View Full Version : How important is a pinned-on gas block?
wild_wild_wes
12-12-09, 17:14
I have a 16" middy with a DD Lite 9.0 handguard and a standard triangle front sight block, which is pinned on. This is my "go-to" gun. I would like to get rid of the gas block, but the bolt-on flip up types don't have my confidence for this rifle. I also would rather not go through the expense of buying a new hand guard, so my question is this: is an exposed but pinned-on low profile gas block considered to rugged enough for serious use?
Any reason you want to change out your current setup?
Your current setup, DD 9" Lite FF HG & pinned Std. FSB, is a great combination.
As for your ?: Any "quality" steel lower profile gas block that is "properly" pinned will be GTG. Once its pinned I couldnt see why it would be any less durable then your current FSB.
TheActivePatriot
12-12-09, 18:11
Examine your reasons for removing the FSB. If you have a valid technical need for a flip-down FSB (i.e. you're running a low-powered magnified scope, etc), it's definitely worth the effort to pin on the new gas block; hard enough blows can shift bolt-on gas blocks, turning the weapon into a straight-pull bolt action.
If you're running a RDS or a 4x or greater magnified optic, consider leaving the FSB as-is. The standard pinned FSB/gas block is more durable than most flip-up front sights, an important thing to consider for a fighting carbine.
wild_wild_wes
12-13-09, 09:25
Interesting....
http://i659.photobucket.com/albums/uu319/horseplay/IMG_4901.jpg
bluepythons
12-13-09, 12:39
Who makes that. I am viewing on my mobile so I can't see very much detail but is that pinned on. If so does it use the same slots from a Standard front sight.
wild_wild_wes
12-13-09, 13:35
No, it's a regular PRI clamp-on.
However, it has been pinned to the barrel at the top front.
On the militarymorons webpage they (he?) have a torture test of the Vltor clamp-on FSB. Pretty interesting food for thought.
http://www.militarymorons.com/weapons/ar.optics2.html#torque
wild_wild_wes
12-13-09, 17:32
Yes, the MM test, plus what my gunsmith told me- he is also a motorcycle guy, and showed me how they use the same bolt-ons on the forks; those bolt over smooth chrome too and are really subjected to abuse.
FYI in the MM test the upper started to deform at the barrel index pin before the gas block twisted any.
Robb Jensen
12-13-09, 18:45
Mk12s used to have set screwed gas blocks. Now they're pinned.
Mk12s used to have set screwed gas blocks. Now they're pinned.
There is your clue...
Robb Jensen
12-14-09, 13:34
There is your clue...
Yep. ;)
Is the potential danger exclusively impact damage, or are there any other possible problems with non-pinned GBs?
Am I correct in assuming that non-pinned GBs that are covered by a FF rail are more robust, or should they be pinned as well?
I think the biggest threat for a non pinned front sight is a sharp impact.
The gas block under a rail will not see the impact. The second problem is heat cycles, this can brake down thread locker and loosen fasteners. The clamp style with staking of the screws is my choice if I had to.
The cost of getting the gas block pinned is small compared to the peace of mind.
wild_wild_wes
12-14-09, 20:48
Mk12s used to have set screwed gas blocks. Now they're pinned.
Yes. Those were of the set-crew variety. As my gunsmith explained, those are the least secure option, as the contact surfaces where locking force is exerted is quite small, at the 12 o'clock position where the block is being drawn down, and of course where the set screws are being forced up. The bolt-on variety is a different story, with a much broader contact area; again, he pointed out this feature on his motorcycles.
Robb Jensen
12-14-09, 21:43
Yes. Those were of the set-crew variety. As my gunsmith explained, those are the least secure option, as the contact surfaces where locking force is exerted is quite small, at the 12 o'clock position where the block is being drawn down, and of course where the set screws are being forced up. The bolt-on variety is a different story, with a much broader contact area; again, he pointed out this feature on his motorcycles.
What kind of operating temps did your gunsmith find at the gas block at the barrel? If so how did it compare to that of the motorcycle forks?
I would not own an AR that did not have a Pinned gas block.
It's the key to the whole system, and if it becomes misaligned just once....it's a single shot... don't care how it's made, set screws can shear or crack... you do want you want.
mil_dot556
12-16-09, 15:05
if you're using a lo pro gas block i always recommend getting a dimpling the barrel for the set screws and pinning, never hurts to have two secure measures.
wild_wild_wes
12-16-09, 22:43
Anyone use the GG&G front flip up/gas block? It is pinned on:
http://img.photobucket.com/albums/v506/chuck1/IMG_0534.jpg
I had my heart set on the KAC....but it is too expensive.
I have always thought that anything that even poses a remote risk to continued operation of your firearm is a no go.
If it's a weapon that you will stake your life on then pinned is the only way to fly, if it's a plinker or range toy then do what ever you want so it looks tacti-cool.
KingsideRook
12-20-09, 12:15
I had a PRI clamp-on FSB rotate a few degrees when a box was dropped on it. It was enough to misalign it with the gas port, and take the gun out of service. The PRI was properly installed, loctite on evenly torqued bolts, but it wasn't enough. I am sure the VLTOR torque test proves their sight can take the abuse, but I'm pretty sure a lot of other brands of clamp-on FSB would fail that test in a heartbeat.
If I install another barrel mounted flip-up FSB like the PRi or ARMS 41B, I'm just going to have my gunsmith install a high crosspin, as shown in wild_wes' post. It's not practical to try to redo a pinned FSB that's already been installed, with a replacement, they're drill once, pin once. That's why clamp-on FSBs exist, but I would pin any one I installed - if it's worth taking off the gun, it's worth getting out the pin punch.
A lot of things happen when the gas block moves even slightly. The alignment with the gas key on the bolt causing it to wear out at an angle,the pressure loss at not striking straight on. Also the off angle that is put on the bolt carrier that will cause early and uneven wear on the inside of your upper receiver. I would never go with a set screw type, IMO it's a cop out and an easy out for a half assed way to do a job.:eek:
pins are a cheap way maybe them too can fail with heat and cooling of the so many different medias working together - if you use cross bolt with a TRUE shank to part size of the barrel slots and part of the ''block '' mating tightly with blue loctite so can work on the weapon if needed .
wild_wild_wes
12-26-09, 21:47
Okay, what if the gas block is a Low Profile type, and it is fully enclosed in the handguard....is pinning still necessary?
Robb Jensen
12-27-09, 05:10
Okay, what if the gas block is a Low Profile type, and it is fully enclosed in the handguard....is pinning still necessary?
The rail over the gas block will prevent things from hitting the gas block possibly knocking it lose, however the rail over the gas block will not prevent the gas block from heating during firing along with the barrel. This heating cooling cycle is 1/2 of what can cause the gas block to come lose. The pin will stay in place during a heating cycle. A thread locking compound will and does break down with heat.
Anyone use the GG&G front flip up/gas block? It is pinned on:
I use the bolt on version of that. It has a full-length clamping sleeve, and is cross-bolt with three bolts torqued to 35 in-lb each (per GG&G ) with Loctite. I haven't had any trouble with it, but if I did I'd have a qualified person add a pin or two.
I would avoid set screw gas blocks at all costs, though.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.