been reloading straight wall pistol cartridges since the mid 70's and for cartridges such as 38/357 and 44 Mag. I've always set the seating depth so that the roll crimp is in the crimp groove or cannelure and don't worry about OAL as long as they fit in the cylinder.

 

[rwsmith]

Could somebody please address this question.....

I asked it above but I think it was blown out of the water by the bearing length theory.

"Aren't all of those velocities low for that load???? 14.5 grains of 2400 with a 158 gr jacketed should be going about 1200 ft/sec or better???"