Inconsistent neck tension / seating pressure causing weird velocities?

[GetReal]

At the range today, friend pulled out his Garmin to give me velocity data. Granted this is a new load, but this rifle always produced great results (for a semi anyway) - high single digit S.D.'s and under 20 ES.

Here's what I saw:

Bullet: 90 Berger Target
Brass: Starline, annealed, LE wilson bushing sizing die
PrimerL: 450 CCI
Rifle: semi 6 ARC


Velocities:

Rds 8 - 12 ................... Rds 13-17
8 - 2843......................13 - 2835
9- 2845 ........................14- 2900
10- 2854.......................15- 2873
11-2857 ........................16- 2898
12- 2874.......................17- 2880
AVG - 2854 ................... 2877
S.D. - 11.1 ...................... 23.3
E.S. 31.2 ......................... 64.0


Possibles for velocity variations: (1) different amt of force needed to seat bullets from case to case. (2) bbl heating up (3) bbl getting dirtier etc

To answer the usual questions: Yes, I anneal. I also use an LE Wilson neck bushing sizer die. I use a K&M press and LE WIlson chamber type seating die. I don't use a mandrel. I don't turn case necks.

 

[3Ackleys]

Not sure a rifle produces the ES- that is load driven. What do the targets look like? If they are good I wouldn't stress over ES.

 

[Mags]

Anneal and mandrel are the best ways I’ve found to ensure consistent neck tension.

What is your cleaning process? Do you chamfer and debur? How long was the ammo loaded for? These are all understated/overlooked components of handload consistency.

I’ve seen wet tumbling peen case mouths, I’ve seen brass over-cleaned, and I’ve seen loaded ammo sit to the point of “cold welding” bullets in the cases. There are a lot of factors that can impact how a bullet seats and how much pressure is required to start it moving (and by extension, affecting velocity).

 

[GetReal]

Not sure a rifle produces the ES- that is load driven. What do the targets look like? If they are good I wouldn't stress over ES.

Yeah... 0.35 -0.45" groups at 100 yd are nice, but a 60 fps ES will not look so good @ 600 - 800 yds.

 

[Zero333]

After annealing I tumble in corn cob/walnut once more to ensure consistent bullet slip.

You want a consistent carbon buildup inside the necks. Annealing burns off that carbon, making bullet slip inconsistent.

Also a consistent inside neck chamfer will help as well. I chamfer inside the neck right before loading.

 

[GetReal]

After annealing I tumble in corn cob/walnut once more to ensure consistent bullet slip.

You want a consistent carbon buildup inside the necks. Annealing burns off that carbon, making bullet slip inconsistent.

Also a consistent inside neck chamfer will help as well. I chamfer inside the neck right before loading.

Thanx for this info. I'm thinking somewhere there in my brass prep is my problem. I guess I'm wondering how much that "bullet slip" can affect velocity. In other words, I'm wondering if I can make a great load for 100 yds have better ES / SD so I can trust it at 6-800 yds.

 

[ebb]

Change of lot number with primers or powder??

 

[GetReal]

Change of lot number with primers or powder??

Everything I shot in this test was same lot #.

 

[Zero333]

Thanx for this info. I'm thinking somewhere there in my brass prep is my problem. I guess I'm wondering how much that "bullet slip" can affect velocity. In other words, I'm wondering if I can make a great load for 100 yds have better ES / SD so I can trust it at 6-800 yds.

One thing I forgot to mention, and thankfully @ebb reminded me... Primers can make or break a load.
Any primer designed for the AR aka CCI-41 / Fed-GM-AR can hurt ES/SD and accuracy.
CCI-450 or Fed-205m is usually a safe bet. Brass quality also matters just as much. CCI-450 are always my first choice for AR rifles and for bolt guns cci-450 & Fed-205m are neck and neck.

But since you're using CCI-450's, what I said is irrelevant.

 

[David Christian]

Did you only shoot 17 rounds? What happened with shots 1-7?

 

[JFrank]

At the range today, friend pulled out his Garmin to give me velocity data. Granted this is a new load, but this rifle always produced great results (for a semi anyway) - high single digit S.D.'s and under 20 ES.

Here's what I saw:

Bullet: 90 Berger Target
Brass: Starline, annealed, LE wilson bushing sizing die
PrimerL: 450 CCI
Rifle: semi 6 ARC


Velocities:

Rds 8 - 12 ................... Rds 13-17
8 - 2843......................13 - 2835
9- 2845 ........................14- 2900
10- 2854.......................15- 2873
11-2857 ........................16- 2898
12- 2874.......................17- 2880
AVG - 2854 ................... 2877
S.D. - 11.1 ...................... 23.3
E.S. 31.2 ......................... 64.0


Possibles for velocity variations: (1) different amt of force needed to seat bullets from case to case. (2) bbl heating up (3) bbl getting dirtier etc

To answer the usual questions: Yes, I anneal. I also use an LE Wilson neck bushing sizer die. I use a K&M press and LE WIlson chamber type seating die. I don't use a mandrel. I don't turn case necks.

What’s new about the load ?

 

[bozo699]

After annealing I tumble in corn cob/walnut once more to ensure consistent bullet slip.

You want a consistent carbon buildup inside the necks. Annealing burns off that carbon, making bullet slip inconsistent.

Also a consistent inside neck chamfer will help as well. I chamfer inside the neck right before loading.

I agree with this 100% however not all the carbon gets burned out when annealed and if you run a nylon brush in the neck and burnish it the bullets will slide in like butter.
Wayne

 

[VA_XTC_Shooter]

Simple as chamber heating up? The second set of shots generally are higher more erratic velocity, I could see a warm chamber causing that.

 

[fkimble@charter.net]

Shots 8-12 each got a little faster than the previous shot. Too clean a barrel, having to recondition its self? Shot 13 looks like an oddball. 14 to 18 look like it has normalized.

Frank

 

[GetReal]

Did you only shoot 17 rounds? What happened with shots 1-7?

Shots 1-2 were foulers. 3 - 7 were another group that I shot before my friend and his Garmin showed up.

Were I to guess, the barrel was speeding up as it was getting dirtier. I'll try some more rounds next range session, without cleaning it.

 

[GetReal]

I agree with this 100% however not all the carbon gets burned out when annealed and if you run a nylon brush in the neck and burnish it the bullets will slide in like butter.
Wayne

Presently I suspect one / both of the following (1) bbl was getting dirty / heating up and 2877 (above) is prettyy near my average velocity (2) I need to keep tuning the load with different brass prep

 

[JFrank]

What’s new about the load ?

 

[GetReal]

@JFrank ....nothing new here. First velocity test of this load. The two 5 shot groups loaded same session. A cuople of loaded rounds had noticeably lighter neck tension when seated.

I SHOULD have marked them. Lesson learned.