09-29-2022, 02:40 PM
grayfox Wrote:Enough talk and theories, we're becoming like Job's friends... OP needs an action list to help him go forward.
I think the discussion has come down to 2 or 3 theories, and no meaningful exchange of new info or support, beyond the items identified about the spring, buffer and buffer tube (RET in above posts), and the observation that the failure is or strongly appears to be, initiated at the extension teeth locations. Personally after going back and forth and sifting through as best I can, I myself am convinced this failure happened due to the fast cyclic-failure during extraction: new key items the location at the extraction teeth, lack of gas/debris spill at the break (soot) and recoil subsystem that is 'way low out of spec. I don't buy that it happened while in battery. Matter of fact, back when I posted the additional examples of kabooms, I was thinking of hypothesizing that perhaps the brass, being potentially stronger, may have mitigated the failure by doing what we call in our industry "leak before break" -- a smaller failure rather than a complete double ended circumferential break -- but thought I would leave that out and not introduce a new rabbit trail. Could be any brass would behave the same, either way that doesn't matter in this case.
But all that aside. It's time instead not to continue a debate of entrenched positions, but to offer some guidance to OP on what to do going forward. These are my suggestions, what I would do:
-- Rule #1, better safe than sorry. Safety first and this applies to this rig but to all loading, shooting and builing operations.
1. I don't believe your brand of brass is at fault, but I would not use any of it that has pronounced ridgelines. Might even post this failed case up prominently in your reloading space for yourself, as a reminder of what can happen!
2. I'm unsure about whether any of the bcg should be used or all replaced. At least I might replace the bolt, it has seen stresses beyond what is normal, what with 16,000-20,000 psi hot spewing gas and all. Might even have a gunsmith examine your barrel extension since it too, especially the lugs, may have some small stress cracks from the incident.
3. If you want to use that load I would first back down and then develop back up, watching for signs. Follow this MO any time you change an item in your otherwise "known" load recipe. Also applies to a new lot# of a "current" powder.
4. Modify/improve your reloading process to include OAL size-checks every case every time. Trim any that are over 1.520 ie, that fail the pass-thru I wrote of earlier.
5. Replace your buffer tube, spring and buffer weight with at least H (or "H1" as sometimes called) weight and standard buffer tube, as '52 writes above. This is minimum weight I would recommend, maybe use an H2 or T2 weight... I'd have both in my spare parts bin so I can try them both.
6. Strongly consider about using the AGB to dial down the gas flow/pressure back to the bcg via the gas tube. Once dialed in you possibly could consider a 2.9 oz (regular weight) carbine buffer but that's up to you - smooth operation, not slam-backs, are what you're after. Do not stay with your weight/spring/buffer tube setup as it is now.
Anyway, life needs to go on, so prudent action steps based on real experiences are what we need to offer now.
In a thread that has turned into a bit of a mess, I think this was a good post. My own advise to OP
#1 - No secret that I'm no a strong endorser of Lapua 6.5 Grendel brass, but will be the first to admit that it is quite reliable when all other components are correct. That said - for myself, I'd switch to another brand like Horandy. Obviosly based on the passionate posts, lots of other uses are able to use it safely.
#2 Get that cycle rate under control! Agree or disagree with others on some things, I am in agreement that the kaboom very possibly could have been avoided if this were fixed. I say this, because those who experience the belting/shelf-issue; are often able to correct it by slowing down their bolt. That belting is deformation of brass in the Kaboom zone of the brass - take it seriously. There's a Johnnys Reloading video where he sees this occure, that's worth the look as well. Your system has a remarkably light BCG system, and that correlates with the Kaboom danger zone warning sign of belt formation - IMHO. Switch to heavier.
#3 Adjustible gas blocks are good in theory, but in my experience I find they carbon lock and end up being a maintenance and setting hassle. In the end, you'll dial it to a setting that works with the weakest ammo, it'll carbon lock there, and that won't be much different than what you're running now. Again, JMHO from my own experience.
#4 I don't thinik you need to resize or trim your factory fresh brass. I know at least one commercial loader and many heavy reloaders who start with factory brass. Nobody does that. By all means, double check, but I rather doubt Lapua resizes their brass all over again in their factory ammo offerings, and I would consider Lapua the last manufacturer on the planet to sloppily have variable case lengths.
#5 Lighten up on your load and work your way back up again. A soon as you see a belt, which I view as a warning sign, stop - and adjust your load, your gas setting, your buffer, or your brass. And preferably more than one. you have a safety warning, if you can change 2 things that indipendantly will make you safer, do that.
#6 Meticulous notes and keep asking questions. Often times I post detailed range reports in various forums on things, not so much for ego (though of course I am awesome and should be sent beer and cookies
); so much as I've learned a long time ago one does not truely assess the activity and results until they document it into a report intended for others. And at times get inputs from others with differeing experiences, to learn from. That's what I would be doing, if I were in your shoes. I'm not in your shoes.