Seating depth or powder tweak?

[broncman]

After reading the seating depth thread in the 6mm section it raises nore questions. I have a load I am fine tuning for my 308 FTR using varget, lapua brass, and 215 bergers.

I worked up a load using the method in Erik Cortina's thread and arrived at a powder charge and then tried seating depth changes. Settled on a load that shoots well with tula primers. I am getting a flyer from time to time that I attribute to gun handling as the gun recoils to a different spot...that is when it throws it. Been pm'ng one of the Michigan Ftr team nembers who has helped me a lot.

Yesterday I tried two different primers. Federal match and cci br. The powder charge was the same as the tula load . This is a max load as more powder in all three primers get slight ejector marks.

The results left me with more questions!

Tula gave me average 2535 fps with a low 20 es
Cci Br primers gave me about 2520 with ES in the 20's
Federal Match gave me SINGLE digit ES with the lowest velocity average of 2495.

Groups were strange....Tula load was a round 5/8" group...one pulling it out...

CCI were stacked directly on top of each other in a vertical line!

The Federal group was in a PERFECT HORIZONTAL line!


So, is this a pressure issue or a seating depth issue brought on by the differences in primary ignition pressure of the primers? LOVE the flat line ES of the Federal primers but got to get them tighter.

I shot with flags in the late evenining in the best no wind day yet! Was very religous in gun hold as well.

I have shot the tula load out to 300 and it maintained 1/2 moa of vertical, but it is hard to ignore the federal single digit ES for five shots!

Tweak seating depth?

 

[jim_k]

Any response to this is going to be a guess. I guess I would seat the Federal-primed rounds 0.015" deeper, and try them next. Besides, that's the easiest thing to do.

 

[amlevin]

I used to be glued to my chronograph numbers and couldn't figure out why those loads that gave me the tightest groups often had larger SD's and ES.

I now don't even bring out the chronograph until I've worked up my load that performs to my satisfaction ON THE TARGET.

Consider that the chronograph can have many errors in how it measures speed. Was the lighting uniform for EVERY shot? Did it trigger exactly the same for every bullet? The device is a compromise as it relies on the bullet "shadow" to trigger the start/stop times. Which part of the bullet did that. What kind of speed error will you get if the start signal came from a point 1/4" back on the bullet and the stop signal from a point 1/4" farther forward. For sensors 18" apart that's a 3 percent error (2.7777777%) or 70 fps on a bullet traveling 2550 fps.

If all you want to measure bullet speed with is an instrument that sells for an average of $300 or so for the better ones, then you have to accept a margin of error.

Look at the target and then use the chronograph to determine an average speed so you can do your ballistic's calculations.

Don't tear your hair out over a high SD or EX when you have nice tight groups on the target. THAT's what they score, not your chrono readings.

 

[broncman]

I do understand the inaccuracies and shortcomings of chronographs and that target performance is the best indicator.

Was amazed at the difference on target from just primers! The pure vertical of one vs the pure horizontal of the other makes me wonder about timing/pressure issues during primary ignition. Basically the bullets initial jump to the lands from the primer ignition?

 

[amlevin]

I do understand the inaccuracies and shortcomings of chronographs and that target performance is the best indicator.

Was amazed at the difference on target from just primers! The pure vertical of one vs the pure horizontal of the other makes me wonder about timing/pressure issues during primary ignition. Basically the bullets initial jump to the lands from the primer ignition?

I used to shoot with a guy who had an interesting way to test primers. He would prime 5 cases and then insert bullets without powder. He'd then fire the powderless cases in his weapon and then measure from the muzzle back to the tip of the bullet. He'd insert a piece of wooden dowel and then mark it with a sharpened pencil at the crown of the barrel. After measuring 5, he'd repeat with 5 of a different primer.

The shorter the measurement on the dowel, the more the energy imparted on the load by the primer.

He also selected his primers by which one gave the narrowest band of markings on his dowel indicating that they drove the bullet the same distance into the lands.

He drove the bullets out of the barrel with a brass rod.

Certainly a different approach but I think I'd reserve this to a barrel I'm just about to replace. Don't know how well the brass rod did with the rifling.

 

[Travelor]

It sounds as if the "problem" is not your reloaded ammo but rather your shooting position. If the rifle is recoiling to a different position is sounds as if your body angle to the gun or grip is changing. DO NOT FORCE YOUR RIFLE TO THE CENTER OF THE TARGET - KEEP ADJUSTING UNTIL IT WILL POINT TO THE CENTER WITH NO FORCE BY YOU.

My preferred method that keeps the sights lined up with MY target is to angle my body at approx a 30 degree angle to the left of my rifles bore (I'm right handed).

Which bipod are you using? I have found that a Sinclair or similarly constructed bipod is far superior to a Harris bipod in shooting F-class.

Give it a try.

 

[BoydAllen]

I think that part of the problem may be testing different primers at the same powder charge, rather than at a proven velocity. I know of at least one famous benchrest gunsmith that views tune as velocity specific. I think that the only way to do a good test of primers...really, is to load at the range, doing a little tuning with each, to see what can be achieved for peak accuracy. For this, I would use the velocity of a proven load as starting point, adjusting powder charge to match it with each primer. and then doing a little experimenting from there, in the same way that the initial load workup was done. IMO a lot of so called testing is flawed, and part of the reason is that one cannot anticipate outcomes when preloading. Most shooters resist setting up to load at the range. It is really no big deal.

 

[mytwo60]

I would also recommend to shoot one round per different primer at a time. Like shoot one round with tula, then one round with cci, then one round with federal.

At 3 different targets of course.

 

[jlow]

This is absolutely correct - it's called round Robin.

