seating depth test 8208xbr/77gr smk

JRBullock1987 · Feb 26, 2024

I just worked up a load for my ar15, it's a rifle length 18" ballistic Advantage barreled upper in .223 Wylde.
A basic lower with a rifle length buffer tube/buffer. This is my first load work up and I want to do a seating
depth test to see if I can tighten the group (just under 1 MOA) up but don't know how far I can seat the bullet. I've
never done a seating depth test and I can't find anywhere that really explains how to properly set one up.
my final load is....
POWDER: IMR8208xbr (23.1gr)
BULLET: 77gr Sierra match-king
PRIMER: CCI #4
BRASS: (once fired): LC (all 21 head stamped)
COAL: 2.258".
TRIMMED: 1.750".
My thought was to start at mag length and work back. These are what I came up with.
2.260"/2.257"/2.254"/2.251"/2.248"
5 round groups and just check for pressure signs and velocities with each new seating depth.
or is 2.251" and 2.248" seating to deep? I've seen as low as 2.255" seating depths with these components on threads.
thanks,

MarshallDodge · Feb 26, 2024

My experience is that recipe shoots well in two bolt actions and two ARs but they have better barrels than BA.

I doubt you are going to see an improvement.

tinker · Feb 26, 2024

JRBullock1987 said:
I just worked up a load for my ar15, it's a rifle length 18" ballistic Advantage barreled upper in .223 Wylde.
A basic lower with a rifle length buffer tube/buffer. This is my first load work up and I want to do a seating
depth test to see if I can tighten the group (just under 1 MOA) up but don't know how far I can seat the bullet. I've
never done a seating depth test and I can't find anywhere that really explains how to properly set one up.
my final load is....
POWDER: IMR8208xbr (23.1gr)
BULLET: 77gr Sierra match-king
PRIMER: CCI #4
BRASS: (once fired): LC (all 21 head stamped)
COAL: 2.258".
TRIMMED: 1.750".
My thought was to start at mag length and work back. These are what I came up with.
2.260"/2.257"/2.254"/2.251"/2.248"
5 round groups and just check for pressure signs and velocities with each new seating depth.
or is 2.251" and 2.248" seating to deep? I've seen as low as 2.255" seating depths with these components on threads.
thanks,

You need to measure where your rifling starts with a hornady AOL gauge. then start about .020" off of that if you can.

I currently load 77 gr smk's and seat them about .050" off the lands.

JRBullock1987 · Feb 26, 2024

MarshallDodge said:
My experience is that recipe shoots well in two bolt actions and two ARs but they have better barrels than BA.

I doubt you are going to see an improvement.

Yeah I have a 20" woa spr barreled upper that I'll start loading for here soon. I just wanted to get the hang of reloading first before I start using it.

tinker said:
You need to measure where your rifling starts with a hornady AOL gauge. then start about .020" off of that if you can.

I currently load 77 gr smk's and seat them about .050" off the lands.

I have a hornady oal guage but imy rifles an ar15 and I don't want to single load. My max will be mag length

simonp · Feb 26, 2024

Your WOA should be a laser with those if you find the right load, my 20” WOA shooting 77’s with Varget shoots in the 3’s if I do my part. Mag length loads.

JRBullock1987 · Feb 26, 2024

simonp said:
Your WOA should be a laser with those if you find the right load, my 20” WOA shooting 77’s with Varget shoots in the 3’s if I do my part. Mag length loads.

Since my woa barrel is stainless I really want to get it cerakoted black before I finish building it. I've been trying to find a good company to get it done. But man do I want to shoot it and develope some loads.

Mauser48 · Feb 26, 2024

Don't bother, especially when you're limited to AR mag length. I'm shooting the 77 smk with 23.2 grains of 8208 in a wylde chambered bolt gun and its money. 2.260" oal. They're jumping over .100" if I remember correctly.

ZA206 · Feb 27, 2024

77 FGMM has a COL = 2.240”, which is where my seating depth testing found best results with LC brass and several powders.

padom · Feb 27, 2024

tinker said:
You need to measure where your rifling starts with a hornady AOL gauge. then start about .020" off of that if you can.

