Planning an AR15 build, worried about center of mass

[Hygienist]

Hey guys,

I'm building an AR15 which will serve no other purpose other than my vision of an "ultimate" AR15. I won't be using it for HD or anything serious since some of the stuff I'm putting in there is mostly untested, so no need to worry about reliability.

I'm mainly worried about it being front heavy.

On the front half, it'll have
16" Medium Contour Barrel (2lbs)
AAC Mini4 Suppressor + Blackout Flashhider (1.10lbs)

Handguard will either be a Noveske NSR (~0.85lbs) or a Carbon Fiber (0.45lbs).

On the back half, it'll be lighter than usual:
Vltor MUR (1oz+ over regular)
Polymer Lower (0.25lbs less than regular)
Lightened bolt carrier and buffer (0.25lbs less than regular)

This should add up to a back half that's about 0.44lbs lighter than usual.

Stock is an LMT SOPMOD.


Now, I've also been contemplating something else: moving to an AR10 Mega MATEN based build if it's too front heavy. I'd keep most everything the same (incl barrel contour) so the front half would be virtually the same weight. However, the heavier receivers would be about an extra 1.0lb total, and also more weight in the back half due to a larger BCG. Would this work if my AR15 build is too front heavy?

[DeltaSierra]

You are overthinking this...

First, going with a polymer lower is, well, not the best idea...

Second, instead of worrying about some "ultimate" AR, you would be much better off simply buying a stock Colt rifle....

[LTMattyL]

Let me be the first to ask, why a polymer lower?

Also, while I don't have a lot of experience, I have to wonder if the lightend bolt carrier and buffer are going to play nice with a suppressor.

Out of curisoity, what is it about a standard AR, like a Colt 6920, that you don't like and what makes this build the ultimate build for you?

As for your balance question, I think it is more of a question of the weight on the ends; using a heavier stock can probaby help balance out a heavy muzzle. ie a MOE or CTR probably wouldn't be the best choice.

[Hygienist]

To the first poster:

The polymer lower's a risk I admit, but I'm willing to take it. This isn't an HD gun or anything and is really just for the fun of it. I"d honestly like to see how a polymer lower works out.

As for just getting a Colt, I'm doing this simply for the fun of putting together what I see as the best parts, etc. and seeing how it works out. If I were to get a Colt it would mean I intend this particular rifle for serious use, which I'm really not intending.

To the second poster:

Polymer lower is a bit of a weight savings, that's it. Apparently New Frontier (the one I'm getting) has strengthened it in previous points of failure so it should be OK. I'm one of those people who likes to try new things for the hell of it, and especially since this isn't a serious build I'm eager to try it.

I'm not getting a Colt 6920 since I'm not sure why I'd want it. If I were to get a 6920 I wouldn't use it for HD and I'm not really much of those SHTF preparing people. That pretty much just leaves recreational use, and TBH I'd rather have this since part of the fun is seeing how my part selection plays out.

I'll be using an adjustable gas system with the lightened components so that should counter the lower mass.

I've considered adding a heavier stock... but whenever I think of that I always think of just upgrading to a MATEN AR10 which would add weight as well while having other benefits (though admittedly the added weight of a MATEN isn't on the ends like a stock which would've been preferable).

[MistWolf]

Ok, somebody has to say it-

SEARCH BUTTON

http://m4carbine.net/showthread.php?t=104848

[Jester67CA]

If you want to go full-nerd, you can calculate it for yourself.

Find a picture of an AR in your barrel length, set X=0 to the front of the magazine well (or anywhere else you please) and use this equation:



You'll need to know two things about each of the parts:
-It's mass
-It's center of mass

If you already have the part, an easy way to get a rough idea of the center of mass is to balance it on your finger. The point where it balances can be used to estimate the center of mass. Then add this value to whatever distance the part lies from the mag-well.

If you don't have the parts, just estimate.

Then you can plug each of the values into a long equation that looks a bit like this:

Xcm = (lower receiver mass)(lower receiver Cm) + (barrel mass)(barrel center of mass) etc. and then divide by the total weight of your gun.

