Seating Depth VS Powder Charge Question.

[DiverDan]

Hi all,

Just working on a load in .308 and I’m about to start powder testing once this cold snap is over.

However, I have a question in regards to bullet seating depth in relation to powder charge.

I will be ignoring how far I am away from the lands and loading from just under mag length, in order to utilise the magazine function of my rifle.

Now am I right In thinking that it doesn’t matter what depth I seat at for my powder test as long as it’s consistent?

Or am I better off loading long (mag length minus a few thou) or going short to SAAMI spec?

What are the differences? Are there any differences? Is there anything else I should consider before I make a decision on what length to load to?

Sorry if it’s a silly or confusing question but I am quite new to this

Thanks all,
Dan.

 

[User00040]

If a 308 does not shoot off a 2.8" COAL, rifle is broken.

 

[NP435]

Hi all,

Just working on a load in .308 and I’m about to start powder testing once this cold snap is over.

However, I have a question in regards to bullet seating depth in relation to powder charge.

I will be ignoring how far I am away from the lands and loading from just under mag length, in order to utilise the magazine function of my rifle.

Now am I right In thinking that it doesn’t matter what depth I seat at for my powder test as long as it’s consistent?

Or am I better off loading long (mag length minus a few thou) or going short to SAAMI spec?

What are the differences? Are there any differences? Is there anything else I should consider before I make a decision on what length to load to?

Sorry if it’s a silly or confusing question but I am quite new to this

Thanks all,
Dan.

If you intend to use the mag ammo must fit, then you need to not have the projectile jammed in the lead of rifling. The dimensions show in most load manuals do not always work perfectly for your rifle so what I do is fit the mag, then look for marks on the projectile from being jammed. Then i seat them deeper until they don't show marks.

 

[HandB]

I have played around with all sorts of bullet jumps but in the end I do as suggested by Caberslash and run both my .308s (a Sauer 202 and an AIAE) with a standard 2.8 OAL irrespective of the bullet type or powder charge and they shoot fine. So I would go with that. I even use the same jump (approx. 80thou) on my 7x57 and that works fine too.

 

[scotch_egg]

2.8 OAL for the .308


Even then make sure it fits in the magazine. Chasing lands is a mugs game when it comes to using a rifle in the field. I’ve been there and regretted it when the bullet is stuck in the rifling and the bolt opened spilling power all inside the action. But by-heck did that rifle shoot. But that didn’t matter when you can’t load a round in it.

You don’t need to worry about taking up powder room. Just make sure you are wearing goggles as you hear that powder crunch as you seat the bullet

 

[Muir]

It's not a silly question. There was a time before a lot of you were born that OAL was expressed as "Seating depth" and it was usually a number beginning with a decimal point.
Still, load to 2.8 OAL or less and you will be fine. ~Muir

 

[JTO]

I have wondered if 'jump' is the only factor in fine tuning by adjusting seating depth. Does 'percentage fill' of the case affect things also?

 

[Bowland blades]

Hi all,

Just working on a load in .308 and I’m about to start powder testing once this cold snap is over.

However, I have a question in regards to bullet seating depth in relation to powder charge.

I will be ignoring how far I am away from the lands and loading from just under mag length, in order to utilise the magazine function of my rifle.

Now am I right In thinking that it doesn’t matter what depth I seat at for my powder test as long as it’s consistent?

Or am I better off loading long (mag length minus a few thou) or going short to SAAMI spec?

What are the differences? Are there any differences? Is there anything else I should consider before I make a decision on what length to load to?

Sorry if it’s a silly or confusing question but I am quite new to this

Thanks all,
Dan.

