Bullet travel for SBR

[ZLBubba]

I'm looking at getting an LWRC M6A3 with a 10.5" barrel, and using an M4-2000 on it. I'm looking for a fun, quick carbine that's going to cycle well every time I pull the trigger. While I know arf.com may answer this faster, the quality of opinions on the Hide is superior, IMO. I'm trying to find out whether a piston system enhances functioning with shorter tubes.

All of my reading tells me that an 11.5" barrel is superior to a 10.5" barrel in terms of weapon cycling. Since the bullet has an extra inch to travel down the barrel, that gives more gas/pressure to cycle the action, thereby enhancing reliability. That makes sense to me, provided I've got the facts right.

So what, if any, difference will a piston make in this equation? Will a piston system be more reliable in a 10.5" barrel since the gas doesn't have to go nearly as far to initiate the cycling sequence? It would seem like the answer is yes, but I thought I'd ask you gents and find out.

 

[The Mall Ninja]

Re: Bullet travel for SBR

i don't think barrel length has a whole lot to do with the cycling operation, where your gas block is does..... with that said, the gas block should be mounted in the same place on both barrels so i don't think it really matters. other things that can help with reliability are correct weight buffers, and a proper length spring. if you are planning to run a can on it you should not have problems cycling although you might want to look into an adjustable gas block to ease the wear and tear, and prevent shearing a gas key.

 

[ZLBubba]

Re: Bullet travel for SBR

The point about bullet travel is that 11.5" is once inch more travel from the gas block than a 10.5", thus allowing for better functioning. That's the conventional wisdom, anyway.

I am interested in learning about buffer springs though. I've heard that can help alot.

 

[gstaylorg]

Re: Bullet travel for SBR

My Sig 556 pistols with 10" barrels have no issues whatsoever with cycling via their short piston. If anything, I'd say it could be cut back a fair amount and still cycle correctly. I realize this may be apples/oranges...I looked at the LWRC website and it's not clear to me exactly what type of piston system they use (Sig is similar to the AK-47).

 

[sobrbiker883]

Re: Bullet travel for SBR

POF-USA's 7.25 inch PDW is arguably our best running system, and an absolute kick in the pants to shoot!
If I were running security from a vehicle for 200-300m and in it would be my number one first choice!

Phoenix PD's SAU diagrees though and runs our 9.25".....


Tim3gun shooting the PDW:
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[ZLBubba]

Re: Bullet travel for SBR

That 9" runs really nice. I think I should add that to the short list of builds for this gun.

 

[Jer]

Re: Bullet travel for SBR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Kahlendrrari</div><div class="ubbcode-body">i don't think barrel length has a whole lot to do with the cycling operation, where your gas block is does..... with that said, the gas block should be mounted in the same place on both barrels so i don't think it really matters. other things that can help with reliability are correct weight buffers, and a proper length spring. if you are planning to run a can on it you should not have problems cycling although you might want to look into an adjustable gas block to ease the wear and tear, and prevent shearing a gas key. </div></div>

Actually, barrel length affects dwell time which can affect cyclical rate.

 

[jakhamr81]

Re: Bullet travel for SBR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body">POF-USA's 7.25 inch PDW is arguably our best running system, and an absolute kick in the pants to shoot!
If I were running security from a vehicle for 200-300m and in it would be my number one first choice!

</div></div>

Just make sure you keep the muzzle out the window of the car or your vehicle mates are likely to kick your ass.

 

[chalwie]

Re: Bullet travel for SBR

LWRC's reliability is related to two things: coating and piston design.
The NiCorr coating covers all contact surfaces. The advanced combat bolt has just been updated to the newer material. All these moving parts traditionally required a lot of lubrication. Build up of carbon materials increase friction and eventually causes failure. LWRC's moving parts slide easily - the coatings increases its inherent lubricity. Some brag and dare to see their LWRC fail by deliberately shooting it without cleaning. The piston's role is to reduce junk from coating the bolt carrier and bolt. The result is a very reliable AR15/M4 style rifle.
The POF's reliability benefits from the same concepts - their coating is called NP3.
Other piston designs enjoy a cleaner bolt carrier/bolt, but don't have the self lubricity compared to these two examples. They use chrome, effective but arguably less effective.