Or you could, you know, just guess based on other people's images...


Here's a blog post that has lots of useful pictures:
http://vuurwapenblog.com/2009/11/25/...e-part-1-of-3/

And here's a calculator that will give you a rough idea. I'd start here. The part selection is limited, though:
http://vuurwapenblog.com/calc22.html

Some extra notes:
-The NSR itself weighs nothing. A big chunk of the weight comes from the barrel nut, which is nice and close to the center of mass.
-A suppressor will probably make your gun a bit front heavy. It tends to be par for the course.
-You can add weights to the stock in order to adjust the balance. A bit of extra weight in the butt stock is barely perceivable.

[Hygienist]

Thanks, I had seen that topic earlier but only skimmed through it since it didn't have mention of suppressors. I was admittedly in the mindset of only looking for topics addressing front heavy-ness caused by suppressors.

I guess if that dude towards the bottom with a med cont SS 16" was a bit front heavy without a suppressor mine will be even more front heavy.

Therefore, would switching to a AR10 build where all the weight is the same except adding ~1.25lbs in the receiver area help? Or not much at all? One of the first posts mentioning the UBR not helping much at all is a bit discouraging since the weight's so far out so I would've thought it'd had a drastic effect... adding 1.25lb's closer to the center of mass would seem to have even less effect. Any one else have thoughts on this? I'm really just speculating at the moment.

[Hygienist]

Originally Posted by Jester67CA

If you want to go full-nerd, you can calculate it for yourself.

Find a picture of an AR in your barrel length, set X=0 to the front of the magazine well (or anywhere else you please) and use this equation:



You'll need to know two things about each of the parts:
-It's mass
-It's center of mass

If you already have the part, an easy way to get a rough idea of the center of mass is to balance it on your finger. The point where it balances can be used to estimate the center of mass. Then add this value to whatever distance the part lies from the mag-well.

If you don't have the parts, just estimate.

Then you can plug each of the values into a long equation that looks a bit like this:

Xcm = (lower receiver mass)(lower receiver Cm) + (barrel mass)(barrel center of mass) etc. and then divide by the total weight of your gun.

Or you could, you know, just guess based on other people's images...


Here's a blog post that has lots of useful pictures:
http://vuurwapenblog.com/2009/11/25/...e-part-1-of-3/

And here's a calculator that will give you a rough idea. I'd start here. The part selection is limited, though:
http://vuurwapenblog.com/calc22.html

Some extra notes:
-The NSR itself weighs nothing. A big chunk of the weight comes from the barrel nut, which is nice and close to the center of mass.
-A suppressor will probably make your gun a bit front heavy. It tends to be par for the course.
-You can add weights to the stock in order to adjust the balance. A bit of extra weight in the butt stock is barely perceivable.

Thanks... I'm not really sure why I hadn't thought of doing this. I'll probably end up doing this unless anyone has actual experience on this subject and would like to chime in with they've seen.

[ra2bach]

Originally Posted by Jester67CA

[b][color="Navy"]If you want to go full-nerd, you can calculate it for yourself.

Find a picture of an AR in your barrel length, set X=0 to the front of the magazine well (or anywhere else you please) and use this equation:

hahaha, I saw this and thought your next response was going to be, "what now bitches?!?"

[Failure2Stop]

So, for clarity, you plan on going to a .308 AR if the front end of your lightweight 5.56 AR is too heavy?

[TehLlama]

If you want it balanced at or around magwell, stay AR-15.

Switch to a MagPul ACS (old gen), fill the stock with 123A batteries for ballast as needed. The SOPMOD is fine for the same thing, the ACS is just a touch heavier.

Noveske NSR or the TROY VTAC Extreme handguard will work great.

If you're really trying to trim weight, dimple the barrel, and shorten/pin it to 14.7". Cutting weight on cycling parts is for running competition reduced power loads, not to saving weight to carry it around. You're looking at top quality barrels, go with top quality ammunition and stick with proven BCG/buffer weights.


