Novice AR builder has questions

[UserNameInUse]

I grabbed a PSA complete lower before the election and am slowly gathering parts. Of course, questions are coming up. I don't think I want or need to become an total expert on AR building and for some things am hoping to rely on the knowledge of others. Please bear with me.

This is going to be more of a target gun and I want to use a rifle length gas system. Those darn PSA emails keep coming and I bought a .223 Wylde 18" 1:7 A2 profile stainless barrel. I was planning on a higher quality 20" 1:8 heavy barrel, but for $99 shipped I figured I'd try this before spending around three times that.

I crudely measured the leade I get with Lake City 5.56 and got 0.075" so I have some confidence this barrel truly has a Wylde chamber. To my eye it looks well made.

Anyway, since the lower has a carbine buffer my first question is, do I just need to change the buffer spring, or are there other parts in the buffer that are specific to the carbine gas system?

Second, I'm shopping 15" full float handguards. What is the purpose for the top Picatinny rail running the full length of the handguard? It seems like 95% of handguards out there have them. I'm not a fan of excess rails and this gun will not have any sights on it. Is there a reason I want the rail?

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[bolus]

You dont need the full rail on the top unless you want to put accessories on it. The only thing would be to make sure you have enough rail for a scope mount. Sometimes I wont have enough room if I want a rear iron site and a scope or red-dot in front of it. Even more room is needed if you want a red dot plus a magnifier plus a back up iron sight plus a attachment point for a sling on the top rail.

I've not had any trouble running a carbine buffer tube, carbine spring and buffer on any rifle. You can fine tune with different spring strengths and different buffer weights. But I've found that the carbine stuff all seems to work for most setups. start with that and if there is a problem. then worry about changing.

 

[Cameron72]

An adjustable gas block is advisable.

 

[UserNameInUse]

Thanks, guys. Like I said no sights, no red-dot. This will have just a scope. I wasn't expecting that answer on the buffer. Glad I asked!

I already bought a fixed gas block so I guess that may be another trial and error thing. Live and learn.

 

[3MTA3]

Here is a similar setup. They were recommending an H2 or H3 buffer, but you need to shoot it to see first. I would expect an 18" barrel with a rifle length system would have a short dwell time and run the risk of being under gassed. Dwell time is based on the distance from the gas port to end of the barrel and when the rear of the bullet is in that part of the bore gas is able to power the system. Perhaps the gas port has a larger diameter to correct this?

Rifle length gas system with a carbine tube and buffer?

 

[bolus]

Thanks, guys. Like I said no sights, no red-dot. This will have just a scope. I wasn't expecting that answer on the buffer. Glad I asked!

I already bought a fixed gas block so I guess that may be another trial and error thing. Live and learn.

If it runs it runs. if it doesnt then fix it. My bump saw has 18" barrel, fixed gas block, carbine tube and spring, H2 buffer and runs fine. I dont have any rifles with adjustable gas blocks but I see the appeal when you get into real fine tuning.

Bump saw build?

 

[v0lcom13sn0w]

i had a rifle length gas system 18" SPR barrel have too small of gas port and wouldnt even cycle an empty buffer assembly. i had to drill it into spec and it has worked ever since.

 

[Cameron72]

If the gas port is too big the adjustable gas block will help save the build but do nearly nothing for a "just right" or too small port. It can only turn down the pressure to the bolt. A Manufacturer may change the port size over time depending on what ammunition is used as a standard.

 

[eldbillbo]

If the gas port is too big the adjustable gas block will help save the build but do nearly nothing for a "just right" or too small port. It can only turn down the pressure to the bolt. A Manufacturer may change the port size over time depending on what ammunition is used as a standard.

That rarely happens Gas ports are usually drilled to spec. Not saying its bad idea but it's kind of an unnecessary expense especially in a 20" barrel and you should be fine with the 18 if its using a mid length gas system which i am sure it is . They are good fine tuning to a specific load or running suppressed. It will only allow as much gas as the factory gas port will allow, it will only be able to limit it. Rarely do 18"-20" barrels suffer from over gassing. It's usually a carbine length gas system that has issues with over gassing and is usually resolved by an H-Buffer or FA style carrier but an adjustable gas block would be good if you are suffering from that problem.

Don't make the mistake of trying to fix a problem that does not exist. I have seen many times where someone hears about some new got to have a part only to put into a perfectly fine running rifle only to start having problems with it.

It's good for building light weight builds where you may run a reduced weight carrier. It may save you from having to buy an h buffer on a carbine by reducing gas. but it's not because of manufacturers changing port size over time.

If you fine tune to a specific kind of ammo then run another ammo that's not as hot you may experience short stroking. They are good to have if you have a specific reason to have it. I have
bought adjustable gas blocks only to end up selling then as I find them unnecessary.

