6gt ARC CDG and light primer strikes

Did you pull the bullet on the non-fired rounds to see if there was powder in the case and if the primer actually fired? What was the sound when you had a non-firing cartridge?

Did you by chance measure the primer pocket depth before hand? Primer seating depth after seating?

I'm not trying to get you headed down any rabbit hole of measuring/sorting primer seating depth on the regular, but mainly as a troubleshooting tool here.

If the primer pocket is fairly tight - and my limited experience with Alpha OCD brass in .308 Win SRP says 'yes' - then you do need to pay some attention to a) what the primer pocket depth is, b) what the primer height (bottom of cup to top of anvil) is, and c) make sure that you're actually seating the primer far enough in to where the anvil has some pre-load/crush/consolidation (all terms for the same thing, depending on the literature/source) so that it will go off reliably. Otherwise it's entirely possible that all you're doing when you drop the trigger is just seating the primer a little deeper - but not actually crushing the pellet and causing it to go off.

I'm not saying that one can't reliably seat by feel, without checking the numbers... but if you're new enough that you didn't realize you had the wrong primer ram in place, you might not be there yet.

I'm guessing you're measuring the depth with the tail of your calipers? Not the best tool, but short of spending $$$ on a dedicated device, certainly usable.

Pocket depth (0.124) minus primer height (0.120) gives a difference of 4 thou. So for the primers to be just touching the bottom, they'd need to be 4 thou below flush. Ideally, for a bit of pre-load/crush, you want them 2-3 thou below *that*, so say 6-7 thou below flush (in this example).

Just food for thought...
7 of 10 is a pretty high share of failures. In some ways, that is bad but in a way it should make it easier to isolate the root cause.

If the ammo situation allows it, I would take about 10 to 20 of those factory rounds with me on the next test session. You may find an obvious cause but if something still isn't right, then I would go back the last ones that were still working and verify they still do.

The fishbone diagram for troubleshooting a bolt gun failure can be long, but you can cut it down by splitting the search between the gun and the ammo.

By chance, have you also checked the headspace/shoulder datum length of your virgin loads versus the factory?
How about the shoulder datum length after firing the ones that did ignite?
While primer seating depths can play a role, so does the way the cartridge sits in the chamber. If a case is short and a chamber is deep, we can get problems.

Did you go back to factory ammo and have no failures?
Did you inspect the bolt and firing pin spring?

_Thor_ said:

I did try to take some measurements after the fact using alpha brass from the same lot that I hadn’t loaded.:

Alpha case primer pocket depth: .122 - .124

Cci 450 height: .1205

The above being true, I would think I need to seat them 2 thou short of the end, right? That said, I measured the no-fire and fired cases primer depth to the best of my ability and got 0.000 on both, which puzzles me.

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My Alpha .308 brass measures a consistent .122" pocket depths and my CCI-450's I use in them measured .121". CCI-450 cup height is ~.113", which means the anvil is protruding above the cup by ~.008" . . . plenty of room for "crush". I typically like ~.003" of "crush", meaning I look to have my 450 primers at .004 below flush (flush being level with the base of the case).

If these 450's are seated flush, then yes, it could cause problem you've had. But you're firing pin protrusion is a factor as well, where if it doesn't protrude enough, light strikes can easily happen. . . especially in combination with primers not seated where they can be struck properly. It would be interesting to see what those fired factory case primers looked like to see the the strike looks like compared to the one's you showed.

Note too that the 450's have a thicker cup than standard (like the 400's are relatively thin), where firing pin protrusion and spring strength can be an issue.

Did you install the barrel?

Is it barrel nut or a shouldered barrel?

How did you set headspace?

Sounds like your trigger may need adjusted I had the same light strike issues…here’s how to make sure it’s adjusted correctly.

I had a similar issue with 6GT Alpha brass. Virgin brass headspace was short so what I do now is jam the bullet ~.010 into the lands. This prevents the case from being pushed forward by the firing pin and I get 100% reliable ignition.

I think it's fairly typical for bolt actions to have 45-50 thou of firing pin protrusion. The headspace would have to be off a *lot* for the firing pin to not fully crush the pellet in the primer and ignite the powder column. @RegionRat might have better hard numbers on that.

_Thor_ said:

Hoping it comes through in the pictures, but the primers on the faulty ones just really look different to me. Very rounded, like a donut. Whatever that is seems abnormal.

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It’s because they didnt make 50-60k psi blowing up to force the material back against the bolt face. You just have a little dimple from the firing pin.

The fired brass being shorter is normal, it will fill the chamber better in subsequent firings. It’s not just getting bigger length wise, it’s swelling up in diameters too. That swelling to fill the cylinder pulls some of that material back a bit, hence the not fully grown in length.