Lastly, for the love of christ, get a real lower. Noveske makes the nicest (FFL), but I've seen Aero Precision lowers (have three, they're great) for under $70 online recently, stick with those.

[Todd00000]

Originally Posted by Hygienist

Now, I've also been contemplating something else: moving to an AR10 Mega MATEN based build if it's too front heavy.?

You know a .308 suppressor can weigh almost double that of a 5.56 suppressor.

[Jester67CA]

I'm going to echo what others have been saying. Balance should be a low priority. Far below which cartridge you plan to use.

I'd keep away from the carbon fiber handguards for your uses.



Although affordable and light. The forearms like this tend to lack the cooling slots which are absolutely vital if you're planning on any sort of sustained fire. The also usually cannot mount BUIS without some work in a machine shop. These handguards tend to be popular with varmint hunters who will only take a few shots and must lug every once of rifle with them.


An alternative is the Lancer Systems Carbon Fiber Handguard. It is fairly expensive at $250+. This one has cooling slots, an extremely badass look, and optional rails. It weighs in at about 11oz with a barrel nut.

I believe Robb Jensen (linked) is running one for 3-gun.

The Noveske NSR is insanely light but is also expensive. A Troy TRX or Daniel Defense MFR are cheaper alternatives. It's worth noting however, that the last two must install a picatinny rail to mount accessories, which adds weight. It really comes down to how much stuff you plan to put at the end of the rifle and how much you want to pay for the slightest lack of weight.

I think you may be making a mountain out of a mole hill with this balance thing. It should be one of your last priorities.

What sort of ranges to you plan to use this gun out to and how quickly will you be firing rounds through it? It probably makes more sense to build the AR in a functional manner and then flute, dimple, or even cut the barrel if you don't like the amount of weight up front.

I'm not exactly sure why I decided to go crazy with this handguard thing. Hope it helps.

Originally Posted by ra2bach

hahaha, I saw this and thought your next response was going to be, "what now bitches?!?"

[C2_Drew]

I'm not sure why you're concerned with balance if the function of this rifle is to be a safe queen. You don't want it to tip over in the safe?

[Sticks]

Let me get this straight. You are going with a poly lower that was "reinforced at previous points of failure"?

Well, someone has to be the beta tester.

In my experience, when a new design has a failure point, and improvements are made to that area specifically, the failure point moves where the improvement ends. Eventually the poly lower is going to be "reinforced" to the point of being larger than a standard aluminum lower, and weigh just as much.

What's the saying...A solution for a nonexistent problem?

[Eurodriver]

What the hell is with this new guy and his blue font?

[glocktogo]

To me, a balanced rig is going to point and transition LOT better than an unbalanced one, even if it's heavier. The rig you're planning now will be all sorts of unbalanced. Ditch the polymer lower idea, ASAP. Now, consider a pencil barrel. I'd stick with a lightweight metal forend personally, but like Jester said, go with the Lancer if you go CF. Running suppressed keeps a lot of heat in the system.

Do you plan to run the rifle unsuppressed off the range much? If not, consider the Brakeout or better yet, the AAC two chamber comp. They will act as a sacrificial blast baffle, extending the life of your can.

I run a regular M42K on an 11.5" 6933 barrel with a DD Omega carbine length rail. It balances out nicely with a Vltor E-Mod stock with two AA batteries in the butt. If I remove the suppressor (or put the dedicated 5.5" .22LR upper with suppressor on the lower), I swap the stock out with a Magpul CTR, which balances those out. Works like a charm.

[Hygienist]

Originally Posted by Failure2Stop

So, for clarity, you plan on going to a .308 AR if the front end of your lightweight 5.56 AR is too heavy?

Yep. Though I can tell you disapprove of this, haha. Since my AR10 build would only add weight behind the barrel nut (mostly) I thought it would be a decent idea to balance it... based on the input though I've decided against 308 AR.

Originally Posted by TehLlama

If you want it balanced at or around magwell, stay AR-15.

