Lots of seating depth and jumping questions...

[thefitter]

I had previously done a OCW and seemed to have found good loads - .308 in 168gr & 175gr.

So I decided to try to find the sweet spot off the lands, and improve the groups even more.

I loaded 6 groups of 5 in .005 longer increments, measured off the ogive. Starting point is the length that I have been using due to magazine constraints.

2.175 - Original
2.180
2.185
2.190
2.195
2.200

To my surprise everything sucked except the last group in 168gr. Different bullet weights need different jumps?

I can go maybe .02 longer before I get to close to the lands. My max would be about 2.220

Should I also load a group off the lands MORE than my original? Say working back from 2.175? Anybody need more jump?

Thanks

 

[MALLARD]

Re: Lots of seating depth and jumping questions...

wait , so is 2.200 when you bullets fits into the lands ? or thats the max magazine length

im going to guess that is when you bullet gets stuck in the lands and not the magazine length.

i might start there , or even 2.300 just to confirm , you call that soft seating or dead length seating , some re-loaders seat their bullets like that.

when you ran your test was your gun fouled ? I would try the test again. Maybe it was an off day ? sometimes OCW changes with tempreture , so ,im not sure.

good luck

 

[thefitter]

Re: Lots of seating depth and jumping questions...

I used the Hornady OAL gauge. My average reading was 2.24125

The instructions said to subtract .020 or .040

2.241
-0.020
-------
=2.221

I'm very close to max loads for both the 168 & 175 so I'm a little leery to get into the lands because of possible over pressure.

I'm starting to wonder if I should be going farther from the lands.

I checked FGMM and they measure at the ogive 2.100, Hornady 2.040

All the loads I used for the OCW test were set right at maximum mag length at 2.175

 

[cooper623]

Re: Lots of seating depth and jumping questions...

generally, you want to seat the bullet .010" to .015" of the lands a grooves but every rifle is a bit different. also i found a very simple and effective make shift gauge that will help alot. heres the link. http://www.handloadersbench.com/forum5/5313.html

 

[SnkBit]

Re: Lots of seating depth and jumping questions...

I measure with a case set up similar to that posted above. I put a fired case into the press and back the sizing die all the way off. Then I ease the die down to where it just contacts the neck of the case. I then EASE it down just enough to begin to size just the mouth of the case to the point that a bullet will slide in and out with slight resistance. Pull the bullet to where its nearly coming out of the case and gently chamber that round. As you extract, hold pressure on the side of the case to avoid your measurement from being skewed by the extractor. Repeat several times and average the measurements. That is your length to the lands. I start .010 jammed so add .010 to whatever measurement you just came up with. You will want to reduce your charge at first and work up to your desired charge or until you get signs of excessive pressure. You can then seat the bullet deeper in increments without fear of overpressure as you pull the bullet further away from the lands.

 

[doc76251]

Re: Lots of seating depth and jumping questions...

I'm digging your thought process but need some info.

Bolt gun or gas gun?

What does "near max load" mean?

You said you were restricted by mag length..... what is different now? Bigger mags, no mags, loading sled, or do you just want to single load to see what you can get?

Looking at your measurements I A$$uME that you have the difference between Ogive and COAL figured out.

You said "My average reading was 2.24125". THAT is the distance to your lands. The "subtract .02 or .04" is legaleaze for "keep the boolets out of the lands so you don't blow your gun up and blame us" and has no bearing on the facts at hand.


So conceptually you could seat your boolet to an ogive length of 2.240" and be off the lands.

Lets call that "max ogive length" = 2.240"

You said that you were seating your boolets to 2.175" to keep them in the magazine and it worked.

Lets call that "Effective length" = 2.175"

Between the two there is 0.065" available from effective to max and nothing worked till you got to 2.20"

My initial guess would be that your OCW data is faulty and you went with the BEST group rather than taking the group in the middle of a string of groups that all printed in the same POI. That is an A$$-Ummp-shun on my part

as I don't know you or your habits but it is a common trap to fall into. If that IS the case your groups going to he!! are to be expected until you reach a length that duplicates the place you were.

