Need help in a 300 black out AR with Lee bullets

[43PU]

So I have a 16” pistol length gas 300. I am trying to run the lee 312-160 bullets PC. I have watched every video on YouTube and I have read every word on this fourm and for the life of me I can’t figure out what’s going on my rounds simply won’t chamber, i made a chamber cast and measured everything and I have between 3-4 thousands of clearance my throat is .311 and the throat on my 312-160 is 308, the neck is .337 and my loaded round is .335, my rifling starts .177 from the case mouth and my ogive starts at .176.... I have no ideas on what’s going on... do you? I can take pics if you need it. I am about ready to throw this thing out the window it will only cycle and feed M80 pulls FMJ
I looked up the Sami specks and measured everything and my chamber is good so that’s not the problem.

[curator]

If you are using "converted" 5.56X45 brass, some headstamps may not work with cast boolits without neck turning. The Lee boolit may also have too wide a nose diameter to allow your loaded cartridges to chamber. Since the nose portion is not touched in bullet sizing it can give problems if there are small flecks of lead between your mould halves when casting. PM me with your e-mail address and I will send you a list of brass that will work with cast. I too had this problem when I began shooting cast in my .300 Blackout but new Starline brass solved the chambering issues. I use converted brass for j-word loads.

[43PU]

It’s all LC11 brass

[curator]

If using LC "converted" brass, you problem is most likely that your boolits have a slightly oversized nose. Have you carefully examined the ones that don;t chamber for rifling marks on the exposed portion? Lee moulds are great but then can throw oversize boolits if there are small flecks of lead between the mould halves or you don't hold them closed with enough force. The "bore ride" section of your boolits should measure .303" or certainly no more than .304." Check this with a c-type micrometer at 30, 60, & 90 degrees to be sure.

[upnorthwis]

PC makes the nose .003-.004 too big. Load some without the PC.

[curator]

PC makes the nose .003-.004 too big. Load some without the PC.

Thanks upnorthwis, I missed the "PC" assuming it was miss-typed "GC" (gas check) You are absolutely correct in that powder coating will enlarge the "bore-ride" portion of the bullet a couple of thousandths so it won't chamber. That's his problem right there! I size my cast .30 caliber boolits to .310 for use in my .300 blackout and have never found the need to powder coat them.

[KMac]

It may be a combination of the bullet and using PC on it that is causing your issue.

I think most people run the 312-155-2r in the BO. If this pic from lee is true to dimensions the 312-160-2r looks longer and maybe even be fatter at the tip. I know I have read that some guys wipe the PC off forward of the driving bands before they bake it to make it fit.
I am not an expert on any of this so take it for what it is worth.

[Itzdapig]

I had the same issues this past week, I had somehow put a crimp on the brass vs just straightening out the flare and it was causing chambering and ejection issues. I fixed the crimp and all is well!

[lreed]

I had the Lee bullet problem with my .300bo,bullet nose .302,with powder coat .303,intermittent jams,bad ones! I solved my problem by making a "apple sizer ring"to eliminate any bullets made by incomplete mold closing etc. I use a good powder coat as sold by Smoke,seems to me his product coats smoother and thinner than HF. Using cut down brass avoid Hornady,Wolf and most other off brands,PMC an exception. I do not use the crimping grove,I very carefully adjusted the seating depth until a handful of dummy rounds of varying head stamps will cycle through with no glitches,take a oal measurement and write it "on the wall" I used a minimum powder charge and worked up,advise doing same with the slightly deep seating. Lee push sizing die was used .309,I get a slight spring back so between .309 and 310. This works for me,but of course your mileage----. lreed