300 AAC Blackout BCG's- Need Schooled!

[Tophernj]

I did a quick search and didn't find anything pertaining to my particular question...

I now have a complete lower and am wondering where to go from here.

I am looking into BCG's and am a touch overwhelmed by the choices. NiB, phosphated, carpenter 158, ad nauseum... Someone on another board suggested the AIM Surplus which to my completely newbie eye looks fine, but am I missing something? I am going to be running a 300Blk gun, un-suppressed naturally(I live in NJ), with supersonic handloads. Is there anything I need to be aware of as it pertains to the BCG's? Any hidden issues with one company or another? Any other suggestions from anyone on which BCG to look into? Budget wise, I'd like to stay around 100-150ish. It's where I'm comfortable.

Thanks as always,

Christopher

 

[otrman]

Ok I'll give it a shot, bear with me as I'm getting over the flu and may ramble. The military spec is phosphate coated chrome lined with carpenter 158 steel bolt that is MPI and HP tested. Does that mean its the best, maybe maybe not. But what it means is it has a specific set of standards that each part must meet. The bolt is the weak part in an AR, lugs wear and break and they can crack around the cam pin hole and around the extractor cut out. Personally I want the hardest best bolt I can get, but even that one will require replacement at some point, usually around the 4,000 to 6,000 round mark. I have seen mil. spec. bolts run longer and shorter. Bolts made from softer steel will wear out faster. But it is a wear part that at some point in time will require replacement regardless of what steel it is made from. As far as the different coatings go it is a personal choice. I have 2 of the Spike's nickle boron bcg, do they run better? Can't tell you, hasn't caused any issues either. Biggest advantage so far is they are super easy to clean, carbon won't stick it, even on the tail of the bolt which usually requires a scraper to get the carbon off. I would advise to stay with any bolt that has been MPI and HP tested, they will be marked as such on bolt body, to minimize possible bolt issues. Hope that helps.

 

[G.barnes]

Stick with the mil spec 158 carpenter bolts. The 8620 is not as strong and you don't save enough to make it worth skimping. I just bought a spikes hpt/mpi tested bolt for 130. The aim surplus are only 30 dollars cheaper. If a company can't even meet a minimum requirement for materials and testing I'm not wasting my money on it. That said I shoot a lot. If you only shoot a hundred rounds or so a year than it probably won't make a huge difference to you.

 

[NWcityguy2]

Since the 300 blackout uses the same bolt as a 223 you can always cross reference the information. People will debate this topic into the ground but I'll give my 2 cents anyway.

Materiel: 158 carpenter steel is what the military currently uses. Unless you want to drop big bucks for a KAC bolt, these bolts are regarded as the most durable. 8620 was the materiel for bolts way back in the day but was too hard and prone to premature failure. It is what the M14 bolt is made out of, but the designs are different and 8620 is not as suitable for a M16/AR bolt. Many budget guns sport a 8620 bolt, but if you are buying aftermarket a 158 bolt isn't much more expensive so there isn't much reason to buy 8620. 9310 is also a newer material and is supposed to be very similar to 158 durability wise, but is cheaper for companies to acquire. My personal upper uses a 158 bolt while my dept. issue AR sports a 8620 bolt. Both will work just fine until they break but the 8620 is more likely to break at a lower round count.

Coatings: Parkerized exterior and chrome lined interior is standard for a good BCG and works really well if you want to run standard ammo through a standard gun. That exactly describes my needs. People who want to turn down the gas with an adjustable port have found that NiB coated bolts (with their significantly reduced friction) work better for that. Not too familiar with Ionbond or the other coatings. I personally think chrome lined BCG's (total, not just inside) are more of a style choice than an improvement of parkerizing.

