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"

 

[FatBoy]

I run 23.3 thrown from a Dillon. So +\- .1, under 77SMKs and Aeromatches and have run at least 3000 this year from Wylde chambered barrels in five rifles and it’s been good in each.

Cases range from range pick up that was small bases to new Norma, Winchester, Starline 223 and IVI. No issues.

I don’t chrono anymore but my 14.5s are around 5 MILs to 600 yards, 16” was 4.8~ish MIL. 18” was about 17MOA. All are 7 twist Wyldes.

Edit: I run a light taper crimp as well, as I don’t prep new brass. Just run it as is on the 550.

 

[wind gypsy]

Is the case capacity in the OP quickload calc accurate? 28.5 grains h20 seems on the small side.

That said, my current bolt barrel (ACE 0.219 bore wylde chamber) seems to build pressure fast. Much over 23.0 XBR gets hot in lapua brass with 77s.

 

[padom]

Is the case capacity in the OP quickload calc accurate? 28.5 grains h20 seems on the small side.

That said, my current bolt barrel (ACE 0.219 bore wylde chamber) seems to build pressure fast. Much over 23.0 XBR gets hot in lapua brass with 77s.

My 28" 219 ACE TL3 barrel has Manzella longer 0.100fb 223 chamber and its the complete opposite of what your seeing.. slinging 80smk @ 2959 and shooting in the 0.1s no pressure

24.4gr H4895

 

[supercorndogs]

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.

23.4 is where I landed. I have actually been shooting some for that ammo to fireform 223ai. Shoots great for that also.

 

[wind gypsy]

My 28" 219 ACE TL3 barrel has Manzella longer 0.100fb 223 chamber and its the complete opposite of what your seeing.. slinging 80smk @ 2959 and shooting in the 0.1s no pressure

24.4gr H4895

Yeah, i'm not sure what to think of it. Could have gotten a 0.218 blank but i doubt it because i waited quite a while after the order for a .219 bore supposedly because they started with only tooling for 218 22 blanks. Mine was chambered by manzella as well.

18" tube, 23.5 H4895, 77 TMK, Lapua brass, cci 450 - 2840 FPS so if I had 10" more barrel like you that means the same load should be over 3k FPS. Just builds pressure fast. Shoots fine and keeps me out of compressed loads so i'm not mad about it.

 

[Edsel]

Cheapo Fulton Armory Pencil Contour Rifle Barrel (by Criterion Barrels), NATO Chamber, 1 in 8" Rifling, Chrome Lined, 20" Length		100 meters
Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, Lake City American Eagle XM193 LPC120 Brass HS at 0.000", IMR 8208 XBR, Remington SR Primers No. 7½
	1) 24.4​	2) 24.5​	3) 24.6​	4) 24.7​	5) 24.8​	6) 24.9​	7) 25​
AVERAGE SPEED	884.0695​	894.2399​	898.744​	904.3444​	911.5847​	913.7571​	915.1394​
STD DEV	7.113203​	10.51101​	7.025966​	9.790118​	13.36195​	4.750439​	5.972237​
SPREAD	19.646​	34.412​	19.031​	29.524​	44.603​	12.12​	18.983​
Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Lake City American Eagle XM193 LPC120 Brass HS at 0.000", IMR 8208 XBR, Remington SR Primers No. 7½
	1) 23.6​	2) 23.7​	3) 23.8​	4) 23.9​	5) 24​
AVERAGE SPEED	837.4729​	838.6488​	842.933​	848.268​	847.5483​
STD DEV	4.139422​	3.648012​	3.881887​	2.851095​	3.615818​
SPREAD	14.327​	11.369​	10.156​	9.695​	11.304​

RED: Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, IMR 8208 XBR 24.4 to 25 grains in 0.1 grain increments (1 to 6), Remington SR Primers No. 7½

#4 (24.7 grains) and #7 (25.0 grains)

GREEN: Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, IMR 8208 XBR 23.6 to 24 grains in 0.1 grain increments (1 to 6), Remington SR Primers No. 7½

