.308 pressure issue

[Josh Umsted]

Found a good load but brass shows pressure signs well below max charge: flat primers, faint extractor marks, and occasional heavy bolt lift.

43.8gr Varget
Berger 168 hybrid
Federal brass, twice fired. Same pressure signs with Lapua.
Federal 210 primers
Criterion 24” 1:10. 250 rounds thru.
2725 FPS

Max charge per Hodgdon is 46gr. Not sure why the high pressure. I’ll adjust the load. Just trying to understand what’s going on.

 

[918v]

Hodgdon’s data is based off a Winchester case which has way more capacity than Federal or Lapua. I dunno how tight your chamber is but that contributes as well. So you should reduce your power charge. Also clean your barrel real good. Make sure there’s no carbon ring.

 

[Ronin22]

Check your H20 capacities virgin vs fired. Fed runs a water grain less than Lapua. Peterson runs a bit less too, but it's stronger brass in the web and pockets. Federal brass has soft web & pockets, the pockets go quick with any decent pressure load. Download till you don't see the high pressure signs and accept what you get for the brass used. BTW, Hodgdon load data has always been listed hot. I've never even attempted their max charges in most cartridges. Hornady data will keep you safe. I can typically load to their max with little issues.

43gr Varget with 168s is pretty standard load.

 

[918v]

Another thought: if you’re touching or close to the lands, back off. That can cause pressure issues as wel. A lot of these variables may not be the cause individually, but combined will cause issues.

 

[Ronin22]

Another thought: if you’re touching or close to the lands, back off. That can cause pressure issues as wel. A lot of these variables may not be the cause individually, but combined will cause issues.

That is a very valid point. Like carts to horses, I bullet seat closer to the lands will result in higher pressures.

 

[rustyinbend]

Always let the rifle tell you what works, and what doesn't. Don't trust "The Book" ... trust what you see and feel after the thing goes "BANG".

 

[diggler1833]

I've ran 44.0gr Varget underneath a 165gr NBT in Federal brass before with zero issues...so I'll agree that your load is light for showing pressure (but different years/lots of brass don't make for a perfect apples to apples comparison).

2,725 is pretty fast for your lighter load, so I don't doubt that you're getting pressure from somewhere. First thing I'd do is as stated above and check for carbon ring as well as clean the copper out of it. If you're jamming into the lands (also stated above) that'll do it too.

Anybody know the bore diameter of a Criterion .308 barrel? Maybe they've got a tight bore or chamber?

 

[Ronin22]

Those 168 Hybrids will run a bit faster with the less bearing surface. I had a Criterion 308 WIN barrel. It shot wonderful and was one of the best looking bores I'd seen with a borescope. Absolutely beautiful, really.

 

[Doom]

Federal and Lapua brass are in the same ball park as far as case capacity goes. Winchester typically has about 2 gn of water greater capacity. While you do seem to be on the low end of max the heavy bolt lift is a sure sign of pressure. If you are loading near the lands then that may be why you are seeing pressure this low.

 

[straightshooter1]

Found a good load but brass shows pressure signs well below max charge: flat primers, faint extractor marks, and occasional heavy bolt lift.

43.8gr Varget
Berger 168 hybrid
Federal brass, twice fired. Same pressure signs with Lapua.
Federal 210 primers
Criterion 24” 1:10. 250 rounds thru.
2725 FPS

Max charge per Hodgdon is 46gr. Not sure why the high pressure. I’ll adjust the load. Just trying to understand what’s going on.

You're particular lot of powder might simply be running a little on the hot side??? That could be because the moisture content has dropped causing a faster-hotter burn???

As mentioned, the case capacity for Federal and Lapua brass are pretty close to the same, though due to variances from lot to lot for brass, there can be no difference or substantial difference between those two brands. If you're closer than .010" to the lands, pressure can quickly spike up as you get closer to touch from there.

If you're loading your cartridges to ~ 2.800 COAL, that 43.8 grs is filling your case's to ~ 101.6% of capacity (assuming your fired case volumes are like mine at 55.5 grs H2O). Filling the case that much is not really any kind of big issue. . . might even be desirable for consistent ignition. And you're getting almost, not quite, 100% of the powder burnt out of your 24" barrel. But it does appear that load is very close to max SAAMI pressure limit and given what you're reporting, you may want to back off a little???

I like to run the 168 SMK's just at about 2660 fps out of a 24" heavy barrel, but with a different powder (AR-Comp or IMR-4064). My Varget wasn't getting me what I was looking for.

As you can tell what the responses, there can be several things that can be involved accounting for your pressure experience. You'll just have to address each issue to see what's really at play in your case.

 

[Josh Umsted]

All very interesting and helpful. Thanks!

Was using this same lot of Varget and same brass in the previous barrel (Remington 20” which wouldn’t group) without pressure signs, so maybe the Criterion chamber is significantly different.

Been seating to max length for the magazine, 2.865”. Tried a seating depth test, working shorter in .003” increments. No effect on pressure signs. Still need to find the lands. Kinda assuming I’m nowhere close to them but could be wrong. The seating depth chosen after my test didn’t work out, anyhow.

 

[Ronin22]

All very interesting and helpful. Thanks!

Was using this same lot of Varget and same brass in the previous barrel (Remington 20” which wouldn’t group) without pressure signs, so maybe the Criterion chamber is significantly different.

Been seating to max length for the magazine, 2.865”. Tried a seating depth test, working shorter in .003” increments. No effect on pressure signs. Still need to find the lands. Kinda assuming I’m nowhere close to them but could be wrong. The seating depth chosen after my test didn’t work out, anyhow.

Pull the bolt, swab out the chamber and insert a piece of sized brass into the chamber. Keep the muzzle up, buttstock on bench. If the empty brass falls free after you push it up into the chamber with your pinky, as in free falls with gravity without getting hung up on anything, then load that piece of brass with bullet long. Insert that long loaded round into the chamber and stop at the first detection of a soft feeling. That's the bullet engaging lands. Rap the butt on the bench and it should fall out. If you pushed too hard, a cleaning rod from the muzzle end will push it loose. Size it down .003 at a time till the round falls free. You will be .001-.002 off your lands. Then you can set your jump from that point.

 

[Josh Umsted]

Pull the bolt, swab out the chamber and insert a piece of sized brass into the chamber. Keep the muzzle up, buttstock on bench. If the empty brass falls free after you push it up into the chamber with your pinky, as in free falls with gravity without getting hung up on anything, then load that piece of brass with bullet long. Insert that long loaded round into the chamber and stop at the first detection of a soft feeling. That's the bullet engaging lands. Rap the butt on the bench and it should fall out. If you pushed too hard, a cleaning rod from the muzzle end will push it loose. Size it down .003 at a time till the round falls free. You will be .001-.002 off your lands. Then you can set your jump from that point.

Used the lo loctite method to find the lands and seated .020” off. We’ll see how that works.
43 gr. Varget was still too much.

 

[wvfarrier]

Something else to verify is that your powder measure was correct.

 

[Ronin22]

Used the lo loctite method to find the lands and seated .020” off. We’ll see how that works.
43 gr. Varget was still too much.

What is your COAL?

 

[Josh Umsted]

What is your COAL?

2.833”
42.8 gr. looks like a happy place.

 

[Ronin22]

2.833”
42.8 gr. looks like a happy place.

That's were I was with the 168HYB. With a 2.860 throat. Groups looking good!

 

[Josh Umsted]

That's were I was with the 168HYB. With a 2.860 throat. Groups looking good!

Forgot to mention I switched to 168 SMK.