338LM Pressure Signs?

[bigedp51]

Loading 338LM for a Savage 112 Magnum Target and I'm seeing flattened primers relatively early on, much before any sticky bolt. With these higher pressure cartridges, are flattened primers not the best indicators? Just due to soft primers?

H1000, 88gr
300gr SMK seated to 0.020" off the lands (3.690 COAL; 0.030" off the lands)
New Lapua brass
Winchester WLRM primers
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For the above load data, I'm getting a very consistent 2690 ft/s out of a 26" 1:10 barrel. Even at 83gr I've seen flattened primers, and saw sticky bolt at 90gr with minor cratering. Never seen ejector marks though.

I'd rather get a consistent and accurate load than punish the brass & barrel for that extra 100ft/s and I know you do your own load development (and for good reason), but I'm just curious as to how plenty of people are doing 92gr and up.

Thanks for any advice.

If the shoulder bump or head clearance is on the long side the further the primer will back out of the primer pocket. When the case is forced back against the bolt face the primer will fold more and flatten at the edges giving a false indication of pressure.

Not long ago I was at the range and picking up my LC 5.56 brass and did a double take. I had picked up a 5.56 case that had the primer crimp removed by hand. This case had the primer pocket excessively beveled and looked like it had a large rifle primer in this case.

Bottom line, anytime a primer can back out of the primer pocket it will show more signs of primer flattening around its circumference. And over sized firing pin holes or beveled holes in the bolt face can also give a false indication of high pressure.

 

[Beneviolence]

Measured lands today and I am .182 off at a COAL of 3.715 with the 300 SMK. A COAL of 3.897 gets me a jam with the 300 SMK. Your results will vary but hardly any stock rig is anywhere near the lands with a SAAMI COAL.
I am going to load up a test at .010 .040 .070 and .100.

Huh..that's odd. I just did this again with with once fired brass and got 3.725" jammed on the lands. That's way shorter than others that I'm seeing. My once fired brass is 2.724" and fresh (all Lapua brass) is 2.715". Seems like the throat of the chamber was cut short.

@Bigedp51; I thought this cartridge is headspacing off the belt, so excessive shoulder-chamber space would just allow for the brass to elongate more instead of allow the primer to pop back.

Also turns out the action screws weren't tight enough...just blue loctited those and torqued them tight.

 

[bigedp51]

Huh..that's odd. I just did this again with with once fired brass and got 3.725" jammed on the lands. That's way shorter than others that I'm seeing. My once fired brass is 2.724" and fresh (all Lapua brass) is 2.715". Seems like the throat of the chamber was cut short.

@Bigedp51; I thought this cartridge is headspacing off the belt, so excessive shoulder-chamber space would just allow for the brass to elongate more instead of allow the primer to pop back.

Also turns out the action screws weren't tight enough...just blue loctited those and torqued them tight.

The 338 Lapua magnum is not a belted case, "BUT" a belted magnum can have as much as .015 head clearance with a thin belt at max headspace.

 

[toddc]

Huh..that's odd. I just did this again with with once fired brass and got 3.725" jammed on the lands. That's way shorter than others that I'm seeing. My once fired brass is 2.724" and fresh (all Lapua brass) is 2.715". Seems like the throat of the chamber was cut short.

@Bigedp51; I thought this cartridge is headspacing off the belt, so excessive shoulder-chamber space would just allow for the brass to elongate more instead of allow the primer to pop back.

Also turns out the action screws weren't tight enough...just blue loctited those and torqued them tight.

I would guess you have a long chamber, the flattened primers plus brass growing nearly .010 seems to point this way.
As your round fires the primer is backing out and when it slams into the bolt the primer flattens, luckily its a Savage and you can tighten the headspace easily. My brass is growing .004 and I am likely to tighten that up slightly as well.

 

[Beneviolence]

The 338 Lapua magnum is not a belted case, "BUT" a belted magnum can have as much as .015 head clearance with a thin belt at max headspace.

Oh jeez, now I feel stupid.

From what you said and others online, it sounds like excessive headspace could cause the flattened primer issues. If that is the cause, once fired brass should not show this, and should show healthy fired primers...?

I'll try making a bump gauge to measure and adjust the FL sizing die to bump the shoulder the appropriate amount.

I would guess you have a long chamber, the flattened primers plus brass growing nearly .010 seems to point this way.
As your round fires the primer is backing out and when it slams into the bolt the primer flattens, luckily its a Savage and you can tighten the headspace easily. My brass is growing .004 and I am likely to tighten that up slightly as well.

I suppose that is the other option to do in conjunction with the above. It looks like with a set of go/no-go gauges, it can be done fairly easily. I'll have to re-form the brass to the appropriate length; hopefully the brass will take that.