Home Forums Hunting & Shooting AR and Tactical Rifles help me buy a forend

Some people just can't get past crapco...

Back during the real rail wars, receivers were chucked up solid and weights were hung off the end. The amount of flex was shocking on some and it had more to do with the barrel nut/rail connection. For most of us it was probably pointless but for soldiers under severe stress of a fire fight, getting the barrel hot and applying pressure via a vertical grip often led to barrels bursting. That also led to the SOCOM barrel best I remember.

What's also important but seldom discussed is an anti rotation feature.

But I quit recommending things around here cause parts is parts right?

(Sarcasm font)

Sure are. .....Or at least that's the case on the one-way flat range.

So even on a flat range it doesn't matter that you can't put just a little more pressure on your gun without throwing off your 3 shot groups?

To most, it probably doesn't matter very much.

Formy is geared toward full house duty weapons, & in that context, he's right of course; there is flimsy, there is stiff & there is really stiff...............most of the better & commonly used stuff by many of us here probably falls into the stiff group, but not as stiff & robust as things like the KAC URX attachment system.

MM

For real testing- a 10 pound weight hung 10 inches in front of the receiver, measuring both rail and bore deflection in MOA. 10 pounds isn’t anything. We measured trained shooters putting 40 plus pounds on the rail when using a VFG.

The best rails will have less then 4-5 MOA of deflection. A BCM for instance will have closer to 8 MOA. Just resting it on a barricade with slight pressure to shoot caN and will shift a BCM 2-4 MOA. A DD RIS II has 8-10 MOA of deflection.

The rails with the least deflection are Geissele MK16, Hodge Defense Wedgelok, and KAC URX. Actually the LMT MRP probably has the least, but we haven’t tested them yet. The ALG is nearly as good as the top rails because of the barrel nut and lockup. The MK14 is decent, but a bit too small diameter, and the MK16 is better.



Rail deflection isn’t just about laser and irons sight zeroes. The rail deflecting is actually bending the upper receiver. Slight, but enough to cause bolt lug breakages sooner. As well there is a slight zero shift due to bore deflection. In general- short barrel nut with a stiff rail puts more pressure into the upper receiver when flexed. Long barrel nut puts less pressure into the upper receiver when flexed.


For just blasting at the range, it probably doesn’t matter for most. However, those rails I mentioned are “better”. Knowing what I know, there’s no way that I’m choosing any other rail but an ALG on a budget... or not in a budget- I have several mates that choose to use the ALG’s after testing above all the others for work guns.....

Right there is the reason you shouldn't mount a scope with one ring on the receiver and one on the rail.

That's very interesting information & very enlightening seeing that it's from actual testing.

Thanks for posting.

MM

I agree with most of what you're saying, but not this one point. If you're fixing the upper in place and loading the rail as described earlier, it doesn't make any difference how long the barrel nut is or how stiff the forend itself is, the upper receiver will see the same amount of load, and distort the same amount.

Of course there can be a difference if your different handguards interface with the receiver differently, but that's not what we're talking about, is it?

Yea. Real enlightening.

Thanks again for the post.

Yes, in order for POI to change, the receiver, which is holding the barrel, must deflect, thus deflecting the barrel with it.

I don't see how it could be otherwise.

MM

Form,
Any experience or general thoughts on the Wilson TRIM rails? I got one used a couple years back and was considering swapping it for a BCM because I like that thin profile, but might just leave it alone if it happens to be a better rail.

I’ve shot Wilson’sbut have never tested them. Sorry.

If you get a 12" Grey Ergonomic Modular Rail (EMR) V3 M-LOK, they are reduced to $99.00 plus free shipping.

I’ve had good results with Aero Precision rails for hunting builds. I’ve also used their enhanced receiver and rail interfaces, and those seem strong enough for any use.

Form,

I've been waiting to see if a 9.5" Mk16 will ever be released on the market. Recently I read there were issues with the 13.5" Mk16 contacting the gas block, have you run into any issues with this?

Not sure on the short MK16 release. Have some and they’re good.


The MK14 has gas block issues with some. Have only had the DD MK12 gas block and the Geissele. Both have been fine.

I haven't seen any MK 16's rails of any size being available.................just an upper with it that is similar to what they are selling (supposedly) to the military.

Do you know who is offering the MK 16's in 13" or 15"?

Primary Arms has some pretty good deals on the MK 14's right now, though, & it seems to use the same length barrel nut as the MK 16 from what I can find out.

MM

No one. You can’t buy the rails as of now.


There are some within the military that are, or have gotten them....

very interesting regards the BCM KMR rails, I bought a couple of them and they are very light weight makes me wonder if this could be the reason I cannot get my 6.8SPC hunting rifle to shoot better than 2 MOA. Thanks Form very good info.

I fail to see how a KMR rail would bend the upper and barrel enough to cause 2-4 MOA shift by shooting off a barricade using slight pressure. I have a KMR and it is the easiest rail I've seen to flex. If you want to move something it takes something stronger than what you're trying to move.

I like my KMR for what it is and have not noticed a 2-4 MOA shift when shooting free recoil or loading a bi-pod.

It doesn't add up.