Jump to content
308AR.com Community
  • Visit Aero Precision
  • Visit Brownells
  • Visit EuroOptic
  • Visit Site
  • Visit Beachin Tactical
  • Visit Rainier Arms
  • Visit Ballistic Advantage
  • Visit Palmetto State Armory
  • Visit Cabelas
  • Visit Sportsmans Guide

First 308 Build


Recommended Posts

Just joined.  I have a couple AR-15's that I built and I have been wanting to build a 308 for a while.  I pulled the trigger and ordered a matched upper and Lower set from SI-Defense.  I looked at a bunch of different brands and settled on the SI-Defense.  I knew that the 308 was a whole different beast than building the 5.56.  So Im here in hopes to get some opinions and suggestions on parts.  Hopefully some reviews on your experiences as well.  


My goals... build a long range rifle but still pick it up and shoot it.  But mainly long range.  


I was able to get alot done this last weekend at the show in Reno.  

Heres what I got so far....


SI-Defense upper- used DPMS parts to complete it (door, spring, etc) DPMS charging handle with Badger tac handle.

SI-Defense Lower-  DPMS LPK ( standard trigger). OD Green Ergo grip

Magpul PRS butt stock (OD Green)....DPMS buffer, tube, and spring.


Parts to order still....

Complete bolt assem.  ( was gonna go with the SI-D nickel boron one)  Thoughts??

2 stage trigger or not??.... Im lost!  So many to choose from.  I got standard triggers on the AR-15's.

Barrel---- going with 20".... from what Ive read, thats perfect for what my goals are.  

I like this one and its in stock... Id get the grey bead blasted finish not the shinny.  Also threaded end.




Full length gas tube and Low pro gas block and  full float handguard/rail.  I really dont want a quad rail.  Only putting a bi pod, Magpul AFG on it.  No need for the bling


Glass--- Vortex PST 6 x 24 Milrad ffp.  


Trying to place the order for the BCG,  and barrel this week.  Pretty sure thats most of it for now.  Any input, opinions, or suggestions are appreciated.  Thanks in advance! 




Edited by medic83
Link to comment
Share on other sites

  • Replies 85
  • Created
  • Last Reply

Top Posters In This Topic

Welcome to the forum!


Fulton carries fantastic barrels, but if it were me I'd wait for a 1-10 twist. A little better for the heavy bullets. BTW, their 18.5" will be good for long range shooting, I'm not quite sure what your goals are.


The SI-d bolt assembly will be fine.


Two stage trigger? Fuck yes! I really like Geisselle. For what you are talking about building, SSA or SSA-E.

Link to comment
Share on other sites

18.5 huh??  Ive read so much poop about barrels.... Some people say that an 18 is gonna be the best... then others say different.  I felt that the 20" is the happy medium.  I want this to be a 1000 yard rifle/ multi purpose.  I was looking at a RRA 20" that was chrome lined, 1:10 twist.   It was a much lighter barrel tho.  I know with the 1:10 Ill have more precision ammo options.  Are you mainly saying go shorter or try to find a 20"barrel with 1:10 twist? SI-D bolt carrier... have you heard anything about them?  I like things to match... I figured that SI-D upper and lower with SI-D BCG would be the best match.  I could be wrong tho..THx

Edited by medic83
Link to comment
Share on other sites

I would say if you can shoot 1000yds, an 18" will do it. A 20" may be a bit better, but not so much if you can do your part. A lot goes into shooting that far, and if you can do it, the 18" will do it for you. I'm will not tell you stay shorter. It would be easier to lug around, but you need to be happy with it. My biggest thing for you is 1-10. After that, you need to figure out what you will want. I hope it helps.

Link to comment
Share on other sites

2 stage trigger or not??.... Im lost!  So many to choose from.  I got standard triggers on the AR-15's.

Barrel---- going with 20".... from what Ive read, thats perfect for what my goals are.  

I like this one and its in stock... Id get the grey bead blasted finish not the shinny.  Also threaded end.




Yes, 2-stage trigger.  Don't know what your goals are, but sounds like longer distance, precision.  A standard trigger sucks for that.  That arena is where a good, light, 2-stage shines.


