300BlkTalk

I'm 79 yrs old, have been reloading for about 60 yrs, I have reloaded just about everything out there so I feel that for the most part I know what i'm doing. I never wanted a .300BLK but got tired of trying to develop a reliable subsonic 7.62x39.. enter 300 BLK. Every thing is new, except the brass which I made from 223/5.6 cut and trimmed to SAAMI specs. I loaded 220 gr Sierra fmjhpbt on top of 8.7 gr H110.

I loaded 10 rounds and walked out to my range. The first 3 rounds fired flawlessly, the 4th locked the bolt to the point I had to take the AR apart and with the aid of a brass drift I knocked the bolt back and ejected the unfired round. I then double checked all of my specs on this round as well as the remainder. all checked out.

I reloaded the mag and when I charged the rifle the sound was kind of "Jammy" and it was. Took the gun apart, got the unfired round out (Different round) and again checked all speccs. I have a Hornady shoulder gage and not only checked it with SAAMI specs but also against a new round. This new round did fire w/o cause as did some of my loads. I have disassembled this rifle approx. 30 times

I have several loaded rounds left some of which will allow the bolt to close into battery and some will not. I painted some with layout fluid in hopes to see a tattle tale sign where it may be hanging up.....negative results. Do to the fact that this is a new upper I'm starting to lean towards the chamber.
Any input will be appeciated.
Rog

In to see where this goes, nowhere near your experience level but I'd be thinking chamber too. What barrel you running?

Do yourself a huge favor and get a slotted Sheridan gauge. That will allow you to see many problems that might be caused by bullet seating, shoulder, brass thickness, etc.

Back to your problem. Check the neck thickness measurement of a loaded round. Max is .3340. The neck might be too thick and causing the jam. What brass are you using? Refer to this link to check for good/bad brass. viewtopic.php?f=141&t=88599

Smus beat me to it, but hearing twice will drive home the importance.

Since you did not say that the bullet stayed in the barrel when you hammered the bolt back, Ill give you probably the two most common problems.

Check the neck diameter and thickness of the brass. Brass no thicker than .013" neck no more than .334" loaded.

Depending on what your donor brass was fired in, a lot of dies seem to have a problem getting all the way to the base to resize.

Compare what you have to SAAMI specs, or rounds that will chamber against those that don't. Most likely it will be base or neck.

You might take a look at this in the handloading section:
viewtopic.php?f=141&t=88599

Oh yeah.

welcome to the forum

Thank you folks for all of your in put and I appoligize for taking so long with my reply but I was waiting for delivery of my Sheridan Slotted Gauge (cute little guy) which I just recieved. I see what all of you were talking about and just where the "Hang up" is. The problem with getting an answere is in most cases it creates another question.

QUESTION: Will clean, resized brass that drops into the Sheridan Gauge change its neck size when introduced to the bullet? I know I can just load up another and find the answer but I have so many rounds to disassemle I thought I would just ask.

To answer dellets' question.....NO! I never had a bullet pull loose from a stuck case.

I want to once again than you for all of your input......no matter how smart we think we are we're never smarter than all of us. Not sure who said that but it sounds like something John Wayne would have throwen out after a gun fight.

Thanks again,

Rog

what headstamp of brass are you using?

you might want to check it against the good/bad/ugly list

some brass when converted has too thick of necks on it and can cause problems for you

viewtopic.php?f=141&t=88599

I have the list and have a mixed bag of "You name it" brass in both 5.56 & 223. I have not as yet sat down to sort it out.

I think I found the easist way to find the "Bad Brass" is to load it all and it will find me.......Haaaa haaaa

Thanks
Rog

kawa wrote:
QUESTION: Will clean, resized brass that drops into the Sheridan Gauge change its neck size when introduced to the bullet? I know I can just load up another and find the answer but I have so many rounds to disassemle I thought I would just ask.

To answer dellets' question.....NO! I never had a bullet pull loose from a stuck case.

Thanks again,

Rog

If the brass drops in before seating the bullet, you only have a few choices. The bullet is in crooked, or the neck is .335+.

Check the thickness of the neck of unloaded brass, .013 is max before you start running into trouble.

If you can twist the cartridge and it drops in, the high side of the bullet is now in the slot.

Make sure there is no burr on the mouth, sometimes you can feel it or just hit it with some emory and it will drop.

I will also drop the base of the cartridge in backwards if it does not fit, but that will show up before it's loaded.

Do take the time to sort your head stamps. Then use the list to cull out the bad. It will save you a ton of grief in the future.

Yes a resized piece of brass will fit into the Sheridan gauge depending on the size of your expander ball. If the ball is on the small size the brass might fit the gauge.