Bullet Seating Depth

[frittsk]

Just got the tool to check my bullet seating depth. The bullet touches that lands at 2.3045" which is 0.0445" longer that the published maximum overall length. I know I need to leave a few thousands of free travel but I'm still at about 2.2945 overall length. Does anyone have any experience with this? Is 2.2945 too long? I have been having trouble keeping a tight group. Usually about 1.5-2.0 inches. I'm hoping that I can increase my cartridge length and tighten up the groups.

[tackdriver]

That lenghth is pushing it for mag length.

[frittsk]

How long should I go?

[tackdriver]

It depends on the bullet and chamber. Unless you have some doctored up mags 2.30 is the absolute max and leaves no room for error. I have some bullets that need to be seated out to 2.200

[frittsk]

The rifle is pretty new and I have only shot about 100 rounds through it. Is it possible that I need to have the barrel machined to seat farther into the receiver?

[tackdriver]

Probably not necessary. Why don't you tell us about your rifle and the ammo you have been shooting.

[Klem]

I take it you have a Grendel AR and not a bolt-gun.

Converting 2.2945" into language I can understand is 58.27mm. 57.15mm is pretty much the max internal mag length of a standard GI .223 mag (I use 56.9 as the max OAL of hand-loads). Depending on what mags you are using; SS perhaps your max OAL will be slightly different, but not much. Unless you want to hand-load your rounds into the breech through the ejection port then it looks like your magazine internal length will dictate the OAL of all your rounds. This means your jump-to-lands will be longer than preferrable but the only way you can change this is organising for a shorter chamber, and doing that could interfere with the reliable auto-loading function of the rifle.

You can still experiment with accuracy and OAL in your AR but just not longer than the internal length of the magazine.

[NugginFutz]

You didn't mention which bullet you are working with, but since they are the most commonly loaded, around these parts, I would assume it is of the VLD variety. VLD's, by their nature, are known to be sensitive to seating depth, and can be a challenge to dial in. Have you had the opportunity to shoot your loads seated @ 2.29", yet?

Most of my rifles shooting Secant or Hybrid Ogive bullets, such as the Amax, work best with a .015" - .020" jump to the lands. Each rifle, of course, has its own appetite.

If we continue the assumption that your load is with a VLD type of bullet, and your barrel has similar appetite, then can we arrive at the following:

Your seated depth at Lands is 2.3045". Back of .020", which leaves 2.285" as your potential "sweet spot".

Coincidentally, my 123 AMax loads group best when seated between 2.230" and 2.260". At 2.260", this also happens to be .020" off the lands in my .264 LBC.

More than anything, though, I would strongly recommend a good reloading manual specific to the cartridge, if you haven't already done so. As has been pointed out, on countless occasions, you can order the 6.5 Grendel Reloading Handbook. It is jam packed with tasty goodness about reloading this great cartridge.

Hope this helps.

[Klem]

The rifle is pretty new and I have only shot about 100 rounds through it. Is it possible that I need to have the barrel machined to seat farther into the receiver?

Unfortunately it is not as simple as what you are suggesting. Possible on a bolt gun but not an AR. Your AR barrel is chambered to co-witness the gas port at the 12 O'Clock position relative to the barrel extension (the piece that screws onto the chamber end of the barrel with all the bolt lug teeth). The only way you could shorten your existing barrel is to shave a full revolution of the thread off to co-witness the extension with the gas port again. I don't know how much shorter that will make your chamber but it sounds inflexible and probably end up too short.

[frittsk]

Thanks for all the great information. Sorry I didn't include more info in my original post. It is an AR and I am shooting 120 grain Nosler Ballistic Tips. I do have some 123 grain A-Max's. I will measure with those to see if the seating depth changes. I have maintained the 2.226 AOL with everything so far. Have not loaded anything longer yet. I do have the 6.5 Grendel Reloading Handbook and will read through it a little more thoroughly.

[frittsk]

Make that 2.260 AOL that I have used so far.

[Klem]

OK, 2.226" (56.54mm) is the industry safe/reliable length for all magazines/chambers. You can load longer and what will limit you is either your chamber, or the internal length of the magazine - whichever comes first.