It’s not just the empty chamber space that the excess firing pin protrusion has to overcome, it’s the cartridge moving in that space over time, and it’s mass absorbing the impact force like a shock or strut, that lessens the impact on the primer. Impact being needed for it to go off.

So it important that it doesn’t have too much free space in the chamber for the case to slide forward into, off of the bolt face. It’s also important that the primer is seated to the bottom of its pocket so it also doesn’t absorb and spread the impact force over space when the firing pin seating it fully to the bottom of the pocket.

_Thor_ said:

So do you have to kindof "waste" the first firing of every piece of virgin brass then? I'd imagine that would be different than what you'd do subsequentl for load developmenty, so you wouldn't want to use those jammed loads during, say, a match. Do you load lighter to just get the fire-forming out of the way?

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No not a waste at all. Typically the first firing of brass coincides with a fresh barrel. What I do is load the 200pc of brass (I typically only get 200 per barrel) jammed with a known, lower charge weight load that typically ends up around 2780ish with 107 SMKs. I'll shoot the first 20 to get data and ensure its about where I expect it. Then I'll use the next 160ish to train with and finish the last 20ish to check speeds again. At that point the fresh barrel is broken in and virgin brass has all been fired.

With this method, the accuracy has always been more than good enough to shoot a match with. However I like to minimize variables for matches so I use the first firing for positional training.

I will say that load development for me is mostly just checking velocity at different charge weights and choosing whatever charge yields whatever speed I want. Groups have always been around 1/2 MOA.

I tend to avoid using virgin brass for load development or matches, mainly because I've bumped into some discrepancies in powder charge between virgin and 1x fired, not necessarily because of the head space so much as its the whole case expanding a bit differently (more) from its virgin state vs from a minimally full-length sized state.

Then again, I'm talking in terms of a somewhat overly fussy F-class shooter. For mag-length stuff thats going to be shot off a barricade, I'm not sure I'd bother worrying about it too much - or if you do, just use up that first firing doing positional practice.

Personally, I don't think 7-8 thou shy on head space is ideal... but I also don't think it's enough to be causing that high of a percentage of misfire - not unless there's something else contributing.

Think about it like this: a lot of people adjust their sizing dies to bump the shoulder somewhere between 2-4 thou, depending on the application. If you follow the actual instructions on most factory dies - ie, raise the ram, screw down to hard contact, lower the ram, screw the die in another half turn and lock it down - it will usually "over size" the cases, with about 8-10 thou shoulder set back.

But nobody cries about that small amount of excess head space causing them misfire in their Savage/Remington/Browning/Tikka/AR, do they?

Is it ideal, no. Is it the root cause of what you have going on here... I'd say also no.

_Thor_ said:

That sounds like a good process to follow. So it sounds like virgin brass isn't really ideal for a match - but out of curiosity, how do those lower charges in virgin brass tend to group for the first firing? Is that 1/2 MOA too, or worse? You can train positional with it, but are you getting enough accuracy out of them that you're thinking "that wasn't my reloads, it was me" on missing?

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Virgin brass isnt ideal for a match to me because it usually coincides with a new barrel. So there are 2 variables at play, a fresh barrel and fresh brass. I don't have enough data to say that just virgin brass wouldn't meet my standards for a match.

I typically see around 3/4 MOA for virgin brass and a new barrel. That level of accuracy would be acceptable for a match.

Virgin brass:
5rds


10rds





Wouldn't shoot that way until I mandreled the necks

Not always but often. I've noticed in several instances where virgin brass shoots noticably better after mandreling. Although, deciding to mandrel is often a result of setting neck tension. I almost never shoot virgin brass without some sort of sizing or mandreling.

A bushing won't straighten a neck like a mandrel will

_Thor_ said:

If there's a mandrel option that's cheaper than the $237 21C is charging,

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21st is 50 for the die body and ring and 24 for a stainless mandrel. You don’t need the full suite of sizes in half thou increments. Just get one turning arbor per caliber, it’ll do nicely.

Some brass benefits more than others, sorta just luck of the draw. But a mandrel will put it all closer to the same at minimum.

Edit: 21st, Sinclair and pma all exchange with one another.

I'm using a Brownells Wilson/ Sinclair mandrel die body($50)and their Tin coated expander
mandrel($20).

spife7980 said:

21st is 50 for the die body and ring and 24 for a stainless mandrel. You don’t need the full suite of sizes in half thou increments. Just get one turning arbor per caliber, it’ll do nicely.

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^ this

I have gotten the full-meal-deal set of expanders from 21st Century for a couple calibers (.224 and .30), because I have a lot of different guns, running different brass, with different applications and different requirements, in those particular calibers - plus I had some OT money burning a hole in my pocket. Definitely falls under 'nice to have', not 'need'. 6, and 6.5, I still have the plain-jane 'OG' Sinclair neck turner mandrels for those, and it works just fine.

