Long stroke vs short stroke...

[Appalachian]

pros/cons? I haven't bought my piston system yet, so I'm wondering what the major differences are, if any.

Thanks.

[Sherwood4MS]

Yeah, long or short?

I would also be very interested in opinions here.
I'm thinking about a LAR side-charging upper with a piston conversion...
but which one -- long or short?
I was googling and became interested in a PWS conversion kit, but I see they are not offering it anymore.

[LRRPF52]

Guys,

Unless you are dead-set on an op-rod driven operating system, I would stick with a standard Direct Impingement system for several reasons. For those of you that have op-rod systems and love them, if they work reliably for you, have a blast as this is not intended as a dig or slam on you and your choices in any way. I can only pass my opinion on and folks take it for what it is.

Ok, I also became interested in piston op-rod systems back when I first saw LAV working with HK on theirs. When I finally held and shot an HK416, I was turned off immediately by the excessive weight in the front, eliminating one of the great things about the AR-center of balance, and that was on a 10" gun. I have also heard of some major problems with the HK416 that resulted in a whole lot of them being taken off the range with LAPD SWAT right after they received them with the HK rep there, and he packed them up and took them immediately back to VA. (I also ran into some LEO's at 2010 SWAT who were trying to sell or trade all their PMAG's for EMAG's since the PMAG won't fit in the 416's unique magwell.)

Then I had the acquaintance of meeting 2 Danish Snipers at FinnSniper 2010, that had returned from Helmand Province last year and said they had at least one kaboom in their battle group due to sand interfering with the push rod and gas block, causing what appeared to be an out of battery firing with the bolt not fully locked.

I also have several friends that have experimented and tried to make some of the conversion systems work, and they ended up with more problems than they have ever seen with a DI gun, to include permanent damage to their extension tubes from carrier tilt, which has been addressed with several of the designs since then, I know, but there were still more malf's. These are guys that shoot high-volume frequently, and attend 2-3 day high-volume courses throughout the year.

Furthermore, I have a close friend who actually manufactures a very well-made op-rod conversion that is highly-respected, but he told me that he was only making them to meet the demand trend in the AR market, although he personally prefers DI. He has had a lot of positive feedback from guys that actually use them overseas, but his comments and preferences seemed interesting to me.

In addition, at least two of the most influential groups of people who have designed op-rod systems in AR's or AR-type weapons, are seen with DI Ar's over 95% of the time in their own professional instructional courses. That would be the gentleman I mentioned earlier using Daniel Defense DI guns, and Magpul Dynamics with AR's instead of the Massada/now ACR.

To me, the consumer precision and high-volume shooter, I have to stand back and say, "If the guys that developed this stuff with months or years of sweat and tears still use DI AR's in the bulk of their work, what does that say about DI versus Op-rod in the AR and my choices,especially since a gas tube costs $11.00 and an op-rod conversion starts at how many hundreds??"

That's just where I'm coming from on it. For the Grendel especially, I would like to suggest maybe buying some dies, brass, bullets, or ammo to last you a while, versus an op-rod conversion. Maybe take that $400-$600 of your hard-earned money and put it towards some nicer glass and mounts, but that's just me. Maybe invest in a dedicated Grendel bolt and barrel extension combo that will take the .444 cartridge base, versus an opened-up 5.56 bolt?

If you do decide to go with an op-rod, please do yourself a favor and research the different operating characteristics and parameters that you will need to optimize your system's reliability. That would include gas port diameter and gas system length, balanced with bolt carrier, drive rod, op-rod, return spring, and buffer weights. It also includes a new bolt carrier that will need to have a shelf or enlarged rear portion to prevent damage to your extension tube from carrier tilt-something the DI gun does not have since the recoil impulse is directly in-line with the bore.

You will also want to have a quality barrel with probably more weight if you are looking to get accuracy out of an op-rod system, since you have moving parts affecting the barrel harmonics with more variables than a free-float design. It can and has been done, but requires more attention to the op-rod design, gas block, and barrel quality or weight. You will also be limited in the types of free-float tubes you can use, as most do not have the clearance for the push-rod or drive rod assembly.

Colt submitted an op-rod AR back in the late 1960's called the Model 703. Guess why it wasn't adopted...Less reliable than the DI M16, costs more to manufacture, more small parts to lose and clean...you get the point.

Colt703-R.jpg
Colt703-L.jpg

I'm not sure how many long-stroke AR op-rod systems there are on the market, but there are plenty of short-stroke ones. Some of the high-price ones have been sent back to the manufacturer over and over, and op-rod guns have been causing a lot of headaches during high-volume courses. I know it's not what you would want to hear, but better to learn from others than spend the money yourselves.

I expect to get flamed for this, but I have to call it like I see it.

LRRPF52

[warped]

You experiences are the same as are for my friends who did work on these in R&D as well as using one OCONUS.

They just really are not worth it.

The negatives outweigh the positives, especially if you polish the tail of a DI bolt and use FROG LUBE on the weapon, dust covers are there for a reason as well as muzzle caps.

[LRS_Ranger]

Very good points.. I own an LWRC, and it's sweet, but I have nothing against the standard DI. I ran my issued DI harder than my personal LWRC (free ammo is great), and never had any problems with it.