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  #1  
Old 08-02-2016, 08:00 AM
Triggershoe
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BB 7-2 Barrel Change



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Looking for guidance from anyone that has removed/installed a barrel on the BB 7-2. I'm interested in approx. how much heat is required to break the bond of the adhesive the Ruskies used for the original barrel install, and what techniques you used to pull the old and subsequently install a new barrel. Also, does the heat required ruin the original "Cerrocoat" type finish on the receiver, making a refinish necessary? I know, I've asked a LOT of questions but need some answers from the Brethren before I would attempt to do this .
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Old 08-04-2016, 06:07 AM
Triggershoe
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So, apparently no intrepid RFC'ers out there that have done a barrel change on the Izhmash 7-2? I find that somewhat surprising! It seems that I may have to enter uncharted territory and go where no RFC'er has gone before. To seek out new "Izhmash" gunsmithing knowledge and skills......Ok, I got a little carried away there! Still looking for some guidance with this. I assume the job would be similar to pulling the barrel on an Anschutz or other rimfire with pressed in/pinned barrels, with the exception that an unknown level of heat will be required simultaneously to break the adhesive bond? Any ideas on what type/brand of adhesive to use (if any) when installing the new barrel? How about pinning instead?
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Old 08-04-2016, 10:58 AM
gordonm1

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I'm a bit cheap and that's why I looked for an accurate Russian .22 and bought a BB. It's my best .22 LR shooter and I wouldn't think of changing the barrel. I think a lot of BB owners have no reason to change their barrels.

I'm curious why you want to change?
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  #4  
Old 08-04-2016, 07:49 PM
jagerman

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Why? Why would you change it besides just the fact that you want to or can? They may not win a beauty but are plenty accurate for what they are. My suggestion buy a pws toggle if you want to switch barrels on a toggle and hope it out shoots the Russian gun

Last edited by jagerman; 08-04-2016 at 07:52 PM.
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  #5  
Old 08-05-2016, 06:53 AM
Triggershoe
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Originally Posted by gordonm1 View Post
I'm a bit cheap and that's why I looked for an accurate Russian .22 and bought a BB. It's my best .22 LR shooter and I wouldn't think of changing the barrel. I think a lot of BB owners have no reason to change their barrels.

I'm curious why you want to change?
gordonm1 and jagerman--- Good questions/observations and suggestions. My "problem" is that I have two of these BB 7-2 rifles. Both were NIB rifles when I obtained them. I bought the second one (#2) because of my experience with the first one (#1). Rifle #1 is just wonderful, and shoots great. Inspection of the bore (yes, with a borescope) on rifle #1 reveals a beautiful, smooth, and almost hand lapped appearance throughout. Five shot groups under 1/2" @50yds are routine, some are MUCH better. Couldn't be happier with #1. However, not so much with rifle #2. I have NOT fired it yet. The visual appearance of the bore is not nearly as nice as rifle #1. There is what I would describe as multiple porosity/slag inclusions in the bore and I personally would not have faith in this barrel for use in competition. For plinking/hunting, hell yes. But I do a lot of CMP type Rimfire Sporter and also some ARA type benchrest matches ("sporter" class), and rifle #1 does very well at these venues. My original plan was to have one rifle set up for Rimfire Sporter (+3 lb. trigger) and the other set up for benchrest and other precision shooting venues at a lighter trigger pull weight. The triggers on these 7-2's are a PIA to adjust, and require removal of the barreled action to do so. But I digress... Now, it COULD be that rifle #2 would shoot OK as is in terms of accuracy, but I thought I would look into a rebarrel on this, so that I would personally feel "good" about rifle #2. I think you guys understand what I am talking about here (the feeling good part)... Or, it could be that you guys think I'm nutz! Sorry for the long post, but you asked me.... I was really just looking for advice on rebarreling
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Old 08-05-2016, 11:45 AM
gordonm1

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The different bore scope view is interesting. I'd say shoot it and foul up the barrel. Do whatever cleaning you do before you use the borescope and look at it again. Some of the roughness you see may get smoothed out with lead/lube. They were so cheap when they started importing them I don't doubt they had rough but tight barrels.

