How fast out of a 20" 308?

[Rotortuner]

OK so i have a 308 that i started load development on. components:

new lapua brass that i resized and trimmed
175gr SMK
Varget
210M primer

I made 7 rounds of each group going up in half grain increments from 41-44.5gr.

Out of the 20" It started out around 2450FPS with the 41 grains and then at the 44.5gr ave was 2616 FPS.

I didnt really start to get any pressure signs. Now my question. I had some good groups with the 42 and 42.5gr loads but i was only pushing about 2485 FPS with those. then the groups opened up and then seam to tighten back up ar the 44.5gr load. Should i explore the 42gr area or should i continue to push it up and see if i can get a load worked out at the 2650FPS and 45gr area? That seams a little how to me out of a 20" gun and laupa brass. Ideas?

CJG

 

[Guest]

Re: How fast out of a 20" 308?

You might try 4198 in that short barrel. We have had excellent results in 16" and 18" AR platforms with it using 155 and 168 SMKs. Varget is the "go to" powder for the 308 but in our experience does best velocity with 24" or longer barrels.

 

[Sig685]

Re: How fast out of a 20" 308?

What are you trying to accomplish with the rifle and load?

Target. Matches. Hunting. Tactical. SD. Anti-zombie brigade?

I sure hope you don't answer "LR competition."

 

[Rotortuner]

Re: How fast out of a 20" 308?

I use it for target shooting. The spot we usually shoot at has targets that begin at 450yds and extend out to 1100. If i could drill steal at 800 I would be pretty stoked. So im thinking if i push the load up a little to 45gr (prbably around 2650fps) or mabe a hair over that and i come into another accuracy node, that might work out for me. I want to stick with the varget because i have about 50lbs of it and need to start using it.

I guess i just wanted to get some opinions on these powder charges in the lapua brass and these velocities out of a 20".

CJG

 

[Rob01]

Re: How fast out of a 20" 308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ekbgr</div><div class="ubbcode-body">Varget is the "go to" powder for the 308 but in our experience does best velocity with 24" or longer barrels.</div></div>

I wouldn't agree with that. I use Varget in my 20" .308 and get about 2690fps with the 178 AMAX. At 22" I was getting about 2710fps. That's with 45grns in BH(win) brass. Get the same with 44.2grn in Lapua brass.

To OP, I would say stick with the 44.5grn load if it is accurate as I would rather have the velocity and accuracy. If no pressure signs I would say go up .2grn to 44.7 and 44.9 and see what happens. 45grns is the listed max with the 175 and Varget.

 

[ReaperDriver]

Re: How fast out of a 20" 308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sig685</div><div class="ubbcode-body">What are you trying to accomplish with the rifle and load?

Target. Matches. Hunting. Tactical. SD. Anti-zombie brigade?

<span style="font-weight: bold">I sure hope you don't answer "LR competition." </span></div></div>

Why do you say that?

 

[Wil]

Re: How fast out of a 20" 308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sig685</div><div class="ubbcode-body">What are you trying to accomplish with the rifle and load?

Target. Matches. Hunting. Tactical. SD. Anti-zombie brigade?

I sure hope you don't answer "LR competition." </div></div>


That's funny... my 20" LTR did quite well in LR competition.. as did the PSS I cut down to 20"...

It's all in the load development. I was shooting 155gr Scenars at 2850 with no pressure, and at remington mag length...

I'm not sure where you're coming from with your comment, but the 20" will hang quite well...

 

[Sig685]

Re: How fast out of a 20" 308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rotortuner</div><div class="ubbcode-body">I use it for target shooting. The spot we usually shoot at has targets that begin at 450yds and extend out to 1100. If i could drill steal at 800 I would be pretty stoked. So im thinking if i push the load up a little to 45gr (prbably around 2650fps) or mabe a hair over that and i come into another accuracy node, that might work out for me. I want to stick with the varget because i have about 50lbs of it and need to start using it.

I guess i just wanted to get some opinions on these powder charges in the lapua brass and these velocities out of a 20".