Testing/Shot peening: You'll see lots of bolts advertised as HPT, MPI, Shot peened or some combination of the three. High pressure tested (HPT) means that the bolt had an over pressure round fired through it and it survived. Magnetic particle inspection (MPI) means it was inspected for cracks that are too small for the human eye to see. Shot peening is done to reduce stress in the bolt itself. My personal opinion is that making bolts is essentially down to a science and I don't see the value in paying for individual testing when I have a return policy and can just swap out a defective product. The only person I've seen speak from a personal experience standpoint on HPT/MPI is Rsilvers, who while he may act a bit curt isn't just repeating something someone told him. http://www.m4carbine.net/showthread...-viable-and-necessary-or-outdated-bureaucracy I think shot peening still has value though.

Bolt Carriers: All but the cheapest ones are 8620 anyway. Any quality bolt comes with a quality bolt carrier.

The best deals in BCGs right now...

http://palmettostatearmory.com/inde...uto-bolt-carrier-group-w-charging-handle.html

http://palmettostatearmory.com/index.php/palmetto-state-armory-5-56-bolt-carrier-group.html

http://www.brownells.com/rifle-part...Banner-_-Rifle Parts-_-M16_Bolt_Carrier_Group

 

[Tophernj]

Thanks all!!! Great info.

C

 

[Trent]

Everything but the barrel is the same.. so stick with tried and true AR best practices.

 

[Tophernj]

Everything but the barrel is the same.. so stick with tried and true AR best practices.

That is the plan.

Does anyone here have any experience with Young Manufacturing bolt carrier groups? There seems to be no information on the materials used in their construction. The lack of staking on the gas key doesn't bother me too much. I am more interested in the phosphated one.

C

 

[NWcityguy2]

I hear good things about them. If you buy one from Rainier Arms they stake them for you.

https://www.rainierarms.com/?page=shop/detail&product_id=1014

 

[oldpapps]

What you are dealing with is a regular, normal AR/M4 with a fat barrel (on the inside). Fatter eats up more gases and generally much more lead being pushed requires a propellant in a diffrent burn/pressure range to function the action.

Did I say anything about the BCG? Nope.

I'm not about to get into it about what is the best AR BCG, who makes the best/worst.

General view held by me and doesn't make it correct, is a Full Auto BCG is a little heaver and will slow down the cycling (a little) but a change of powder will negate this.

So, just follow the advise above. Use whatever you use in a small bore AR/M4.

This is not exact science. Go with it and enjoy the process.

 

[Walkalong]

An AR 15 BCG will run with a rifle buffer, but a full auto BCG will not reliably eject some super sonic loads. Not enough speed.

A FA BCG will be fine with all but the heavier carbine buffers. You can always lighten up a rifle buffer by removing a weight or two.

Just something to consider. I am not sure what buffer that stock uses.

I bought this AIM BCG to go in place of my Model One Sales AR15 BCG for my 300 BLK that has an A2 stock and rifle buffer. I will either have to lighten up my buffer, or use the BCG elsewhere. I do not want to use it elsewhere.

 

[Trent]

The assembly of a 300 AAC blackout is trivial.

Once you get one assembled, if you reload, the real work begins.

Next year I'll begin the process of getting my CMMG upper to run good. I'm only going for subsonic; no interest in supersonic (my gas system isn't set up for it, per CMMG).

I've got various bullets to work with from 210gr Barnes, 220gr Sierra Matchkings to 240 gr lead slugs.

I don't expect finding a good load, that runs well, will be too difficult since I'm going for subsonic only. Nor do I expect the OP to have any issues getting a gun to run well with supersonic only.

The real difficulty comes in getting a gun working that runs BOTH subsonic AND supersonic. The gas port pressure, gas system length, and barrel length all come together to create a very difficult target to hit; a supersonic load with the right port pressure pulse, and a subsonic round that also has the right port pressure pulse.

All of my research to date has led me to believe that getting both to work well on the same upper is incredibly difficult and not always possible. Which is why I elected to go subsonic only on mine; I have plenty of long range guns, but wanted to fill the role of a very accurate short range heavy-thumping high capacity semi-auto that can lob them out to 200 yards with good effect.

Anyway, 300 AAC is one of the few systems I've seen where Reloading truly becomes part of the process, to get the firearm to run smoothly and efficiently. Which is part of the reason why I was drawn to it in the first place.

