Question around Ejector Marks/Heavy Bolt Lift

[littlepod]

Got a new 308 built, I was using a Tikka 20" CTR previously. I had bought a bunch of this ammo - http://www.outbackammo.com.au/308-win-168gr-sierra-hpbt-matchking/

The Tikka 20" CTR was shooting it great, outshot FGMM, had low SD's grouped well so I bought a ton of it. It chrono'd out of the 20" CTR at 2698fps.

In the new 308, 24", tight match chamber, I am getting a pretty heavy bolt lift off my Terminus Zeus. The ammo groups really well, low SD.

But I'm getting really heavy bolt lift about 70% of the time, and then when that happens, I also am getting ejector marks on the brass -

The times that I don't get any heavy lift, or ejector marks, I'm not seeing any decrease in velocity at all off the Chrono.

Some people say that it could be high pressure signs and Terminus/Curtis Vector designs are prone to not handle any high pressure as the bolt gets locked down and is prone to the heavy lift. I called the gunsmith and he said maybe that it was some sort of bolt slap which could show as a high pressure sign but not really, where the shoulders are not perfect and are expanding and pushing the brass into the boltface.

If it's a high pressure sign then I risk piercing the primer and pitting my bolt face, which I definitely don't want to do on a new action.

Thoughts?

 

[Kadams1563]

Check OAL to the lands and check headspace.

I’m sore the custom Build has much tighter tolerances

bullet might be in the landscausing pressure.

 

[littlepod]

Check OAL to the lands and check headspace.

I’m sore the custom Build has much tighter tolerances

bullet might be in the landscausing pressure.

Bullet is closer to the lands, from measuring the ogive. I dont' recall the exact numbers. I know my other ammo isn't as close to the lands. I guess factory ammo, made for factory bores with much longer freebores. It's not in the lands when loading, smooth loading/bolt close/live round extraction. Only spent brass / lift after firing I'm seeing the issues.

 

[Supersubes]

Ejector marks/and swipes are simply the extreme end of the bolt thrust that causes a heavy bolt lift in the first place. All that needs to happen is for the pressure to exceed a certain point and you’re there, sticky bolt and/or ejector marks. Doesn’t matter the duration of the excessive pressure.

I dont buy the action type argument at all. Makes zero sense to me. I think what your builder might be trying to explain is an excessive headspace situation where the case head it allowed to get a running start at the bolt face before smacking into it. Not sure I totally buy that either, but maybe. Any chance your builder polished the chamber? If you have the ability, take some measurements of the cases pre and post firing. Trying some FGMM would be a good route too.

 

[littlepod]

Ejector marks/and swipes are simply the extreme end of the bolt thrust that causes a heavy bolt lift in the first place. All that needs to happen is for the pressure to exceed a certain point and you’re there, sticky bolt and/or ejector marks. Doesn’t matter the duration of the excessive pressure.

I dont buy the action type argument at all. Makes zero sense to me. I think what your builder might be trying to explain is an excessive headspace situation where the case head it allowed to get a running start at the bolt face before smacking into it. Not sure I totally buy that either, but maybe. Any chance your builder polished the chamber? If you have the ability, take some measurements of the cases pre and post firing. Trying some FGMM would be a good route too.

FGMM and Prime shoot fine. They also shoot a bit lower in velocity. I'll do some measurements. I guess ultimately there's no easy fix and I should just shoot different ammo. Probably spending a lot of time on a rabbit hole that isn't really salvageable. I'm going to be starting handloading my own ammo anyway. I guess I could reload all this ammo re-use the 168gr SMK's and put different powder in it or something, re-use the primer etc.

 

[Chudzy]

Do you mop your barrel after cleaning with solutions? Excess lubrication or cleaning products may cause the brass to not expand and fill the space properly. The back pressure can cause a heavy bolt lift that way. Just a thought.

 

[littlepod]

Do you mop your barrel after cleaning with solutions? Excess lubrication or cleaning products may cause the brass to not expand and fill the space properly. The back pressure can cause a heavy bolt lift that way. Just a thought.

I cleaned with wipe-out and dry patched it until clean. Haven't put anything else through the barrel.

 

[918v]

Tight chamber bad

 

[390fe]

2,698 fps from a 20 inch barrel is pretty hot in my opinion. The fact that FGMM and Prime eject properly without either sticky bolt lift or ejector marks - and have lower velocities would suggest that there is nothing wrong with your chamber or barrel.

 

[1moaoff]

Outback tends to run on the hot side. I've seen a few guys try to run it but they trashed the brass nd couldn't reuse it. Others do great with it. I have atleast 1 barrel that loves it and I would buy a ton of it if the price was what it was.

That's the factory ammo curse. Some rifles dont like what we want them to.

 

[Brux]

The Outback ammo that I have tried in 223 and 308 has been loaded HOT and velocities run higher than norm.

 

[Deleted member 10043]

I never get anything other than SAAMI spec chambers to avoid this sort of stuff.