Throating.

[Rooter pig]

Have any of you guys had a throat reamer made to lengthen the throat of a 300 bo chamber?
Then you could shoot a cast bullet with a longer and more accurate drive band... More to hold the bullet straight.
I've measured a cmmg 300 barrel and it bumps about .020 north of the case mouth . It would open up a lot more cast bullet possibilities .

[yondering]

You can buy or rent throating reamers, don't need to have one made. Long throating is common in some applications, although I've never found the need for it in 300 Blk. Most of what I shoot is cast bullets.

[Rooter pig]

Thank you sir for the reply. The two Noe molds I have , have the small step-in just above where I crimp. I guess that makes them a bore ride? I have a couple dozen mold for marlin lever rifles and they all have a 60/40 or 70/30 ratio between drive band vs ogive. I have to seat my ranch dog 30/30 bullet way below the neck to get to chamber in a ar 300 bo ,as it has more drive band than the Noe.

[yondering]

Yeah, bore rider bullets are not a great idea in the Blackout or any other caliber in the AR15; reliability tends to be iffy. A lot of 30/30 bullets give good accuracy in the Blackout, but don't feed well because of features like bore ride sections.

You could throat the chamber to eliminate part of that problem, but you'd have to throat it pretty deeply, and that is a problem in itself, where the bullet has a long jump before engaging the rifling. That tends to cause skidding in the rifling.

Better to just use bullets that fit the Blackout better.

[Rooter pig]

Thanks again sir.

[popper]

Are you sure you aren't confusing the throat with the bore? Unless the chamber was one badly, the throat (bore)should start where you say it does. Reamer run deeper will move the lands farther, I don't think that is what you want. If a long bore rider, size the nose to fit just under bore dia. My normal boolit for BO has the drive band 1/10" into the bore - shots fine. Also have a 185gr RD style that I size the same, shoots fine and doesn't jam the lands. The WFN feeds in lancer mags but not Pmags. I also use 150gr SPP and they don't feed in the Lancer but do in the Pmag. Has to do with the front of the mag design.

[yondering]

I'm not confusing anything, and the OP wasn't either. Do some research on what a throating reamer is and does; it's not the same as a chamber reamer.

[popper]

.02 north of mouth is start of throat, pushing that forward won't help. Neither will lengthening the throat either. He needs to size to throat, not bore. The dia. And taper could be increased. Retread his post.

[dbod]

Have any of you guys had a throat reamer made to lengthen the throat of a 300 bo chamber?
Then you could shoot a cast bullet with a longer and more accurate drive band... More to hold the bullet straight.
I've measured a cmmg 300 barrel and it bumps about .020 north of the case mouth . It would open up a lot more cast bullet possibilities .

viewtopic.php?t=95866

[xdmalder]

Bruce are you still crimping right at the edge of the drive band with those NOE 230 bullets? Are you sizing at .310 or above? You may just have and extremely tight freebore like I did and need to size at .309. I started seating those 230's you sent me at .310 and needed to seat the front driving band in the case mouth or my bolt would not go into battery. Then I started looking at SAMMI case specs. I sized to .309 and now can crimp in the crimp goove. Give it a try and see if that solves anything. My guess is it will. The problem with reaming is it will remove the chrome lining or nitride finish if it is present.