223, 69 SMK, IMR 8208 OCW

[Ballistic308]

This is the third time I've performed this test and I finally have some usable results. The first two test where subject to shooter and equipment error and didn’t show any trends towards where the OCW should have been; third time was the charm.

Here are the rifle and load specifications:

Rifle: home built 223 AR-15, 20” SS bull barrel, 1:8 twist, rifle length gas system http://www.midwayusa.com/viewProduct/?productNumber=173618

Bullet: 69 SMK
Brass: Winchester
Powder: IMR 8208
Primer: WSR
Test COAL: 2.260”
Distance: 100 yards

The velocity I'm getting really shocked me as my chony read 2980 fps on a 10 shot average, but I will get the true velocity when I shoot I get my true zero's and work it backwards from there.

I started at 23.0g and worked up in 0.3g to 25.5, Hodgdon states a maximum charge weight of 23.8g, but as I and others have seen this powder is either under rated or very pressure tolerant. I started to see primers flatten out around the 25.3g – 25.5g area. IF YOU DECIDE TO WORK UP PAST THE MANUFACTURERS LIST MAXIMUM CHARGE START AT 23.0 AND WORK YOUR WAY UP LOOKING FOR PRESSURE SIGNS.


<span style="font-weight: bold">Charge weights:</span> I settled on 25.1 and shot a seating depth string.

<span style="font-weight: bold">Seating Depth:</span> I'm thinking I will reshoot 1.853" (2.253") and 1.844" (2.244") to see what happens at 200 yards.

(Ignore page 2 dot 1, just proofing other loads and I shot the wrong dot)

 

[308sako]

Re: 223, 69 SMK, IMR 8208 OCW

IMR 8208 XBR is an excellent propellant for the 5.56.

I have used it with 55 Nosler BT's and found that 26.0 grain in my custom QPQ'd 18" Rock Creek 5R barrel was best @ 3122 ft/secs.

Favorite load in Colt 6724 with Sierra 77 SMK's is also 7/10ths of a grain over <span style="font-weight: bold"><span style="font-style: italic">suggested .223 Remington book maxi</span>mum</span> and it rocks to 1,000 yards. Velocity is 2850 ft/secs.

My best 69 SMK load is same as the 77 grain and it is a one holer at 100 yards. Velocity 2935 ft/secs.

All velocities quoted from Oehler 35P chronograph.

Visiting Cannon Beach in 10 days or so... is that your AO?

 

[Ballistic308]

Re: 223, 69 SMK, IMR 8208 OCW

yes the powder is a great one. My next test is the 77g so I'll watch for the area you suggested.

I live just west of Portland...Bring your raingear if your going to the beach this time of year.

 

[308sako]

Re: 223, 69 SMK, IMR 8208 OCW

We always pack that gear... nice change from the desert.

We try the beach twice a year whether or not we need it.

23.3 and 24 are the nodes you will find

 

[Ballistic308]

Re: 223, 69 SMK, IMR 8208 OCW

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: HumungoSpheres</div><div class="ubbcode-body">We always pack that gear... nice change from the desert.

We try the beach twice a year whether or not we need it.

23.3 and 24 are the nodes you will find
</div></div>
I figured so as I've extrapolated a node at 24.1.

 

[turbo54]

Re: 223, 69 SMK, IMR 8208 OCW

Interesting... I was just chatting with some national match shooters about 8208xbr yesterday.

They were claiming some guys claim the 8208 won't cycle their ARs fully/properly.

Can anyone speak to that point?

 

[Ballistic308]

Re: 223, 69 SMK, IMR 8208 OCW

It cycles my three just fine, two are carbine length gas systems and one is a rifle length. There's too much to an AR to assume it's soley the powder and by this I mean they could have heavier buffers, not enough lube, adjustable gas blocks, etc. which can reduce the bolt speed.

What charge weight are they using?