Be careful deciding on a longer length based on the dimensions of other people's guns and magazines. Just measure your mags with a set of calipers, and then measure the length it takes to touch the lands of each type of bullet you hand-load. Don't forget the throat will erode as you shoot more rounds which means the jump lengthens over time. You need to check every 1,000rds or so and adjust your OAL accordingly.

[NugginFutz]

OK, 2.226" (56.54mm) is the industry safe/reliable length for all magazines/chambers. You can load longer and what will limit you is either your chamber, or the internal length of the magazine - whichever comes first.

Be careful deciding on a longer length based on the dimensions of other people's guns and magazines. Just measure your mags with a set of calipers, and then measure the length it takes to touch the lands of each type of bullet you hand-load. Don't forget the throat will erode as you shoot more rounds which means the jump lengthens over time. You need to check every 1,000rds or so and adjust your OAL accordingly.

+1

On the throat erosion, let me add that those who run hotter loads tend to see faster erosion. This is another reason why highest velocity is not my chief concern, when developing loads.

[seatleroadwr]

Most of my mags will hold a 2.300" cartridge. The cheaper magazines seem to hold longer rounds. AR stoner mags will hold 2.29 without a problem and 2.30 in some cases. With the bullet you reference I'd say you have a much longer than average throat or a very funky headspace. I lengthened my throat by .060 and that particular bullet hits the land at 2.280. Still, longer is better as far as I'm concerned, providing the lands are not unreachable. Your gun should shoot a little faster at a little lower pressure with a little less powder compression than a gun with a shorter throat.

[Klem]

Reaming a longer throat means you can seat the bullets longer, that is until the magazine length limits that idea. You can still ream longer than the magazine but that just means the bullets loaded to fit your magazines will have further to jump before engaging the lands. Target Rifle shooters prefer short jumps-to-lands as it enhances accuracy so there's no point in reaming a throat longer than your magazines will allow.

I use the ballistics program Quickload and manufacturer tables to supplement the usual check of flattening of primers to give an idea of the peak chamber pressure. I recommend starting 10% below recommended and working up slowly. Every chamber is unique and minute differences in internal diameter of the lands will make a big difference in the starting friction, and pressure profile as the bullet starts moving.

There's every chance your peak pressure will be higher with a shorter throat (all other things being equal).

[LRRPF52]

QL needs to be custom modeled to get any accurate data for the Grendel. JASmith is one to talk with about this.

As to the 120gr Nosler BT, I don't think it can be loaded out so long in most chambers, without jamming the lands (pressure spike).

[LR1955]

Thanks for all the great information. Sorry I didn't include more info in my original post. It is an AR and I am shooting 120 grain Nosler Ballistic Tips. I do have some 123 grain A-Max's. I will measure with those to see if the seating depth changes. I have maintained the 2.226 AOL with everything so far. Have not loaded anything longer yet. I do have the 6.5 Grendel Reloading Handbook and will read through it a little more thoroughly.

FTK:

You have fired 100 rounds of different loads and are frustrated that you can't find one you think is accurate?

Find the overall length where the bullet just touches the rifling. Back off .020 or so and see if it fits the magazine with some play at the tip. If it fits the mag and stands off from the lands, most likely you will be fine. The limiting factor in most cases is the magazine length.

And remember that if your load is so sensitive to overall length that a difference of .01 inches means the difference between the best and worse performance, you need to find another load.

You may need to focus your attention on position development and simple marksmanship skills as well.

LR1955

[frittsk]

I just loaded up some round at 2.285 OAL and they seem to work fine in my magazines. Once I get a chance to shoot, I will report the results.

Thanks again everyone for your help! Much appreciated!

[LRRPF52]

Before you shoot those, did you check where or if you are jamming into the lands with the 120gr NBT? Color the bullet shank to ogive area on a dummy cartridge loaded to that COL, and see what happens when you chamber it. If there are land markings on the bullet, and it is difficult to extract, you are jammed into the lands, which will cause significant peak pressure with anything even near a max load, and you probably don't want that.

Did you load the 120gr NBT's to 2.285", or the 123gr Hornady's?

I just looked over 28 different 120gr NBT loads from forum members and industry sources, and all of them but one are 2.225"-2.250". Most are 2.240" COL.

[frittsk]

Chieftain,

I am a little over 0.045" from the land at 2.260 OAL. That's why I load some at 2.285 to get me within 0.020" from the lands. I loaded the 120gr NBT's. Thanks for the heads up!