I currently load 77 gr smk's and seat them about .050" off the lands.

Not in an AR.. loading 77smk to lands or close is longer than magazine max coal...

Get yourself ASC mags and you can load 77smk out to around 2.30" COAL. Still can't grt to lands but can get closer...

I found 77TMK like to be closer to lands in 223 Wylde AR... but my 77smk/8208 seating depth found beat accuracy at 2.485

FredHammer · Feb 27, 2024

JRBullock1987 said:
Since my woa barrel is stainless I really want to get it cerakoted black before I finish building it. I've been trying to find a good company to get it done. But man do I want to shoot it and develope some loads.

Better would be to black nitride that barrel. Cerakote is just an expensive paint.
Give the WOA about 150rnds to settle in the gas port metal migration
I've had more BA barrels shoot better out the gate than WOA, like a bunch more.
77SMK at 2.250 is pretty much a universal COAL for ARs.

JRBullock1987 · Feb 27, 2024

FredHammer said:
Better would be to black nitride that barrel. Cerakote is just an expensive paint.
Give the WOA about 150rnds to settle in the gas port metal migration
I've had more BA barrels shoot better out the gate than WOA, like a bunch more.
77SMK at 2.250 is pretty much a universal COAL for ARs.

If I was gunna nitride it ide probably shoot it first and break it in then nitride it. I've heard that bc nitride is much harder than stainless it doesn't break in the same. I read a lit of benchrest shooters break theirr barrels in then nitride them. But idk if that's bullshit or not.

JRBullock1987 · Feb 27, 2024

padom said:
Not in an AR.. loading 77smk to lands or close is longer than magazine max coal...

Get yourself ASC mags and you can load 77smk out to around 2.30" COAL. Still can't grt to lands but can get closer...

I found 77TMK like to be closer to lands in 223 Wylde AR... but my 77smk/8208 seating depth found beat accuracy at 2.485

Thanks I'll have to check out some asc mags

ma smith · Feb 27, 2024

8208 is more accurate at higher MV,
so you want max COAL.

Otherwise you pressure out sooner.

77SMK is engineered for 2.26 COAL,
and to no be jump sensitive.

77SMks do show alot of OAL variation,
IMHO, The best advice is sort bullets.

Just my $0.02

abn31c · Feb 27, 2024

JRBullock1987 said:
If I was gunna nitride it ide probably shoot it first and break it in then nitride it. I've heard that bc nitride is much harder than stainless it doesn't break in the same. I read a lit of benchrest shooters break theirr barrels in then nitride them. But idk if that's bullshit or not.

I have a 25 CM 28", I put about 150 rounds thru it and then sent it off to be nitrided. I've got about 400 rnds on it now without any noticeable throat wear. I'll do it on future builds as well.
135 berger makes 2820 with 38.1 rl16.
Before nitride it took 38.9 to make 2820.
.02

MTRecon · Feb 27, 2024

I didn't know what to start with so focused on the powder charge first.

For my AR mag length loads I used 2.250" and worked up the charge with Ramshot Tac and found a sweet spot.

For single shot long range work I measured the lands and tried the same powder charge but changed the OAL. Best load turned out to be .040" off the lands.

My method is probably flawed but I did come up with a couple loads that shoot great.

padom · Feb 27, 2024

Here my 20" WOA SDM 77SMK/8208 load workup, seating depth test and load confirmation groups. As you can see, tuning seating depth shrunk my group right up.

padom · Feb 27, 2024

Here my 73 ELD-M / 8208 Load workup, seating test and 100yd load confirmation

JRBullock1987 · Feb 27, 2024

padom said:
Here my 20" WOA SDM 77SMK/8208 load workup, seating depth test and load confirmation groups. As you can see, tuning seating depth shrunk my group right up.

