.308 pressure issue

J

Josh Umsted

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Sep 16, 2024
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#1
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.
 
#2
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.
 
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#3
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.
 
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#5
918v said:
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.
Click to expand...
That is a very valid point. Like carts to horses, I bullet seat closer to the lands will result in higher pressures.
 
#7
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?
 
#8
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.
 
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#9
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.
 
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#10
Josh Umsted said:
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.
Click to expand...
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.
 
#11
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.
 
#12
Josh Umsted said:
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.
Click to expand...
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.
 
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#13
Ronin22 said:
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.
Click to expand...
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.
 
#16

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#19
Josh Umsted said:
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.
Click to expand...
The max for 168 gr in Hornady manual is 44 gr of Varget, with a velocity of 2600 fps 22" barrel, Hornady brass, 2.8" for the 168 ELDM...11th edition page 510.
So it appears you are over pressure for your rifle...try 2625 fps on your chronograph for 2" longer barrel as your velocity and pressure symptoms will dissappear. For your lot of powder.

Varget has been all over the place at times in burning rate from lot to lot.
With lots of complaints of not getting velocity of the last 8 lb jug or over pressure from the new lot on Accurate Shooter and Precision Shooting over the years.
 
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#21
I just went through this exact same issue last week with my 308 bolt gun.

Berger 168s, Fed brass, Varget powder, etc.

I start showing pressure signs on anything above 43.5gr with this Federal brass. I can get closer to 45 using Norma and even Hornady (odd), but I don't have a chrono to measure whether it's beneficial or not. I'm only getting faint extractor marks on maybe 1/5th of the case head, flattened primer, and heavier bolt lift than normal. Several of them have blow-by around the primer.

My plan is to try another primer, then different brass...if still the same, I'll just accept that it's what this gun is happy with.
 
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#22
LinkLow said:
I just went through this exact same issue last week with my 308 bolt gun.

Berger 168s, Fed brass, Varget powder, etc.

I start showing pressure signs on anything above 43.5gr with this Federal brass. I can get closer to 45 using Norma and even Hornady (odd), but I don't have a chrono to measure whether it's beneficial or not. I'm only getting faint extractor marks on maybe 1/5th of the case head, flattened primer, and heavier bolt lift than normal. Several of them have blow-by around the primer.

My plan is to try another primer, then different brass...if still the same, I'll just accept that it's what this gun is happy with.
Click to expand...
.308 Norma cases definitely have more case volume than Federal brass and so does some Hornady brass. So, it stands to reason that one can get more powder in them without having the same pressure issues.
 
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#23
straightshooter1 said:
.308 Norma cases definitely have more case volume than Federal brass and so does some Hornady brass. So, it stands to reason that one can get more powder in them without having the same pressure issues.
Click to expand...
Even 42.8gr is on the edge of too much pressure. 2660 fps.

Had to change primers and groups opened up a bit. Bolt closed hard. Need to readjust sizing die I guess.

Gonna work around the next lower node, 41.5gr.
 
#24
Apologize if it was already mentioned, but we used to carry some "baseline" ammo to debug things in the field.

So, say a rifle was acting badly with the user's handloads and the gun was otherwise considered safe to test. We would run some baseline ammo through to cut down the troubleshooting fishbone. If the rifle shot at least decent with the standardized baseline ammo, then we cut the troubleshooting list way down.

In your example, say we had a box of FGMM and we had run it in the past. We would borescope your bbl to see if we should clean before we did anything, and we would also inspect the bolt and receiver lugs. Then we would proceed to try some of the FGMM.

In your example, it would either show pressure and velocity that indicated a problem with the rifle, or it would show no pressure or abnormal velocity and we would know to troubleshoot the ammo.

A significant percentage of the time, the rifles were fine and it ended up being the ammo. Every now and then, we would scope and see a copper mine and a serious scrubbing before we tested brought it back to normal... and yet some novice's ammo was still bad. In those examples, they were grateful to know there was nothing wrong with their rifle.... Good Luck and in for the range reports.
 
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#25
You can't take more than these components and barrel will give you.
It doesn't matter what you want or would like or what others are getting for velocity.

