Cracked FSB, weld it?

mhanna91 · #1 11-27-10, 00:07

Hey everyone. Tonight I cut down the FSB on my new BCM hammer forged 16" midlength upper. I had a heck of a time getting the thing back on the bbl, and had to use a hammer. When I put the rear taper pin in, the bottom of the FSB/gas block split, and I was ticked. I am pretty sure it cracked while I was whacking on it to get it on the barell. I did not grind any further than I needed to when I was cutting the sling swivel off, so I am not sure why it was weak enough to crack.

Would it be possible to simply weld the crack up and grind it down smooth? Would it be a good fix? Would the heat from the weld mess with the barell steel? I know that cutting the pinned FSB is the most secure way to acheive a lo-pro gas block, and I do not want to have to use one with set screws, nor do I want to spend the extra $40 on one.

Any help would be much, much appreciated.

Thanks,
Mark

Belmont31R · #2 11-27-10, 00:10

Email BCM. I would not weld it.

stifled · #3 11-27-10, 00:16

I would not weld it. I'd buy a low profile gas block. Or possibly another FSB and cut it down, but I don't know how stubborn I'd be in that situation.

MistWolf · #4 11-27-10, 00:30

Welding at best, is a temporary solution. To do it right, you'd have to remove some of the damaged area & build it back up. Otherwise you'll just be snotting a blob over the crack. You'll also need to jig it to hold the correct diameter, then re-cut. If welded as is, it will be loose on the barrel.

Anytime time a hammer is used as a substitute for a press, there is risk of damage.

No, I don't know from personal experience- why do you ask??

Eric D. · #5 11-27-10, 00:34

Just to be safe, I'd get a new gas block. I definitely wouldn't weld it as is. If you can somehow squeeze the gap closed, then I would consider it - A short, solid spot weld would not harm the barrel as far as heat. Stay away from the corners as they will easily melt and round off, and obviously avoid welding to the barrel.

Just curious, what kind of machine do you have? I've got a 110V Millermatic 135 that works great. I've never had a chance to try MIG with it but FCAW has served me well for years.

Fidalgoman · #6 11-27-10, 00:36

There is a lot of stress when you drive a taper pin through. By relieving the FSB so much and the hole shown, you simply broke it from too little metal. Buy a low profile block and live happily ever after.

mhanna91 · #7 11-27-10, 01:20

Email sent to BCM, however I do not expect them to do jack, its my fault. I basically asked them for advice just like I am doing here. I dont think I could be happy with a lo-pro gas block unless I dimpled the barell, cranked the hell out of the set screws and then staked them. Would this suffice?

usmcvet · #8 11-27-10, 04:08

I would not weld it either. I would always wonder and obviously it is a crucial part of keeping your gun operational.

I've been looking for an A1 or A2 FSB and had not luck, any one have a source.

SMC Nubby · #9 11-27-10, 05:52

Quote:

Originally Posted by usmcvet

I would not weld it either. I would always wonder and obviously it is a crucial part of keeping your gun operational.

I've been looking for an A1 or A2 FSB and had not luck, any one have a source.

Found this while I was looking at some other alternatives.A2 Style Gas Block

On topic: For the cost of a new block and considering that you would likely need to remove the block to weld it properly anyway, I'd just count that as tuition on AR smithing.

Robb Jensen · #10 11-27-10, 08:07

Contact Paul at BCM. He may have a FSB that came off a BFH barrel that wasn't need particular builds, and as long as the two barrels were made around the same time you might be able to use a FSB from another barrel.

If he doesn't have one to sell you I'd say just buy a LaRue low pro gas block and install it on the barrel and pin it. If both taper pin holes are cover but a rail you could use a shorter gas block like the Troy or VLTOR.

mhanna91 · #11 11-27-10, 08:32

Yes, the rail is a 13.8" troy so both holes will be covered. What would be the best way to go about pinning a low profile block? I have seen the jigs used for dimpling the barells for set screws, but have not seen anything like that for actually drilling for a pin. Also, with the factory pin holes exposed to the weather, would they possibly start to rust? Should I coat them with something?

Robb Jensen · #12 11-27-10, 09:08

Quote:

Originally Posted by mhanna91

Yes, the rail is a 13.8" troy so both holes will be covered. What would be the best way to go about pinning a low profile block? I have seen the jigs used for dimpling the barells for set screws, but have not seen anything like that for actually drilling for a pin. Also, with the factory pin holes exposed to the weather, would they possibly start to rust? Should I coat them with something?