Is that 1.858 cbto = to 2.240 coal? Bc I have 1.878 cbto for those components as 2.260 coal? Or are my numbers off on the cbto

padom · Feb 27, 2024

JRBullock1987 said:
Is that 1.858 cbto = to 2.240 coal? Bc I have 1.878 cbto for those components as 2.260 coal? Or are my numbers off on the cbto

2.248 my notes say. And remember CBTO is a reference measurement, not an exact or comparative measurement. Everyone's tools are different and these tools are not scientific measurement tools. They are for measuring to a reference point with your tool on your ammo, so you know where to go from there. So my numbers arent comparable to your numbers.

JRBullock1987 · Feb 27, 2024

padom said:
2.248 my notes say. And remember CBTO is a reference measurement, not an exact or comparative measurement. Everyone's tools are different and these tools are not scientific measurement tools. They are for measuring to a reference point with your tool on your ammo, so you know where to go from there. So my numbers arent comparable to your numbers.

Ok cool thanks. I was just thinking that over. So my thought was to start at 2.260 and work back in .2 gr increments to 2.250 or .3gr increments to 2.248. Did you start with 2.260 and work backwards and just watch for pressure signs?

padom · Feb 27, 2024

JRBullock1987 said:
Ok cool thanks. I was just thinking that over. So my thought was to start at 2.260 and work back in .2 gr increments to 2.250 or .3gr increments to 2.248. Did you start with 2.260 and work backwards and just watch for pressure signs?

All my data is above. So I did my load development at 1.8645" Ogive and worked AWAY from the lands from there... you can see on my above targets where the group tightened right up..

Do your load development at 2.26 or 2.265, find the center of your node, and then do seating depth working back 0.003 increments from there.. the barrel will tell you what it likes when you find one that shrinks up compared to the others if all the rest of your testing/prep/position is consistent

You generally watch for pressure going into the lands, not away from the lands. That's why most guys start into the lands and work back (not done when loading for mag fed AR)

JRBullock1987 · Feb 27, 2024

padom said:
All my data is above. So I did my load development at 1.8645" Ogive and worked AWAY from the lands from there... you can see on my above targets where the group tightened right up..

Do your load development at 2.26 or 2.265, find the center of your node, and then do seating depth working back 0.003 increments from there.. the barrel will tell you what it likes when you find one that shrinks up compared to the others if all the rest of your testing/prep/position is consistent

You generally watch for pressure going into the lands, not away from the lands. That's why most guys start into the lands and work back (not done when loading for mag fed AR)

I see. Thanks. I was thinking the more compressed the inside the cartridge, the more pressure.

diggler1833 · Feb 28, 2024

My .223 Wylde bolt gun (Krieger barrel) shoots the factory 77gr Sierra ammo into just under half-MOA...OAL is something like 2.230. It is jumping a TON at that length.

As said above, you'll run out of mag length in your AR before you get up close to the lands of your barrel with that chambering.

Guys are going to have their various opinions and magic elixirs regarding seating depth testing. I personally have found it to be productive, especially if I'm getting a 10-20% uncalled flier percentage. However I would personally at least start off at .010 each time (again, my elixir and my results) if I were to determine that I needed to play with seating depth. Going .003 at a time is a great final step to see where your ultimate accuracy window begins and ends.

FredHammer · Feb 28, 2024

diggler1833 said:
My .223 Wylde bolt gun (Krieger barrel) shoots the factory 77gr Sierra ammo into just under half-MOA...OAL is something like 2.230. It is jumping a TON at that length.

As said above, you'll run out of mag length in your AR before you get up close to the lands of your barrel with that chambering.

Guys are going to have their various opinions and magic elixirs regarding seating depth testing. I personally have found it to be productive, especially if I'm getting a 10-20% uncalled flier percentage. However I would personally at least start off at .010 each time (again, my elixir and my results) if I were to determine that I needed to play with seating depth. Going .003 at a time is a great final step to see where your ultimate accuracy window begins and ends.

Are you killing hogs with .223? If so, what bullets you using? 24yrs ago I started out vermin reducing a ranch with an AR15 M855, then went to 77SMK, but still with pack shooting we would find too many full of holes and 1/2 mile away. So, third year we switched to various semi-auto 308 platforms, and even with ball ammo, it would anchor them much better for follow ups or dead checking if we didn't hit vitals. 155AMAX has been the reigning champ for 20yrs!

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