16” barrel discussion

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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Austin26
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16” barrel discussion

Post by Austin26 » Wed Dec 11, 2019 9:32 pm

Hello,

I've read the FAQ and a couple threads that seemed to want to address my question but never did. I'm pretty ignorant of barrel specs and bullet shape, grain, and powder differences and what each do. I've a lot of practical experience with the M16 and other weapons but no actual education on it. I'm seeking a ln accurate longer range 16" 300 BLK with supersonic rounds only and need help with what barrel to go with. What I'm leery of is going with a typically acquittal 1:7 twist that accommodates both sub and supersonic rounds. I'd prefer not to compromise as I'm looking for only supersonic and whatever bullet grain helps with longer range accuracy. From what I've read, it would appear something like a 1:9-1:12 twist with flat back of the bullet (not boat tail) may be what I need, though I don't know the grain. I've heard a light grain would be affected by the environment too much to be consistent and logic is telling me a heavy bullet would also have issues as the drop would be more though correctable.

Yes I do know the 7.62x35 isn't meant to be a tack driver. I'm very comfortable with the AR-15 though and want to see how accurate I can get it. I thought about just going AK but somehow I guess I'll always be not so comfortable being around the "enemy's weapon".

So, to restate, what combination of barrel specs such as twist and ammunition choice such as grain would help me to attain the most accurate 300?

I'm building it now and need to make a barrel decision at some point.

Thank you in advance!

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dellet
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Re: 16” barrel discussion

Post by dellet » Thu Dec 12, 2019 12:41 am

Welcome to the fun Austin.

Real quick let me introduce you to the fun of the cartridge.

What does most accurate mean and at what distance? “longer range” has no meaning. So I’m guessing half MOA at 6-800 yards.

Does “preferring not to compromise” include a budget of $3000+ before optics and $2 per bullet?

Basic MOA to 300 yards under $1000 is also possible.

A little direction of what you want to accomplish would be helpful in pointing you in the right direction.
300 Blackout, not just for sub-sonics.

Austin26
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Re: 16” barrel discussion

Post by Austin26 » Thu Dec 12, 2019 9:25 am

Thank you, and yes I should more clearly define my parameters.

Background: Marine infantry, qualified low expert for shooting (iron sights, 20" M16, various distances and stances... Some CQB on the move, some sitting, prone, out to 500m.) I built a 6.8 AR a few years ago.

Current build happens to be mostly Aero Precision as they seem to be the best bang for the buck these days. Been very impressed with their stuff. Lower is Aero, with Geiselle SSA-E trigger, Aero lower parts and buffer Carbine assembly.

Upper will be Aero monolithic. Unsure about BCG and barrel, obviously.

Budget of around $700 for BCG and barrel but I have a feeling I'd be plenty happy with something for half that. I expected ammo to cost a dollar a round or more to get that accuracy. And yes I'm thinking 1 MOA at 100m for this setup would be a difficult but attainable goal, I hope, though I'm unfamiliar with this cartridge.

A similar accuracy to my M16 would be wonderful though not expected!

Thanks again!

Austin26
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Re: 16” barrel discussion

Post by Austin26 » Thu Dec 12, 2019 9:34 am

I don't know the exact dimensions but the 500m human shaped targets I could hit 4/5 times on average. I don't know what MOA @ 100m that would translate to but I'd guess 1 MOA would be plenty comparable or moreso.

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dellet
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Re: 16” barrel discussion

Post by dellet » Thu Dec 12, 2019 10:33 am

That makes it a bit easier. MIL Spec is 2 MOA so cutting that in half is no problem.

Start with a quality bolt carrier group. Lewis Machine and Tool (LMT) make an enhanced version. The two main features are a full face bolt that fully supports the head of the case and an extended cam path to lengthen dwell time. This supports the cartridge in the chamber better in firing conditions and helps with managing over gassed conditions.
https://lmtdefense.com/parts/l7q3

Then a custom barrel. Make sure you can have the gas port sized smaller than normal. No reason to have an 1/8” hole drilled in the barrel when all you will need is about .070”. Carbine gas length and choose twist according to what bullet you will be using. I all you will be shooting is short 110-125 grain bullets, you can get by with something as slow as 13-15. If you want to shoot some of the longer copper solids or some 150’s you might need as fast as 1/9. I have two 1/10’s and still shoot plenty of 200+ grain subs.

