300 BO AR and MP 311-410

[sukivel]

I'm trying to load the MP 311-410 HP pc'd for my 300 BO AR-15. I am having cycling issues with this lighter weight bullet. I have worked up to max with IMR-4227 and the round fires and ejects but the bolt closes on the next round being fed and jams it up.

I have several other Hodgdon and IMR powders, but should I look to a faster or slower burning powder?

Any other tips or suggestions? I really want this cast boolit to work! I load an NOE 230 grain boolit with 4227 and it works great, but I need a lighter, and flatter, HP for quick action coyote/bobcats around the farm.

[John McCorkle]

What is the barrel details...ie... barrel length and gas system length?

Absolutely should be able to get a good working load but this can be more complex if you have something with a very heavy buffer and very short dwell time

In short though alot of folks have good success with that bullet in 300 blk so take heart, it's been done many many times before

Sent from my moto g power (2021) using Tapatalk

[imashooter2]

Sounds more like a magazine problem to me. What magazines are you using? If you single load one, does the bolt lock back?

[sukivel]

What is the barrel details...ie... barrel length and gas system length?

Absolutely should be able to get a good working load but this can be more complex if you have something with a very heavy buffer and very short dwell time

In short though alot of folks have good success with that bullet in 300 blk so take heart, it's been done many many times before

Sent from my moto g power (2021) using Tapatalk

8.5" barrel

1:8 twist

FWIW...My JHP Sierra 110 grain loads, Lee 155 gr cast loads, and 150 gr RN loads all work flawlessly.

[sukivel]

Sounds more like a magazine problem to me. What magazines are you using? If you single load one, does the bolt lock back?

I use Magpul magazines and have not once had an issue with any other load. Yes the bolt locks back when single fed.

[imashooter2]

If the bolt locks back when single fed, you have a magazine problem. If they are standard .223 magazines, then the forward ribs often cause feeding issues based on where they contact the boolits, either pinching the cartridge stack or pushing the boolit nose off the feed ramps as they strip. The easy solution is to either file them down a bit or buy dedicated 300 BLK magazines that already have the ribs cast lower.

[imashooter2]

Also, is the nose “pointy” enough to use the feed ramps in the barrel extension? I have no luck with round nose or flat nose projectiles. They all jam on the locking lugs.

[sukivel]

If the bolt locks back when single fed, you have a magazine problem. If they are standard .223 magazines, then the forward ribs often cause feeding issues based on where they contact the boolits, either pinching the cartridge stack or pushing the boolit nose off the feed ramps as they strip. The easy solution is to either file them down a bit or buy dedicated 300 BLK magazines that already have the ribs cast lower.

After you fire the last round, or single feed with the mag in, the bolt stays open. It's supposed to do that. I/we must be describing something differently. It is a standard magazine, but with ALL of my other 300 BO loads, everything functions perfect. 110 gr, 155 gr, up to 232 gr all function great.

[sukivel]

Also, is the nose “pointy” enough to use the feed ramps in the barrel extension? I have no luck with round nose or flat nose projectiles. They all jam on the locking lugs.

Yeah it is pointy, except the hollow point. My 150 gr RN JSP loads feed great, that's why I'm perplexed.

I'm starting to remember why I enjoy single shot rifles more...

[imashooter2]

After you fire the last round, or single feed with the mag in, the bolt stays open. It's supposed to do that. I/we must be describing something differently. It is a standard magazine, but with ALL of my other 300 BO loads, everything functions perfect. 110 gr, 155 gr, up to 232 gr all function great.

If the bolt locks back, it indicates you have plenty of gas and bolt travel and so it isn’t the powder or bullet weight that is the problem.

This isn’t all your other loads. This one is a problem. The behavior of the rifle strongly indicates it is a magazine problem with this particular boolit. Most magazine problems with the BLK have to do with the forward rib on .223 magazines. It contacts .30 caliber bullets differently than .22 caliber.

When you fill the magazine, do the cartridges stack smoothly down the sides, or does the rib pinch the column towards the center off the sides of the magazine box? If it does, then this causes the cartridge stack to bind and the next cartridge may not be in position to strip in the very short time allowed by the bolt travel.

When a cartridge strips off the top of the stack, does it travel forward straight and hit the feed ramps or is it pushed towards the center and jam on the locking lugs?

These are the most common failures with 300 BLK in .223 magazines. Good luck!

