Help needed on a 300BLK reload

[MaxG66]

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.

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 in the chamber, 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. I checked the primers with a loupe and there were no marks at all. The firing pin never hit the primer.

thanks all!!!

MG

(I have some pics but can't figure out how to get them in this dang post)

[Regaj]

Sounds like your handloaded rounds are being misshapen somewhere in your loading process. It could be your gun - but the fact that your other handloads (and your factory rounds, per your previous posts) chambered and fired okay would strongly suggest that it's your latest creations.

Do you have a way to measure your base-to-datum? The lack of a firing pin strike suggests a severely set-back shoulder. And a bulged case just below the shoulder would explain the rounds jamming in your chamber.

An overly cranked-down sizing die could cause that.

Other details would help... the type of bullet, the type of brass, provenance of the brass (purchased new, from factory ammo fired in your gun, miscellaneous range brass), and where the marks on the extracted rounds were.

[dellet]

What exact bullet are you using?

Sounds like it is not the one used in the data you got the length from.

What is loaded neck diameter?

[20X11]

Buy a Sheridan "cutaway" case gauge. It will show you the error of your ways.

[MaxG66]

What exact bullet are you using?

Sounds like it is not the one used in the data you got the length from.

What is loaded neck diameter?

It appears to be a Hornady Interlock 180gr. It may be something slightly different, as my records indicate this was a Midway Blem purchase.

It looks like the pics of the Hornady Interlock but with a boat tail.

The weight is definitely 180 per my scale. And the diameter is .308.

[MaxG66]

Buy a Sheridan "cutaway" case gauge. It will show you the error of your ways.

Just did. Thanks for the advice.

The load data I'm using, albeit from multiple sources, is almost certainly wrong. Maybe I don't have the bullet I think I do, though I don't see data for any 180 gr bullet that isn't listing a COL around 2.2". I can set the bullet deep enough to fit in the gauge, if that's the issue, but then how do I know where my boundaries are for working up a load?

FWIW, I remeasured all of the test rounds and they were at the 'proper' COL per the documentation. The brass is once-fired mixed, cut down 223, the same brass I've been using and the same batch of brass that my other handloads are working with. There is no bulge in the cases when they go out of the die / into the gun. Trim length is 1.363".

I did a web search and found someone asking the same question, also about this batch of blems. I think the issue is the bullet, i.e. the bullet not being what the recipe I'm using is referring to, but I don't know how to find what it really is, and, like I said, all the load data I can find in books and online all say about the same COL, which seems the most likely culprit to me. But, obviously, I'm missing something.

[rebel]

There are a couple reasons that could cause your round to go click. dellet beat me to the first one. I won't confuse you with the rest as we need to handle the first. Do you have a way to measure bullet base to ogive? If not , can you determine if bullet is engaging the rifling. It might be a good thing you had a click.

[MaxG66]

There are a couple reasons that could cause your round to go click. dellet beat me to the first one. I won't confuse you with the rest as we need to handle the first. Do you have a way to measure bullet base to ogive? If not , can you determine if bullet is engaging the rifling. It might be a good thing you had a click.

No, I don't have a bullet comparator.

[dellet]

You don’t need a comparator, but it makes it easier.

What is the diameter of the neck of a loaded round?

Pull the upper, remove the bolt carrier group. Seat a cartridge by finger pressure. It should fall out.

Take anther piece of empty brass, seat a bullet to the length you are using, if the other round stuck, and the neck diameter is less than .334”. If that one sticks, keep seating the bullet deeper .010” at a time until it quits. That will be your max length.

This is all based on you being able to take a sized piece of brass with no bullet and insert it into the barrel as above and it falls out under its own weight.

[MaxG66]

Neck diameter is .339 to .340.