Give me some more info and I'll see what I can do to help.

Cheers,

Doc

 

[thefitter]

Re: Lots of seating depth and jumping questions...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: doc76251</div><div class="ubbcode-body">I'm digging your thought process but need some info.

Bolt gun or gas gun?

<span style="color: #3366FF">Bolt</span>

What does "near max load" mean?

<span style="color: #3366FF">Book max</span>

You said you were restricted by mag length..... what is different now? Bigger mags, no mags, loading sled, or do you just want to single load to see what you can get?

<span style="color: #3366FF">
Bigger mag, although today I single loaded.</span>

Looking at your measurements I A$$uME that you have the difference between Ogive and COAL figured out.

<span style="color: #3366FF">Yes</span>

You said "My average reading was 2.24125". THAT is the distance to your lands. The "subtract .02 or .04" is legaleaze for "keep the boolets out of the lands so you don't blow your gun up and blame us" and has no bearing on the facts at hand.

<span style="color: #3366FF">I'm a rookie. I've been handloading now for a little over a month.</span>


So conceptually you could seat your boolet to an ogive length of 2.240" and be off the lands.

<span style="color: #3366FF">Yes
</span>
Lets call that "max ogive length" = 2.240"

You said that you were seating your boolets to 2.175" to keep them in the magazine and it worked.

<span style="color: #3366FF">Well it was were I started everything. Because I thought it was desirable to have the longest bullets that would fit and feed. I eventually found a powder charge that shot pretty good. So I wanted to see how much better it could get.</span>

Lets call that "Effective length" = 2.175"

Between the two there is 0.065" available from effective to max and nothing worked till you got to 2.20"

<span style="color: #3366FF">Yes, but it only worked in the 168 the 175 was still crap.
</span>
you went with the BEST group rather than taking the group in the middle of a string of groups that all printed in the same POI....

<span style="color: #3366FF">Not sure I understand this. I went through 3 cycles. The first was starting at 6 different loads x 5 rounds @ .5 gn increments within published range and then to 6 different loads x 5 rounds @.1 gn increments, then 2 loads x 20 rounds to finalize selection.</span>

Give me some more info and I'll see what I can do to help.

Cheers,

Doc </div></div> Thanks

 

[snipedogg]

Re: Lots of seating depth and jumping questions...

What bullet are you running? You said what weight, but didn't say which bullet.

 

[thefitter]

Re: Lots of seating depth and jumping questions...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Snipedogg</div><div class="ubbcode-body">What bullet are you running? You said what weight, but didn't say which bullet. </div></div>

SMK

 

[vman]

Re: Lots of seating depth and jumping questions...

I load everything for my .308 long.

Cant currently give you an ogive-head length as im at work, but my scenars are 2.960" OAL base-to-meplat, and i think around 2.3ish" to the ogive... accuracy is very good.

Unless i knew my neck tension was 100% consistent all the way around the neck, my action was trued, zero runout and concentric cases, only then would I feel confident that a decent jump wont hurt all that much.

 

[doc76251]

Re: Lots of seating depth and jumping questions...

OK, now were getting some where.

What is your load data? charge weight, brass, primer, boolet type, I may not have your book

?

Barrel twist?

OCW is a process not to find the best group but to find the load that does not vary in POI (Point of Impact) when conditions change. The "round robin" technique is useful for removing variables and is a great method. When searching for an OCW load you will see the bullet impacts move on the paper in relation to the point of aim (POA), usually up and left if you are firing progressively hotter loads. What you are looking for IS NOT the best group but the series of groups that STOP MOVING.

