IMR 8208 XBR AND 77gr SMK IN A GAS GUN

[Edsel]

Just wanted some opinions on this powder and bullet combination for an AR with a 20” barrel and an adjustable gas block.

Typical loads I see online involve charge weights between 23 to 24 grains with a 77gr SMK at 2.24” for Mk262 clones (23.8 grains typical).

From what I can see, this is an accepted norm.

QuickLOAD suggests pressures in excess of of 73,000 psi using this combination, putting it deep into the red zone.

Safe to go this high?

Starting at 23 grains.

 

[alamo5000]

Have you considered looking up load data from the manufacturer of the powder? That would be a better place to start (rather than starting a thread about something that can be looked up in about 3 minutes)

 

[Edsel]

Have you considered looking up load data from the manufacturer of the powder? That would be a better place to start (rather than starting a thread about something that can be looked up in about 3 minutes)

They are much more conservative than the range stated.

However, many of the Mk262 “clone loads” fall in the range as stated above.

That is my concern.

 

[alamo5000]

Here is a link with 15 full length videos on cloning that round.

 

[Edsel]

Here is a link with 15 full length videos on cloning that round.

I have seen those videos.

Many of his loads also fall into the red.

 

[Edsel]

The particular video in that series applicable to what I’m doing is this one.

 

[BoilerUP]

All I know is RP, LC, Hornady and Lapua cases have all looked fine with 23.5-23.8gr XBR under a 77gr SMK from a whole bunch of different barrels for me. Using CCI450s, primers don't look flat and there isn't cratering.

24.0gr duplicated BHA Mk262 velocity, but 23.5-23.8gr shoots better for just a skosh less speed.

YMMV, etc

 

[Edsel]

I suppose I should clarify that I’m curious about the oft - quoted 23.8 grains, seems a bit too warm.

 

[Edsel]

All I know is RP, LC, Hornady and Lapua cases have all looked fine with 23.5-23.8gr XBR under a 77gr SMK from a whole bunch of different barrels for me. Using CCI450s, primers don't look flat and there isn't cratering.

24.0gr duplicated BHA Mk262 velocity, but 23.5-23.8gr shoots better for just a skosh less speed.

YMMV, etc

What can one expect from case life?

Is the load brutal on brass?

 

[BoilerUP]

What can one expect from case life?

Is the load brutal on brass?

I don't think anybody would claim RP to be super high quality brass, but I've got 5 loads on some with this recipe and primers go in just fine.

Is it hot? Yes.

Is it unsafe? IMO, no.

 

[Edsel]

I don't think anybody would claim RP to be super high quality brass, but I've got 5 loads on some with this recipe and primers go in just fine.

Is it hot? Yes.

Is it unsafe? IMO, no.

Thanks.

This gives me a useful idea on what to expect and plan for

 

[sinister]

If you have a correctly built-assembled rifle with a decent 20-inch match-grade barrel and can not get it to shoot sub-MOA groups with loads charged at 23.4 grains of 8208 pushing bullets from 69 to 80 grains there is something wrong with it.

 

[alamo5000]

I have seen those videos.

If you have seen those who are you trying to get information from? A guy that has been reloading for 35 or 40 years and has produced a formal series of 15 videos on the specific subject all with real world results captured on video, but apparently that isn't enough.

If that is not enough information I don't know what to say other than you need to go test it out yourself.

Asking questions on a forum is fine but stuff like this is irritating because you are wasting everyone's time and Internet bandwidth. I'm pretty sure that no one here is going to go take your rifle out to test for you. Seriously, what kind of answers are you actually looking for?

 

[Bacarrat]

77gr SMK with 24gr XBR is the go to load. Me a several friends have shot thousands of rounds of this very load.

 

[nn8734]

View attachment 8764682

Just wanted some opinions on this powder and bullet combination for an AR with a 20” barrel and an adjustable gas block.

Typical loads I see online involve charge weights between 23 to 24 grains with a 77gr SMK at 2.24” for Mk262 clones (23.8 grains typical).

From what I can see, this is an accepted norm.

QuickLOAD suggests pressures in excess of of 73,000 psi using this combination, putting it deep into the red zone.

Safe to go this high?

Starting at 23 grains.

Who cares what QL or GRT says - no way to know for sure until you engage in RTDE with your rifle and aforementioned components.

Let us know where you ended up once you do so.

 

[Edsel]

If you have a correctly built-assembled rifle with a decent 20-inch match-grade barrel and can not get it to shoot sub-MOA groups with loads charged at 23.4 grains of 8208 pushing bullets from 69 to 80 grains there is something wrong with it.

One of my ARs which uses a 20” White Oak Armament Shilen “Ratchet Rifling” 1:8 barrel shoots all sorts of 55 and 62 grain trashmunition fairly consistently in 2” groups at 100 yards.

I’m hoping it’ll do better with handloads, but that rifle’s last in line because it just shoots so well.

Figure I’ll adjust the gas block for “late” ejection.

 

[flogxal]

I have read / heard from 6.5 Grendel users that 8208 recent batches (last 1-2 yrs) carry more energy than in years past. Have not reloaded long enough to say I've seen it myself. I've worked up a few recipes in GRT for 5.56 and 77gr, I will check those for what GRT suggests.

EDIT: GRT with 77gr Sierra HPBT and 8208, with case volume 31.8gr water, shows 23.9 gr at 56,944 PSI and 2626 fps in a 16" barrel. This is not confirmed by live fire, just a GRT prediction.

 

[Edsel]

Who cares what QL or GRT says - no way to know for sure until you engage in RTDE with your rifle and aforementioned components.

You might say I’m overly cautious, and was hoping others with more experience with this combination would raise something that hasn’t occurred to me.

Let us know where you ended up once you do so.

Most certainly will.

 

[Edsel]

I have read / heard from 6.5 Grendel users that 8208 recent batches (last 1-2 yrs) carry more energy than in years past. Have not reloaded long enough to say I've seen it myself. I've worked up a few recipes in GRT for 5.56 and 77gr, I will check those for what GRT suggests.

That’s good to know. I have this one lone pound which is 4 years older than the rest.

I’ll set this one aside.

 

[WillHugh]

I'd start in the low 23s and work your way up. I settled on 23.3 in a couple of my rifles (~2680 fps in a 16"). I tried 23.8 and was getting pretty bad ejector marks on LC brass. A buddy uses it as has standard load though, so will differ rifle to rifle.

 

[padom]

23.6gr 8208 with a 77smk @ 2.245 is a tack driver in my WOA barrels for many years.

 

[Mauser48]

I use 23.2. Shoots really good.

 

[memilanuk]

23.2 and a 77 TMK were the secret sauce out of my 20" WOA for MR-ART class.

 

[ma smith]

I suppose I should clarify that I’m curious about the oft - quoted 23.8 grains, seems a bit too warm.

I'd look for speed max in the 2,700-2,730fps window, a half-step or so below Mk262 nominal of 2750fps.

Also, make sure to RTFM for some basic orientation, note that short-throat saami-spec chambers are going to hit pressure faster. Max book is 22.0 in saami spec at 2650 fps in 24in test bbl. Note that sierra doesn't recommend/publish for a 5.56 nato chamber in the AR section.

We can speculate why they don't do this, but part of the reason is they probably don't want people doing stupid stuff with high-pressure XBR loads in gas guns...

 

[Edsel]

We can speculate why they don't do this, but part of the reason is they probably don't want people doing stupid stuff with high-pressure XBR loads in gas guns...

Like our much - vaunted "Mk262 Clone Loads"