#4 (23.9 grains)

 

[Edsel]

Mid - price heavyish White Oak Armament Shilen Service Rifle Barrel, Wylde Chamber, 1 in 8" Ratchet Rifling, 20" Length		100 meters
Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, Lake City American Eagle XM193 LPC120 Brass HS at 0.000", IMR 8208 XBR, Remington SR Primers No. 7½
	1) 24.4​	2) 24.5​	3) 24.6​	4) 24.7​	5) 24.8​	6) 24.9​	7) 25​
AVERAGE SPEED	878.7522​	888.624​	888.1413​	890.6968​	896.8454​	907.0558​	903.5583​
STD DEV	5.38196​	11.70219​	7.844106​	8.387023​	8.667786​	7.578201​	6.77029​
SPREAD	17.433​	33.264​	23.733​	30.895​	31.375​	22.461​	26.078​
Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Lake City American Eagle XM193 LPC120 Brass HS at 0.000", IMR 8208 XBR, Remington SR Primers No. 7½
	1) 23.6​	2) 23.7​	3) 23.8​	4) 23.9​	5) 24​
AVERAGE SPEED	837.2784​	835.6724​	834.8497​	837.7597​	841.6948​
STD DEV	2.915875​	3.639955​	3.676056​	5.708446​	2.66755​
SPREAD	8.816​	11.292​	12.903​	19.294​	8.263​

RED: Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, IMR 8208 XBR 24.4 to 25 grains in 0.1 grain increments (1 to 6), Remington SR Primers No. 7½

#1 (24.4 grains), maybe - but discounting fliers, they seem to fit in a 2" x 2" box.

GREEN: Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, IMR 8208 XBR 23.6 to 24 grains in 0.1 grain increments (1 to 6), Remington SR Primers No. 7½

#3 (23.8 grains) to #4 (23.9 grains), maybe.

They all look the same, for the most part

This barrel is odd; regardless of garbage trashmunition (from prior outings) to gourmet match ammunition - the output is always the same, much like what is pictured above.

"Guaranteed 2 MOA accuracy - with everything."

 

[Edsel]

Bottom of the barrel heavy $99 AR Stoner Varmint Contour Rifle Barrel, Wylde Chamber, 1 in 8" 5R Rifling, 24" Length		100 meters
Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, Federal Value Pack BP223BL Brass HS at 0.000", IMR 8208 XBR, Remington SR Primers No. 7½
	1) 24.4​	2) 24.5​	3) 24.6​	4) 24.7​	5) 24.8​	6) 24.9​	7) 25​
AVERAGE SPEED	908.6009​	914.5375​	917.4145​	925.9411​	923.766​	937.0274​	940.3853​
STD DEV	10.68733​	4.836572​	8.308032​	7.123946​	4.904918​	6.454211​	10.07498​
SPREAD	36.133​	13.552​	31.458​	22.169​	16.141​	23.103​	28.46​
Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Federal Value Pack BP223BL Brass HS at 0.000", IMR 8208 XBR, Remington SR Primers No. 7½
	1) 23.6​
AVERAGE SPEED	848.9969​
STD DEV	3.074791​
SPREAD	9.034​
Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Lake City American Eagle XM193 LPC120 Brass HS at 0.000", IMR 8208 XBR, Remington SR Primers No. 7½
		2) 23.7​	3) 23.8​	4) 23.9​	5) 24​
AVERAGE SPEED	​	850.0961​	855.9725​	855.7923​	859.8074
STD DEV		2.848821​	3.994885​	4.241267​	4.420767​
SPREAD		10.351​	13.281​	13.527​	14.481​

RED: Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, IMR 8208 XBR 24.4 to 25 grains in 0.1 grain increments (1 to 6), Remington SR Primers No. 7½

#1 to #7 all look the same except for #2 (24.5 grains)...

GREEN: Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, IMR 8208 XBR 23.6 to 24 grains in 0.1 grain increments (1 to 6), Remington SR Primers No. 7½

...as do #1 to #5, except maybe for #2 (23.7 grains) to #4 (23.9 grains).

