PDW builds - Lets see them, and share results

If you cut a barrel down to a shorter lenght and tread it for a flashider, how would anyone know you didn't buy it that way.

Because when the police pinch your dumbass, they will find that your firearm was never registered as a restricted and that you modified it making it prohibited.
 
My AR is RESTRICTED. Already registered. A 14.5 is restricted. So is a 10.5. I am trying to research cutting it back (or having it cut back for me).

I presume i could buy a new (shorter) barrel and install it.

Since the gas tube and port would remain unchanged, am i correct in assuming it would cycle the same?
 
My AR is RESTRICTED. Already registered. A 14.5 is restricted. So is a 10.5. I am trying to research cutting it back (or having it cut back for me).

I presume i could buy a new (shorter) barrel and install it.

Since the gas tube and port would remain unchanged, am i correct in assuming it would cycle the same?

Mmmm maybe.

I spoke with LMT and they recommend only using only 5.56 in their 10.5's because of cycling issues.
 
My AR is RESTRICTED. Already registered. A 14.5 is restricted. So is a 10.5. I am trying to research cutting it back (or having it cut back for me).

I presume i could buy a new (shorter) barrel and install it.

Since the gas tube and port would remain unchanged, am i correct in assuming it would cycle the same?

Just buy a shorter barrel with low profile gas port and pre-installed gas block. You shouldn't have any issues and then you can sell the old barrel. No, the gas tube setup is different for a SBR AR (Suputin could fill you in the details better than I can).
 
"No, the gas tube setup is different for a SBR AR (Suputin could fill you in the details better than I can)"


I have seen occasional references to this concept. I would like to hear more, since it is counter-intuitive. Why would cycling change if barrel is shortened beyond the gas port?
 
"No, the gas tube setup is different for a SBR AR (Suputin could fill you in the details better than I can)"


I have seen occasional references to this concept. I would like to hear more, since it is counter-intuitive. Why would cycling change if barrel is shortened beyond the gas port?

lol no one listened to me say earlier about dwell time?

usually shorter ARs have shorter gas tubes, and the gas port is moved closer to the chamber to increase dwell time, so the gun cycles more reliably, it does increase pressure,

in other words, shortening the barrel by too much, without getting a shorter gas tube/moving the port closer to the chamber, reduces the amount of time the action has to cycle.

you can buy a 10.5" upper and throw it on the lower without breaking any laws.
 
lol no one listened to me say earlier about dwell time?

The whole thing should really be moot, because the discussion is once again turning back to how to make a prohibited SBR barrel. Whether it works or not, it's illegal. Anyway, this is a *picture thread* for SBR and PDW builds - so those that wish to continue should kindly take the discussion elsewhere.
 
The whole thing should really be moot, because the discussion is once again turning back to how to make a prohibited SBR barrel. Whether it works or not, it's illegal. Anyway, this is a *picture thread* for SBR and PDW builds - so those that wish to continue should kindly take the discussion elsewhere.

I agree with Blaxsun and so to put us back on the right track....one of my all time favourites...and yes it's a Norc...LOL

upclose2.jpg
 
talking about things like dwell time is not illegal...

someone asked about pressures and such in SBRs,

some people like to learn about the physics behind these things...

heres a picture to explain what I mean, how the different gas systems work,
pressuregraph.jpg


anyways, higher pressure, + less dwell time is why most SBRs have a faster/harder action, that is more prone to malfunctions then guns that operate at lower pressures with longer dwell time.
 
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Thank you!!!! Now we are getting somewhere.

My Norc M4 would have the carbine gas system, right?

I noticed that when I shot it the bolt seemed to be quite violent, as if it is over-gassed. i don't like the idea of beating up a rifle, especially when I am only shooting holes in paper 25 yards away (CQB).

For this reason I load my CQB ammo with fast powder (680) to drop the port pressure. Muzzle velocity is down to about 1500 fps. It is like shooting a BB gun, but it still cycles 100% I am guessing the pressure port is bigger than it should be.

So if I have the barrel cut from 12.5" to 10.5", the theory is that the reduced dwell time will reduce bolt energy. OK, because it looks like that would actually be a step in the right direction, since the bolt is now too violent with full power ammo.
 
Thank you!!!! Now we are getting somewhere.

My Norc M4 would have the carbine gas system, right?

I noticed that when I shot it the bolt seemed to be quite violent, as if it is over-gassed. i don't like the idea of beating up a rifle, especially when I am only shooting holes in paper 25 yards away (CQB).