 

[2ndPanzer]

Re: 223, 69 SMK, IMR 8208 OCW

I have heard that as well, but it seems it was either A. using an 80, and it wouldn't lock the bolt back, which happens alot with 80's because people tend to load them so light for fear of pressure or use the wrong powder type for it. or B. they used a light charge in the 22.x range with a 77. They get " pressure" signs, but then again they are using standard SR primers instead of mags or military ones. The cci 400 will flatten out with mild charges of varget, and this powder is a wee bit hotter and likes to run a little more pressure. You need to run magnum or milspec primers for alot of the 77 loads that require a higher pressure. I don't believe its the powder, more so the lack of enough powder in there because of the use of inappropriate primers for the charges needed with this powder. Check the charts, the 8208 has some pretty high numbers pressure wise when compared to the old standby 223 powders. I use the Wolf SRM, because they have a harder cup. They aren't any hotter than regular, and most magnum primers aren't either. Some are, but most are not, but they do all have a harder cup. The BR primers do too.

 

[turbo54]

Re: 223, 69 SMK, IMR 8208 OCW

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2ndPanzer</div><div class="ubbcode-body"> I have heard that as well, but it seems it was either A. using an 80, and it wouldn't lock the bolt back, which happens alot with 80's because people tend to load them so light for fear of pressure or use the wrong powder type for it. or B. they used a light charge in the 22.x range with a 77. They get " pressure" signs, but then again they are using standard SR primers instead of mags or military ones. The cci 400 will flatten out with mild charges of varget, and this powder is a wee bit hotter and likes to run a little more pressure. You need to run magnum or milspec primers for alot of the 77 loads that require a higher pressure. I don't believe its the powder, more so the lack of enough powder in there because of the use of inappropriate primers for the charges needed with this powder. Check the charts, the 8208 has some pretty high numbers pressure wise when compared to the old standby 223 powders. I use the Wolf SRM, because they have a harder cup. They aren't any hotter than regular, and most magnum primers aren't either. Some are, but most are not, but they do all have a harder cup. The BR primers do too. </div></div>

Thanks!

22.X gr Varget for a 77SMK sounds LIGHT to me. 24.5(ish) seems to be about right. Obviously, the 8208 is attractive because it meters well. I'd be willing to drop charges into match ammo with 8208, whereas I'm not willing with Varget.

 

[308sako]

Re: 223, 69 SMK, IMR 8208 OCW

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2ndPanzer</div><div class="ubbcode-body"> I have heard that as well, but it seems it was either A. using an 80, and it wouldn't lock the bolt back, which happens alot with 80's because people tend to load them so light for fear of pressure or use the wrong powder type for it. or B. they used a light charge in the 22.x range with a 77. They get " pressure" signs, but then again they are using standard SR primers instead of mags or military ones. The cci 400 will flatten out with mild charges of varget, and this powder is a wee bit hotter and likes to run a little more pressure. You need to run magnum or milspec primers for alot of the 77 loads that require a higher pressure. I don't believe its the powder, more so the lack of enough powder in there because of the use of inappropriate primers for the charges needed with this powder. Check the charts, the 8208 has some pretty high numbers pressure wise when compared to the old standby 223 powders. I use the Wolf SRM, because they have a harder cup. They aren't any hotter than regular, and most magnum primers aren't either. Some are, but most are not, but they do all have a harder cup. The BR primers do too. </div></div>

Thanks!

22.X gr Varget for a 77SMK sounds LIGHT to me. <span style="text-decoration: underline"><span style="font-style: italic"><span style="font-weight: bold">24.5(ish) seems to be about r</span>igh</span>t. </span> Obviously, the 8208 is attractive because it meters well. I'd be willing to drop charges into match ammo with 8208, whereas I'm not willing with Varget. </div></div>

I found this charge area to be excessive in 5.56 NATO chambered rifles. It would also be 1.3 grains above recommended book maximum (see Hodgdon's web site) By all means work up slowly to your rifles accurate maximum. Go safely!