First semi-auto build, how is this spec?

[BikePilot]

Hi all, I'm putting together my first semi-auto. I'm hoping to build a 308 that is relatively light, handy, soft-shooting, and accurate within 1 MOA. It'll mostly be used inside 300yrds (I have an AX for reaching out further). How does this parts list look? Anything you'd change or that will not work together? Any major parts I've forgotten? I've done lots of reading/research, but would not be shocked if I missed something along the way. I hope to put it together in a few weeks. I'll likely be ordering a suppressor for it eventually, but it'll be unsuppressed for at least a year. I'm hoping I'll be able to screw the suppressor on, turn the gas down, and carry on without much hassle in a year or two.

Receiver set	Mega Maten Billet Ambi set
Trigger	Geissele SSA
Barrel	JP Supermatch 18" with Thermal Dissipator and headspaced bolt
Carrier	V Seven Titanium
Adjustable Gas Block	JP Low Profile 0.75"
Hand Guard	JP Gen III 15.5"
Stock	Magpul UBR
Grip	Magpul MIAD AR10
Buffer / Spring	JP SCS2-10 (3 pack spring weights, standard weight)
Lower Parts Kit	JSE "White Box"
Charging Handle	Mega Slide Lock

 

[MNhunter1]

Inside 300 and first semi-auto build, I would recommend a small frame AR15 platform in 6.8 or 6.5 if hunting, .223 Wylde if strictly for targets, coyotes, or smaller critters. You've got a nice build there with some premium parts no doubt, but it seems a bit overkill for what you briefly outlined (relatively light, handy, soft-shooting, and accurate within 1 MOA. It'll mostly be used inside 300yrds). An AR15 platform will be lighter, softer-shooting, likely easier to shoot more accurately, and plenty sufficient for inside 300y. It also doesn't come with all the proprietary headaches and lack of interchangeability you're going to see with the large frame platform.

Personally, I'd pick an ARPerformance 6.8 barrel to free float, SLR adjustable block, and your choice of trigger and built around around that.

 

[BikePilot]

Thanks! I definitely appreciate those aspects and it makes complete sense, but I really want a 308. And by light and soft shooting I mean by 308 standards. I don't expect it to feel like an AR15. I realize it'll be heavier and much more recoil than small frame cartridges.

 

[Trigger Monkey]

I'd get the Geissele SSA-E over the SSA and switch the V7 for a JP LMOS to keep as many things from the same company as possible.

 

[BikePilot]

I'd get the Geissele SSA-E over the SSA and switch the V7 for a JP LMOS to keep as many things from the same company as possible.

Thanks! The SSA-E is similar but with a lower pull weight right? I like the idea of the JP LMOS carrier and that was my first plan. It wasn’t in stock at the couple of dealers I called so I started thinking about the v Seven. I’ll work a bit harder to find a JP carrier.

 

[oniak]

How about just buying a complete JP rifle in the caliber of your choosing? Piecing together a large frame semi from individual parts is not as straight forward as piecing together a standard AR from what I hear. Not all large frame components are plug and play with other manufacturer's components.

As stated above, if you want the experiencing of building it yourself, I would stick with a standard AR platform (small frame).

 

[drewthebrave]

Nice list. I initially considered building a lightweight, large-frame AR in 6.5 Creedmoor, but then I realized that an AR15 in 6.5 Grendel covered my needs better in that regard - and for a lot less money. The Creedmoor build then moved to a slightly heavier, budget friendly direction.

However, before I shifted my focus, I had narrowed down on a Rubber City Armory Titanium BCG as an alternative to the JP LMOS. You might want to search for that as an alternative.

And I agree with Trigger Monkey: if you're going to spend Geissele money on a trigger, get the SSA-E. Otherwise, I'd rather get a LaRue MBT-2S that compares very well with the regular SSA for a lot less money.

 

[BikePilot]

Thanks I’ll check out that bcg option as well. Sounds like an ssa-e is the way to go. I’ve got an ssa laying around so I’ll probably start out with that and swap out if it’s not satisfactory.

 

[Mwalex]

I would lean toward a Full mass carrier for a Longer dwell time and reduced recoil compared to a low mass bolt.

 

[BikePilot]

I would lean toward a Full mass carrier for a Longer dwell time and reduced recoil compared to a low mass bolt.

Thanks! I was wondering about that vs having more weight moving around. If I turn the gas down until it's only just enough do you think it'll increase the dwell enough? I may just but both and experiment.

 

[MontanaMan]

Inside 300 and first semi-auto build, I would recommend a small frame AR15 platform in 6.8 or 6.5 if hunting, .223 Wylde if strictly for targets, coyotes, or smaller critters. You've got a nice build there with some premium parts no doubt, but it seems a bit overkill for what you briefly outlined (relatively light, handy, soft-shooting, and accurate within 1 MOA. It'll mostly be used inside 300yrds). An AR15 platform will be lighter, softer-shooting, likely easier to shoot more accurately, and plenty sufficient for inside 300y. It also doesn't come with all the proprietary headaches and lack of interchangeability you're going to see with the large frame platform.

Personally, I'd pick an ARPerformance 6.8 barrel to free float, SLR adjustable block, and your choice of trigger and built around around that.