Didn't expect the POI to go way up high, though. Groups definitely accentuated by rifle cant.

 

[Edsel]

Why are AR15s so difficult to shoot for the average shooter?

Ok, I recognize that the answer is better fundamentals, full stop. But this is what I see. Go to any range, see a bunch of AR15s on the line, and for most of the shooters it is all they can do to put their rounds inside a 12" diameter target center at 100 yards. It doesn't seem to matter...

www.snipershide.com

Not very happy with the session, overall.

Couldn't stop squirming behind these ARs...

Not helped by the fact that the groups are being shot round robin...

...Load 1, Rifle 1. Load 1, Rifle 2. Load 1, Rifle 3...

Unlike 20 pound bolt - action rifles (or my light, svelte Tikkas!) which do their best to remove the shooter from the equation, every little twitch on the scope reflects disproportionately on paper.

EDIT: These barrels appear to be slooooooooow!...

23.2- 23.6gr is pretty well known node for AR's with 75/77gr bullets...

Maybe I'll try some slower loads in the future.

 

[ma smith]

FWIW, I'd check all the usual mechanical stuff like loose bipod/optic mount/pic/arca rails/forends etc before making any decisions. 3 inch POI shift is a possible hint theres a problem somewhere and it's not the ammo.

A POI Error of ~1 to 1.2 mil is nominally the ∆ to zero ± 275-300 yds or whatever (check your ballistic calculator).

 

[Edsel]

FWIW, I'd check all the usual mechanical stuff like loose bipod/optic mount/pic/arca rails/forends etc before making any decisions. 3 inch POI shift is a possible hint theres a problem somewhere and it's not the ammo.

A POI Error of ~1 to 1.2 mil is nominally the ∆ to zero ± 275-300 yds or whatever (check your ballistic calculator).

With the third rifle?

You're right - I'll need to examine it.

 

[Edsel]

Cheapo Fulton Armory Pencil Contour Rifle Barrel (by Criterion Barrels), NATO Chamber, 1 in 8" Rifling, Chrome Lined
20" Barrel
Tulammo .223 Remington, 55 grain, FMJ, Steel, Berdan Primed, Russian
AVERAGE SPEED	2892.4
STD DEV	44.0
SPREAD	158.3
Lake City 5.56 x 45mm, 62 grain, FMJ, Brass, Boxer Primed, NATO, XM855
AVERAGE SPEED	3086.9
STD DEV	24.9
SPREAD	155.0
Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, Lake City American Eagle XM193 LPC120 Brass, IMR 8208 XBR, Remington SR Primers No. 7½
	24.4​	24.5​	24.6​	24.7​	24.8​	24.9​	25​
AVERAGE SPEED	2900.491​	2933.858​	2948.635​	2967.009​	2990.764​	2997.891​	3002.426​
STD DEV	23.33728​	34.48494​	23.05107​	32.11981​	43.83842​	15.58543​	19.59395​
SPREAD	64.45538​	112.9003​	62.43767​	96.86352​	146.3353​	39.76378​	62.28019​
Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Lake City American Eagle XM193 LPC120 Brass, IMR 8208 XBR, Remington SR Primers No. 7½
	23.6​	23.7​	23.8​	23.9​	24​
AVERAGE SPEED	2747.615​	2751.473​	2765.528​	2783.032​	2780.67​
STD DEV	13.58078​	11.96854​	12.73585​	9.353985​	11.86292​
SPREAD	47.00459​	37.29987​	33.32021​	31.80774​	37.08662​

 

[Edsel]

