how fast is to fast?

[normandinpatriot]

Anybody know what the max velocity should be from an 18" 1:10 barrel in an AR/LR 10? before being "over pressured"?? 167gn bullets? 175gn??

[normandinpatriot]

Not gonna lie...

With experience on this forum, I am very surprised t not have a SINGLE response....

I asked this question seriously... How fast is to fast... I was surprised by the chrono readings i got.... 2601 average for the 167gn Lapua 308, and for LC M118LR 2625fps average....

Your input is greatly apreciated!

[00tec]

Those numbers are close to what it should be. My only 308 is a much longer barrel, so I couldn't compare.

Do you gave any signs of overpressure on the case?
My hand loads for my 223 flatten primers pretty good, but I like it hot (26" barrel, 40gr, 3715fps)

[bradbn4]

My thoughts is to look up the loading data for that bullet / barrel combo. What style bullet?

> 175 smk

Most of the load data that I found indicate that is getting close to max pressure depending on the powder used.

That reminds me, I have a 'fresh' 308 barrel for my encore.

[<MADDOG>]

I will add my load for that barrel length and 175 SMK is 2534 FPS at 5660'.

I load for accuracy, so I am sure I pushed it faster, but I did not keep the data points. Off the cuff, I would think 2650 (+/-) would be a near the top of achievable FPS with an 18" AR and 175's. My $0.02.

[Delfuego]

Not gonna lie...

With experience on this forum, I am very surprised t not have a SINGLE response....

You need to tell us. Every rifle, barrel, bullet and powder is different. We cannot tell you when you hit "pressure", let alone max pressure. If you are serious, you need to know what pressure and "over pressure" look like. There are plenty of signs to alert or warn you, heed them all. My load could blow your face off and vice-versa. If you want speed get a longer barrel. You (and everyone) should go for consistency rather than speed.

[ray1970]

Ten times the caliber (in mm) times the barrel length is your standard formula.

So for your rifle...

7.62 x 10= 76.2

76.2 x 18= 1,371.6 FPS


There you go. Anything over that and the rifle may explode killing everyone in a forty foot radius.

[normandinpatriot]

Those numbers are close to what it should be. My only 308 is a much longer barrel, so I couldn't compare.

Do you gave any signs of overpressure on the case?
My hand loads for my 223 flatten primers pretty good, but I like it hot (26" barrel, 40gr, 3715fps)

Thanks for responding!

Yes, i have flattened primers on the the Lapua ammo and a mild ejector mark that i understand to be common for the AR/LR 308 platform. The Lake City M118 LR has cratered primers, some popped and cratered primers and similar ejector marks as to the Lapua. The Lapua specs a 2600 fps rating and the M118LR specs 2559? 2595? I cant remember... I was surprised to see both ammo with readings so fast as most velocity testing seems to be done in barrels longer than 18", usually it seems 24 or 26" barrels are used.
As for my rifle... CMT matched billet upper and lower, JP High Pressure bolt, Lantac bolt carrier, Heavy Buffers 5.5oz. Buffer and matching spring, Odin Works ADJ gas block,Ballistic Advantage 18" 1:10 barrel...

Delfeugo, I am not looking for velocity as a target to hit, I am looking for what seems reasonably safe, I understand what you said. With factory loaded ammo, "overpressure" signs should not appear with out cause... I am trying to gain knowledge to eliminate looking in the wrong direction. I have shot Both Hornady and Sig ammo both also rated at 2600fps with absolutely ZERO signs of overpressure. I did not have a chrono at the time so I do not know what velocity actually was...

Bradbn4... I have the latest Hornady loading book. It shows a lower velocity for their 175gn projectile but makes no mention of barrel length.

[bradbn4]

the reloading info I looked at was for 24" barrel using generic 175 - 180 weight bullets - no reference on the shape of the bullet. That was online stuff - most of my reloading books are a bit dated. I have never setup for 308 reloading - got the equipment - but I never found a place I wanted to shoot at for distance.

[SideShow Bob]

Ten times the caliber (in mm) times the barrel length is your standard formula.

So for your rifle...

7.62 x 10= 76.2

76.2 x 18= 1,371.6 FPS


There you go. Anything over that and the rifle may explode killing everyone in a forty foot radius.

You can?t mix metric & SAE. So that would be 1,371 MPS. The conversion factor is M X 3.281 = Feet. So, 1,371 x 3.281 = 4498.031 FPS.
At about the second shot, your barrel is spitting out molten Copper & lead.......

Hopefully you aren’t shooting tracers.......