 

[eldbillbo]

Anyway, since the lower has a carbine buffer my first question is, do I just need to change the buffer spring, or are there other parts in the buffer that are specific to the carbine gas system?

Is the carbine buffer and spring in a carbine buffer tube? if so yes you are fine. If not and you have a A2 buffer tube you will need to get a A2 buffer and spring.

Second, I'm shopping 15" full float handguards. What is the purpose for the top Picatinny rail running the full length of the handguard? It seems like 95% of handguards out there have them. I'm not a fan of excess rails and this gun will not have any sights on it. Is there a reason I want the rail?

nope rails are just for sticking a bunch of junk on your rifle that you will probably never use. The only good purpose for one is if you want to have back up flip up sights it gives you a way to mount them which I have found to be most useful purpose for them.

 

[UserNameInUse]

Stuck in the house yesterday I decided to assemble the parts I have so far. My plans changed to using a Boyd's wood stock so the carbine buffer is going to go. Waiting on a PSA nickel boron BCG, charging handle, and the Boyd's stuff. This is really fun.

Here is my question. I want to attach a sling swivel stud to the handguard for bipod attachment. The handguard is two pieces, split vertically. I am thinking of running a screw through them with a countersunk nut similar to what you have on a revolver grip to hold them together. Then a wide flat metal piece inside, threaded for the stud. If I can come up with a jig I might use a biscuit joiner to cut a square surface in the handguard for it.

Am I making this too complicated? Other ideas would be appreciated. I do want a stud rather than a rail mount so there are no extra adapters involved.

 

[HB of CJ]

You would be much happier with a full length RIFLE butt stock and buffer group running a USGI spec rifle buffer and buffer spring? Dunno. Is your gas block steel or aluminum? How is it attached? Taper Pins or set or pinch screws?

If your gas block is easily end user removable, then run the rifle and see how it gases. If need be, if under gassed, easy to gently increase the gas port diameter. I for one am not familiar with successful adjustable AR15 gas blocks.

Edit by HB: .... Oh ... you are going to use beautiful wood. Good! Also a rifle length wood butt stock? Thank you. You might be happier. If you have any specific questions regarding PROPER barrel torquing ... just ask. Glad to help.

Respectfully. Hundreds of builds. Uncounted rebuilds.

 

[DirectDrive]

If your Boyd's handguard is not free-floating, you are making a mistake mounting a bipod on it (for a precision rig).
Last time I used a Harris bipod it only required a sling swivel stud present to mount it.

 

[UserNameInUse]

Yes, rifle butt stock and handguard. Gas block is steel and clamp on. I HATE driving set screws into nicely finished metal. Barrel nut is torqued. I used white grease, torqued to 30 ft-lbs + a little more to line up the nut. Regardless of people's preferences, I'm sure it will be just fine.

DD, it is not my intention to build a "precision" rig. I don't really have a need for one. This is all about fun.

 

[DirectDrive]

Yes, rifle butt stock and handguard. Gas block is steel and clamp on. I HATE driving set screws into nicely finished metal. Barrel nut is torqued. I used white grease, torqued to 30 ft-lbs + a little more to line up the nut. Regardless of people's preferences, I'm sure it will be just fine.

DD, it is not my intention to build a "precision" rig. I don't really have a need for one. This is all about fun.

As long as it works for you.
Just wanted you to know about bipod pressure on the barrel.
It's a common oversight.

I would break it in with full power, USGI ammo such as Lake City XM193 or M855.
Get it running with that.
Then if you want to experiment with weaker .223 or import stuff you will have a baseline already established.

It's cool to light up a new build and it just runs.

 

[Boboclown]

A bipod mounted on a non-free float isn't inherently bad if its zeroed on the bipod and constant pressure is applied each time.

But other than that its fun to use one. If you know what you're doing one can compensate for the drift from zero when using a bipod.

 

[DirectDrive]

A bipod mounted on a non-free float isn't inherently bad if its zeroed on the bipod and constant pressure is applied each time.

But other than that its fun to use one. If you know what you're doing one can compensate for the drift from zero when using a bipod.

It would be OK for a fun gun but not for a serious precision rig.
You would want to have a free float handguard for that.

And free float is so easy to do on the AR platform.

 

[Boboclown]

Of course, for a serious precision build you're going to try and go all out to squeeze every ounce of precision you can get.

Just saying that with a non-free floating handguard a bipod could still be used and compensated for (just gotta know how much of a drift it causes and go from there). For a fun gun, or even a "duty" gun.

 

[UserNameInUse]

... And free float is so easy to do on the AR platform.

Not in wood.

 

[DirectDrive]

Not in wood.

Wood is a sin on an AR.