Random velocity migration with same charge weights

[chrisb97]

Hi all, I've recently started trying to do load development on a 338 edge and have run into an issue. Running adg brass and berger 300 elite hunters I found that 90 grains h1000 shot the best so I went back out to fine tune some seating depth. Starting 15 thousands off the lands i moved back in .005 increments to tighten up my groups and ES. What I found was my velocity moving all over the place and sometimes fliers in my groups that coincide with velocity spikes. My brass prep includes annealing, resizing with a .001 shoulder bump, trim and chamfer, flash hole deburr, .0015 neck tension, and powder charge is thrown with a rcbs chargemaster link and a hand trickler to get it withing 1 or 2 kernals. I have tried 2 different primers and don't have access to other types. These groups shot from left to right all have the same charge weight and are moving back .005 each group. I'll include the velocities and group size from initial testing as well. Velocities are measured with a Garmin xero. Any thoughts on the large es and random huge jumps in velocity?

 

[MagnumManiac]

If you are experiencing wild shifts in velocity with the same powder charge but different seating depths, then your load is right on the verge of overpressure when you started, regardless of actual pressure signs showing themselves. Moving the bullet closer to the lands is raising that pressure.

I have stated this here before, my own 338 Edge exhibited wild pressure excursions, I thought it was from the tight neck chamber I chose, after removing the barrel and running in another normal neck chamber, excursions persisted, then I went to a +P chamber (Proprietary), this resulted in no more excursions but the velocity nor accuracy were there anymore. Sold the action and moved on, kicked myself for not keeping it. 3.85" mag box, Jewel trigger, trued and set-up with .300" thick pinned recoil lug…oh well.

Cheers.

 

[chrisb97]

If you are experiencing wild shifts in velocity with the same powder charge but different seating depths, then your load is right on the verge of overpressure when you started, regardless of actual pressure signs showing themselves. Moving the bullet closer to the lands is raising that pressure.

I have stated this here before, my own 338 Edge exhibited wild pressure excursions, I thought it was from the tight neck chamber I chose, after removing the barrel and running in another normal neck chamber, excursions persisted, then I went to a +P chamber (Proprietary), this resulted in no more excursions but the velocity nor accuracy were there anymore. Sold the action and moved on, kicked myself for not keeping it. 3.85" mag box, Jewel trigger, trued and set-up with .300" thick pinned recoil lug…oh well.

Cheers.

Thank you for your reply. I am moving away from the lands not towards the lands which I understand can also raise the pressure. During initial testing I didn't start seeing any pressure signs till 91.5 grains with a very slight click on the top of the bolt with the primer still nice and round and the brass not leaving an ejection mark. With a 30 inch barrel I think my velocity should be where it is around that 2800 mark so it's leaving me a little stumped. Do you think switching powders would be the best move?

 

[MagnumManiac]

I also ran a 30" barrel, mine was a Brux 9" twist.
To be honest, I never tried H1000, mine saw Retumbo, US869 and H50BMG with RE25 using 265g ABLR thrown in.
I was getting just below 2900fps with those 3 powders and 300g Berger Elites.
You may want to change your neck interference, light neck tension can cause a bullet to move on primer ignition, this may also be causing your issue. Try .003"-.004" to see if it changes.
I only use light neck interference when I am running loads touching, because the bullets can't move forward.
There are many variables that cause this, one may also be the ADG brass being thicker.

Cheers.

 

[waveslayer]

How accurate is your node, have you measured the neck thickness on your brass, neck tension variances, I'd find a better node.

Fliers on cold bore, warm, hot bores?

 

[chrisb97]

How accurate is your node, have you measured the neck thickness on your brass, neck tension variances, I'd find a better node.

Fliers on cold bore, warm, hot bores?

Neck thickness is .014 and I am using a whidden die set with a neck bushing for setting neck tension. I do not have a ball micrometer to test runout. Fliers happen cold or warm. I just ordered a keg of retumbo to give a new powder a try as well. I have tried remington 9 1/2M primers as well as cci 250s. If I try to go higher to the next node I am fairly certain I will pressure out first and I don't want to drop down into the lower node as it was a little slow for my taste and I was not seeing the accuracy I liked. Rifle has around 130 rounds down the tube.

 

[chrisb97]

I think given the data I am going to redo the test at 91 grains instead of 90 and play with seating depth there, and if that doesn't work a powder switch to retumbo is in order unless anyone has any other helpful advice?

 

[ncwg2boatguy]

I take it 215M primers are unicorns in your area? They never disappoint for burn ,ignition consistecy and data for me. I just always get better results.

 

[coueskiller43]

Do you have another scale to check against your RCBS? I use mine to throw charges but I check the weight and trickle in on another scale. This has helped my ES.

 

[ShtrRdy]

I would try more neck tension first. Like 0.003".

Are you doing a cleaning step that gets the brass squeaky clean and shiny?

 

[243winxb]

.0015 neck tension

Bullets moving to soon on primer firing. Increase neck tension.

If magazine feed, check last round in magazine before firing.
Has OAL changed?

 

[waveslayer]

Or you can swap the barrel of you're not happy with it. Try Retumbo or N570 even RL33 for the 300's

 

[Mikecr]

Your testing demonstrates why seating testing after powder is backwards.
Seating is NOT tuning, but prerequisite to tuning.

Back off the charge away from a powder node and repeat the seating test.
Pick what appears best coarse seating (no matter how ugly) and start over with powder testing (tuning) using that CBTO.
Once you have these 2 attributes set, revisit seating for very fine tweaking within it's seating window. This, just for tightest group shaping.
You can also work on neck tension tuning, keeping your current interference (1.5thou, that's fine), but adjusting neck sizing LENGTH.

 

[Beluebow]

Couple things you could try that wouldn't be huge changes.

1.More shoulder bump.... .001 would be pretty much the variance of fired brass over a decent lot size. Try .002-.003 bump to get a clean bolt drop on a stripped bolt.
2.More neck tension...again very easy test. .002/.004/.006 with your best powder charge and seating depth. It will show you what it likes.