Converting a 7400 barrel to a 7600 barrel

[Boondox]

I already did it but haven't fired it yet. Here's the full story below.

I went on a hunt for a blued 7600 barrel in 308 or somebody who had and would change the bracket from 30-06 to 308. No dice on either; I'd still prefer a 7600 308 barrel but nobody has one.

A guy had a 7400 barrel for sale that was 308, told me to just convert it to a 7600 barrel. Made sense they're the same gun minus the action. So I bought the barrel, heated up the gas block and knocked it off. Crazy the size of the gas port in the barrel it's 1/8" or better.

A old gunsmith I was talking to said just weld the port hole closed and Bob's your uncle. In my haste and excitement of my quest for a barrel I thought it was a hell of a idea.

So I took the MIG and welded the hole closed, settled on MIG cause it was the least amount of heat to get the job done. Now my question is to all you real gunsmith fellas; am I good to go or was misinformed? Inside the barrel is clean and shiny, no heat marks even around the hole; just a neatly plugged hole. As you know it's not at or just ahead of the chamber it's just under the front of the forearm.

 

[jackieschmidt]

I would have made a small slug to tap into the hole, ( making sure it wasn’t protruding into the ID, then a small tack to cap it with the mig welder.

That would insure that no bleed by found it’s way into the bore.

 

[Boondox]

I would have made a small slug to tap into the hole, ( making sure it wasn’t protruding into the ID, then a small tack to cap it with the mig welder.

That would insure that no bleed by found it’s way into the bore.

I'm not metallurgist but the way I see it it's safe to fire ya? I mean, from the size of the hole in the barrel for the gas port I really can't see pluggin it bein a bad thing. I was honestly ( no pun intended ) blown away at how big the hole is for the gas port. I did stick a steel bore brush inside to the port hole just in case any slag went inside the bore it'd melt into the bristles instead of stick to the inside of the bore.

If I really had too I could drill the weld out and tap it for a grubbers then tack it. This is my first time doin a job like this. I can drill, tap, thread, refinish wood and metal work on triggers and everything else of that sort... But it's the first time welding anything on a barrel.

 

[jackieschmidt]

of course, for that very small spot you welded, the puddle temperature did exceed the transformation temperature of the alloy steel barrel. That means that small spot will more or less be in an annealed state. But since it is pretty far down the barrel, the pressure has already dropped to a level to where I doubt there would be any problem with strength.

 

[Boondox]

of course, for that very small spot you welded, the temperature did exceed the transformation temperature of the alloy steel barrel. That means that small spot will more or less be in an annealed state. But since it is pretty far down the barrel, the pressure has already dropped to a level to where I doubt there would be any problem with strength.

See this is the kind of answer I was lookin for! My senior smiths on gunnutz ( Canadian gun forum ) are a bunch of asshats and just give me stupid answers that are of zero help.

I've got sets of 4 loaded up for this barrel. 168 grain ballistic tips, once fired Winchester brass, federal 210 GMM primers and 42 to 44 grains of varget in .5 grain increments. I'm trying to keep the speed low on purpose to keep the pressure down and the velocity as well so the Btips break on through to the other side! Yeah yeah yeeeeaahh!... Sorry, Jim Morrison took over there for a second.

I probably could have found a used 7600 in 308... But that 308 wouldn't be MY RIFLE. My baby, my pride and joy. I had to sit and have a real long heartfelt talk with my rifle while she was still wearin her 30-06 barrel to explain that her hot rod, fire breathin love is hard on my shoulder even before surgery. She's just gotta slip on a new dress for a couple years till I'm able to tolerate her tough love again.

My 30-06 is the first and only rifle I've used since I bought it new 16 years ago. I did shoot a buck with my late uncles 308 760 last November though, promised him I would.

 

[Boondox]

Not gonna lie, being a American gun forum I definitely expected this thread to take off real quick. I mean that with absolute respect, Canadians aren't as gun horny as our neighbors; I definitely am, but most aren't

 

[Jonnyofalltrades]

With all due respect, Jackie, I have to disagree about the weld area being annealed. The weld itself likely went down through the critical temperature slowly enough, but there will be a Local Brittle Zone(LBZ) in the base metal around the weld that was quenched by the mass of cold metal around it. Much smarter people than I have written many words to explain it all. Just Google local brittle zones if you want more info. Generally some pre- or post heat-treatment will reduce the hardness (like gently heating with a propane torch to get a blue color)

Sorry Boondox, but you can't get away from us dumb Canadians that easy!

 

[Boondox]

With all due respect, Jackie, I have to disagree about the weld area being annealed. The weld itself likely went down through the critical temperature slowly enough, but there will be a Local Brittle Zone(LBZ) in the base metal around the weld that was quenched by the mass of cold metal around it. Much smarter people than I have written many words to explain it all. Just Google local brittle zones if you want more info. Generally some pre- or post heat-treatment will reduce the hardness (like gently heating with a propane torch to get a blue color)

Sorry Boondox, but you can't get away from us dumb Canadians that easy!