Mid - price heavyish White Oak Armament Shilen Service Rifle Barrel, Wylde Chamber, 1 in 8" Ratchet Rifling
20" Barrel
Tulammo .223 Remington, 55 grain, FMJ, Steel, Berdan Primed, Russian
AVERAGE SPEED	2889.6
STD DEV	39.9
SPREAD	130.9
Lake City 5.56 x 45mm, 62 grain, FMJ, Brass, Boxer Primed, NATO, XM855
AVERAGE SPEED	3061.6
STD DEV	14.9
SPREAD	54.4
Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, Federal Value Pack BP223BL Brass, IMR 8208 XBR, Remington SR Primers No. 7½
	24.4​	24.5​	24.6​	24.7​	24.8​	24.9​	25​
AVERAGE SPEED	2883.045​	2915.433​	2913.85​	2922.234​	2942.406​	2975.905​	2964.43​
STD DEV	17.65735​	38.39303​	25.73526​	27.51648​	28.43762​	24.86286​	22.21224​
SPREAD	57.19488​	109.1339​	77.86418​	101.3616​	102.9364​	73.69095​	85.55775​
Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Lake City American Eagle XM193 LPC120 Brass, IMR 8208 XBR, Remington SR Primers No. 7½
	23.6​	23.7​	23.8​	23.9​	24​
AVERAGE SPEED	2746.976​	2741.707​	2739.008​	2748.556​	2761.466​
STD DEV	9.566519​	11.94211​	12.06055​	18.7285​	8.751805​
SPREAD	28.92389​	37.04725​	42.33268​	63.30053​	27.10958​

 

[Edsel]

Bottom of the barrel heavy $99 AR Stoner Varmint Contour Rifle Barrel, Wylde Chamber, 1 in 8" 5R Rifling
24" Barrel
Tulammo .223 Remington, 55 grain, FMJ, Steel, Berdan Primed, Russian
AVERAGE SPEED	2957.4
STD DEV	42.1
SPREAD	154.2
Lake City 5.56 x 45mm, 62 grain, FMJ, Brass, Boxer Primed, NATO, XM855
AVERAGE SPEED	3172.0
STD DEV	19.3
SPREAD	79.1
Hornady 55 grain FMJ-BT 2267B at 2.200"COAL, Federal Value Pack BP223BL Brass, IMR 8208 XBR, Remington SR Primers No. 7½
	24.4​	24.5​	24.6​	24.7​	24.8​	24.9​	25​
AVERAGE SPEED	2980.974​	3000.451​	3009.89​	3037.865​	3030.728​	3074.237​	3085.254​
STD DEV	35.06341​	15.86802​	27.25732​	23.37253​	16.09225​	21.17523​	33.05439​
SPREAD	118.5466​	44.46194​	103.2087​	72.73294​	52.95604​	75.79725​	93.37271​
Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Lake City American Eagle XM193 LPC120 Brass, IMR 8208 XBR, Remington SR Primers No. 7½
	23.6​	23.7​	23.8​	23.9​	24​
AVERAGE SPEED	2785.423​	2789.029​	2808.309​	2807.718​	2820.891​
STD DEV	10.0879​	9.346527​	13.10658​	13.91492​	14.50383​
SPREAD	29.63911​	33.95997​	43.57284​	44.37992​	47.50984​

 

[Edsel]

Finally got the values converted to Imperial.

Do the velocities look proper to you?

I'm under the impression that this combination of IMR 8208 XBR for 55gr and 77gr bullets is rather slow.

It's something like 100 to 150fps slower than QuickLOAD estimates.

When I "true" QuickLOAD by adjusting the Brisance value - it suggests that my pressures are on the low side (!).

I already have some loose primer pockets with the hotter 77gr loads.

 

[spife7980]

You are certainly up there in pressure if not over. Trust your primer pockets, not an untuned software.
23.6 is about where I stop testing myself because I know thats where lapua and lc get loose pockets at in a bolt gun. Your crapier brass in a gas gun is a worser case proposition.

 

[whatsupdoc]

22" Kreiger Rifle gas (.218 Bore) most .224 barrels have .219 bore.

Federal Factory FC262 ammo 77SMK 2873 FPS

Magtech OTM 77 Factory ammo 2921 FPS

Magtec Case, 77SMK, 23.2gr IMR8208, CCI450 2835 FPS

 

[padom]

My latest 20" White Oak Precision Krieger 1-7 is 2815

23.4gr
8208
77smk
205M
NT 5.56 brass
2.248

 

[Edsel]

You are certainly up there in pressure if not over. Trust your primer pockets, not an untuned software. 23.6 is about where I stop testing myself because I know thats where lapua and lc get loose pockets at in a bolt gun. Your crapier brass in a gas gun is a worser case proposition.