Someone will be along to help with the rebarrel questions
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  #7  
Old 08-05-2016, 06:44 PM
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Quote:
Originally Posted by Triggershoe View Post
So, apparently no intrepid RFC'ers out there that have done a barrel change on the Izhmash 7-2? I find that somewhat surprising!
Not when you consider the barrel is epoxied to the action. Too much pain for not enough gain, given the barrels are generally considered to be quite good for the price [originally, not now that the rifles are selling at 3x their original asking price.]

WRT your later post, just lap the barrel on #2 & see if you can slick it up enough. Then molyfusion it, and see if that enables it to shoot accurately w/o leading up.

Quite frankly, as long as the last 10cm of barrel before the muzzle & the crown are good, the only thing you're likely going to need to worry about is excessive leading & needing to clean more often than you'd like. The 22lr is pretty forgiving vs. a high intensity CF round.
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Old 08-10-2016, 07:46 PM
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Izhmash Barrels

My advice is to put the borescope away, thoroughly clean the barrel and just shoot it.

I have two Izhmash rifles, a Bi 7-2KO and CM-2KO both bought new. The barrels on my rifles, (and I assume all 7-2KO and CM2-KO), have hard chromed bores, a specialty of Russian firearms makers and particularly Izhmash. I believe this is because they perform better in extreme cold. Chrome plating is brittle and highly stressed, its surface when examined under a microscope is a maze of extremely fine cracks. Chromed barrels tend to need a long break in period to smooth the edges of the cracks - after which in a 22lr they should last for ever.

When first cleaning these barrels they felt very rough and tended to foul. After a few hundred rounds with regular cleaning the fouling diminished and the bores felt much smoother. The 7-2KO now has about 4000 rounds through it and shoots superbly. It is used in competition, cleaned after every meeting and the bore feels as smooth as glass. CM -2KO is not yet used as much but is shaping up to be a very precise rifle.

I wouldn't dream of changing a BB barrel without giving it a chance to prove itself.

Last edited by Tasman; 08-11-2016 at 05:29 AM. Reason: extra detail
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Old 08-11-2016, 08:33 AM
Triggershoe
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Quote:
Originally Posted by Tasman View Post
My advice is to put the borescope away, thoroughly clean the barrel and just shoot it.

I have two Izhmash rifles, a Bi 7-2KO and CM-2KO both bought new. The barrels on my rifles, (and I assume all 7-2KO and CM2-KO), have hard chromed bores, a specialty of Russian firearms makers and particularly Izhmash. I believe this is because they perform better in extreme cold. Chrome plating is brittle and highly stressed, its surface when examined under a microscope is a maze of extremely fine cracks. Chromed barrels tend to need a long break in period to smooth the edges of the cracks - after which in a 22lr they should last for ever.

When first cleaning these barrels they felt very rough and tended to foul. After a few hundred rounds with regular cleaning the fouling diminished and the bores felt much smoother. The 7-2KO now has about 4000 rounds through it and shoots superbly. It is used in competition, cleaned after every meeting and the bore feels as smooth as glass. CM -2KO is not yet used as much but is shaping up to be a very precise rifle.

I wouldn't dream of changing a BB barrel without giving it a chance to prove itself.
Tasman----I'm way ahead of you... I have already lapped out the bore (BB rifle #2) to the extent possible, although my skillset in this area is somewhat limited. Tried JB bore compound initially, it didn't really help much. I then used some 800 grit silicon-carbide compound that I had on hand. Much better results, and followed that with another application of the JB. Bore finish is much improved, however there are still substantial slag inclusions/porosity present. Definitely NOT smooth as glass like my first 7-2 (BB rifle #1). I guess I shouldn't be so lazy and learn how to post pictures here so everyone can see what I have been talking about. I CAN send them via email to anyone really interested. Suffice to say the bore on #2 is NOT very pretty in there... "Precise" would not be how I would describe it. Rifle #1's barrel, perhaps...