I'm a Canadian too. Embarrassing thing to say these days to be honest. I wasn't sayin we're dumb, I'd assume you're on gunnutz so you know how helpful the guys are on there. Within the first 5 posts of a thread it's turned into a completely off topic pissin match between members about somethin other than the original topic.

 

[Jonnyofalltrades]

Yep, it can go downhill fast. We're all world class experts in our own minds.
This is one of the most respectful forums I've ever been on.

 

[Boondox]

Yep, it can go downhill fast. We're all world class experts in our own minds.
This is one of the most respectful forums I've ever been on.

It really is, I lurked around for a few months before I signed up. Folks here don't just chide in, if they don't know or don't got nothin good to say they just don't say it

 

[akajun]

I have taken shot out ar15 service rifle barrels, and turned them into carbine barrels, and some of the 26" WOA long gas system barrels into 20" lightweight service rifle barrels for juniors. I drill and tap the old gas hole for a set screw about halfway down, then loctite it in place. Never had an issue.

I would be worried that the heat would warp /distort the bore, causing accuracy issues. But if I had to weld it Id use tig, or even tig brazing with Silver Solder

 

[Timberyote]

Canadians aren't as gun horny as our neighbors; I definitely am, but most aren't

You obviously don't live in my area!

 

[jackieschmidt]

With all due respect, Jackie, I have to disagree about the weld area being annealed. The weld itself likely went down through the critical temperature slowly enough, but there will be a Local Brittle Zone(LBZ) in the base metal around the weld that was quenched by the mass of cold metal around it. Much smarter people than I have written many words to explain it all. Just Google local brittle zones if you want more info. Generally some pre- or post heat-treatment will reduce the hardness (like gently heating with a propane torch to get a blue color)

Sorry Boondox, but you can't get away from us dumb Canadians that easy!

That is why you place the barrel in an oven and preheat the parent metal to around 300 degrees.
Any time we weld anything that is considered an alloy steel in a tempered state, we always preheat and use a low hydrogen rod or wire.

The 300 degrees I is well below the transformation range of just about any alloy steel, so there is no danger of changing the mechanical propertire of the parent metal.

 

[Jonnyofalltrades]

That is why you place the barrel in an oven and preheat the parent metal to around 300 degrees.
Any time we weld anything that is considered an alloy steel in a tempered state, we always preheat and use a low hydrogen rod or wire.

The 300 degrees I is well below the transformation range of just about any alloy steel, so there is no danger of changing the mechanical propertire of the parent

Yes, that is certainly best practice.

 

[Wild Bill IV]

I worked in the oil patch in a Fab shop!!! Drilling Rig towers are made of chrome moly steel, 4140 or 4130!! Race car frames use the same alloy!! I believe some rifle and shotgun barrels are also made from C-M steels!!

Several times, I would Magnaflux all the welds for cracks!! Circle mark the cracks with red marker, circle the pipe below the crack with red tape, and have the shop Forman pull the tower into the shop!!! Two certified welders would work on each crack!!! One with a rose bud torch tip, and the other with stick rod!!! 4100 series alloys have to be slowly preheated before welding, and slowly, SLOWLY quenched after the weld to eliminate crystallization!!! And, some of the welds I found on the tower were crystallized with cracks all around the weld!!! Somebody that wasn't certified made those welds!!! I then had to Magnaflux their welds to certify inspection of the tower!!!

I HAVE TO SAY THIS AS AN ENGINEER, DO NOT APPLY ANY HEAT TO ANY PART OF A FIREARM, UNLESS YOU KNOW THE MATERIAL TYPE, AND YOU KNOW WHAT YOUR DOING!!! IF YOU DON'T KNOW, FIND A WELL QUALIFIED GUNSMITH!!!!

 

[snert]

Wild...brother...I gotta turn my hearing aid down when you write!!!!!!!!!!!!!!!!!! Excited?

 

[Jonnyofalltrades]

Hope you don't mind, Bill, but I'll just keep on using a soldering iron to loosen loctited screws, a heatgun to remove stubborn choke tubes and brakes, and a torch to silver solder on sight ramps and such.
No offense....

P.S. I used an oxy-acetylene torch to recontour a Mauser bolt handle just the other day. Sorry.

 

[jackieschmidt]

Hope you don't mind, Bill, but I'll just keep on using a soldering iron to loosen loctited screws, a heatgun to remove stubborn choke tubes and brakes, and a torch to silver solder on sight ramps and such.
No offense....

P.S. I used an oxy-acetylene torch to recontour a Mauser bolt handle just the other day. Sorry.

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