Sometimes ya just can't get there. It is what it is.

Lots of maybes, ...maybe ya need to turn necks if the brass neck is too thick, causing a big pressure spike. Do a bullet case plunk test on your fired cases.

Get a new barrel, try a different lot of powder or a different powder.

Or use hybrid cases that will take the pressure...simple.
And I always turn neckd with these, as ya don't need a pinch point at high pressures.

So with hybrid cases you can run 168 gr at 2940 to 2960 fps area in a 22" barrel...or go 30" for 3255 fps, ...in the 308 you have options.
Lots of choices...
 
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#26
Josh Umsted said:
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.
Click to expand...
Looking back through this thread I found this and it brings up an important point. Remington 700 308W chambers are nowhere near the same as any chamber cut with a SAAMI spec reamer. There is so much free bore that a 168SMk
seated to the lands may not have any bearing surface in the case mouth. Essentially creates a larger chamber.
 
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#27
Doom said:
Looking back through this thread I found this and it brings up an important point. Remington 700 308W chambers are nowhere near the same as any chamber cut with a SAAMI spec reamer. There is so much free bore that a 168SMk
seated to the lands may not have any bearing surface in the case mouth. Essentially creates a larger chamber.
Click to expand...
But long throats also masks pressure signs, like Weatherby chambers. So is it the small increase in combustion area or that heavey bolt lift and ejector marks happen at higher PSI?
 
#28
Doom said:
Looking back through this thread I found this and it brings up an important point. Remington 700 308W chambers are nowhere near the same as any chamber cut with a SAAMI spec reamer. There is so much free bore that a 168SMk
seated to the lands may not have any bearing surface in the case mouth. Essentially creates a larger chamber.
Click to expand...
Likewise, the RPR's have a lot of free bore as well. I've loaded 168 SMK's where the case necks were holding onto only ~.185" of the bearing surface and .010 off the lands. It's not a problem for hand feeding, but I don't think I'd want to load them that what for mag feeding. ;)
 
#30
Doom said:
Looking back through this thread I found this and it brings up an important point. Remington 700 308W chambers are nowhere near the same as any chamber cut with a SAAMI spec reamer. There is so much free bore that a 168SMk
seated to the lands may not have any bearing surface in the case mouth. Essentially creates a larger chamber.
Click to expand...
That's 5.56 Nato vs 223 Remington chamber....not 308 Winchester with the long throat on the military chamber for their longer 62 gr bullets over the orginial 55 gr fmj.
All sporting arms manufacturers use SAMMI finish reamers.
That's the idea to standardize all sporting arms so all the ammo will fit all the mass produced 308s.
Gunsmiths can change that on individual rifles like Ackley improved, but all Winchester, Savage, Remington 308s should be very close to identical.
 
#31
supercorndogs said:
But long throats also masks pressure signs, like Weatherby chambers. So is it the small increase in combustion area or that heavey bolt lift and ejector marks happen at higher PSI?
Click to expand...
Long throats do not mask pressure.
They decrease start pressure.

Why Weatherby has long throats is to decrease start pressure, as they would be over pressure in normal throat lengths.
So they can increase powder a bit, the bullet jump relieves a bit of the start pressure before hitting the rifling.
Resulting in a increase in velocity but no increase in pressure.

Seating the bullet out, will drop pressure and velocity without increasing the powder charge....as long as your not up against the rifling or seating into the rifling.

Seating into the rifling will jump start pressure 8k to 10k, With no velocity advantage.
Full metal jacket and all copper bullets have double the start pressure of jacketed lead bullets, and should be treated accordingly...Barnes recommends .050" jump to the rifling minimum.
Never force a copper or fmj bullet into the rifling with a maximum load for a jacketed lead core bullet...massive start pressure will result.
 