So... if you were buying these for actual neck turning, you generally want to expand the case necks on virgin brass, and then use a mandrel that is 0.001" smaller as a pilot in the neck turner itself. For .308 Win, that would look like a 0.307 expander in the die, and a 0.306 expander as the pilot in the turner.

If you're just planning on expanding necks for reloading - not for neck turning - then it gets a lot simpler. Pick a mandrel that is 0.002 or 0.003 smaller than your nominal bullet size. Usually that's the easy-button go-forth-and-do answer. Sometimes, if you're a little bit OCD, things like brass spring back start messing with the numbers turning out *exactly* the way you want them to. If the gun shoots acceptably, don't worry about it. If you want to know more, get some pin gauges off Amazon so you can get a better read on what the neck ID is a) after F/L sizing and b) after expanding with the mandrel.

It took me *forever* to figure out WTF people were talking about, using neck turner pilots for expanding case necks as a regular part of reloading. Mainly because everyone else was apparently using Sinclair (not sure if 21st Century was even around at that point. They certainly weren't well known if they were), and I was using K&M... which uses a different setup where the neck expander is 0.308, and the pilot is 0.307, and they were very much not interchangeable (completely different shape).

My process looks like: (assuming fired brass) anneal, tumble (dry media), spray lube (usually gets some inside the case mouth), decap, brush neck ID, F/L size, expand, trim/chamfer/deburr, tumble off lube, prime, charge, seat. Depending on the use case, I may put some lube inside the case neck prior to charging/seating.

_Thor_ said:

The Sinclair ones are OOS, but I see what you mean now about the 21c ones being less than I thought. So with 21c having every half-thou increment under the sun, should I get -.001, aka .242 for 6 gt? I don't really understand why people are recommending .002-.003 neck tension but -.001 mandrel sizes in various places.

And what is the difference/need for a turning arbor? Not much info on the 21c site except that they say "you can use the arbor *as* an expanding mandrel". Do I need both?

And I assume this is not a substitute for FL sizing, right? So you would FL size, then mandrel, then clean? Or if using their dry moly lube, maybe you can FL size, then clean, then mandrel?

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Before the half thousands increments and people mandreling the neck for seating bullets, people used a turning arbor and expanding mandrel for neck turning only.
Turning arbor =.002 below bullet diameter, expander mandrel =.001 below bullet diameter. That was the old convention at least. I go for .002 under bullet diameter.

_Thor_ said:

Thanks, that helps a lot. Your process sounds like what I need to be aiming for.

One more question, though a little off topic. I've realized I may have the wrong Forster sizing die. I watched this video and discovered that Forster has 3 different sizing dies - the "FL Sizing Die", the "Bushing Bump Neck Sizing Die", and the "Bushing FL Sizing Die". I have just the "FL Sizing Die", which I believe means it doesn't accept bushings and only has an expander ball. Do you have any insight as to whether I would get inferior results using this die for sizing, with just an expander ball followed by the -.002 mandrel I'd be looking to get vs getting the proper bushing FL sizing die? The confuse things further, I saw some chatter on older posts that says "expander balls are just as good as mandrels", etc.

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I've got the Forster FL Sizing Die and the Forster Bushing Bump Neck Sizing Die. I don't use the expander ball in the FL sizing die as it just produces poor results in terms of neck TIR and consistent shoulder bumps. So, I use the FL sizing die without the expander ball and use an expander mandrel to get the necks to the neck tension I want, which produces much much better sizing consistency. Even better, I've had my sizing die honed so that it doesn't reduce the neck so much that the expander mandrel doesn't have to do much work to expand the neck. . . producing outstanding results. If you to with a Bushing FL sizing die, you won't get quite as good results as the latter, as I've been there, done that, trying various brands of FL bushing sizing dies. It's an extra step using an expander mandrel die, but for me, I find it's well worth it.

_Thor_ said:

Thanks, that helps a lot. Your process sounds like what I need to be aiming for.

One more question, though a little off topic. I've realized I may have the wrong Forster sizing die. I watched this video and discovered that Forster has 3 different sizing dies - the "FL Sizing Die", the "Bushing Bump Neck Sizing Die", and the "Bushing FL Sizing Die". I have just the "FL Sizing Die", which I believe means it doesn't accept bushings and only has an expander ball. Do you have any insight as to whether I would get inferior results using this die for sizing, with just an expander ball followed by the -.002 mandrel I'd be looking to get vs getting the proper bushing FL sizing die? The confuse things further, I saw some chatter on older posts that says "expander balls are just as good as mandrels", etc.

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As with most things... "it depends".

The plain old Forster F/L sizing die (no bushings) actually works surprisingly well. The expander is located differently on the decapping stem than on other brands, so (in theory) the case is a little better supported when the expander is pulled back through the neck.