This simply means that you have found where the vibrations in your platform are farthest from the muzzle and by proxi have the least impact on its location. I believe Dan Newberry and Chris Long have written the process down although a lot of folks seem to miss this part in reading it. Here is his web site.

http://optimalchargeweight.embarqspace.com/

It DOES NOT give you the most PRECISE load for your rifle. You figure that part out by playing with seating depth and changing the primer around. After you are done playing with seating depth you may find it necessary to run the OCW again to make sure you are still in the "middle". You may also find that you need to go to the next higher or lower barrel node to gain maximum performance. What it does do is give you a BAND of velocity variables that does not affect your POI.

In my personal rifle I found 44.0gr of Varget in a LC Match case lit by a FGMM primer under a 175SMK or 178 AMAX to be my OCW and my ogive length of 2.190" to be the most precise. It also gives me a 30*F +&- area of stability. So, I can shoot my rifle at 65*F (where I tested) or at 95*F or at 35*F and have good solid 100 yard dope. Slight variations in case weight/capacity and powder charge can also be negated. Remember variables are cumulative.

Other topics:

155's are good to 1K and beyond, 175's are the same. 168's are ballisticly challenged and should be reserved for 700 yards and in. Ask Brian Litz why, he's got math to back it up, I just know they aren't 1K performers to a great degree.

If you have a 12 twisted tube stick with the 155's, if you use the 175's DRIVE THEM FASTER to overcome the twist rate (2700 - 2750 seems to work well).

Hope that helped more than it confused.

Cheers,

Doc

 

[thefitter]

Re: Lots of seating depth and jumping questions...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: doc76251</div><div class="ubbcode-body">OK, now were getting some where.

What is your load data? charge weight, brass, primer, boolet type, I may not have your book

?

<span style="color: #3366FF">IMR 8020 XBR
SMK 175 = 42.2
SMK 168 = 43.4

Brass - FGMM factory

Primer - CCI BR2
</span>

Barrel twist?

<span style="color: #3366FF">1-10</span>

OCW is a process not to find the best group but to find the load that does not vary in POI (Point of Impact) when conditions change. The "round robin" technique is useful for removing variables and is a great method. When searching for an OCW load you will see the bullet impacts move on the paper in relation to the point of aim (POA), usually up and left if you are firing progressively hotter loads. What you are looking for IS NOT the best group but the series of groups that STOP MOVING.

<span style="color: #3366FF">I'm still having trouble with this. I don't know why. I tried a ladder test at first with 6 loads @ .5 gn intervals but they all landed within 1/4" and I could not see any horizontal patterning to zone in one so I went to what I thought was a OCW test, which I guess I did wrong. At the end of it all I did find a load that would put everything fairly consistently in a 1/2" ragged hole.
</span>
This simply means that you have found where the vibrations in your platform are farthest from the muzzle and by proxi have the least impact on its location. I believe Dan Newberry and Chris Long have written the process down although a lot of folks seem to miss this part in reading it. Here is his web site.

http://optimalchargeweight.embarqspace.com/

It DOES NOT give you the most PRECISE load for your rifle. You figure that part out by playing with seating depth and changing the primer around. After you are done playing with seating depth you may find it necessary to run the OCW again to make sure you are still in the "middle". You may also find that you need to go to the next higher or lower barrel node to gain maximum performance. What it does do is give you a BAND of velocity variables that does not affect your POI.

In my personal rifle I found 44.0gr of Varget in a LC Match case lit by a FGMM primer under a 175SMK or 178 AMAX to be my OCW and my ogive length of 2.190" to be the most precise. It also gives me a 30*F +&- area of stability. So, I can shoot my rifle at 65*F (where I tested) or at 95*F or at 35*F and have good solid 100 yard dope. Slight variations in case weight/capacity and powder charge can also be negated. Remember variables are cumulative.

<span style="color: #3366FF">One thing I did not think of is that there has been a 10-12 degree variation in temp these past couple of weekends. Previous two weekends were 36, today was 46-50.</span>

Other topics:

155's are good to 1K and beyond, 175's are the same. 168's are ballisticly challenged and should be reserved for 700 yards and in. Ask Brian Litz why, he's got math to back it up, I just know they aren't 1K performers to a great degree.

