AA#9 158 JHP 357 Chrono Results and BC Gap Question

[PzShrekt]

Got my Labradar on sale for $250, and I was doing some load development a few days ago. All loads shot via Model 66-3 with 0.007”-0.008” BC gap. Loads 1 and 2 are both using Magnum primers, #3 and #4 use Standard primers. All brass used was PMC. Most accurate and best results were with #2. Does my BC Gap have anything to do with this wild variation I find in my loads? Pretty much none of these .357 loads are near max with my Hodgdon’s and Speer Data (uses CCI 500), older Alliant data calls for CCI 500s to be used in the 158 gr range with AA#9, starting = 13.5, max=14.9

I’ve also loaded 125 gr Berry’s plated bullets using AA#5 and Titegroup for a .38 +p load with a firm enough crimp to prevent bullet jump in my 66-3, these are all loaded near max using Hodgdon’s data. Disappointingly nowhere near the 950-1000 fps average I’ve been expecting. What gives? In your guy’s experience, does having a large BC gap give you wider ES and SD values? I heard SW tried for 0.003” to 0.008” of gap, mine is on the larger side.

7.6 gr AA#5 COL 1.440”
Avg Vel: 828.5 fps
Hi: 894
Lo: 706
Es: 188
SD: 38.45
A lot of scorching of case mouth. Slightly sticky on extract, tested with 7.8 was tested to be a pretty hard extract by me using Model 15.

4.8 gr Titegroup COL 1.440”
Avg Vel: 818 fps
Hi: 876
Lo: 765
ES: 111
SD: 29
Slight scorching of brass mouth. No resistance to extract, some tumble out.


Here’s my load .357 loads:

#1
158 gr Zero Bullet Company SJHP
12.0 gr AA#9 with CCI 550 SPM Primers
Seated to 1.570” to Cannelure
Slight Crimp via Lee FCD and resize.

Avg Vel: 1068
Hi: 1107
Lo: 919
ES: 188
SD: 55.6
Good accu, one chamber had a hard extract, everything else tumbles out with gravity, very clean brass.


#2
158 gr Zero Bullet Company SJHP
12.4 gr AA#9 CCI 550 SPM Primers
Seated to Cannelure ~1.570 Resized via Lee FCD, NO CRIMP
PMC .357 Brass

Avg Vel: 1115 fps
Hi: 1137
Lo: 1093
ES: 44
Std Dev: 16.4
Good accuracy, very slightly sticky extraction


#3
Same Components and COL
CCI 500 SP Primers
13.0 grains AA#9
No crimp just resized via FCD

Avg Vel: 1085 fps
Hi: 1146
Lo:1019
ES: 127
SD: 46.3
Good accu, easy extract of cases without stickiness, clean brass.


#4
Same Comps and COL
CCI 500 SP
13.5 gr AA#9
No Crimp just resized via FCD

Avg Vel: 1126
Hi: 1202
Lo: 1040
ES: 162
SD: 60
Not as good accu as #3, extract is slightly sticky, clean brass.

 

[stansdds]

Barrel-cylinder gap has a small effect on velocity, so I would not assign that as the reason for variation between published velocity and the velocity that you are achieving. It certainly will not cause or change the extreme spread in velocity.

 

[PzShrekt]

Barrel-cylinder gap has a small effect on velocity, so I would not assign that as the reason for variation between published velocity and the velocity that you are achieving. It certainly will not cause or change the extreme spread in velocity.

Any clue on making my loads more consistent? Deeper seating, etc, I already use magnum primers AND I use an FCD for all my loads.

 

[alwslate]

Try fully resizing your brass to get a grip on the base of the bullets. Roll crimp all bullets.

 

[stansdds]

There are things you can do to reduce the ES. Brass of one brand from the same batch. Resize and trim brass to the same length, straight wall revolver brass typically needs to be trimmed only once, the cases will not stretch like bottle neck cases. Use the same brand and type of primer. Uniform powder charges. Uniform bullet seating depth. Uniform case mouth crimp. Those things help, but you will still need to play with the amount of powder used as the powder charge will effect combustion consistency and that will effect the ES.

 

[Forrest r]

A lot of little things end up affecting the overall results.

You never stated what bbl length that 66-3 has. The longer a bullet is in a bbl, the more the cylinder gap comes into play. shooting 38spl's in a 357mag will also have an effect on velocity. A picture of a cut-a-way revolver cylinder. If you look at where the the sides of the bullets are touching the cylinder walls, you'll see a "step" in the cylinders. That "step" is the throat cut into the chambers of the cylinders. The further a bullet has to jump to that step, the more pressure/velocity is lost.

As others have stated, full length sizing is huge. A consistent short start pressure ='s a more even/consistent burning of the powder. Bullet neck tension does this, the end result higher velocities/consistent velocities.

Myself, I roll crimp all my straight walled cases. I also use a heavy roll crimp on everything. It might wear brass out quicker. But I found out a long time ago, they make more brass as I type. The only jacketed bullets I use in the 38spl/357mags are my own home swaged jacketed bullets. They have a large/deep cannelure for heavy crimps.

Loading 148gr wc's in 38spl cases, the bullets are seated long (to use in 357mag revolvers/that throat in the cylinder thing pictured above). With a 3.3gr load of bullseye and a heavy crimp.

