MP and LEE molds for 300 AAC are two different diameters?

[Airheadbit]

I've been sneaking up on casting 300 AAC bullets for the last couple of years, as I found 'stuff' I thought I'd need I would purchase it. I have the following molds:

https://www.mp-molds.com/product/mp-...-gc=plain-base
MP 300 BLCK 311-235 HP mold Brass 3 cavity

https://www.mp-molds.com/product/mp-...b-gc=gas-check
MP 300 Blackout 311-230 Grain solid mold Aluminum 6 cavity

https://leeprecision.com/search.php?...keep_https=yes
LEE TL309-230-5R

https://leeprecision.com/mold-dc-c309-200-r.html
LEE C309-200-R

I picked up a 1000 rounds of .308" #10100 TMJSP 220gr Berry Blackout .300 AAC

But here is the problem:
LEE molds are .309
MP Molds are .311
Berry bullets are .308
The cases I'm making out of 5.56 after forming are .308, what do I do with the cast bullets? I found LEE sizing dies for .309 and .311 but not .308 and I was planning on powder coating the cast bullets. I've surfed around this forum looking but haven't found answers yet.

I'm a retired USPSA shooter that has never cast a bullet but have loaded tens of thousands on Dillion equipment over the years.

[yovinny]

If Im understanding correctly, your asking about expending your reformed cases to except cast at .311" ?
I use the Lyman 31 M and it works for me, but there are other expanders available also. It adds an extra step is the only downfall.

[Airheadbit]

Why are the bullet molds not .308? Both LEE (.309) and MP (.311) molds are not .308.
Am I suppose to size the bullets to .308?
If I am to size the bullets how does powder coating effect the overall sizing?
Case wall at (max .013) .013*2=.026+.308=.334 which is the MAX for SAAMI

[Soundguy]

I like to have at least .001 over size bullets for good bore sealing.

[Mk42gunner]

I'll try to answer your question, although I do not have a .300 AAC Blackout/ .300 Whisper.

There are a couple of reasons you want a slightly larger diameter with a lead alloy projectile versus a jacketed one. The first is that a cast bullet normally performs better when it absolutely fills the rifling grooves in the barrel. The second is that if the projectile leaves gaps, you will get gas blow by, which can cause leading.

The easy way to ensure this is to size the bullets one, two, or even three thousandths over groove diameter. depending on just how large the throat of your chamber actually is. Not what it is supposed to be, what it is in reality. You do still need a bit of clearance for the case neck to release the bullet upon firing.

The picture you show also has an answer. Directly above the cartridge name is a Maximum cartridge/ Minimum chamber note. There has to be tolerances for anything that is successfully manufactured. If the measurements really did match, the gun won't run very long, if at all.

Speaking of .30 caliber rifles, anything other than the .30 carbine and .300 Blackout is generally sized to .310-.311" for a nominal .308 groove diameter. I don't cast for those rounds, so my go to size for the .30-30, .308, and .30-06 is .311". Others that I respect use .310".

Only if I run into chambering issues would I go smaller. That hasn't happened yet. Some do report good results with .308 or .309" diameters though.

No idea on powder coating, I use a traditional lube.

Hope this helps,

Robert

[reddog81]

I size all my 300 BLK bullets to .311. I have the Lee 230 grain mold and have had the same terrible results with it as most people have had with it. I'd try their 200 grain bullet before getting the 230 grain one. The 150 grain Lee one also works well for me if you're not stuck on using the heavy bullets. I have an NOE version of the Lyman 311299 (looks similar to that 200 grain Lee one) and it works well.

[Airheadbit]

The LEE/Midway TL309-230-5R I purchased last year, the LEE C309-200-R I just purchased but only paid $18. I hunted down two other threads on the TL309-230-5R dated back to 2012, it appears it works for some and others hate it. After spending a few hours reading about the issues I've come to the conclusion I should buy .309, .310, .311 and .312 sizing dies for my power coated bullets experiments. I have several uppers with different barrel lengths meaning one bullet sized x, loaded with powder y, n grs or x*y*n rounds per upper, sounds like fun and a computer program to keep track. But at least now I understand a little more about why I couldn't find an answer to the sizing question. I'm hoping the MP 300 Blackout 311-230 mold with 6 cavities will be my main shooter.

[jonp]

I use the Lee in my 300 and it seens to work well

[popper]

Depends entirely on the barrel. Slug it or just fire some and see how they do. I size my BO 3085 and that works in 3 guns. A 4th needs 3095. You can use emory paper to enlarge a Lee 308 push thru but actual size will depend on the alloy (soft is smaller). NOE makes neck expanders (and bullet sizers) in various sized. You may need to turn necks or be selective in the brass you use. PPU seems to have thicker case wall. You may also have trouble with the nose dia., too large to chamber.

[gwpercle]

What diameter does your barrel slug to ... this would be the first thing to check / first place to start .
Get that info in hand and work out boolit size .
Some go by the throat but I have always worked with bore size and gotten good results ...
hang in there , it will get worked out !
Gary

[Airheadbit]

Barrel Slug? I'll have to visit my winter location, I have some sinkers that would work along with all my brass rods and soft mallets. I got my chop saw and jig working and can now cut cases that are all the same length but I was having issues with the decapping/neck sizing die, seems you can't really use a LEE shell holder in a RCBS JR2, way too loose, had to find and order a #10 RCBS shell holder (only a 100% markup). So there is two issues: Bullet sizing and Case neck sizing. Seems the LEE die sizes the case neck to .306, RCBS and Hornady both make Decapping rod Expanders that come in one thousandths steps and RCBS has decap/sizing dies that came in one thousandths steps BUT RCBS is Out of Stock on expanders and dies but I did find Hornady had some expanders still, along with Rosie to explain 'stuff'... I'm going to try the LEE APP for bullet resizing, at $64 it can swag cases and size bullets from bullets and cases stacked in tubes or there is an auto-feeder for the APP for $250.

How much can you 'shape/size' bullets? If my barrel is at .307 that would explain the jacketed .308 bullets but what about the MP molds at .311 then powder coating on top of that?
@popper, I tried to visit NOE but their site or a router is down today.

[imashooter2]

Every Lee mold I have cast is well over the nominal size listed. Choose your diameter, load a dummy and make sure it chambers and extracts. I couldn’t chamber anything above .310 diameter, which works fine since my groove diameter slugs .3075-.308.