CJG </div></div>

You're probably going to get between 2550-2650 tops with the 20 inch barrel. According to JBM you should be transonic at 1000 yards, with an MV of 2650. I use Varget and Lapua brass in my .308 also, but my barrel is somewhat longer. I would say that you will have a lot of fun drilling the steel at 800 yards, as long as you can read the wind. I don't even think you need to push it to 45gr, but if you want you can do that, at the expense of shorter brass life. For up to 800 yards, an MV of 2550-2600 will be excellent and if you find an accuracy node in that area, so much the better; accuracy will be more important here than velocity. At around 2600 you have more flexibility to find the accuracy.

 

[Rotortuner]

Re: How fast out of a 20" 308?

Thanks for the info. Ya the problem with just running 44.5 is that my gun doesnt really like that. it like 42-42.5 but then im only pushing 2475-2500 fps. So i suppose that load would work for shorter range as a reduced power load, otherwise i think the next accurqacy node is going to be around 45-46gr and 2625-2650fps which I think is going to start to punish my brass a little.

CJG

 

[okiefired]

Re: How fast out of a 20" 308?

My experience...45 g varget, fed GMM brass, 78 degrees,br 2's, 178 amax's, 2.810 OAL = 2606 fps out of a factory LTR. Went to 45.6 with only slightly flattened primers but the 45 was the best accuracy.

okie

 

[mattmcg]

Re: How fast out of a 20" 308?

Personally I always like to find my maximum (where I start to see signs of pressure) and then work my way down to find the accurate load. This way I have the flattest trajectory with an accurate load.

Since I have Quickload up and running from a previous post, let me see what their model predicts for you given the specs you posted.

Specs:
Sierra 175 MK HPBT
Varget
308 Win
OAL 2.800"
20" barrel length

Given that, here are the pressure profiles and velocity predictions (MAP pressure max 60191):
Grain wt - pressure - fps
44.5gr - 60202 - 2589fps
44.0gr - 58119 - 2562fps
43.0gr - 54117 - 2506fps

So looks like 44.5 might be toward the top of your load limit. That is also a compressed load (104.4% full) from the model. You can see if you can drive it to 45.0gr but be sure to look for signs of pressure as you are working up. From there find your max and drop down in 0.2gr increments until you find your magic load.

Hope that helps. Standard disclaimers apply. Be safe and work up before working down.

 

[LA_Lawman]

Re: How fast out of a 20" 308?

Im running 45.0gr varget in winchester brass (18" barrel). Hodgdon lists it as a compressed load. I have had very good accuracy with mine. .368in @100yds is my best from the bipod.

I did bracket a load and had very good results with 44.7gr Varget.

this load is spec'd by hodgdon at 2690fps. Which seems to be close to the BH load.

 

[Asm1]

Re: How fast out of a 20" 308?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wil</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sig685</div><div class="ubbcode-body">What are you trying to accomplish with the rifle and load?

Target. Matches. Hunting. Tactical. SD. Anti-zombie brigade?

I sure hope you don't answer "LR competition." </div></div>


That's funny... my 20" LTR did quite well in LR competition.. as did the PSS I cut down to 20"...

It's all in the load development. I was shooting 155gr Scenars at 2850 with no pressure, and at remington mag length...

I'm not sure where you're coming from with your comment, but the 20" will hang quite well...
</div></div>

One spot shooting(FT/R) vs field /tactical use is two diffrent things,I would dout he ever leaves his matt and has a rifle for such( heavy long) and would most likley be better side by side vs our short sticks unless you pack to get to an A.O. or field/tactical macth then the coin is on the other side. we all tend to see it from our side and there are diffrent sides and needs to each his own..

 

[ReaperDriver]

Re: How fast out of a 20" 308?

To the OP - I'm seeing the exact same thing using 175SMKs and RL-15 powder. I found one accuracy node at about 42.8 grns of RL-15 but they are really slow out of my 20" at about 2495-2510. The accuracy seems to fall apart at about 43.4 but I'm going to continue to try to go hotter to see if I can get into the 2600fps range with that powder and bullet.

The light loaded bullet held verticle fine out to 400 and 550 yds (shot yesterday) but even with 5-7 mph of wind - they were moving sideways a LOT compared to the much hotter 168AMAXs I was shooting side by side with them. So I think (hope) there will be another accuracy node in that 2600-2650 with my 175 SMKs.