The OP hasn't indicated if reloading will be part of his process, but if so, I recommend doing a lot of research and study.

Next year I'll post up my journey on the "subsonic" end of the scale as I work through the process myself. I have plans to get a couple more 300 AAC uppers built next year as well, in different configurations, so I can fully understand the process.

-T

 

[oldpapps]

Trent,

The OP lives under the oppression of the 'Left Coast', so no suppressor for him. I live out that that checker-board with little round circles 'they' see when flying from one left coast to the other and I have no interest in subs.

I agree, finding 'the' loads is the fun with the 300. If you haven't looked, there are many loads listed, for all needs, on '300blacktalk'. I even have some of my loads listed.

http://www.300blktalk.com/forum/viewforum.php?f=185


Its a hoot.

 

[Trent]

I live in Illinois, which has no suppressor rights.

I wanted to fill the role of light brush gun. 30-30/7.62x39 fills the role but the bullets are too light. The moment I saw 300 AAC can be loaded with 220 gr I was hooked. That was the selling point for me. Because I also shoot heavy 308 bullets out of my 300 Win Mag, and I have a large variety left over from testing load work-ups with it.

The other "wow" factor for me, is I can readily shoot 220-240 grain lead slugs out of a semi-auto rifle; something that I DO NOT have on any other platform. This means I can turn the 600-some pounds of old wheel weights in my garage in to free plinking bullets. So it also became my *most* economical shooting platform in rifle form. Previously only my handguns were really suitable for the wheel weight alloy. The only thing remaining to do is get a small supply of antimony to raise the hardness slightly.

With the price I paid for the lead alloy, years ago, and the huge ready supply of casings I have from years of shooting 223 that can be converted, I'll be shooting 300 AAC blackout for about 7 cents a shot this coming year.

Someday when I retire to a more friendly state, I'll undoubtedly get a can for it. But in the meantime it'll absolutely serve a role, in that it'll be the cheapest-to-shoot AR-15 platform I can practice with.

-T

 

[Tophernj]

Trent,

The OP lives under the oppression of the 'Left Coast', so no suppressor for him. I live out that that checker-board with little round circles 'they' see when flying from one left coast to the other and I have no interest in subs.

I agree, finding 'the' loads is the fun with the 300. If you haven't looked, there are many loads listed, for all needs, on '300blacktalk'. I even have some of my loads listed.

Its a hoot.

I'm on the left coast only if your looking south from north...

Yup, I'm in NJ. No cans for us. Hence the use of supersonic ammo for me 90% of the time. I will be running some subs just for the hell of it but it will not be my main focus.

I do reload and right now am having a really fun time gathering all the components. I've gotten a fair amount of 223 brass for free from some friends and I've done a touch of horse trading as well. For bullets I have from 110gr Hornady A-Max to 165gr cast to play with so far. I'll be looking for some 220's in the near future. I fell in love with the thought of this cartridge simply because of it's versatility. So many bullet weights, so much to do, so little time.

Thanks all this is a fascinating conversation.

C

 

[oldpapps]

Tophernj,

Left is not a direction, per say, but a political affliction. The 'left' coast is on both the Atlantic and Pacific and several places in between.

I edited my previous entry to include a proper web address. This is for cast bullets, one layer up is for all loading. Three stickie and one is just loads.

Back to your BCG question.

I built my 300 BlackOut upper with the though that I would switch it back and forth with an upper in .223/5.56 (Wylde chamber). This was a good idea but.... I couldn't stand it and built a dedicated lower for the 300 upper. I have no will power some times.
I used a PSA BCG, no frills for the 300 and a FullAuto BCG for the .223/5.56. I have never seen a need to trade them to see if they would work. They do fine as is. I run all BCGs wet with Mobile One and have found that a very cheap dentures 'sonic' cleaner will hold a BCG and covered with Hoppies, will be very clean when the battery runs down (over night).
Just some thoughts.

 

[Tophernj]

Thanks Oldpapps. For the link and the explanation. Much appreciated.

Merry Christmas to all!!

C