Switch to a MagPul ACS (old gen), fill the stock with 123A batteries for ballast as needed. The SOPMOD is fine for the same thing, the ACS is just a touch heavier.

Noveske NSR or the TROY VTAC Extreme handguard will work great.

If you're really trying to trim weight, dimple the barrel, and shorten/pin it to 14.7". Cutting weight on cycling parts is for running competition reduced power loads, not to saving weight to carry it around. You're looking at top quality barrels, go with top quality ammunition and stick with proven BCG/buffer weights.


Lastly, for the love of christ, get a real lower. Noveske makes the nicest (FFL), but I've seen Aero Precision lowers (have three, they're great) for under $70 online recently, stick with those.

Thanks for the battery advice. If it does turn out front heavy I'll probably end up dimpling then... thank goodness dimpling can be done on stuff I've already bought instead of having to buy something new entirely, haha.

Originally Posted by Todd00000

You know a .308 suppressor can weigh almost double that of a 5.56 suppressor.

I'll be using an AAC Mini7 which weighs about the same-ish as the Mini4. Although that is a good point... future 308 mini suppressors might weigh more than their 556 counterparts. More reason for me to ditch the 308 idea, haha.

Originally Posted by Jester67CA

I'm going to echo what others have been saying. Balance should be a low priority. Far below which cartridge you plan to use.

I'd keep away from the carbon fiber handguards for your uses.

...

I'm not exactly sure why I decided to go crazy with this handguard thing. Hope it helps.

Thanks for the input on the HG! I'll probably keep the Lancer as my definite fall back handguard if the one I picked out doesn't pan out. The one I picked is the
http://www.apcustomusa.com/ar15.html
which has vent holes as you recommended and also mountable for slots in all 4 directions (if you ask for it, anyway). I don't think it'll be as sturdy but it is lighter... I'll admittedly be buying this having to test if the less sturdiness has any practical consequences.

Originally Posted by Sticks

Let me get this straight. You are going with a poly lower that was "reinforced at previous points of failure"?

Well, someone has to be the beta tester.

In my experience, when a new design has a failure point, and improvements are made to that area specifically, the failure point moves where the improvement ends. Eventually the poly lower is going to be "reinforced" to the point of being larger than a standard aluminum lower, and weigh just as much.

What's the saying...A solution for a nonexistent problem?

Yeah, I'm not gonna lie... I'm pretty much beta testing here haha. I don't really have any delusions about this build, most of the stuff is unproven and untested. I'd like to see if they really did fix it, and if not... I have a forged lower lying around I'll just slap onto it. Polymer would be ideal, though, if they actually did what they promised.

Originally Posted by glocktogo

To me, a balanced rig is going to point and transition LOT better than an unbalanced one, even if it's heavier. The rig you're planning now will be all sorts of unbalanced. Ditch the polymer lower idea, ASAP. Now, consider a pencil barrel. I'd stick with a lightweight metal forend personally, but like Jester said, go with the Lancer if you go CF. Running suppressed keeps a lot of heat in the system.

Do you plan to run the rifle unsuppressed off the range much? If not, consider the Brakeout or better yet, the AAC two chamber comp. They will act as a sacrificial blast baffle, extending the life of your can.

I run a regular M42K on an 11.5" 6933 barrel with a DD Omega carbine length rail. It balances out nicely with a Vltor E-Mod stock with two AA batteries in the butt. If I remove the suppressor (or put the dedicated 5.5" .22LR upper with suppressor on the lower), I swap the stock out with a Magpul CTR, which balances those out. Works like a charm.

I'm going with a Mini suppressor with the intent of keeping it on pretty much 24/7. Thanks for the compensator tip, I'll probably slap that on.

Thanks for your input on balance with a suppressor as well. Very interesting you'd need an E-Mod to balance it. I'll definitely have to do something about my stock if that's the case.

[SteadyUp]

Originally Posted by Eurodriver

What the hell is with this new guy and his blue font?

Special snowflake syndrome?

I wish people would just stick to the standard font and color that the majority of people use. It's easier to read, given the background colors of this site, in my opinion.