Working up a new load. Faint ejector marks, help!

[farmer7]

Hello, I'm new to the forum. Look forward to learning more! Been reloading for 19 years but have much to learn!

Anyway my issue is I'm getting pressure signs. I bought a bag of once-fired .308 Lapua brass for working up some new loads for a new Tikka Supervarmint 20" I bought before using the new Lapua brass I have. I worked up a load using 155 Amax N140 and CCI BR2s. I used the OCW method and obtained very satisfactory results.

I settled on 45.3 N140 @ 2706 fps which I know is over VV's book but I experienced no pressure signs when I worked it up initially.

Since firing more on a hotter day recently, 19ºc. I noticed very light ejector marks on some cases. I then scrapped that load and worked up a load with 178gr Amax using the same components. The load I worked up to was 43.7 but settled on 42.8 as I had a common POI on the charge weight above and below. Velocity was 2499 fps.

Subsequently I noticed I was also getting VERY light ejector marks on some cases with this load so I scrapped it too.

Today I worked up a load using 168gr SMKs and with N140 and am getting marks from 41.9 grs, a full grain below VV's usually conservative data. As it was an OCW I was shooting one cartridge at each charge round robin style and inspecting the cases very carefully after each shot. I fired the first shot from each charge weight all the way up to 43.4 and got no marks. On the second string I got an ejector mark at 41.9 grains but as the first group of charge weights showed nothing I carried on and didn't get another until 42.8 grs , C.O.L was 2.800". I thought the SMKs much shorter bearing length would reduce pressure a lot. The 42.8 charge I'd like to use averages 2523fps.

Anway I'm looking for some guidance please! Sorry its such a ramble and I hope it makes sense.

Am I skating on thin ice? Do I possibly have an unusually soft lot of Lapua cases? I checked my cases and chamber for oil, none found.

The velocities dont seem excessive but it is a 20" barrel. All bullets are seated to fit my magazine and well clear of the lands.

The ejector marks are all faint and on a casual look arent visible but they're there all the same. Bolt lift isnt heavy either.

Any advice gratefully received!

(E.T.A. If someone was able to put my loads in QuickLoad just for reference it would be appreciated!

.308, 20" barrel.
155 Amax, Lapua Case, 45.3 N140 2706fps
168 SMK, Lapua case, 42.8 N140 2523fps
178 Amax, Lapua case, 42.8 N140 2499fps )

Just visible beside the 'L' in Lapua:

[Alpha1]

Please don't take this the wrong way I read your post with interest but I don't know what OCW means or POI could you enlighten me please.

[farmer7]

Sorry Alpha1, by OCW I meant Optimal Charge Weight, see here: http://optimalchargeweight.embarqspace.com/ . I've used his method for several rifles and it works for me! Just have issues at the moment though!

When I said POI I meant point of impact.

[Alpha1]

Thank you.

[The Cupcake Kid]

It's difficult to see a mark in that photo, so it must be very light. Primer doesn't look cratered and you say bolt lift isn't stiff.

All things considered and taking into account the load data and velocities you're reporting, I wouldn't say you're pushing the pressure too high. Did you full resize the brass? Have you tried firing it again with the same load after fire-forming in your chamber?

[dromia]

http://www.full-bore.co.uk/viewtopic.php?f=11&t=8480

[ovenpaa]

Quickload shows the 168 SMKs at 2519fps with a pressure of around 53k and all three loads are under max pressure. Personally I would not be unduly worried and I certainly push my .308 loads a bit quicker with Lapua brass and N140 when I used it.

[farmer7]

Thanks for the replies everyone. Also cupcake kid I'm neck sizing after the first firing and still getting the marks.

I've never had an ejector mark on any reload before and I must say it is making me uneasy. When you reach pressure high enough to flow the brass would it normally flow on every charge at that same weight? With my loads I'm getting a mark on some at 43.4, maybe 2 or 3 out of 5, and even going down to 41.9 I'm getting them at about the same rate.

Thanks very much for the quickload info ovenpaa, at least I know I hadn't just gone totally over the top! Puts my mind at rest a little! Also I just noticed QuickLoad has the velocity at 2519 fps v my actual 2523 fps, scarily accurate! I'll need to get myself a copy for reference.

Quickload shows the 168 SMKs at 2519fps with a pressure of around 53k and all three loads are under max pressure. Personally I would not be unduly worried and I certainly push my .308 loads a bit quicker with Lapua brass and N140 when I used it.

Could I have an unusually soft lot of Lapua? Should I ditch it and work up with my new box?

[John MH]

Make sure your cases are completely free of any lube and that your chamber is dry. If you are getting ejector marks on your cases the brass is flowing back under pressure, reduce the powder charge until it stops. The thing that is most likely to happen in parallel with this is that your primer pockets will enlarge to the point that they will no longer hold a primer in place at which point the brass will be scrap.

[farmer7]

I checked both my cases and chamber for any lube or oil, but both were ok. Also some cases are now on the third firing and primer pockets haven't loosened.

As for reducing loads I worked back to 41.9 and am still getting them intermittently, the 43.4 loads are intermittently getting them too, so hasnt made any difference there. I'm not trying to hot rod my .308 but at 41.9 my velocity is only averaging 2450 fps, I hadn't intended the rifle to be relegated to super short range!

Has anyone ever heard of overly soft Lapua cases?