accuracy effect of PRI rail /mk12 mod 0 type setup

[Drifter™]

I have some questions regarding the full-length rail that affixes to both receiver and PRI handguard of a Mk12 Mod 0 <span style="text-decoration: underline">type</span> setup. (I'm not attempting to exactly duplicate the Mk12 Mod 0, so nostalgia and "correctness" can be set aside for this particular thread.)

I realize that the rail provides flexibility regarding scope mounting, and supposedly makes for a rigid connection of upper receiver and handguard, but obviously there are numerous cantilever AR scope mounts that allow mounting an optic without contact to the handguard and without using the spr / arms /swan-type rail.

How does this full-length receiver/handguard rail affect accuracy? All else being equal, using the same PRI carbon fiber handguard, would accuracy using the rail versus using a cantilever mount instead be better, worse, or the same? Does the rail make the rifle any more or less temperamental regarding POI shifts when using different shooting positions (sand bag position under handguard, bipod use, etc)?

Any feedback regarding the accuracy aspect would be appreciated.

Thanks

 

[KM375]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

Im not sure how the Mod 0 set up would effect accuracy, I get that it provides a stable,secure free float tube to the receiver. However the Mod 1 they simply did away with the ARMs rail and used a different Railed interface. I have the Mod 0 and love the way it shoots. Its is a bit more weight than that of the Mod 1.
However, I have been looking at the GAP and Larue and it seems that both of those systems. Appear to have a rail system that attaches to the top rail of the receiver in some manner giving them a similar rise or profile of the Mk 12 Mod 0. Perhaps the Larue and GAP guys can provide a better insight.

 

[Ro_Bird]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

I carried a MOD O for while (OEF). Most shooting was done off of bipods, slings, or ruck. I never had any noticeably shift of POI. I don't think that in most "normal" cases you will see much flex in the rail. Unless you mounted the optic way out on the end and then really cranked down on the tube. But I think you will find mounting an optic way out on the end is not very useful anyways.

 

[TackleberryH3]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

The PRI handguard is a free-float tube that optimizes accuracy. The less there is touching the barrel, the fewer chances there are of altering the accuracy. Anytime you have anything attached to a barrel, you change the harmonics of that barrel. That alters accuracy. With a combat rifle, such as the M4 or M16A4, you are not concerned so much with pinpoint accuracy. The guy sitting in a hide with a KAC M110 or a Mod 0 is. That is why the railed handguards on the M110 and Mod 0s are free-floating.

 

[Drifter™]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

Thanks for the replies.

But not so sure that my question was properly asked...

Generally speaking, cantilever scope mounts for AR's are designed so that the mount contacts only the upper receiver and not both the receiver and handguard. Yet the Mod 0 setup uses a rail that obviously contacts both.

Does the full-length PRI / ARMS / SWAN rail enhance accuracy when using the PRI carbon fiber handguard?

Or does the availability of modern cantilever mounts make the full-length Mod 0-type rail unnecessary on similar non-clone setups?

If the rail enhances accuracy, I might consider it. If it's simply added weight with no effect on accuracy, I'll probably pass.

Thoughts...?

 

[TackleberryH3]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Drifter_1</div><div class="ubbcode-body">Thanks for the replies.

But not so sure that my question was properly asked...

Generally speaking, cantilever scope mounts for AR's are designed so that the mount contacts only the upper receiver and not both the receiver and handguard. Yet the Mod 0 setup uses a rail that obviously contacts both.

Does the full-length PRI / ARMS / SWAN rail enhance accuracy when using the PRI carbon fiber handguard?

Or does the availability of modern cantilever mounts make the full-length Mod 0-type rail unnecessary on similar non-clone setups?

If the rail enhances accuracy, I might consider it. If it's simply added weight with no effect on accuracy, I'll probably pass.

Thoughts...? </div></div>

The rail on the Mod 0 merely provides a monolithic mounting space to mount the scope and any other necessary optic equipment without affecting the accuracy. As I mentioned before, the less you have attached to the barrel, directly or indirectly, the more consistently accurate the weapon will be. If you look where my scope is mounted in the picture of my Mk12 Mod 0 (top pic), you can see the importance of having the rail.