Something else to look at is how the revolver is actually functioning. Weak fp hits will cause erratic ignition that leads to huge swings in velocity and lower than normal velocities. "Tuned" revolvers don't play well with hard primers and powders that are notorious for having complete burning issues.

Multiple data points are a good thing (more than 1 firearm testing loads). Awhile back I did head-to-head testing with:
2400 VS H110 VS MP300 using a cast 170gr fn bullet.
I used 357mag revolvers with a 2 1/2" bbl, (3x) 4" bbl's, (3x) 6" bbl's, 8" bbl & 10"bbl'd contender. After the testing I found that that 8" bbl was junk. It barely had higher velocities than the 3 6" bbl's used in the testing. I also found an excellent load for that 2 1/2" bbl'd 357mag. A full house load of 2400 pushing a cast/coated 170gr fn bullet clocks in @ 1200fps in this 586 pictued below.

Sounds like you need to take all the pieces and parts that are put together to do your testing & change/test 1 thing at a time looking for improvements in performance.

 

[taz666]

Great advice as always.

 

[mtgianni]

I find that AA 9 takes a heavy crimp to burn properly. I would suspect that is the reason for the spread in your hi-low readings and accuracy.

 

[PzShrekt]

Good replies on all, let me get in detail of what I actually do with my brass. I tend to do all my loads using the same headcase, I’ve never trimmed my brass, I don’t anneal them, but what I do is decap in a universal decapper, tumble in ceramic bead media with vinegar and soap, rinse and repeat with a wax based car soap, and then let dry on a towel, I get clean bead blasted looking brass with shiny primer pockets, which then gets run through a Lee full length decapper/FL resizer which swages the brass down to 0.367” near the mouth to mid length, tighter than my FCD which FL resizes only to 0.378”. Cases are then primed on the press hard to get the primer below flush on my Lee Single Stage O ring press, haven’t had a misfire since I’ve done this.

I drop my charges using a Lee Powder Measure, verified by a digital scale, the cases are already belled to accept my rounds. When I seat, I typically get within 0.003” of my desired OAL, then I run these through the Lee FCD to achieve better case and neck tension, if this causes my lead rounds to lose tension, I simply just crimp them. Btw my gun is a stock 4 inch model 66-3

I’ve tried to anneal some magnum Starline brass in the past to get better seating consistency, heat six second on a MAPP torch until slightly glowing, then drop into a bucket of water, as I understand that’s how brass anneals, opposite of steel. I find that with those cases I keep getting really sticky extraction, regardless of what loads I use, so they may potentially be over pressured somehow, so I stopped annealing.

 

[stansdds]

I've never seen the need to anneal handgun brass. Annealing is to maintain ductility (softness) of case mouth and neck of bottle necked rifle brass. It is possible that in annealing your revolver brass that you are also softening the body of the brass as well as the case mouth. the softer brass of the case body will not spring back as well, so it swells from combustion pressure and does not contract enough to allow for smooth ejection.

 

[chief38]

I have reloaded the same 38 special and 357 magnum cases time after time and have never annealed them. I've never had any issues either. I cold not tell you how many reloading cycles they have gone through but they are mostly 40 - 50 years old! Some are so old some of the nickel plating is wearing off and those I usually toss after shooting one last time. No big deal, I have tens of thousands of cases in that caliber. My 357 brass gets less of a workout as I shoot them way less, however none have been annealed and none have issues.

 

[PzShrekt]

So an update, it turns out that for my favorite AA#9 loads in .357 Mag, that being a 12.6 to 13.0 grains behind a Zero 158 JHP, my es and sd values improved SIGNIFICANTLY following a tilt up and then back down, or when I fire the first shot in a full cylinder.

Guess people saying AA#9 isn’t position sensitive are wrong about it.

Now ES is like 100-120 instead of 180-200, SDs are close to 40-50 instead of 80 or so.

Anyone got any experience with Dacron filler helping with the ES and SD on a .357?

 

[Rock185]

I've never tried to position the powder in a case just so. What I've observed in using the AA powders though, mostly AA-7 and AA-9, is that extreme spreads tighten up when loads are at or near the maximum.

 

[alwslate]

So an update, it turns out that for my favorite AA#9 loads in .357 Mag, that being a 12.6 to 13.0 grains behind a Zero 158 JHP, my es and sd values improved SIGNIFICANTLY following a tilt up and then back down, or when I fire the first shot in a full cylinder.

Guess people saying AA#9 isn’t position sensitive are wrong about it.

Now ES is like 100-120 instead of 180-200, SDs are close to 40-50 instead of 80 or so.

Anyone got any experience with Dacron filler helping with the ES and SD on a .357?

Most all powders are position sensitive to some degree but something is still wrong with your handloads. My .357 loads with plain cast SWC bullets with a firm roll crimp in the crimping groove and magnum primers usually have ESs of 20 fps or less with any powder.

 

[Forrest r]

Be careful with Dacron, it's extremely easy to ring the chambers in the cylinders. I use it from time to time with cast bullets in the 308w.

 

[WR Moore]

Just to get comparison data you might want to break down and run some factory ammo across the chronograph. You also need to realize that not every chamber in the cylinder is identical. Finally, velocity uniformity only really matters when you're shooting waaaay out there as it affects bullet drop and wind drift.