That one company that makes a jig for dimpling also makes one for drilling pin for VLTOR and similar gas blocks.

I don't use one of those. I use a milling machine and mill a flat spot on one side of the gas block (barrel is already mounted in the gas block) and then drill a 7/64" hole through both at the same time and then change drills and drill a 1/8" hole though both. If using sharp drills you should be able to use a straight pin or ream the hole with a taper pin reamer and use a taper pin. Both work excellently.

If you're worried about rust in the holes on the barrel you can use RIG (rust inhibiting grease) on the barrel and holes. It works very well for this application. I sometimes use it on my own parkerized barrels where they'll be covered by a rail. I rub a thick coat of it on and rub it into the finish well. Then wipe off the excess. It'll smoke a lot the first time you get it really hot but it'll still protect against rust etc. It sort of creates a waxy barrier.

lethal dose · #13 11-27-10, 09:09

Send the bbl and low pro gb to Steve at adco. Tell him to repark your bbl then PIN your gb on. Robb may also be able to offer this service, however I don't believe he can repark (he used norells last I knew).

HeavyDuty · #14 11-27-10, 10:50

I personally would just dimple and use a good setscrew GB - if it's under the rail, I wouldn't worry about pinning. IMO pinning is only essential with an exposed GB or FSB.

mhanna91 · #15 11-27-10, 10:57

Unless I am mistaken, I dont think that my barell will need to be re-parked. Stupid me did not even think to check out Adco, they will pin a lo-pro block for $45. Thats not too bad of a deal. I dont have a mill, and the jig will probably cost about the same as what it would cost to have Adco do it, so I may go with them. Since they only put one pin in, would it be worthwhile to have them dimple my barell and put two set-screws in as well? This service is only $10, I figure the stronger the better, right?

lethal dose · #16 11-27-10, 12:38

One pin is plenty... no point in dimples and screws. Set screws are inferior when compared to a pin. If your bbl was parked under the fsb, you won't have to repark. If it wasn't, is repark where the fsb was as the new gb likely won't cover the fsb marks. I do believe BCM parks under fsb.

mhanna91 · #17 11-27-10, 12:46

You are correct, my barell is parked under the FSB. I figured that one pin would probably do it, but I was not sure. I am new to all of this.

mhanna91 · #18 11-27-10, 20:54

Got an E-mail back from BCM. I guess this is what I will be doing. They were very helpful! Gives me some piece of mind that this advice came from the factory.

Hi Mark,
Got the pics, thanks!
Yes, I can see the crack.

I am going to guess, even if left as is - that gas block is going to be very
solid. When you remove it, it won't be easy.

I would recommend replacing with a low profile gas block and retaining
screws. If installed correctly, and a extended rail covering it from
impact, they are not coming out. When we remove front sights, it takes
about 2 minutes. When we remove our low profile gas blocks it takes about
20 min with MAP gas to get it free. The set screw is set into the dimple
and secured with loc-tite. It's a pain to remove.

Otherwise look at the DD clamp on low pro gas block. Those work as well.

Eric D. · #19 11-27-10, 21:09

Awesome, BCM customer service at its finest.

Quote:

Originally Posted by mhanna91

Got an E-mail back from BCM. I guess this is what I will be doing. They were very helpful! Gives me some piece of mind that this advice came from the factory.

Hi Mark,
Got the pics, thanks!
Yes, I can see the crack.

I am going to guess, even if left as is - that gas block is going to be very
solid. When you remove it, it won't be easy.

I would recommend replacing with a low profile gas block and retaining
screws. If installed correctly, and a extended rail covering it from
impact, they are not coming out. When we remove front sights, it takes
about 2 minutes. When we remove our low profile gas blocks it takes about
20 min with MAP gas to get it free. The set screw is set into the dimple
and secured with loc-tite. It's a pain to remove.

Otherwise look at the DD clamp on low pro gas block. Those work as well.

mhanna91 · #20 11-29-10, 21:04

http://www.bravocompanyusa.com/Danie...-p/dd-9111.htm

What is everyone's thoughts on these DD clamp on blocks? They cover up the holes left from the origional FSB, and BCM reccomended them in another email they sent me. Has anybody used one and know that they stay put?