[tayous1]

I have the same mold and found that unless the OAL? I had to make mine I believe 2.100 OAL to make it feed it worked but looked odd. I was not even able to push the Boolite down up to the lube ring but I used H110 and it cycles in my 18 inch and 7.5 inch barrel with no problem.

[tayous1]

If the bolt locks back, it indicates you have plenty of gas and bolt travel and so it isn’t the powder or bullet weight that is the problem.

This isn’t all your other loads. This one is a problem. The behavior of the rifle strongly indicates it is a magazine problem with this particular boolit. Most magazine problems with the BLK have to do with the forward rib on .223 magazines. It contacts .30 caliber bullets differently than .22 caliber.

When you fill the magazine, do the cartridges stack smoothly down the sides, or does the rib pinch the column towards the center off the sides of the magazine box? If it does, then this causes the cartridge stack to bind and the next cartridge may not be in position to strip in the very short time allowed by the bolt travel.

When a cartridge strips off the top of the stack, does it travel forward straight and hit the feed ramps or is it pushed towards the center and jam on the locking lugs?

These are the most common failures with 300 BLK in .223 magazines. Good luck!

How do you take care of this problem?

[imashooter2]

You can fool with the seating depth to vary where the boolit ogive contacts the rib to allow the cartridges to stack straight and against the sides of the magazine box if that is the problem. The rib pushing the boolits to the center to jam in the lugs is harder to solve with seating depth, but sometimes it can be done.

Easiest is to buy purpose made 300 BLK magazines that have the rib cast lower to allow for the larger diameter boolits to ride correctly. You can also disassemble and file down the ribs of Magpul .223 magazines for the same effect.

[tayous1]

You can fool with the seating depth to vary where the boolit ogive contacts the rib to allow the cartridges to stack straight and against the sides of the magazine box if that is the problem. The rib pushing the boolits to the center to jam in the lugs is harder to solve with seating depth, but sometimes it can be done.

Easiest is to buy purpose made 300 BLK magazines that have the rib cast lower to allow for the larger diameter boolits to ride correctly. You can also disassemble and file down the ribs of Magpul .223 magazines for the same effect.

Are there rib casts that you can buy to replace the 223 ones? I have notice when I try to load the 230gr on a magazine I can't get 30 rounds in them and the magazine will hang up.

[imashooter2]

No, but there are dedicated 300 BLK magazines with the lower ribs from the factory. Magpul and Lancer make good ones. I like translucent smoke Lancer’s to set them apart from my Magpul .223 magazines.

Magpul dedicated 30s or 20s, $15.15 each:
https://www.midwayusa.com/product/1018507080?pid=977210

Lancer's, $5 more:
https://www.midwayusa.com/product/1022346310?pid=985277

I didn’t shop, just looked at Midway. You might find better deals.

[Bashby]

Read the third post in this thread.
https://www.ar15.com/forums/armory/300-Blackout-Master-Thread/42-385765/

It explains how to determine what OAL will feed properly

[tayous1]

Read the third post in this thread.
https://www.ar15.com/forums/armory/300-Blackout-Master-Thread/42-385765/

It explains how to determine what OAL will feed properly

That's good information! Use to like going there a lot had since 2001 but they now uphold rules to people who are members.

[tayous1]

I'm using a 7.5 inch barrel. Bought some followers that where made for 300blk I will rate them when I get them if they work with the shorter OAL.

[tayous1]

I have nothing to do with these company! Just saw a solution to a problem!

https://muddy-river-customs-llc.myshopify.com/products/300-black-out-3d-printed-follower?variant=39570674188440

[imashooter2]

What problem are they intended to solve? I don’t see any claims.

[popper]

No, the problem with the short bullets is they don't always feed right and get pulled forward in the mag by the one above it or the BCG. Rims need to NOT have any rough spots. They get pushed to the front of the mag, bolt hits them and nose jams in the feed ramp. Don't load more than 4 in the mag so spring pressure isn't so great helps, I still get a jam once in a while. Try those 110gr half jackets - lots of jams. Always bang the mag on something hard to seat the cases against the back of the mag helps too. A proper solution would be a mag with smaller internal dimensions.

[Drew P]

I had problems with mag pull mags in 300bo, so, that’s likely your problem. But, one little piece of gold I picked up along the way is that you need to seat the bullet so that the rib in the magazine contacts the bullet at the point which measures .250”. After heeding this my cycling got waaaay better.

Also worth pondering: a sheet metal mag will always have more internal volume than a plastic mag. Volume matters when you are trying to stuff cartridges with bullets 4x the size of the designed parameter into the mags designed for 223.