For me, and a lot of other people, the problem with the way factory F/L sizing dies and their expanders work is they squeeze the neck down a little *too* small (they have to account for *every* kind of brass on the market, and some have thinner neck walls than others) and then pull the expander ball back out to open things back up. Best case scenario, it's going to over-work the necks a bit more than really necessary, and could (in theory) lead to early onset of split necks (assuming no annealing) or cause the neck (and shoulder) to be pulled/stretched back out, undoing some of what you just accomplished by F/L sizing and bumping the shoulder back.

If you can, do a little experiment: F/L size some cases, with no expander. You should be able to remove the expander ball from the stem, and leave it in for decapping-only. Adjust the die so that you get the desired shoulder bump. Measure the neck wall thickness, and the neck OD and ID, shoulder bump / headspace dimension, and write all that down. Pay particular attention to the ID number, relative to the nominal bullet diameter.

Next, without changing anything else, put the expander ball back on the stem, and put it back in the die. Size some more cases. Take the same measurements, and write them down as well. What values changed?

Do the same thing again, but put a bit of lube inside the case neck ID. Imperial dry neck lube works well, and won't have any adverse effects on the powder later, but for the sake of this experiment, pretty much anything will work. LIttle bit of case lube on a q-tip, if nothing else. Worry about making the process 'scale' later. Same measurements, again writing it all down. Notice any difference?

Now, if you have an appropriately sized mandrel, say 0.002 under nominal bullet diameter, we can try that. Take those cases from the first step, where you took the expander ball out of the F/L sizing die, and run them over the mandrel (little bit of lube here won't hurt). Again, measure and record.

In general, you'll probably see that the results from the first test give you very much undersized necks - enough so that it'd probably be hard to actually seat a bullet in the case, without damaging one or the other. After the second test, you'll probably see the neck ID is a bit closer to the nominal bullet diameter, minus 2-3 thou. *BUT*... the shoulder may have been pulled forward, and the case OAL might be longer as well. After test #3, you should see the neck ID about the same, but less stretching of the neck/shoulder. Maybe none at all, or perhaps there'll still be a little, but it'll be more consistent. And for the last test, the case head space should stay right where you originally set it, and the neck ID will be pretty close to the mandrel diameter, maybe a hair (half thou to a thou) smaller, due to brass spring back. Some of this will depend on a few things: how thick the necks were to begin with, how hard the particular alloy is, whether the cases have been annealed or not, etc.

If, after test #4 you like the overall results, but want a little smoother feel - and to work the brass less - you can call Forster and send the die in to get the neck 'honed' to a specific diameter. That is going to be somewhat brass dependent. I'd say take the neck OD after expanding them with the mandrel, minus 2-3 thou. The process is fairly inexpensive, with usually decent turn-around times.

As an example, I have a Forster .308 Win 'National Match' F/L sizing die with the neck honed to 0.333". For the brass I typically use (Lapua), that works out just about perfect. Out of the box, the brass is 14.5-15.5 thou neck thickness. If it's some stuff that I used for my FTR match gun, it's probably neck turned to 14 thou even. Loaded round neck diameter with the neck turned stuff is about 0.336", and my match chambers are 0.343" and fired cases come out @ 0.341-0.342". So sizing the necks down to 0.333" in the die generally yields necks that are 0.333-0.334" (usually there's a tiny bit of spring back, even with annealing), and running them over a 0.306" mandrel typically nets me necks that will pass a 0.3055- gage pin, just about perfect.

Apologies for speaking in .308 Win, rather than 6mm-whatever, but it's the cartridge I've spent the most time fussing over so the numbers come readily to mind. Hopefully you can interpolate what I'm saying to your application.

Using a F/L die that uses neck bushings allows you to experiment a little with the bushing size. Maybe go a size smaller, so that with the combined spring back when necking down, and expanding up, you end up with a slightly snugger grip on the bullet. Or maybe go the other way. The problem with the Forster bushing dies is that they don't use 'standard' sized neck bushings that most of the rest of the industry does ie LE Wilson 0.500" dia. x 0.375" tall bushings. Whidden, Redding, SAC, BC Micron and others all use that same size. But not Forster. It's not that what they use won't work, just that they're not interchangeable with anything else.

In theory, using a non-bushing F/L sizer does have one advantage - there's less risk of donuts forming at the neck/shoulder junction, where the bushings can't really get to effectively. Personally, I've had very little to no issues with that *actually* being an issue in real-world use, but that may be cartridge/case dependent. If it is something you worry about, you have the OG shoulder bushing dies by Neil Jones, in which the neck bushings has part of the shoulder angle built into it. The SAC Modular F/L sizer, and the Cortina die are (much) newer versions that use the same idea - but again, with their own bushings that are not interchangeable with anything else. Again, they all work, they just kind of lock you in to that one supplier's ecosystem.

Well, that turned into more of a War-n-Peace novel than I intended. Hopefully some of it's actually useful