Next AR: .300 BO or 7.62x39?

[awp101]

Working through some thoughts and ideas for the next AR build. No special purpose for this one, just a fun time shooter. If I use a lower and other parts I have on hand, I can go either .300 BO or 7.62x39. Taking the similarity in ballistics off the table this is what I've come up with:

7.62x39
Pros
I've got over 1K of mixed surplus and Wolf on hand and only an SKS to feed.
Can (usually) be fed cheaper than the BO

Cons
Requires new bolt and mags
Reports of bolt failures seem to show up regularly in searches
Feed can be sketchy until you find the "right" mags
.310-.311 bullet choices are more limited compared to .308

I'd have no problem running it as a 10.5" pistol or a 16" carbine. If I go 10.5" I'd be curious how well it suppresses. If HPA/SHUSH ever get passed I'd like to build at least 1 .30 cal can just because.

.300 BO
Pros
Uses the same bolt and mags I already have
Lower initial cost
Easily suppressed if I ever get into that game
.308 bore so more bullet choices

Cons
More expensive to feed
Geared more for subsonic and suppressed shooting which I may not get into

If I go for the BO, it would be a 10.5" pistol that might get turned into a poor mans SBR. I just don't know if there's any advantage if most of my shooting will be with supersonic loads (like 90% or more).

Thoughts? Other than I'm neurotic and OCD?

[Encore64]

The biggest con is the AR was designed to feed straight cases. The heavily tapered 7.62x39 tends to damage the bolt over time. Approach that with caution...

[mobjack]

I vote 300 Blackout too. The feeding issues with the 7.62X39, along with weaker lugs, and more bolt thrust, rule it out for me. I am a big Blackout fan, with three ARs and a bolt gun in that caliber. Blackout can be cheap to load using scrounged 5.56 brass. 308 bullets are more readily available, along with costing less than the 310 ones. These are "the good ole days" you can build an AR for little of nothing now a days. If you want, build both calibers.

 Palmetto State Armory has what you need!!

Mobjack

[awp101]

Jul 20, 2017 14:25:33 GMT -5 Encore64 said:

The biggest con is the AR was designed to feed straight cases. The heavily tapered 7.62x39 tends to damage the bolt over time. Approach that with caution...

I hadn't heard the bolt damage was related to the tapered case. I've seen all kinds of theories about poor heat treat, the enlarged face, wrong steel chosen, etc but not case taper. Interesting and it would explain why it happens across most of the manufacturers instead of just 1 or 2 or why it doesn't happen in batches as would be the case for a bad heat treat.

Two more cons x39 I didn't think about in the original post are possibly needing a heavier hammer spring for surplus ammo and modifying the firing pin (or replacing it with an "enhanced" model).

Jul 20, 2017 16:25:03 GMT -5 mobjack said:

These are "the good ole days" you can build an AR for little of nothing now a days.

Amen! I moved some stuff last summer to pick up common parts I thought I might need in case the election turned out bad. I got in before the pre-election frenzy hit it's peak and resisted most of the Black Friday AR sales so I'm trying to reap the benefits now. Unless I can find a compelling argument against the .300, I will most likely order what I need for that upper this weekend. It won't be whiz-bang top shelf tactical but rather it'll serve as a working man's gun just fine.

I was too young and/or too broke to buy any pre-bans before they became pre-bans. I don't intend to let this "golden age" pass by so easily.

[dougader]

If I ever get it going, my next will be the 300 BO. You can take deer with it in supersonic form, and it's just plain fun in subsonic / suppressed mode.

[cas]

7,62x39... what you may very well find is you can't make that Wolf ammo fire. Not without extra strength hammer springs. Had that issue with mine and saw it many times when I worked at the range.

7.62x39 has the deck stacked against it in the AR. It was the first caliber AR I owned, and it would be the last one I'd ever choose again.

[sportster]

Get the 300 blackout. You can load it up to near 30-30 levels with lighter bullets and it functions fine even out of a longer barrel. I'm a fan of them as I own two right now. One 11 inch barrel and a 16 inch barrel.

[Encore64]

I don't mean to belittle the 7.62x39 cartridge.

I have both a CZ 527 Carbine and a Ruger #1 chambered in it. Its a fine round in a good rifle.

But, it was designed to feed at an angle in an auto. The AR was designed to feed straight into the chamber. It binds the bolt as it feeds.

Many tells of bolt problems, but the issue is with the cartridge, not the bolt.

[CraigC]

.300BO all the way. Thinking seriously about doing a braced pistol. My TiRant .45 should be out of NFA jail any day now.

[magnumwheelman]

I'm not voting, as I'm not really an AR guy... but a lot of good points have been brought up... if you were asking about another rifle... I'm all over the 7.62 X 39, & have both bolt action & semi auto rifles in that caliber... ( even have a $89.00 SKS, that I turned into a tack driver, just because... it's easily capable of MOA groups out of cheap steel cased spam can ammo... but it's not an AR, ... love my CZ carbine in 7.62 also... but again, it's not an AR... guessing since the 300 was designed around the AR. it would be a better round for that rifle

[awp101]

OK, thanks for the input and votes. I ordered a barrel yesterday. Which one? I'll let Klaus makes the announcement...



10.5" barrel and the plan is to buy/build a ~6" extension that will serve as a permanently attached muzzle device. If/when HPA/SHUSH is passed it will become the body of a can. This way I don't have to SBR it and if the law is changed I don't have a 16" barrel with another 6"+ of suppressor hanging off the end.