So long as your off the rifling it does not matter till your way too deep into the case ( which only a rare kind of idiot would do ) . In my experiance seating depth is not a big factor in a factory rifle shooting std hunting ammo. Sure if you have a minimum tolerance , one at a time built bench gun and your looking for slight improvement with custom or high grade match bullets .
To qualify my words , i used to compete fairly successfully for a fair while in FTR etc . For hunting purposes we should avoid getting too close , too hot or too anal ! Likely to create more issues than it solves under field conditions .
Good brass, N140 and a bullet around 140 grains or so set off with a good match primer like cci BR
Dont waste too much ammo , especially at these time of high cost and poor availability IMHO

 

[cjs66]

Aye, as most have said, 150gr or 168gr decent bullet and a case full of N140 loaded to OAL of 2.800, go n shoot stuff. The reloading books have over all length data for a reason.

cjs

 

[jthyttin]

Barnes suggests this for load development, click "Loading guidelines" on top part of page:

Load Data

Find reloading guidelines and data for your Barnes Bullets products.

www.barnesbullets.com

And Berger instructs you like this for their VLD bullets:

VLD - Making it Shoot

VLD bullets are designed with a secant ogive. Berger VLD bullets are consistently and exceptionally capable of putting game down quickly

bergerbullets.com

Bottomline is, if you play with COAL for accuracy, use big enough steps in initial testing. Remember also, that large group (or equivalent) will tell you that the load is not good. Small group just tells you the load has potential to be good. But also settle for something that is accurate enough, chasing the last fractions is usually pointless and anyway requires large number of components, time, barrel life etc.

 

[ChesterP]

Keep it simple. Load to 2.800 and vary the load. N140 will give you decent results with 150g class at anything from 42 to 44gr. Varying charge will have similar results to varying seating on barrel harmonics wrt bullet barrel time. You don't have to worry about it, just pick a load that works best with your bullet of choice at 2.8 OAL and go and shoot it. Percentage fill comes into uniformity of ignition. You get more consistent ignition results generally by picking a propellant for your bullet that achieves close to 100% burn rate at as close to full case but even slight compression is fine. The theory being the lower the fill ratio, the more variable the pressure/time curve can be. N140 is an ideal powder as you achieve a decent fill ratio at mag length for most hunting bullet weights normally used, the most popular being 150 to 165gr. RS50 equally as good if sticking with single base powders.

 

[Laurie]

Berger advise people to use a starting load only for COAL variance tests, then when best results there are obtained from a particular seating depth, keep that constant and start raising / varying powder charges to get best results. Personally, I've always done it the other way round as the OP intends and see little reason to change now. The golden rule in any event is to only change one variable at a time whichever method is adopted.

However, when we get into tiny COAL changes, we're talking match loads, and as several people have posted, whilst playing with COALs is fine for single shot custom-throated jobs, it's at best unnecessary and at worst a bad idea when loading for most off the shelf magazine fed sporting rifles. (Custom specified and built varmint and other extra long-range rifles are often a different matter being in practice match rifles taken into the field and often loaded with the more frangible high-BC match bullets too, likewise wringing the best out of a factory rifle used solely for paper punching with single-shot loading.)

In order to keep life simple, the best approach is to choose traditional form bullets with relatively short, blunt ogives/nose sections that are jump-insensitive. VLDs and other long-nose secant form bullets which are sometimes very jump-affected can sometimes make it near impossible to get good results at magazine constrained COALs. 'Good' that is on paper, but is a three-quarter MOA, or even a 1-MOA rifle/load too poor for stalking and that the much desired (and boasted about) 'under half-MOA performance is somehow essential? I've been reading gun magazines for long enough to remember when the old American hands would write about the days when as recipients of borrowed and review rifles, the 30-06/270 class test example that consistently put three shots into an inch and a half at 100 yards was a 'keeper', and the tester negotiated its purchase with the supplier. As one writer ruefully put it some twenty or thirty years ago, the American shooting public is so hung up on accuracy these days, "you couldn't give such a rifle away now even if it was wrapped in five-dollar bills!"

 

[Chasser]

I have wondered if 'jump' is the only factor in fine tuning by adjusting seating depth. Does 'percentage fill' of the case affect things

As close to 100% case fill, within safe limits of course, the less deviation in velocity

 

[Border]

Some good videos with Eric Cortina explaining this subject.

 

[chelsea7513]

Thanks for the upload border, I'm getting into reloading now and this is a very good video, that explains things easier than most things I've watched and read!

 

[Utectok]

Load all the test rounds to Saami length. If it doesn’t shoot change the bullet choice