If you have a 12 twisted tube stick with the 155's, if you use the 175's DRIVE THEM FASTER to overcome the twist rate (2700 - 2750 seems to work well).

Hope that helped more than it confused.

<span style="color: #3366FF">I'm confused but it can only get better.</span>

Cheers,

Doc
</div></div>

Thanks

 

[thefitter]

Re: Lots of seating depth and jumping questions...

I could use a recommendation on which direction I should go tomorrow, closer to the lands or start backing off my original starting point? Do some rifles prefer a longer jump?

I'm still concerned about getting to close at the charge weights I'm running. Am I overly concerned?

Thanks

 

[doc76251]

Re: Lots of seating depth and jumping questions...

Well I guess I'm out. I've never used that powder and have no data on it at all. I can't even begin to guess which direction to point you with it.

That being said with that 10 twisted tube you should be seeing better things with the 175's??????

My GUESS would be to load them faster and longer then see where they start showing pressure. Load to max mag length and play with the powder charges, kinda backwards but it might work for you. I just don't know with that powder.

Cheers,

Doc

 

[vman]

Re: Lots of seating depth and jumping questions...

Fitter, if your going to play around with seating depth, its easier to do this first and then play with charges later.

And yes you are being overly concerned. Seating depth does change pressure, but unless your loads are hot and THEN you decide to jam into the lands and possibly add more... then your looking for trouble.

Try loading them as long as your comfortable with. If thats to the lands with hand feeding the bullets then go with that. If you prefer mag length, go with that. If you can get to the lands with mag length still acheivable, then your lucky.

I have heard of some guys with decent loads, fiddle with seating depth and then discover their groups shrink. Thats just lucky of them.

You must understand that both seating depth and charge weights will affect pressure, which in turn will affect MV and accuracy. So modifying one will surely have an affect of the other be it big or small.

My way of thinking is that kissing the lands is a good thing, so i just do that from the start. Then i determine MAX. Then I investigate inbetween.

You know your on the right track when you have bullets in the same horizontal plane at 300 yards.

 

[thefitter]

Re: Lots of seating depth and jumping questions...

So what I'm reading is that I'm not really using a hot load I'm just near book max.

As long as I'm not actually into the lands at this load I should be fine with pressure.

Maybe I did it right by loading to max mag length and then finding a decent load that works with that after all.

I think I'll try a little movement in BOTH directions this morning and see what happens.

2.1700
2.1600
2.1500

2.2100
2.2200
2.2300

Worst cast is that the mag length IS the length for this rifle, and I've already got a load for that.

Doc- yes you would think that this 1-10 would work best with 175 but it never has. Even with factory ammo it's preferred the 168. This sucks because I got it to shoot heavy. I've got 8lbs of Varget and VV coming, I'm going to see if it can get better.

Thanks

 

[thefitter]

Re: Lots of seating depth and jumping questions...

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: thefitter</div><div class="ubbcode-body">So what I'm reading is that I'm not really using a hot load I'm just near book max.

As long as I'm not actually into the lands at this load I should be fine with pressure.

Maybe I did it right by loading to max mag length and then finding a decent load that works with that after all.

I think I'll try a little movement in BOTH directions this morning and see what happens.

2.1700
2.1600
2.1500

2.2100
2.2200
2.2300

Worst cast is that the mag length IS the length for this rifle, and I've already got a load for that.

Doc- yes you would think that this 1-10 would work best with 175 but it never has. Even with factory ammo it's preferred the 168. This sucks because I got it to shoot heavy. I've got 8lbs of Varget and VV coming, I'm going to see if it can get better.

Thanks </div></div>

Got some weird results in the 168gr:

2.1700 - poor
2.1600 - good
2.1500 - poor

2.2100 - poor
2.2200 - poor
2.2300 - good

In the 175gr everything was poor except the 2.200.

I'm going to try 10 rounds each of these:

168gr

2.1600 - to double check
2.2300
2.2400

175gr

2.2200
2.2300 - try again
2.2400