308 win short barrel silencer selection

[600]

I'm building a 308 rifle and needs some help to build this.

Here are some background data...

Maximum range unsuppressed: 600 yards
Maximum range suppressed: 328 yards

Barrel length: 16" or 20"
Barrel twist: 1/12 or 1/10

Silencer type: QD as I want to use it suppressed and unsuppressed without carrying around a thread protector/brake.

Ammo unsuppressed: 150gr up to 175gr
Ammo suppressed: 200gr (the only thing I have access to) (want this to go subsonic if possible)

So with these data, what barrel is "THE BARREL" to go for in my situation?

[silencertalk]

You wouldn't want 1/10 or 1/12 twist for subsonic use.

Use 1/8 or faster twist.

AAC has a 1/8 twist 18 inch barrel.

[600]

With 1:8 twist can I still shoot succesfully out to 600 yards without overstabilizing the lighter bullets such as 150gr?

I still need the rifle to shoot just as well without the silencer with 150gr stuff.

[600]

...and does the barrel length not matter at all?

[silencertalk]

With 1:8 twist can I still shoot succesfully out to 600 yards without overstabilizing the lighter bullets such as 150gr?

You cannot over-stabilize a bullet but there are many people who think that faster than needed twist can reduce precision (it can, in theory, especially with crappy bullets), which is why bench-rest shooters would not use a faster twist than needed.

On the other hand, there are other people who prefer fast twist for 150 grain bullets because it helps them expand. I am one of those people, but this effect is not commonly known.

So I would use 1/7 or 1/8 twist specifically for 150 grain bullets, and consider the fact that it works with subsonic as a bonus.

So yes, it is fine. Probably even fine for thin-walled 110 grain bullets, but they will blow up in 1/4 twist.

[RJT]

Barrel length won't matter a bit. I run 2 .308s with 1:10 twist, one 18", the other 20". Both are equally accurate out to 600yds, and I think the dope charts are different by a couple clicks between the 2.

[ranb]

I've found that subsonic 180 grain RN is the heaviest for 1-12, 220 RN for 1-10. 1-8 is good for subsonic 240 boat tails.

Randy

[600]

Just as I thought the final decision was near th 1:8 twist pops up! Hmm....well it looks like the 1:12 is way too far for a "universal twist" that can do a little bit of everything.

According to my knowledge the shorter I want my barrel and the longer I want to shoot the heavier bullets I must use. So that puts a faster twist in favour right?

But too fast a twist can result in the theoretical over stabilization phenomenon, fragmentaing some bullets and increased barrel wear. Isn't this correct?

[ranb]

A 308 win 155 grain bullet at 2950 fps and a 1-10 twist is spinning 17700 rpm.
A 300 blk 125 grain bullet at 2200 fps with a 1-8 twist is spinning 16500 rpm. The only bullet fragmenting problem I've ever heard of other than sabot loads is 55 fmj 5.56 in the 1-7 twist barrels.

If you are shooting only subsonic, use a 1-8, if sub and super, use 1-10 and limit yourself to the 220 grain RN. They are nearly as nice as the 240 grain hpbt in the 1-8 twist. You should be just fine with 1-8 twist and supersonic ammo also.

Randy

[600]

Hmmm the 1:10 might be the way to go. As I discovered the 308 is not that ideal to go subsonic.

[RJT]

The .308 is beyond ideal for sub-sonic use. The only thing that makes 300AAC BO better, is the ability to run it ultra reliably in SBR'd AR platforms.

[600]

A 308 win 155 grain bullet at 2950 fps and a 1-10 twist is spinning 17700 rpm.
A 300 blk 125 grain bullet at 2200 fps with a 1-8 twist is spinning 16500 rpm. The only bullet fragmenting problem I've ever heard of other than sabot loads is 55 fmj 5.56 in the 1-7 twist barrels.

If you are shooting only subsonic, use a 1-8, if sub and super, use 1-10 and limit yourself to the 220 grain RN. They are nearly as nice as the 240 grain hpbt in the 1-8 twist. You should be just fine with 1-8 twist and supersonic ammo also.

Randy

Do I risk baffle strikes due to instability if firing 240gr in a 1:10? To me the 1:10 is pretty universal and is a "do it all" twist.

[T-Rex]

.308 is great suppressed.

in my 20", 1:10 bbl, I use 220RN for subs
I also use this rifle for supers, out to 600yds (longest I have access to)

in my 17", 1:8 bbl, I use 240hpbt for subs
I've only fired 150 spitzers through it at supersonic, they were fine (only to 100yds)

[600]

Thanks for the answer. The 1:10 looks good.

[eastern_hunter]

Have a 1:10 16.5" Remington M700 SPS. Has been restocked with an aluminum cradle and removable magazine). Is fitted with a 7.62 Specwar with a brake mount. Tend to run 175 gr OTMs supersonic (M118 or SMKs). Precision is excellent.

The Specwar is easy to mount and dismount and has a positive lock. Takes to noise right down to comfortable and reduces recoil very significantly!

[ranb]

Do I risk baffle strikes due to instability if firing 240gr in a 1:10? To me the 1:10 is pretty universal and is a "do it all" twist.

Supersonic no, subsonic yes.

Ranb

[600]

Thanks ranb!

By the way, I notice that many people have their barrel in od numbers like 16.25" and 16.5". Any reason behind this, are they some kind of sweetspot for barrel length vsvelocity or something?

[T-Rex]

Thanks ranb!

By the way, I notice that many people have their barrel in od numbers like 16.25" and 16.5". Any reason behind this, are they some kind of sweetspot for barrel length vsvelocity or something?

The federal law is anything under 16" is an NFA SBR.
We keep them 1/4"-1/2" longer to stay out of FFMITA prison.

[600]

Thanks ranb!

By the way, I notice that many people have their barrel in od numbers like 16.25" and 16.5". Any reason behind this, are they some kind of sweetspot for barrel length vsvelocity or something?

The federal law is anything under 16" is an NFA SBR.
We keep them 1/4"-1/2" longer to stay out of FFMITA prison.

Ok, makes sense