Also switching primers at a max load is generally regarded as a NO NO...

 

[BoydAllen]

Good point. I forgot to mention that.

 

[Pres100]

You might also try to repeat the same exact experiments to compare (like conditions permitting, of course)

 

[Erik Cortina]

Back to the OP's question.

Adjust seating depth in .003" increments to tighten up the groups.

If you have a small group but big ES, don't waste your time going long range, it will more than likely not work regardless of how small the groups are at close range. 20 ES is not bad, but single digit is better.

 

[jsthntn247]

I'd work perform another 100 yard test with the federal primers just as you did with the Tula. Since you know your close to an ocw charge, back off .4 grains then work back up in .2 gr increments until you find the sweet spot with those primers.

 

[BoydAllen]

+1

 

[300 RUM]

Back to the OP's question.

Adjust seating depth in .003" increments to tighten up the groups.

If you have a small group but big ES, don't waste your time going long range, it will more than likely not work regardless of how small the groups are at close range. 20 ES is not bad, but single digit is better.

I want to give an example, then ask a question.

In a recent load development cession I loaded in .010 varrience in seating depth sets starting with a .005 jamb, then picked the best group from that and loaded +/- .005 from there to tighten the group up.

Do you think there could be an even tighter group in between ?

 

[amlevin]

Back to the OP's question.

Adjust seating depth in .003" increments to tighten up the groups.

If you have a small group but big ES, don't waste your time going long range, it will more than likely not work regardless of how small the groups are at close range. 20 ES is not bad, but single digit is better.

I want to give an example, then ask a question.

In a recent load development cession I loaded in .010 varrience in seating depth sets starting with a .005 jamb, then picked the best group from that and loaded +/- .005 from there to tighten the group up.

Do you think there could be an even tighter group in between ?

The only real answer would be to try it.

 

[aj300mag]

After reading the seating depth thread in the 6mm section it raises nore questions. I have a load I am fine tuning for my 308 FTR using varget, lapua brass, and 215 bergers.

I worked up a load using the method in Erik Cortina's thread and arrived at a powder charge and then tried seating depth changes. Settled on a load that shoots well with tula primers. I am getting a flyer from time to time that I attribute to gun handling as the gun recoils to a different spot...that is when it throws it. Been pm'ng one of the Michigan Ftr team nembers who has helped me a lot.

Yesterday I tried two different primers. Federal match and cci br. The powder charge was the same as the tula load . This is a max load as more powder in all three primers get slight ejector marks.

The results left me with more questions!

Tula gave me average 2535 fps with a low 20 es
Cci Br primers gave me about 2520 with ES in the 20's
Federal Match gave me SINGLE digit ES with the lowest velocity average of 2495.

Groups were strange....Tula load was a round 5/8" group...one pulling it out...

CCI were stacked directly on top of each other in a vertical line!

The Federal group was in a PERFECT HORIZONTAL line!


So, is this a pressure issue or a seating depth issue brought on by the differences in primary ignition pressure of the primers? LOVE the flat line ES of the Federal primers but got to get them tighter.

I shot with flags in the late evenining in the best no wind day yet! Was very religous in gun hold as well.

I have shot the tula load out to 300 and it maintained 1/2 moa of vertical, but it is hard to ignore the federal single digit ES for five shots!

Tweak seating depth?

Your load with the Tula primers are on the high edge of tune, hence the flyer. Drop the charge weight by .2gr and retest. The CCI load is showing the need for more pressure (vertical stringing). Since you're already high you'd have to drop down to a lower node. The Fed load is also showing a need for more pressure, you might try seating closer to the lands though I'm thinking the components being used aren't compatible for that specific load. Horizontal stringing can come from shooting without flags or missing a switch/build up. You'll have to judge if the spread is comparable to the intensity of the wind.

Moving the bullet will make a nice round group smaller, I haven't experienced removing horizontal/vertical out of a group by changing seating depth.

 

[broncman]

Went back to the range late yesterday with some more tula loads and federal loads. Tula loads ended up .1 gr less than the federal loads.

Interesting thing was seating depth. I did get the horizontal federal load to come in tight by seating deeper. I will not post a pic untill I see if it is repeatable. The Tula load also performed the best group wise at the same seating depth as the federal.

I have been using Excell to loadmap these loads and overlay the data in a chart. So far , for all powder loads, their is a sweetspot in seating depth that gives lowest ES and SD that remains constant regardless of charge weight.
It appears to be holding true for primers as well.

Group size then seems to be in a velocity node at that depth, regardless of primer/powder combo used to attain the same velocity(using same powder)...

That is what I am seeing so far....


The Federal primer load if not a Fluke will be my best ever 5 shot group in a 308...

 

[Erik Cortina]

Went back to the range late yesterday with some more tula loads and federal loads. Tula loads ended up .1 gr less than the federal loads.

Interesting thing was seating depth.I did get the horizontal federal load to come in tight by seating deeper. I will not post a pic untill I see if it is repeatable. The Tula load also performed the best group wise at the same seating depth as the federal.

I have been using Excell to loadmap these loads and overlay the data in a chart. So far , for all powder loads, their is a sweetspot in seating depth that gives lowest ES and SD that remains constant regardless of charge weight.
It appears to be holding true for primers as well.

Group size then seems to be in a velocity node at that depth, regardless of primer/powder combo used to attain the same velocity(using same powder)...

That is what I am seeing so far....


The Federal primer load if not a Fluke will be my best ever 5 shot group in a 308...

I know, that's why I suggested that you adjust it!

 

[jim_k]

"Best group ever" is never a fluke, if it's at least 5 shots. I only save the targets if they are at least 5 shots, for future reference. BTW, how much deeper did you seat to get the good group?