I'll 2nd all that for sure & that's the very best advice in this thread.

But if you're bound & determined on the large frame then I'd suggest:
A Bartlien or Rock barrel from Craddock because they are much less finicky than any JP & it would be a 6.5 as there's just not much reason to choose a 308 over the 6.5 in today's world, even for a 300 yd gun, IMO and I'd make it 20" for numerous reasons.
A full weight BC from any of several good sources because it's fool proof & easy
SLR adjustable gas block because it simply the best & has easy access for adjustments & is easy to clean
SLR handguard (Ion Series) because it's way better in every respect than the JP; Geiselle is also better as an alternate
SSA-E trigger (or the SSA with a lighter trigger spring) because it's a no brainer for the same money
Geiseller Super Charging handle because it's simply the best available

MM

 

[GUNNER10]

Hi all, I'm putting together my first semi-auto. I'm hoping to build a 308 that is relatively light, handy, soft-shooting, and accurate within 1 MOA. It'll mostly be used inside 300yrds (I have an AX for reaching out further). How does this parts list look? Anything you'd change or that will not work together? Any major parts I've forgotten? I've done lots of reading/research, but would not be shocked if I missed something along the way. I hope to put it together in a few weeks. I'll likely be ordering a suppressor for it eventually, but it'll be unsuppressed for at least a year. I'm hoping I'll be able to screw the suppressor on, turn the gas down, and carry on without much hassle in a year or two.

Receiver set	Mega Maten Billet Ambi set
Trigger	Geissele SSA
Barrel	JP Supermatch 18" with Thermal Dissipator and headspaced bolt
Carrier	V Seven Titanium
Adjustable Gas Block	JP Low Profile 0.75"
Hand Guard	JP Gen III 15.5"
Stock	Magpul UBR
Grip	Magpul MIAD AR10
Buffer / Spring	JP SCS2-10 (3 pack spring weights, standard weight)
Lower Parts Kit	JSE "White Box"
Charging Handle	Mega Slide Lock

Looks like a heavy mix master built from quality parts that may or may not play well together.

What is you budget for this exercise in futility?

 

[Nimothy]

How about just buying a complete JP rifle in the caliber of your choosing? Piecing together a large frame semi from individual parts is not as straight forward as piecing together a standard AR from what I hear. Not all large frame components are plug and play with other manufacturer's components.

As stated above, if you want the experiencing of building it yourself, I would stick with a standard AR platform (small frame).

This is my thoughts exactly, if you aren’t well versed in gas gun starting with the large frame will make you pull your hair out and in the end be way more money than just buying one off the shelf. Buy once cry once.

 

[Black max]

You will also need a .936 gas block instead of the .750.

 

[BikePilot]

Looks like a heavy mix master built from quality parts that may or may not play well together.

What is you budget for this exercise in futility?

Thanks! Budget isn’t a constraint. I could buy a complete JP, but I like building and tinkering with things and want to have a go at it. I’m not likely to get good at building these if I never try! You mention heavy, where could I easily save weight? I don’t want to go any shorter on the barrel. I’m guessing this will work out to be between 8.5 and 9lbs.

 

[BikePilot]

You will also need a .936 gas block instead of the .750.

Thanks! JP’s website says .750 diameter at gas block. Am I missing something on this? https://www.jprifles.com/buy.php?item=JPSM308-18L11R7

 

[Mwalex]

Thanks! JP’s website says .750 diameter at gas block. Am I missing something on this? https://www.jprifles.com/buy.php?item=JPSM308-18L11R7

Nope.

 

[Tchitcherine]

What finish option are you looking at for the JP barrel? I suspect there can be implications on heat transfer to the dissipator, which could determine how effective it is vs. looking cool. Suggest you call JP and consult with them on this.

 

[BikePilot]

What finish option are you looking at for the JP barrel? I suspect there can be implications on heat transfer to the dissipator, which could determine how effective it is vs. looking cool. Suggest you call JP and consult with them on this.

Thanks, the plain stainless is what I was looking at. I figured I could even lap it to the heat sink, then use a little artic silver compound to maximize transfer.

 

[MontanaMan]

Other than just "looking cool" heat dissipators are just not needed unless you are doing lots of successive mag dumps.................just sayin'.

And you really don't want to be doing that with a SS barrel.....................but then again................................

YMMV, carry on.

MM

 

[Tchitcherine]

Thanks, the plain stainless is what I was looking at. I figured I could even lap it to the heat sink, then use a little artic silver compound to maximize transfer.

Take 5 minutes to call them, they can advise you on what thermal compound they actually use, and whether there is any point in lapping. They are experts, and I have found they are friendly & helpful.

 

[oniak]

Honestly, if you are only shooting inside of 300 yards a nice .223 or 5.56 build will be more than adequate. Everyone needs an AR in .223/5.56!

 

[BikePilot]

Thanks, yes I agree, this isn't my only semi, just the first one I'm building from parts. Not meant to be a substitute for for a 223 or other small frame caliber. I'll occasionally shoot much longer distances, that's just not the primary useage for this one as I like my AX too much for that! For this build I'm definitely doing a 18" 308. For background this isn't even close to my first semi auto and I've been shooting for over 30 years. I've just never built one before. I've shot enough to know what I want out of this specific one. The question is how best to get there.