The cantilever mount is used to mount a scope forward without having to mount part of it on the railed handguards.

Since there is limited space on the picatinny rail on top of the upper receiver, the cantilever allows the user to have the optic mounted forward without mounting it on the handguard rails. The cantilever mount makes space available for the scope and the BUIS to be mounted on the receiver.

 

[Ro_Bird]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

Well ok then, I'd say "No". The full-length PRI / ARMS / SWAN rail which is found on the MOD 0 will not enhance accuracy if you will compare it to other quality FF rails such as but not limited to the Knights rails found on the MOD 1. If anything you're just adding one more thing that might go wrong, one more level of complexity to your mounting solution. That being said I've never had an issue with the MOD 0 rails.

Generally I'd say the cantilever mounts do make the full-length Mod 0-type rail a bit unnecessary these days and if you're looking to save weight, a cantilever mount might be a smart way to do so.

 

[Drifter™]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RoBird</div><div class="ubbcode-body">Well ok then, I'd say "No". The full-length PRI / ARMS / SWAN rail which is found on the MOD 0 will not enhance accuracy if you will compare it to other quality FF rails such as but not limited to the Knights rails found on the MOD 1. If anything you're just adding one more thing that might go wrong, one more level of complexity to your mounting solution. That being said I've never had an issue with the MOD 0 rails.

Generally I'd say the cantilever mounts do make the full-length Mod 0-type rail a bit unnecessary these days and if you're looking to save weight, a cantilever mount might be a smart way to do so.
</div></div>

Thanks RoBird. That's the type of feedback that I was seeking.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: krm375</div><div class="ubbcode-body">

...I have been looking at the GAP and Larue and it seems that both of those systems. Appear to have a rail system that attaches to the top rail of the receiver in some manner giving them a similar rise or profile of the Mk 12 Mod 0. Perhaps the Larue and GAP guys can provide a better insight.</div></div>

Yes, it does appear that the GAP and LaRue OBR use a top rail that ties the upper receiver and handguard together. And both have earned a reputation for accuracy.

Any additional feedback would be appreciated.

 

[lwrkeysfisher]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

I use a PRI carbon fiber tube and have noticed POI shift when I use a bipod and drive it hard. For the most part it is not a big deal, but I do think the rail would stiffen things up a bit.

However, I have not purchased the rail, nor have I changed handguards so it must not be that bad.

 

[Oakland Tactical]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

FWIW my MOD 0 is as accurate as you can ask out of a combat rifle, it shoots no shit .5 inch 5 round groups with regularity and is stiffer than a wedding dick. I think you could ask anyone with a High Caliber Supply built upper and they will repeat the statement above. As stated above GA, Larue, POF and now Seekins are using the MOD O type system and these companies arguably make the most accurate rifles in the industry.

 

[frog5215]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

Does the this is to do, the MOD O is a SOB to the upper, HB, and SWAN properly set up.
My is a .22, barrel from CLE, shoots 1/2 MOA (often 3/8-.40).

 

[hyena74]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

i have a mod o in 6.8spc. it is by far my favorite ar. it has the full swan rail and is just built like a tank. the extra weight and complexity is just fine with me.

now if i could just figure out how to build a mod 0 in a 308...

 

[Elvis]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hyena74</div><div class="ubbcode-body">i have a mod o in 6.8spc. it is by far my favorite ar. it has the full swan rail and is just built like a tank. the extra weight and complexity is just fine with me.

now if i could just figure out how to build a mod 0 in a 308... </div></div>

I just had one done in .260

Order the handguard, SPR rail and gasblock from PRI. You can get the ARMS 40 from them too. Get a .30 cal Ops Inc brake and collar. Get an SPR contour barrel cut. Either assemble yourself or send it off to a smith. Had GAP do mine since I'm currently overseas.

 

[Drifter™]

Re: accuracy effect of PRI rail /mk12 mod 0 type setup

Thanks for the additional replies.

Still undecided on whether to go rail or no rail...