#32
45-90 said:
That's 5.56 Nato vs 223 Remington chamber....not 308 Winchester with the long throat on the military chamber for their longer 62 gr bullets over the orginial 55 gr fmj.
All sporting arms manufacturers use SAMMI finish reamers.
That's the idea to standardize all sporting arms so all the ammo will fit all the mass produced 308s.
Gunsmiths can change that on individual rifles like Ackley improved, but all Winchester, Savage, Remington 308s should be very close to identical.
Click to expand...
Not going to argue the point but you are wrong. Remington's 308W have a long free bore and it is not per SAAMI. Try and load a 168 SMK 0.010" off the lands in a 700 and only the boat tail would be in the case mouth. No, it is not just my rifle. Those of us who reload for this rifle are familiar with this.
 
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#33
Doom said:
Not going to argue the point but you are wrong. Remington's 308W have a long free bore and it is not per SAAMI. Try and load a 168 SMK 0.010" off the lands in a 700 and only the boat tail would be in the case mouth. No, it is not just my rifle. Those of us who reload for this rifle are familiar with this.
Click to expand...
Probably NOT wrong....you are not informed.
No argument needed.
I have loaded many thousands of rounds for factory Rem 700s.


it's called tolerence, which all gun manufacturers must adhere to, and most likely in SAAMI spec ...which is quite generous or there would be a recall, if discovered.
Many of these barrels are not chambered with a reamer, but hammer forged chamber and rifled all in one hammer forging operation.
There is a plus .015" tolerance added to the length of the free bore, so the bullets can be seated out or a longer jump to the rifling and still be in SAMMI spec.

Chamber headspace is actually ten thousands total!... min to max.

Add that to the cartridge min in the specs and a min cartridge and a max headspsce chamber.
A new factory 308 cartridge could be .013 from hitting the shoulder in the 308 max chamber and still be in SAAMI specs!

And many of you were concerned about plus .001" to .004" headspace!
When you can actually have a max chamber .010" above min, and a cartridge .003" shorter than min chamber for a total of .013" excess space and still be in SAAMI specs.
Not good for reloaders...one shot only.

So here's a SAAMI reamer Rem 700 rifle I chambered tight headspace.

168 gr Sierra tipped MK 2.970" hits rifling
169 SMK 2.922"
308 AR 10 16" auto loader barrel purchased from WC very accurate barrel.
169 gr SMK 2.926" hits the rifling.
There are two rifle examples with SAAMI reamers. The boat tail is close to out of the neck....but with the added free bore tolerences it could be out even farther and still be in SAMMI specs.
You can order a shorter freebore reamer of your choice and have your gunsmith chamber a barrel for you... but it won't be a SAAMI spec reamer.
 
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#34
45-90 said:
Probably NOT wrong....you are not informed.
No argument needed.
I have loaded many thousands of rounds for factory Rem 700s.


it's called tolerence, which all gun manufacturers must adhere to, and most likely in SAAMI spec ...which is quite generous or there would be a recall, if discovered.
Many of these barrels are not chambered with a reamer, but hammer forged chamber and rifled all in one hammer forging operation.
There is a plus .015" tolerance added to the length of the free bore, so the bullets can be seated out or a longer jump to the rifling and still be in SAMMI spec.

Chamber headspace is actually ten thousands total!... min to max.

Add that to the cartridge min in the specs and a min cartridge and a max headspsce chamber.
A new factory 308 cartridge could be .013 from hitting the shoulder in the 308 max chamber and still be in SAAMI specs!

And many of you were concerned about plus .001" to .004" headspace!
When you can actually have a max chamber .010" above min, and a cartridge .003" shorter than min chamber for a total of .013" excess space and still be in SAAMI specs.
Not good for reloaders...one shot only.

So here's a SAAMI reamer Rem 700 rifle I chambered tight headspace.

168 gr Sierra tipped MK 2.970" hits rifling
169 SMK 2.922"
308 AR 10 16" auto loader barrel purchased from WC very accurate barrel.
169 gr SMK 2.926" hits the rifling.
There are two rifle examples with SAAMI reamers. The boat tail is close to out of the neck....but with the added free bore tolerences it could be out even farther and still be in SAMMI specs.
You can order a shorter freebore reamer of your choice and have your gunsmith chamber a barrel for you... but it won't be a SAAMI spec reamer.
Click to expand...
Understood.
 
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