For this reason I load my CQB ammo with fast powder (680) to drop the port pressure. Muzzle velocity is down to about 1500 fps. It is like shooting a BB gun, but it still cycles 100% I am guessing the pressure port is bigger than it should be.

So if I have the barrel cut from 12.5" to 10.5", the theory is that the reduced dwell time will reduce bolt energy. OK, because it looks like that would actually be a step in the right direction, since the bolt is now too violent with full power ammo.

If you don't have any experience with AR-15's, then how would you even know that the bolt action to too "violent" as you like to put it? :nest:



.
 
Thank you!!!! Now we are getting somewhere.

My Norc M4 would have the carbine gas system, right?

I noticed that when I shot it the bolt seemed to be quite violent, as if it is over-gassed. i don't like the idea of beating up a rifle, especially when I am only shooting holes in paper 25 yards away (CQB).

For this reason I load my CQB ammo with fast powder (680) to drop the port pressure. Muzzle velocity is down to about 1500 fps. It is like shooting a BB gun, but it still cycles 100% I am guessing the pressure port is bigger than it should be.

So if I have the barrel cut from 12.5" to 10.5", the theory is that the reduced dwell time will reduce bolt energy. OK, because it looks like that would actually be a step in the right direction, since the bolt is now too violent with full power ammo.

It should be quite normal for military guns to be over-gassed for the sake of reliable operation, shouldn't it? I think you should look up MysticPrecision's thread on his Norc M4, as he does go into a fair bit of detail on the workings of a platform that was new to him as well.
 
the theory is that the reduced dwell time will reduce bolt energy. OK, because it looks like that would actually be a step in the right direction, since the bolt is now too violent with full power ammo.

no... dwell time being reduced does just that, reduces the amount of time the bolt has to fully cycle before pressure is lost,

the only thing that will make the bolt action "less violent" is moving the gas port further down the barrel (IE reduce chamber pressure)

dwell time is the TIME the action has to make use of the pressure (which goes up the closer the gas port is to the chamber)

so the action would be just as "violent", but a fraction of a second shorter, it might still shoot, but it might make it more unreliable and wont reduce the "violence" of the action


dont get your gunsmith to cut down AR barrels... its a hassle and likely to cost more then if you just bought the barrel length you want, it will come pre tapped for the gas system...

heck go out and buy a 10.5 norinco upper for like 400 bucks and save yourself the hassle of installing the whole upper
 
"If you don't have any experience with AR-15's, then how would you even know that the bolt action to too "violent" as you like to put it?"

Who said I don't have any experience? I am asking questions about how they work so I understand better how to play with/modify what I have. The Norc is my 5th or so.

I had a Colt with a 9", but did not shoot it much. But it worked very well. i once put a 20X scope on it and used it to test 45gr ammo for muzzle flash. It grouped about 2" and 200 yards. I was impressed.

Regular ammo in my 20" feels quite soft compared to the bolt slamming in the M4. This is why i think it too violent. And the fact I can down load by about 1000 fps and it still works suggests it is over-driven.

If someone has a 10.5" upper for sale, i might just go that route. But I have a heavy 16" upper almost complete (in the junk bin). I am inclined to build that up as my "long" rifle and then have the M4 bobbed.

I am sure those of you who built PDWs must have put some thought and research into what would work before assembling the parts.

BTW, the chart above makes it clear that 5.56 is not the best caliber choice for a very short barrel PDW that might have to be used.
 
No cutting period, since you're not considered a manufacturer, any cutting would result in a prohibited weapon. This retarded piece of legislation probably results from the politicians hearing the phrase "cut-off shotgun" one too many times.

Send it to a gunsmith and they'll be "re-manufacture" it to a shorter length. Or just buy a new barrel.

Even as a manufacturer we are NOT allowed to cut down AR barrels.
Yes I KNOW this is stupid, but most gun laws are stupid by design.
On NON restricted rifles and shotguns anyone can cut a barrel down to 18.5"
On handguns anyone with talent and a verifiers number can cut a barrel down to 4.2", but for whatever reason restricted semi auto rifles are in a different game when it comes to cutting down a barrel.
If in doubt call 1800-731-4000 and ask to speak with 1 of the gun techs at the lab in Ottawa the extension is 1090
 
PDWs Rock!

Picture time again... This is my latest project (still missing a few parts for the upper).

Hera-Noveske-Knight-Socom, although we might as well just call it 'Franken PDW' - because with the exception of the upper and compensator from Hera, every other part is from a different manufacturer. The balance on this thing is near perfect, and the weight is just insane (should come in just over 5.5lbs with optic). :evil:

This thing is going to be an absolute riot to shoot! :ar15:

pdw-rocks.jpg
 
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