Good to know, re: Lapua brass - that’s a useful index I could relate with.

Still makes me wonder what the heck’s going on…

FWIW - charges were dispensed with one of those Autotricklers, and brass was annealed with an AMP machine. Velocities are tracked by a Garmin Xero C1.

22" Kreiger Rifle gas (.218 Bore) most .224 barrels have .219 bore.

Magtec Case, 77SMK, 23.2gr IMR8208, CCI450 2835 FPS

My latest 20" White Oak Precision Krieger 1-7 is 2815

23.4gr
8208
77smk
205M
NT 5.56 brass
2.248

Where would you think the issue lies?

I’m getting slow bullets across the board, in three different ARs.

Your 20” and 22” rifles are getting better velocities with less powder, compared to my 24” barrel.

 

[ma smith]

OEM for XBR powder here is Hodgon (ADI), their book max is 23.2 which is nominally 2,792 fps but only beause the extra 4~ inches of test-barrel (24in test bbl). Most mk 262 clone loads, in 18-20inch barrels, are around but just short 2,750 with XBR, final results of course depending on your specific bbl/chamber combo etc.Speeds approaching 2,800fps in only 20in of bll is almost certainly overpressure, as are loads using loads at 24.0+ grains etc.

Sierra 6th Ed. Manual for comparison. Note this is 'bolt gun' section because Sierra doesn't publish XBR in the AR section for .223 rem. Either way, Sierra shows a much lower level of charge and accordingly slower speeds vs Hogdon, but its showing somewhat similar data in terms of grain for grain velocity. 2650 at 22.0 is 100fps over their load of 21.0gr, so presumably 23.0 grains is around 2,750 which starts to track pretty close to the above Hogdon book max of 23.3 @ 2972 in 24in pressure barrel.

 

[Edsel]

Sierra 6th Ed. Manual for comparison. Note this is 'bolt gun' section because Sierra doesn't publish XBR in the AR section for .223 rem. Either way, Sierra shows a much lower level of charge and accordingly slower speeds vs Hogdon, but its showing somewhat similar data in terms of grain for grain velocity. 2650 at 22.0 is 100fps over their load of 21.0gr, so presumably 23.0 grains is around 2,750 which starts to track pretty close to the above Hogdon book max of 23.3 @ 2972 in 24in pressure barrel.

Sierra Matchking 77 grain HPBT 9377 at 2.240"COAL, Lake City American Eagle XM193 LPC120 Brass, IMR 8208 XBR, Remington SR Primers No. 7½
	23.6	23.7	23.8	23.9	24
AVERAGE SPEED	2785.423	2789.029	2808.309	2807.718	2820.891

Discrepancy, though between a bolt and a gasser, seems a bit much…

 

[spife7980]

Your speeds aren’t slow.

 

[Bantam1]

In my 18" Douglas barreled gas gun, I see about 2660 with 23.5 XBR in Lake City brass, Fed 210M and 2.248. If i change the primer to Rem 7.5 it will go about 2690-2700. Your speeds are fine. This barrel is a little on the slow side, but it is very accurate with this load. If I change to Lapua brass the SD is 3-5 and ES is 10-12 going 2660. With the LC the SD and ES goes up.

 

[Edsel]

Your speeds aren’t slow.

In my 18" Douglas barreled gas gun, I see about 2660 with 23.5 XBR in Lake City brass, Fed 210M and 2.248. If i change the primer to Rem 7.5 it will go about 2690-2700. Your speeds are fine. This barrel is a little on the slow side, but it is very accurate with this load. If I change to Lapua brass the SD is 3-5 and ES is 10-12 going 2660. With the LC the SD and ES goes up.

Thanks for the reassurances.

If anything, this probably works out more as a practice session with my (neglected) ARs more than anything else.

I'll give it another go once circumstances permit.