6.8 SPC Forums banner
1 - 11 of 11 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
I recently built a 6.8 with a shilen 24" SS heavy barrel with a 1:11' twist. I've been working on a load for it as it seems pretty finicky on what it shoots accurately.I am loading 110 gr. Vmax projectiles and using H322. I am close to the Hornady manuals max load of 28.1 gr. Hodgen's max load is 29.5. I think my rifles ideal load is somewhere in between. ( so far, the hotter the load the more accurate)
My question is, I see most guys here shoot a maximum of a 20" barrel, should I be concerned about pressure if I exceed the Hornady max load?
Thanks in advance for any advice.
 

·
Registered
Joined
·
4,811 Posts
yes and no. You need to know the danger signs of loading beyond such as flattened or cratered primers and swipes and such. Going with a shorter barrel is not going to change that. SLOWLY work your way up and pay attention to what you case is telling you. Be careful and consider trying a few different powders such as AA2200
 

·
Registered
Joined
·
1,043 Posts
Barrel length has zero influence on chamber pressure. Lots of other things like actual bore diameter, throat length, leade angle, land height, and probably more dimensions effect chamber pressures shooting identical ammo in two different rifles.

I suspect your barrel just doesn't like 110 grain V-Max bullets. My go to bullet for accuracy in 6.8 SPC is Sierra 115 grain Match Kings. 28.0 grains of H322 with that bullet usually prints around 1" groups at 100 for me.
 

·
Premium Member
Joined
·
826 Posts
Hodgdon lists the max for H322 at 29.0
H335 is listed with a max of 29.5
Keep an eye on the listed pressures on the min/max data... The more data you can utilize helps to judge your bass condition and pressure.
 

·
Registered
Joined
·
139 Posts
my 16" vs 20" results, yours will vary

I have factory 20" and 16" DPMS rifles. My 16" always shows pressure signs before the 20" and the difference is big. Not sure why that is but I think it's more a function of chamber/throat reaming than anything else. Maybe a gas port/system variance? I use the 16" for load work ups and take whatever gain I get from the extra length of the 20", usually about 100 fps from my top loads. But as usual, others' results will vary. 20" is rifle length gas (will never get one of those again) and 16" of course is carbine length.
 

·
Super Moderator
Joined
·
12,228 Posts
I recently built a 6.8 with a shilen 24" SS heavy barrel with a 1:11' twist. I've been working on a load for it as it seems pretty finicky on what it shoots accurately.I am loading 110 gr. Vmax projectiles and using H322. I am close to the Hornady manuals max load of 28.1 gr. Hodgen's max load is 29.5. I think my rifles ideal load is somewhere in between. ( so far, the hotter the load the more accurate)
My question is, I see most guys here shoot a maximum of a 20" barrel, should I be concerned about pressure if I exceed the Hornady max load?
Thanks in advance for any advice.
Not really. Hornady and pretty much everyone else publish loads for SAAMI spec'd chambers and not SPC II. I generally start my load work up at about half a grain below published max loads and keep an eye out for pressure signs.
 

·
Registered
Joined
·
1,756 Posts
I have factory 20" and 16" DPMS rifles. My 16" always shows pressure signs before the 20" and the difference is big. Not sure why that is but I think it's more a function of chamber/throat reaming than anything else. Maybe a gas port/system variance? I use the 16" for load work ups and take whatever gain I get from the extra length of the 20", usually about 100 fps from my top loads. But as usual, others' results will vary. 20" is rifle length gas (will never get one of those again) and 16" of course is carbine length.
Carbine gas is less preferable than mid gas and may be why it shows pressure before your 20. I would buy a rifle gas before a carbine gas.
 

·
Registered
Joined
·
1,065 Posts
I shoot a 6 groove 1:10 24" barrel. I tested H335 in .2gr increments up to 30.6. Started to get really flat primers and over gassed ejection. After 30.0 I started getting random stringing at each increment.

What type of rifling does your barrel have?

My load data:
Hornady 110 BTHP
S&B case
29.6gr H335
WSR primer
2.265-2.270 COAL
Light crimp

Shoots sub MOA out to 500 meters for me, I just posted a pic of a .8 MOA group on steel at 300 meters I shot yesterday. I also use an adjustable gas block that is turned down 10 clicks I believe.

-Alexander
 

·
Registered
Joined
·
1,490 Posts
A longer barrel does not increase pressure. As the powder burns it creates a gas. That gas pushes the bullet down the barrel. The further down the barrel the bullet goes the more volume there is for that gas to fill. Peak pressure is reached in the first few inches of the barrel. The further the bullet goes the more the pressure drops. That's why the gas port for a carbine gas system is smaller than a rifle gas port. The higher pressure at the carbine port pushes more gas into the barrel. At the rifle gas port you need a bigger hole to allow the same amount of gas.

There are many other factors that can increase pressure as others have mentioned. That's why you start low and work up. Just because a reloading manual lists a max load does not guarantee that load is safe in your firearm. Watch for cratered primers swipes flat primers etc. When those signs show up you have reached your max load.
 

·
Registered
Joined
·
139 Posts
Carbine gas is less preferable than mid gas and may be why it shows pressure before your 20. I would buy a rifle gas before a carbine gas.
Only issue I've had with the rifle gas is that some powders will not work as reliably as in the 16" I like to work up loads that function at top performance in both rifles so have had to discount some very popular powders because of it. Other than that no problems. I hear the mid-length is the way to go so if I ever do upgrade that's what I'll try. For this one I'm thinking maybe an adjustable gas port will do the trick.
 

·
Registered
Joined
·
690 Posts
pressure

i shoot a 20" ARP target 5 R bbl. i'm using 29.3 of H322 for my 110 VMAX and get 2717 MV. In that bbl and load combo i wouldn't want to go any hotter. i can go up to 29.5 of H322 for the Hornady 110 BTHP and that is max for that bullet. The VMAX is a little longer and takes up more space in the case. i believe this is the reason it shows signs of pressure before the 110 BTHP does, even though they're the same weight. Both loadings are lights out accurate out of that bbl.
 
1 - 11 of 11 Posts
Top