 

[Explorer]

Re: Bullet travel for SBR

" Since the bullet has an extra inch to travel down the barrel..."

I'd bet its not that easy. Looks to me like the variables include powder burn rate, bullet weights, pressure peaks, port placement and diameter, and distance from port to muzzle. All of which I am not an expert on!

And coatings and DI vs piston add even more variables.

I shoot a 10.25" and 11.5" DI pistols (off the shelf configurations), both work great.

 

[ZLBubba]

Re: Bullet travel for SBR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Explorer</div><div class="ubbcode-body">" Since the bullet has an extra inch to travel down the barrel..."

<span style="font-weight: bold">I'd bet its not that easy. Looks to me like the variables include powder burn rate, bullet weights, pressure peaks, port placement and diameter, and distance from port to muzzle. </span>All of which I am not an expert on!

And coatings and DI vs piston add even more variables.

I shoot a 10.25" and 11.5" DI pistols (off the shelf configurations), both work great. </div></div>

All variables are held constant except the barrel length. Same ammo, same port placement, same diameter, do you get better functioning from a 10.5" piston platform than you do a DI platform? Boiling it all down, that's the issue at hand since we can control other variables. It seems like the basic answer is: yes, both LWRC and POF function well at barrel lengths 10.5" and under.

 

[Mo_Zam_Beek]

Re: Bullet travel for SBR

ZL - as with many things on the net - I doubt you are going to get a rock solid answer. I will tell you my anecdotal DI story. I have 10.5 LMT and an 11.5 6933. I shoot a lot of Wolf. The 11.5 will eat anything and has since day one right out of the box. The 10.5 will not eat Wolf 55s. It does just great with Wolf 62s. It does just fine with factory brass 55s (Q3131 or whatever). Both are solid with BH 75s, 62 grn Federal Fusion rounds, and my 77 grn match load. Both run H1 buffers with no other changes beyond a standard build. Having been through the SBR thing and not being one that needs to ride in a car on a daily basis I personally think 11.5 or even 12.5 is the length. Both are short enough to keep the weapon shouldered and open a door that swings into you with no issues and that little extra length does seem to make a difference in a DI gun. I know you are asking about a piston.


Good luck

 

[RyanScott]

Re: Bullet travel for SBR

DI works. This I know from experience. I don't have enough experience with piston guns to know that they work or not.

 

[ZLBubba]

Re: Bullet travel for SBR

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mo_Zam_Beek</div><div class="ubbcode-body">ZL - as with many things on the net - I doubt you are going to get a rock solid answer. I will tell you my anecdotal DI story. <span style="font-weight: bold">I have 10.5 LMT and an 11.5 6933. I shoot a lot of Wolf. The 11.5 will eat anything and has since day one right out of the box.</span> The 10.5 will not eat Wolf 55s. It does just great with Wolf 62s. It does just fine with factory brass 55s (Q3131 or whatever). Both are solid with BH 75s, 62 grn Federal Fusion rounds, and my 77 grn match load. Both run H1 buffers with no other changes beyond a standard build. Having been through the SBR thing and not being one that needs to ride in a car on a daily basis I personally think 11.5 or even 12.5 is the length. Both are short enough to keep the weapon shouldered and open a door that swings into you with no issues and that little extra length does seem to make a difference in a DI gun. I know you are asking about a piston.


Good luck </div></div>

Thanks for sharing your experience. That somewhat confirms the usefulness of an extra inch of bullet travel from the port to the muzzles in DI rigs There is a chance I may convert my current rig to an SBR anyway, but as it stands, I only have one AR and that's downright un-American. I need at least a couple more.

 

[Inogame]

Re: Bullet travel for SBR

"I only have one AR and that's downright un-American."

Sir, I couldn't agree more... I was just thinking that about myself.