These guys will build a barrel exactly how you want.
http://www.x-caliber.net/custom-ar-barrel

If MOA is all your goal is don’t get too hung up on twist. I have shot everything from 1/5-1/11. Sub MOA accuracy to 200 yards with every twist with supers.

You might consider an adjustable gas block even with the smaller port, it will allow for extremely fine tuning the cycling. But I’ve probably already exceeded your budget, it will be close.

Trigger, barrel and BCG are where I spend the most money and I think it pays the most dividends on target.

Hope that helps some.
300 Blackout, not just for sub-sonics.

Austin26
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Re: 16” barrel discussion

Post by Austin26 » Thu Dec 12, 2019 12:49 pm

Wow, thank you so much for all of this information. Over the coming day or two I'll be trying to learn more about some of the terms you used and their impact on what I'm going for so as not to waste your time by asking a dozen questions I might be able to look up.

Do you happen to have links or sources for me to learn about: adjustable gas blocks and why cycling matters for accuracy, how to choose what kind of ammo for what I'm going for, and types of rifling and pros and cons? I've already tried learning about each of those (except the cycling) before and hadn't gotten a good grasp of the topics so maybe you can direct me to a good source.

I didn't expect such a detailed and immediate response, thank you! And yes, even a 2 MOA @ 100m I'd be content with though it would be nice to less.

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Re: 16” barrel discussion

Post by bearcatrp » Fri Dec 13, 2019 8:51 pm

Since your building and want long range, may want to consider a 300 HAM'R barrel.
https://shopwilsoncombat.com/300-HAMR/products/1072/

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rebel
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Re: 16” barrel discussion

Post by rebel » Fri Dec 13, 2019 9:51 pm

Austin26 wrote:
Thu Dec 12, 2019 12:49 pm
Wow, thank you so much for all of this information. Over the coming day or two I'll be trying to learn more about some of the terms you used and their impact on what I'm going for so as not to waste your time by asking a dozen questions I might be able to look up.

Do you happen to have links or sources for me to learn about: adjustable gas blocks and why cycling matters for accuracy, how to choose what kind of ammo for what I'm going for, and types of rifling and pros and cons? I've already tried learning about each of those (except the cycling) before and hadn't gotten a good grasp of the topics so maybe you can direct me to a good source.

I didn't expect such a detailed and immediate response, thank you! And yes, even a 2 MOA @ 100m I'd be content with though it would be nice to less.
I think you'll be surprised at the cartridges level of precision. If built as dellet suggests, good barrel, good bolt, gas port optimized I would think with way better than mil-spec trigger you would be pleased. Suggestions of other cartridges have already been made and possibly made again, however when loaded to the constrictions of magazine length - the advantages diminish. Any hand loader will tell you that a few more grains of powder gives some velocity advantage but not versatility. With that being said, I'd go with a 1/10 in case
you ever want to dabble in the sub realm, which is part of the rounds appeal. Many is the guy that said no subs and was buying a suppressor a year later :mrgreen:
You can't beat the mountain, pilgrim. Mountains got its own way.

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dellet
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Re: 16” barrel discussion

Post by dellet » Sat Dec 14, 2019 1:24 pm

Unless you reload, it appears you probably don’t, I would stay away from something like the 300 Ham’r until there is more available ammo.

This link will take you to a number of discussions about enhanced carriers, it might answer some other questions along the way. Pay attention to member DR. Phil he has links to different studies.

search.php?keywords=Enhanced+bolt+carrier
300 Blackout, not just for sub-sonics.

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Re: 16” barrel discussion

Post by popper » Sat Dec 14, 2019 7:19 pm

My carbine is 1:10 18" carbine gas NO carbine (collapsible) stock. 110vmax, 125sst, 150gd, 145 cast all work fine. Get MOA with plainbase cast @ 2100 fps, even better with jacketed. Maybe 1:12 twist, no slower for sure. Xcaliber can make what you need. Add an adjustable gas block, Areo Smod forend is good. My barrel was made by McGowen but they are owned by someone else now, old guy had heart problems. Lancer mags. Timney 4# trigger as I hunt with this rig. Yea, has a Nikon scope.

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