[tayous1]

What problem are they intended to solve? I don’t see any claims.

Not buying a whole new magazine but buying a follower that you can replace an 223 follower?

To me getting a a few of these followers are cheaper then buying one 300 blk magazine unless I'm missing something?

[imashooter2]

The followers aren’t a problem. The magazine body is the problem. Specifically the ribs in the front of the 5.56 magazines pinching the cartridge stack IF the bullet body is too large where it contacts them.

[Drew P]

The followers aren’t a problem. The magazine body is the problem. Specifically the ribs in the front of the 5.56 magazines pinching the cartridge stack IF the bullet body is too large where it contacts them.

Correct. Try a c products mag. And seat them as I outlined. You’ll be shooting pretty

[tayous1]

Correct. Try a c products mag. And seat them as I outlined. You’ll be shooting pretty

Any C products mags or is there one I should buy? I'm sure I have a few laying around the house just have to find them

[imashooter2]

My opinion again… If you’re going to buy magazines, buying dedicated 300 BLK units will make your life easier. Otherwise try the ARFCOM instructions with what you already have.

[tayous1]

My opinion again… If you’re going to buy magazines, buying dedicated 300 BLK units will make your life easier. Otherwise try the ARFCOM instructions with what you already have.

What ones?

[imashooter2]

I like Lancer because they have translucent smoke bodies that differentiate them from my 5.56 magazines. Magpul have different texture on them, but are opaque black plastic, same as the 5.56 magazines. Just make sure you are buying the dedicated BLK part numbers. Companies like to advertise standard 5.56 magazines as “5.56, .223, 300 BLK.”

There are Midway links in one of my posts above, but if you shop you may be able to find them cheaper.

[Drew P]

Any C products mags or is there one I should buy? I'm sure I have a few laying around the house just have to find them
I would just say any metal mags that are not magpul, but if you really start to look at the situation with a critical eye you will be able to identify the reasons why some mags don’t work, while at home just loading and looking. I’ve had good luck with all my c prod

[Rapier]

I use the 230g in my BO, as well, however, in the end, switched to the 6mm Mongoose, to push 80g FBSP bullets up to 3k, so they do not go flying all over the farm. The last yote I dropped, did not have through and through penetration, bullet entered and exploded DRT. I doubt you can ever get what you want in velocity out of the BO case. I am building a 24 GPC at the moment to get about 3,200.

[sukivel]

So an update to my original post...

After looking at several mags, load data, and seating depths I tried several things, and it appears I have rectified my problem.

The first thing is I was way under powder charge. The only published data I could find was for a 16" barrel, and mine is 8.5". I was initially attempting to stay at roughly 1700ish fps so I was loading slightly below starting powder charge and the lighter 130 gr cast bullets were battling to get the bolt back all the way. But again that data is for a 16" barrel. That's my hypothesis anyhow.

Second, I was seating the bullet to the crimp groove, which is very short for the 300 BO, and the new round was not smoothly feeding fast enough and allowing the bolt to close on it. Also to add 1 grain of powder ( which is still under a starting load), I needed to seat the bullet out further for it not to compress.

Third, I have been using 30 rnd Pmags for all of my other 300 BO loads and they all function great, but I noticed I had been using a 20 rnd Pmag to function test these instead, and for some reason I found through testing some other rounds that the 20 rnd mag experienced some problems.

After adjusting those three things I have gotten this little MP 311-410 to cycle a half mag through, but I want to function test a little more. The funny thing is, after firing half a mag of these and then the other half a mag of my NOE 232 gr subs, I really don't like those loud little suckers coming out that close to my face! They seem "hot" compared to my 232 subs. I was also down on my range and found that with my Sierra 110 JHP zero on the rifle, I was able to still hit my 10" plates out to 100 yds with the dot on center target. My main reason for the cast 130 gr HP was for 100 yd predator defense, and apparently I can get there with the subs, which are funner to shoot, so...

I'm still like these little hollow point boolits though...

[popper]

The ribs in the 223 pmags only contact the shoulder of lower rnds, no the top 2. Will cause lower rnds to bind but not a feeding problem. The front of 223 mags can be a problem. They were designed for a small pointy well feeding bullet. Even lancer mags were designed for a normal COAL. Pistol gas and 15gr 4227 is enough pressure to cycle and get 1400 fps. 18 gr for 1700 fps and pressure is high at port. Most all will give muzzle flash as powder is slow.