Can't lower my S.D. HELP!!!

[m249]

I have tried different powder, different powder chargers, different primers, and seating depths. What else should I try? I will do anything at this point. My S.D. is stuck around 18.2. Right now I am shooting a HS precision HTR in 300 win mag. load is hornady brass, 190 VLD, last load was 77.6grs of H-1000, fed 215m primers.

Would moving the chrono farther back from the bench make a difference?

 

[SBruce]

What kind of chrono are you using?

How close is it to the bench when you're getting 18.2?

What kind of ES are you getting with the load that's giving 18.2 SD?

Average muzzle velocity?

 

[J E Custom]

Have you tried H4831 and a large rifle primer instead of a magnum primer ?

Sometimes a standard primer will lower SDs.

Also make sure that bullet to case neck tension is consistent. (Sometimes to get constant tension
you must turn all of the necks the same).

Just a thought

 

[cfvickers]

I have had the same problem with my 300 win mag. I get the best ES and SD numbers with Fed GM210M primers and, believe it or not, Hybrid 100V and a 168 berger, charge is 70.5 grains at 3.485. yes that is very long for a .300 win mag. but mine is one of those older model 700s with a very long throat but a magwell to hold it. I have not tried the bergers but that is about what I got from 190 hornady interlocks. I use the load but I am not shooting over 400 yards with it and it is shooting 1 hole groups at 100 and 3/4 inch at 200. Doubt if this helps much but I feel your pain.

 

[diriel]

Have you annealed the necks? Work hardened necks will cause real bad ES / SD. Also, as stated, try non magnum primers. Win LR primers are actually real good with H1000, Wolf LR, and Fed 210m are also real good options. Magnum primers *USUALLY* only come into their own when you head north of 90 grains of powder, and/or are using slow ball powders. Also, if you shoot extreme cold weather -20 F. or below, then using a Mag primer can make a difference. I find the Win LR primers to be a good balance of Almost as hot as a Mag primer, but still "mild" enough to give good chrono numbers once you have your other things like Neck Anneal, Seating Depth, Brass Prep done.

Good Shooting,
Gary

 

[m249]

I haven't done anything to the case necks. I have been using a CED M2 chrono about 10 to 12 feet away form the bench.

My ES has been up around 50 if I remember right. My muzzle velocity has been averaging around 2800.

I'll load some up this week with some 210 match primers and see what that gives me.

 

[cowboy]

I would be on the same thought pattern as SBuce on this. A chrony of any make or model can do some funny things at times. Try moving your Ced M2 out to 20'0" from your muzzle (that should prevent any irregular muzzle blast)- go to a ballistic calculator when you are done and play with it to get your true muzzle velocity - it'll be 30-50 fps higher. I see where you are from Wisc. If your chrony is setting on snow - I'd lay a tarp under it to prevent any irregular glare from the snow. Some guys are now totallty enclosing their chrony's with a box to prevent this also.
Any chance you can borrow another chrony and set the 2 up back to back?
I about rebarreled a rifle one winter and come to find out it was all a brand new chrony's fault - really my fault as I didn't know any difference.
When this doesn't work - then back to switching components as others have said.

 

[RockZ]

Try Ramshot Magnum powder.
I've had great luck with it in my 300win and 208AMAX

If you want to stick with H1000 you will have to keep trying different powder charges since that is the biggest determining factor for ES and SD.

 

[rscott5028]

If you want to stick with H1000 you will have to keep trying different powder charges since that is the biggest determining factor for ES and SD.

Do you mean to say that accurately weighed powder to <1/10 of a grain is the biggest determining factor in ES/SD of the MV even after you identify and stay within a decent accuracy node?

I would've thought consistent neck tension would be next, provided you're using good match grade components and stable powders under decent environmental conditions?

 

[TexasHunter]

A couple of thoughts that haven't been mentioned.

(1) Try a couple of benchrest brass prep tricks like deburring your flash holes and uniforming your primer pockets. I found this to make a fairly significant difference in cheap brass.

(2) Instead of (1) buy a box of Lapua brass and try that. It doesn't need any prep.

(3) You may have done this, but if not, set the COL to touch the lands and then vary the powder drop until you get a one hole group.

(4) Make sure you are not oversizing the shoulder. Even though the case headspaces on the belt, you don't want to push the shoulder back more than .001.

(5) Have you checked the runout on your loaded rounds?

(6) What type of barrel and how many rounds?

(7) What's your cleaning regimen?

Hope this helps
Dale

 

[RockZ]

It is important to have consistent charges.
But what you are looking for is a powder charge that gives consistent velocities.

If you are testing at 100yds you may find a load that puts all of your shots in one hole.
But at longer range has a huge vertical due to velocity variance.

I load at the range and work up loads through the chrono looking for good veloctiy spreads.

 

[rscott5028]

Thanks RockZ,

Sounds like you're not just looking for a node with a small group. You're also trying to find one that's consistent velocity... I'll buy that.

I tend to fixate on lots of brass prep as TexasHunter described (starting with Lapua or Norma brass) since it's something I can control before I go to the range.

 

[RDM416]

Are you shooting all the rounds at one sitting or comparing results from several times to the range? What is the weather? By weather, I am mainly interested in cloud cover. Any chrono will read differently in the sun than it will with cloud cover. Light, variable cloud cover or periodic clouds, then sun can really mess you up since the light is changing a great deal between shots. This may sound strange, but you might try setting up a large umbrella to shade your chrono to help even out nominal changes in ambient light.

 

[cowboy]

This may sound strange, but you might try setting up a large umbrella to shade your chrono to help even out nominal changes in ambient light.

Now that is a good idea - why didn't I think of that?