Seating Depth for 308

[Jarhead69]

I am new to reloading and have been reading all that I can find (which is overwhelming to say the least). I have a Remington 308 700P 5R 1/10 twist barrel. In reading some of the post about seating bullets, I see a lot about seating as close to the rifling for better accuracy. I purchased an O.A.L. Gauge and a bullet comparator kit to measure this. The bullet I'm using is the Hornady 178 gr ELD-X. After taking the measurements it came in at 2.9770 so backing it off .020 - 0.40 would put it at 2.9570 - 2.9370 to start.. Does this sound correct? I didn't expect to see this wide of a variance from the standard 2.80 OAL. Also, are shooters only doing this by loading one round at a time, as my magazine will only go to 2.880.
Appreciate any insight into this.

 

[Big Mc]

I am new to reloading and have been reading all that I can find (which is overwhelming to say the least). I have a Remington 308 700P 5R 1/10 twist barrel. In reading some of the post about seating bullets, I see a lot about seating as close to the rifling for better accuracy. I purchased an O.A.L. Gauge and a bullet comparator kit to measure this. The bullet I'm using is the Hornady 178 gr ELD-X. After taking the measurements it came in at 2.9770 so backing it off .020 - 0.40 would put it at 2.9570 - 2.9370 to start.. Does this sound correct? I didn't expect to see this wide of a variance from the standard 2.80 OAL. Also, are shooters only doing this by loading one round at a time, as my magazine will only go to 2.880.
Appreciate any insight into this.

As far as seating depth goes I let the gun tell me what it likes. Don't have a gun that has a Mag. so just about anyting goes. Just my two cents Tommy Mc

 

[Chiquita]

From my experience deal with bullet seating when you have a good working load that has low ES and low SD. Once that is under control and acceptable to you then deal with seating depth.

Different shooter will have different experience.

If I am off base, I am sure I will be set straight.

 

[Orr89rocz]

Sounds plausible. My 308 with a berger 175 vld is touching lands at about 2.941” oal.

 

[RegionRat]

The view on magazine length versus single feed rounds because they are too long, depends on the game you play.

For example in Service Rifle, the magazine length is roughly 2.25" but the ammo for the 600 yard lines is often made too long to fit. That sport tolerates this since the stage is usually 20 rounds in 20 minutes. So single feed is expected as part of the rules and making them long doesn't matter. As a result, most of us will shoot SMK 80 or bullets that like to be much longer than the magazine but only on that stage.

In your case, it really depends on if you are interested in games that are single feed. If that fits the rules, then being over mag length is an option. I am going to recommend you search for both options here in a minute since your rig has a magazine.

As for arriving at the most efficient path to load development, that is your option as well. You can decide to run a charge development test at magazine length first since that is one obvious constraint and see what you can find. Your goal at that point is the best charge node and group size for a seating depth at or below magazine length. (Here is where I always recommend folks baseline some FGMM or Black Hills ammo in case they ever need a baseline for debugging. It uses a different brand of bullet but is still worth the study. This would be a 175 SMK at 2600 FPS from a 20" bbl.)

When you check for charge, just park yourself at something that functions well in the magazine and sweep your charge range searching for any sings of high pressure at the highest end and any sings of an obvious node. Your depth sweep should have two priorities, searching for a node at or below mag length, and then one that extends out beyond mag length.

https://precisionrifleblog.com/2020/03/21/bullet-jump-and-seating-depth-reloading-best-practices/



Ideally you will find the best charge and seating depth for both kinds of loads, the ones for magazine feed and the ones for single feed. Many times the best ones have a large jump that means it also fits the bill for magazine feed. In your rifle, this is often the case and the additional benefit is those deeper nodes are more durable so you don't find yourself chasing the lands with wear.

 

[Ned Ludd]

You are dealing with two constraints here. The first would be whether you need/want to seat bullets so that loaded rounds can be fed from a magazine. The second would be whether that particular bullet prefers being seated within a certain [close] distance to the lands that would preclude feeding from a magazine.

If you need to feed from a mag, determine the longest COAL you can have that will still reliably feed. Set that as your "zero", or "reference point", then optimize seating depth by shortening COAL in small increments (i.e. moving the bullet farther away from the lands). You should be able to find a seating depth window that works for that bullet, even though it may be jumping a fair distance. Because you don't know exactly how far off the lands it may be necessary to seat the bullet, you might try to cover a wider range of seating depths in larger increments first, then fine tune using smaller increments within a narrower seating range that appears to be optimum.

If you are OK with single feeding rounds, determine COAL with the bullet seated at just "touching" the lands. Set that as you zero/reference point, then again optimize seating depth by shortening COAL in small increments (i.e. moving the bullet farther away from the lands). It is not uncommon to find an optimized seating depth within about .030" or so of the lands. I don't particularly care to seat bullets into the lands for a variety of reasons unless they will not tune in anywhere else. With this approach, you can always go back and seat bullets longer (i.e. into the lands) if you don't identify an optimal seating depth with the bullets seated off the lands. I have rarely found that to be necessary with the bullets I typically use, but it is an option that is always available, if necessary. Just remember that if you find it necessary to seat the bullets into the lands, the loaded rounds will still be too long to feed from a magazine.

