Help Tweaking a Load

[Vince]

Howdy all.

I need some help tweaking a load for my .338 Win Mag with a 26" tube. I'll try to provide all the relevant data and see what you all suggest.

Contact With The Lands: 3.477"
Caliber: .338 Win Mag
COAL: 3.330"
Bullet: 200 Grain AccuBond
Group Size: 1.28"

I'm looking to improve the group size and was thinking of seating the bullets deeper but I'm unsure how much deeper to try. I could also go longer if that seems better and I'm willing to try either. The longest I can go is 3.340" however for my magazine box. I have heard that Accubonds like some bullet jump and I seem to be getting that.

Powder: IMR 4350
Charge: 71.0 Grains
Min Charge: 69 Grains
Max Charge: 73.0 Grains

I was also thinking of varying the powder charge by 0.3 Grains in either direction to see if that improves things.

70.5 Grain Group: 1.8"
71.5 Grain Group: 3.1"

In a three shot string I get the classic two close, real bloody close most times, and another way out there. I'm also thinking of trying IMR 4831 as that's the only other powder I have on hand that I have data for in my Nosler manual.

My thinking leads me to believe I may have the wrong powder for this bullet and rifle combination but I'm not inclined to try another powder and AA3100, no longer in production according to my powder supplier, is unavailable. I'd prefer to stick with Hodgdon and IMR powders if possible as they are the easiest for me to acquire.

Thank you,

Vince

 

[HeathSexton]

When I get 2 and 1 I start working in .005" at a time and it will usually tighten right up.

 

[Sas874runner]

I would seat the bullet further out by .005" &.010"as well add in by the same amounts and see where the group starts to tighten up. I would bet it tightens up the further out you go. If you can and are not limited by magazine length

 

[Vince]

When I get 2 and 1 I start working in .005" at a time and it will usually tighten right up.

Do you seat deeper or go longer?
What is the minimum length I can seat a bullet, the 200 Grain AccuBond in .338 Win Mag as I'm constrained by my magazine box seating longer. Max COAL is 3.340" and I'm loading at 3.330" right now.

Vince

 

[HeathSexton]

I work the seating depth in/deeper by .005". So if I was having 2/1 @ 3.330" my next batch would be at 3.325" then 3.320" etc.

 

[Vince]

I work the seating depth in/deeper by .005". So if I was having 2/1 @ 3.330" my next batch would be at 3.325" then 3.320" etc.

Thank you.

 

[Vince]

Another question:

What is the deepest I can go according to SAMMI spec?

 

[dubyam]

SAAMI does not give minimum COL guidelines, to my knowledge, for rifle rounds. All pistol rounds should be considered minimum lengths, as the issue of deeper seating shrinking the compression chamber is far more pronounced in straight walled pistol rounds, and can lead to nasty pressure spikes. You can seat as deep as you like, right up until you get to the ogive of the bullet, as it's not wise to seat deeper than that.

I'm in agreement with Heath, as to the direction of seating change, too. I've seen rifles give me two close and one outlier, and shortening up COL has been good for bringing the outlier in a bit. You may find it's a heat issue with the barrel, if COL changes don't help it. If the barrel is floated when cold, but when hot begins to develop pressure along one side of the barrel channel or the other, it can cause that third shot to be a flyer. Easy test for this, if COL tweaks don't fix it, is to fire two, let the rifle rest long enough to return to ambient temp, and fire two more. If all four are close and tight, take a look at your bedding.

 

[wayno945]

Hodgdon's website lists 4064, 4895, H414 as potential powders for the 200 GR Speer. Velocity from their max loads is within 50 FPS of the powders you tried. Might be worth a shot with your ABs if you have some lying around.

 

[gerry]

It does sound like you are real close, and have gotten some good advice so far. By tweaking the depth and maybe even the charge slightly you should get a great load. Along with what Wayno just suggested Varget might be real good with the 200's or lighter as well.

 

[Vince]

Thank you all. :grin:
I knew I came to the right place.

Vince

 

[Vince]

I just ran up some test loads with IMR 4831 to shoot tomorrow.
After that I'll reassess and evaluate. Then, if I don't get something better than what I've already gotten, I'll start tweaking the IMR 4350 load.
Thank you all for the help. I'm crossing my fingers about the 4831 and hoping. The reason I decided to try the 4831, even though it burns slower, is because I'm pushing them out of a 26" tube with a muzzle brake added on. The barrel is an honest 26". I got to thinking maybe a slightly slower powder would do better in the longer barrel but I won't know until I try it.
If this doesn't work I'll try some other powders.

Vince

 

[remingtonman_25_06]

Half grain increments is adequate for normal magnum case size, usually even for fine tuning.

I suggest going up and and down .5g increments from your current load, as well as .010" deeper sets on the OAL, only AFTER you nail the powder charge.

sounds like your as long as you can go already and still reliably function so only way to go is deeper.

remember to only change one variable at a time when testing loads and keep good records.

If that doesnt work, try another powder or two. If that doesn't work try a primer swap or two. Still dont work, well then try a different bullet and start all over