Length Study

[bh-ltr]

Ok went out to the range to test seating depth. I've never ever mucked with it before. I've always just used the SAAMI OAL and did OCW then stuck with that load. I'm about to load up 1K rounds and thought before doing that I'd spend a little time and do a length study.

So the load I'm using:
175SMK
Lapua Brass
44.3g Varget
Remington 9.5 primer
2.800 OAL Control

Rifle:
Remington 700 LTR 20" bbl
AICS Stock
Viperskins
Holland Radial Muzzle Brake
S&B PMII 5-25 DT CM CW
Badger 20MOA Rail, Seekins x-high (1.25") 34mm rings
Firing Position: Prone

Conditions:
1940 ft DA
77.8 Deg F


I then shot a 4 shot group with each tested load and varied by 0.010" for each load. I also threw in another 2.800 load that I ran on my mandrel die to see if doing that extra step could help and result in more consistent neck tension. (I was hoping not as I buy Lapua brass for its consistency and always dig finding out when a reloading step can be skipped). I didn't go over 2.840" as I wanted to make sure and be very safe when loading into 10 round AICS magazines. In the end looks like I'll load up my 1K rounds at 2.810" OAL. Which should be good and easy since I reset my die to be zeroed out at 2.800. Just dial her to +10 and I'm ready to go. However in the end I'm glad I put in the time to do this but based on the group sizes here and the difference that the whole test shows I don't see a whole lot of value to be gained in doing this. That being said the value in the extra confidence that my load is good by doing this is not zero.

Here were my results:

2.800 Control Load:

2.800 Run over the mandrel die:

2.810:

2.820:

2.830:

2.840:

 

[8nbait]

That is a nice test you did there. I have also found if you develop a load at a certain OAL then that OAL is usually within .010 of where you should be with that charge. I developed my 6.5 creedmoor load around a seating depth of .120 jump since that is what length I needed to have .260 of the bullet in the neck. I never saw a need to change it either and it has held up nicely for over 1200 rounds even with some erosion.

 

[bh-ltr]

Huh I didn't look at my own data all that closely. Perhaps 2.82 is better. Might just have to load em at 2.815 for shits and giggles.

 

[Queequeg]

I like the idea.

How about a broader sample size though? Extrapolating from a single four shot group at each COAL isn't as statistically significant as you might find once you run off the other 976 rounds you are about to embark on.

And then there is the whole notion of what they are doing at 300, 500, 800 yards, etc.

That said, an average COAL of 2.825" has been working out great for me.

 

[bh-ltr]

Yea but who wants to go out and test all those things at varying distances and all that. Its taken me years to finally care enough to go this far. And were I to continue using 2.800 for another 1K rounds I doubt it would change much. Once you get out to longer ranges the wind is going to cause more change than the OAL difference. Now I think its time to get the ammo I shot up today cleaned and into the rest of the primed brass that I have all sorted out. I should have that all cleaned, sized, trimmed, and primed tonight. Then next weekend I should be able to get all 1K charged and seated in one sitting. I always like to try and do that step in as large of a batch as I can.

~Brett

 

[Queequeg]

So it's really more of a test drive than a study?

Federal's GMM 175 comes in at 2.80" and it runs fine in my guns. It is entirely possible that the differences in COAL are far more important in match chambers of high end tubes, than in factory guns with hammer forged barrels! My Remingtons all have a lot of free bore. I was amazed how short the leade of my Savages are, by comparison!

I don't blame you on the work and expense involved in shooting a bunch of groups at various distances but certainly only 6 groups of 4 shots each, at 100 yards isn't something I would count on.

I agree about doing large batches as well.

Good luck!

 

[Spot-on]

I think 2.82 will be better, because as you get throat erosion you will effectively get an equivalency to your 2.810 results. In other words, you'll get good results a little longer without having to change seating depth.

Huh I didn't look at my own data all that closely. Perhaps 2.82 is better. Might just have to load em at 2.815 for shits and giggles.

 

[timelinex]

You didn't say what your chambers oal is. Whatever it is, load your rounds .01 jammed into the lands and enjoy your results. I've done oal testing on all my loads, but most the time it ends up a waste of time, jammed into the lands has always been most accurate for me. It's a huge debate though b, so others will disagree.


But in reality if you are already sub .5 moa, just leave it and go out to shoot!

 

[bh-ltr]

You didn't say what your chambers oal is. Whatever it is, load your rounds .01 jammed into the lands and enjoy your results. I've done oal testing on all my loads, but most the time it ends up a waste of time, jammed into the lands has always been most accurate for me. It's a huge debate though b, so others will disagree.


But in reality if you are already sub .5 moa, just leave it and go out to shoot!

Its a stock remington chamber so if you load that far out you then have a single feed rifle. Since thats not acceptable I went with what can fit in the magazine.

~Brett

 

[bh-ltr]

So it's really more of a test drive than a study?

Federal's GMM 175 comes in at 2.80" and it runs fine in my guns. It is entirely possible that the differences in COAL are far more important in match chambers of high end tubes, than in factory guns with hammer forged barrels! My Remingtons all have a lot of free bore. I was amazed how short the leade of my Savages are, by comparison!

I don't blame you on the work and expense involved in shooting a bunch of groups at various distances but certainly only 6 groups of 4 shots each, at 100 yards isn't something I would count on.

I agree about doing large batches as well.

Good luck!

Agreed its more of a quick test than a study. However I also feel that even at longer range the dependant variable would become smaller than other uncontrollable variables. However if I was to do a full up study it would take a LOT more ammo. It would probably also be quite stupid to do because by the time I figured out the actual best load the rifle would have eroded and changed based on the number of rounds fired. Then I'd have to do it all over again.

All in all I'm looking forward to getting out to another longer range. The range I'm a member of its only good to 200 yards and they frown on people not shooting from benches let alone jumping down to take shots quickly. Thankfully I was the only one out there so I was able to take my shots from prone. But I forgot my mat so I just laid out on the concrete and gravel. Gotta say my elbows are not happy with my decision. But I did have fun. Beats yard work!

~Brett

 

[bh-ltr]

I think 2.82 will be better, because as you get throat erosion you will effectively get an equivalency to your 2.810 results. In other words, you'll get good results a little longer without having to change seating depth.

Good point! 2.82" OAL it is!

 

[targaflorio]

Changing your seating depth affects two significant variables: bullet jump and the powder capacity of the case. I would caution against seating bullets out longer once your max charge is set for fear of seating in the lands and spiking pressure. It's safer to start jammed and work seating deeper.
A larger case capacity allows you to use more powder and achieve higher velocity at lower peak pressure. The new Berger loading manual does an excellent job covering that topic and Berger usually encourages seating bullets out if your throat allows and mag length isn't an issue.
Every cartridge is different though. 308 win seems to work real well around the book specs, around 2.8".

 

[bh-ltr]

Changing your seating depth affects two significant variables: bullet jump and the powder capacity of the case. I would caution against seating bullets out longer once your max charge is set for fear of seating in the lands and spiking pressure. It's safer to start jammed and work seating deeper.
A larger case capacity allows you to use more powder and achieve higher velocity at lower peak pressure. The new Berger loading manual does an excellent job covering that topic and Berger usually encourages seating bullets out if your throat allows and mag length isn't an issue.
Every cartridge is different though. 308 win seems to work real well around the book specs, around 2.8".

Agreed however with a stock remington chamber its usually the magazine box that limits your OAL.

~Brett