One caveat to either of these approaches is that if you have to change the seating depth of the bullet by a very large amount, pressure will increase for a given charge weight as the bullet is seated farther and farther from the lands and the effective case volume decreases. Just be aware of this and decrease the charge weight if necessary.

Berger has a protocol that was originally designed for optimizing seating depth with VLD bullets (link below), which can sometimes be finicky with respect to optimizing seating depth. It was intended to cover a very wide seating depth range initially so as to identify a particular seating depth region where a given bullet grouped better than when seated elsewhere. That region could then be tested again in finer increments to fine-tune a final seating depth. This protocol should work with a variety of bullets in addition to VLDs. Again, the key is that it covers a very wide seating depth range initially, helping you narrow down an optimized seating depth range. One approach might be to try this method, single feeding all the loaded rounds as you carry out the testing. Once you have identified the optimal seating depth region, you can determine from the loaded rounds whether they will feed reliably from a magazine. If so, you're GTG using a mag. If not, you can always single feed them if that is acceptable to you.

Getting the Best Precision and Accuracy from VLD bullets in Your Rifle

VLD bullets are designed with a secant ogive. This ogive shape allows bullets to be more efficient in flight (retain more velocity = less drop and wind deflection). While this result is desirable for many rifle shooters the secant ogive on the VLD bullets produces another result in many rifle.

bergerbullets.com

 

[Jarhead69]

Thanks to everyone for your responses and attached articles, much appreciated.

 

[miningshawn]

You are dealing with two constraints here. The first would be whether you need/want to seat bullets so that loaded rounds can be fed from a magazine. The second would be whether that particular bullet prefers being seated within a certain [close] distance to the lands that would preclude feeding from a magazine.

If you need to feed from a mag, determine the longest COAL you can have that will still reliably feed. Set that as your "zero", or "reference point", then optimize seating depth by shortening COAL in small increments (i.e. moving the bullet farther away from the lands). You should be able to find a seating depth window that works for that bullet, even though it may be jumping a fair distance. Because you don't know exactly how far off the lands it may be necessary to seat the bullet, you might try to cover a wider range of seating depths in larger increments first, then fine tune using smaller increments within a narrower seating range that appears to be optimum.

If you are OK with single feeding rounds, determine COAL with the bullet seated at just "touching" the lands. Set that as you zero/reference point, then again optimize seating depth by shortening COAL in small increments (i.e. moving the bullet farther away from the lands). It is not uncommon to find an optimized seating depth within about .030" or so of the lands. I don't particularly care to seat bullets into the lands for a variety of reasons unless they will not tune in anywhere else. With this approach, you can always go back and seat bullets longer (i.e. into the lands) if you don't identify an optimal seating depth with the bullets seated off the lands. I have rarely found that to be necessary with the bullets I typically use, but it is an option that is always available, if necessary. Just remember that if you find it necessary to seat the bullets into the lands, the loaded rounds will still be too long to feed from a magazine.

One caveat to either of these approaches is that if you have to change the seating depth of the bullet by a very large amount, pressure will increase for a given charge weight as the bullet is seated farther and farther from the lands and the effective case volume decreases. Just be aware of this and decrease the charge weight if necessary.

Berger has a protocol that was originally designed for optimizing seating depth with VLD bullets (link below), which can sometimes be finicky with respect to optimizing seating depth. It was intended to cover a very wide seating depth range initially so as to identify a particular seating depth region where a given bullet grouped better than when seated elsewhere. That region could then be tested again in finer increments to fine-tune a final seating depth. This protocol should work with a variety of bullets in addition to VLDs. Again, the key is that it covers a very wide seating depth range initially, helping you narrow down an optimized seating depth range. One approach might be to try this method, single feeding all the loaded rounds as you carry out the testing. Once you have identified the optimal seating depth region, you can determine from the loaded rounds whether they will feed reliably from a magazine. If so, you're GTG using a mag. If not, you can always single feed them if that is acceptable to you.

Getting the Best Precision and Accuracy from VLD bullets in Your Rifle

VLD bullets are designed with a secant ogive. This ogive shape allows bullets to be more efficient in flight (retain more velocity = less drop and wind deflection). While this result is desirable for many rifle shooters the secant ogive on the VLD bullets produces another result in many rifle.

bergerbullets.com

Nedd,

I started to respond to this thread but soon realized that no-one could have said it better. Excellent post.

 

[Doom]

Rem 700. Forget seatng anything longer than about 2.850”. You have a long throated chamber, as do all 700s. Follow miningshawns recommendation.

 

[D-4297]

Not even touchin this one . Been covered with a very large blanket .