The Fulton 18.5" stainless, medium weight barrel with a 1:10 twist will do a metric poop-ton better at longer distances than the barrel you listed/linked.  You need heavy bullets to go distance.  Heavy bullets are long.  You need a fast twist to stabilize a longer bullet (the projectile).


The 18.5" sounds like it will better suit your needs, if I have your needs correct.  Don't get all wrapped around the axle about barrel length.

Link to comment
Share on other sites

Just called SI-D today. Ordered the Nickel boron BCG. Ordered it unassembled so it will ship out today! Gonna order the barrel as soon as I figure out wtf to get. I guess I am stuck on the length. I want 1:10 but I can't find one in a 20". I want to reach out to a 1000 yards. I guess that's why I was stuck on the 20".

Link to comment
Share on other sites

You're all jacked up over this barrel-length thing, ain't ya? 


Calculate your velocity loss for the 1.5" of barrel you'd be giving up, with the 18.5" instead of the 20". 


You'll be shocked - it's not much.


Now, figure out what max weighted projectile a 1:12 twist will stabilize, and do the same for a 1:10.  You need HEAVY projectiles to get accurate at 1k yards, man.


Get over the barrel-length thing you've got going on...

Link to comment
Share on other sites

^^^^ This is what I've been trying to say guy. You are seriously only going to loose 150fps. That's it. You as a shooter will make more of a difference

98 and Edge are right. The 18.5" vs 20" is less than a 100 fps difference. From 18" to 20" you really only gain 50-60 fps per barrel inch. So your debate is over a measly 75-90 fps?!? After 20" the gain in speed drops to about 40fps per barrel inch and after 22" the gain in speed drops to about 30fps per barrel inch.

If you shot a Sierra Match HPBT 168gr out of a 20" barrel, you'd likely achieve a muzzel velocity of approximately 2,650-2700 fps. That same bullet in a 18.5" barrel will travel about 2,575-2,625 fps. This is especially true with the 1:10 twist stainless steel barrels. The high pressure barrels really secure muzzle velocity.

You want accuracy? Remember the analogy of breaking a bunch of sticks vs breaking one stick? In that same thought, think of breaking a stick in half, then breaking it in half again, and again, and again. Everytime you break the stick it gets harder and harder to do. Barrel harmonics are the same. If you have two barrels of matching thickness, contour and design, yet one is longer than the other... The shorter barrel will be more rigid when shot. The longer barrel will slightly vibrate more, causing a difference in the barrel harmonics. The purpose of a bull barrel is to make longer barrels more rigid. An 18.5" barrel is inherently more accurate than a 20" barrel of matching statistics. For a 20" barrel to surpass the 18.5" barrel in accuracy, it must be considerably thicker and heavier. Faster bullets don't necessarily mean more accurate.

Edited by Robocop1051
Link to comment
Share on other sites

Shooting out to 1000 yards and being accurate out to 1000 yards are 2 completely different things. If you're looking to build a tack driver then most off the shelf barrels won't work as they aren't designed to shoot accurately past 500-700 yards. 90% of all AR's (AR-10 & AR-15) shoot 1.5-2.0 minutes which is no where near accurate enough for 1000yards. When you're trying to make consistant hits out to 1000 yards you really want put a lot of thought and emphasis on the barrel and BCG and your goal for 100 yards should be a .5 minute. As for barrel length, 18" or 20" really comes down to the build of the barrel. Give me a 21" Noveske or 20" GAP, SACS, or Larue barrel and they'll outshoot just about any off the shelf 18" barrel out there. Now, 3 out the 4 companies I just listed aren't offering 7.62 barrels anymore for resale and most custom barrel builders have extended wait periods, and a premium price usually north of $500. On that note, an 18" barrel is naturally more rigid and "should be" more accurate.


Couple of bullet points

2 stage trigger (an absolute must in long distance accurate shooting)

free floated rail/handguard (Mega's MKM upper is similar in design to Larue's OBR as the rail never comes in contact with the barrel nut)

Muzzle brakes are not necessary but reduce felt recoil and provide easier follow up shots

20MOA scope mount/rings/base


And unless you're familiar with shooting long range you might want to start reading on it because you'll have to calculate




Barometric pressure

Spin drift

Wind input



Coriolis Effect

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...