Help needed on 300BLK reloads

[MaxG]

This is one I haven't encountered before.

I'm loading 180 gr BTSP 300BLK cartridges. Hodgdon and other references say to set at 2.21" COL or very close to that (Speer says 2.18"). This puts the case edge well short of the cannelure, but I don't think that matters (which could be one of my misconceptions.)

I loaded up 4 each of 4 different charge loads, to see which one worked the best to load the rest of the inventory with. I started at 13.0 grains of Lil Gun, but that really doesn't matter as for what happened (or didn't) next.

I loaded the first set into some PMAG 300BLK mags (not 5.56), loaded the first round into the gun, and heard the dreaded 'click' when I expected a 'bang'. I tried to pull the charging handle back and it was jammed pretty good. With some persuasion, I did get the round out. This is what it looked like (it's the short one below.)




The rounds were the same length when I put it in the gun. After puzzling a bit, I loaded some more, same result. No bang, jammed round. Different mag, same result. I had brought some other rounds (also handloads) with me and loaded them to see if I was losing my mind or my gun. They worked perfectly.

WTH happened? The other rounds also compressed, but not like the first one. I measured the bullet to make sure it was in fact a .308 bullet, though I don't know why that would keep it from firing, and they were fine.



I measured the rest of the batch I hadn't chambered, or attempted to chamber, and they were in fact 2.21".



I noticed some marks on one of the rounds when I finally got it out of the chamber and it had a scratch in it, though I don't know if this was caused by the bolt coming forward or the somewhat violent extraction with the charging handle.



I've never seen this happen before. The other rounds that worked fine in the same gun/mag/etc... were at 2.23", slightly longer than the ones that didn't work.

What's going on? Any ideas? This is a new one for me.

thanks all!!!

MG

 

[nortac]

Any primer strike on the round that didn't go off? Did the bolt go fully into battery? I don't recall the specified proper COAL, but it sounds like the bullet was seated too far out and prevented the bolt from going fully into battery, light or no primer strike?

 

[MaxG]

I'll check the primers tonight. I didn't notice any primer strike. It must have been very light if at all.

A bullet with a cannelure doesn't HAVE to be seated there, right? That would put the COL significantly shorter than any data I saw, but, that does sound right with the results I got.

I seriously thought something was wrong with my bolt, firing pin, etc... but the two other rounds I put in were perfect.

 

[nortac]

I suspect that although the COAL may have been within spec, the shape of the ogive of that particular bullet caused it to be thrust into the lands and even though the bullet pushed back into the case, perhaps the bolt was slightly out of battery preventing a sufficient primer strike. Just my guess. I'd seat those bullets to the cannelure and maybe even use a taper crimp.

 

[MaxG]

I did use a Lee Factory crimp, FWIW. I'm concerned the powder charge recommendation would change significantly with the bullet seated that much deeper. But maybe that's the reason for the relatively large range in the Hornady manual.

 

[HARMON]

I subscribe to nortac's theroy.
Luckily (or perhaps that is a safety feature) you did not have a proper primer strike, because if that load was compressed and slightly out of battery things could have went sideways.

 

[MaxG]

I looked at the rounds with my fountain pen loupe. There was no primer strike at all.

 

[nortac]

In addition to seating the bullet deeper, if you are concerned about decreased case capacity/compressed load, etc. Work up some loads with reduced charges, just a few each charge weight and increase until you get the function that you want or see pressure signs like a flattened primer, etc. But stay within the published data, of course. YMMV

 

[MaxG]

I think that's the way to go. I'll load a dummy round tonight and find where the COL is where it will actually fit. Or, maybe I'll just set to cannelure and start with the min Hornady charge. That may be the reason there's such a wide range in the charges they list for that bullet. It still seems more than weird to me that the COL is that much 'off' from what will work in the gun. Here's where I get a little out of my depth, as probably shows, but I sure didn't think there was that much variance in chambers from gun to gun where a 2.2" COL would work for one gun, but to get the same cartridge to work in another gun, COL needs to be roughly 1.9". Really weird.

 

[nortac]

It seems a lot of bullets loaded in the .300 BO are more spire point than spitzer, which would give a different Ogive to lands engagement for the same COAL. Just guessing. Exactly which bullet are you using?

 

[MaxG]

I was led to the answer by some good direction on another board. The issue is the brass that I used to form the cases out of .223 brass. I'd heard of 'good brass' vs. 'bad brass' for 300BLK conversion, but having never had an issue and never sorted brass by manufacturer, I wrote it off as apparently not a very big deal. Yep, potentially a big deal.

Some 223 brass has a thicker wall than others, which produces a wider case neck than will fit in the chamber. The ID of the mouth is fine after sizing, but since the walls are too thick, the OD is too thick. Thus, the reason to separate the 'good' vs 'bad' brass before wasting time and components on assembling rounds that will never fire.

Thanks for the advice and good discussion on this.

 

[nortac]

Glad you figured it out. So what kind of "bad brass" did you use?

 

[MaxG]

I haven't even checked yet! lol

When someone suggested that could be the issue, I measured the neck width and found it wider than a few samples from a prior batch of handloads that worked, and, of course, wider than what the chamber would accept. I briefly also checked a few unloaded cases in my 'primed-and-ready-to-charge' bin, and they were too wide also.

There is a list of good/bad brass at the 300BLK forum site, but the magic number, I believe, is a wall thickness at the neck of > .013 won't work. I ordered a recommended case gauge to make my rather large upcoming sorting task easier. I've loaded close to 1,000 rounds of 300BLK since I got back into the frustrating hobby last year.

 

[nortac]

Hornady makes a good bullet puller...just saying!

 

[MaxG]

I've got a Lyman, and I'll probably have carpal tunnel by the time I'm through the pile...