Tasman, I doubt that the bores on the 7-2's are chromed. Maybe on the 7-4's and the like? I could be wrong of course. Anyway, back to rifle #2. After the lapping, preemptively chamfered/polished the chamber entry, as a bunch of the 7-2's I have examined have a VERY sharp chamber entry, and tend to shave a tiny bit of lead off the bullets upon feeding. I also tuned the trigger up a bit, and lightened the pull to about 1.5 lbs. As far as accuracy, the proof is in the pudding as they say... Shot a few 5-shot groups at 25 yards (GECO "bolt action" ammo) off the top of my range bag, scope at 9X. The best groups were well under 1/4", with the smallest being 0.166". Remember this is at 25 yards. I guess the accuracy is somewhat acceptable despite the less than perfect bore. I won't know FOR SURE until I test further at 50 yards off of my front rest and rear sandbag bench set-up. We'll see....
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Old 08-11-2016, 10:09 PM
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Pictures would help perhaps I will PM you with my email address.

To get back on topic the barrels on both my rifles are pinned and not glued. Evidence is that penetrating oil seeps through the barrel/ receiver interface so you could check this with yours. In this case I would expect barrel change to be a simple matter provided you have a lathe. Remove the pin, drive out barrel with brass drift and hammer, machine new barrel to light push fit and Loctite it in. I have done a few on other rifles.

Re plating; both my barrel bores appear to be plated with something, if not chrome perhaps electroless nickel. I am assuming this from the surface of the flared muzzle counterbore which is very hard by my crude scratch test. If not plating there is some kind of heat treatment possibly nitriding, which I gather Anschutz use on their biathlon rifles. On reflection this might be the most likely - the barrels are certainly extremely hard all over. I found this when I tried to drill into the 7-2KO barrel when fitting a scope mount, cobalt drills wouldn't look at it. I put this down at the time to work hardening due to the cold hammer forging process. I am a metallurgist but retired so I don't have access to the testing equipment to determine for certain.
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Old 08-12-2016, 07:04 AM
Triggershoe
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Quote:
Originally Posted by Tasman View Post
Pictures would help perhaps I will PM you with my email address.

To get back on topic the barrels on both my rifles are pinned and not glued. Evidence is that penetrating oil seeps through the barrel/ receiver interface so you could check this with yours. In this case I would expect barrel change to be a simple matter provided you have a lathe. Remove the pin, drive out barrel with brass drift and hammer, machine new barrel to light push fit and Loctite it in. I have done a few on other rifles.

Re plating; both my barrel bores appear to be plated with something, if not chrome perhaps electroless nickel. I am assuming this from the surface of the flared muzzle counterbore which is very hard by my crude scratch test. If not plating there is some kind of heat treatment possibly nitriding, which I gather Anschutz use on their biathlon rifles. On reflection this might be the most likely - the barrels are certainly extremely hard all over. I found this when I tried to drill into the 7-2KO barrel when fitting a scope mount, cobalt drills wouldn't look at it. I put this down at the time to work hardening due to the cold hammer forging process. I am a metallurgist but retired so I don't have access to the testing equipment to determine for certain.
Tasman-- Regarding whether the 7-2 barrels are glued, if yours is an original Izhmash installation I'm betting it IS. I also noted the oil seepage at the tenon while thoroughly cleaning mine after lapping, using compressed air to blow/dry everything off. I could see tiny "bubbles" forming at the joint. I think all this means is that there are minute voids in the glue/metal interface, allowing a path for solvent to leak through. I could be wrong, but I sure would not try to remove a 7-2's barrel without heat. Regarding the bore finish, the two 7-2's that I have do not appear to have any type of plating. I agree that the barrels may have possibly been nitrided. That's a very interesting comment about trying to drill yours. If a cobalt drill bit wouldn't touch it, that surface must have a very high Rockwell number.
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Old 08-13-2016, 09:02 AM
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You might want to try contacting Altius for info since they offer rebarreling services for Izhmash rifles.

http://www.altiusguns.com/
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Old 08-13-2016, 07:19 PM
Triggershoe
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Originally Posted by Silas View Post
You might want to try contacting Altius for info since they offer rebarreling services for Izhmash rifles.

http://www.altiusguns.com/
Silas, I have been in contact with Altius via email. I fine gentleman named Marc gave me some good suggestions regarding deciding what to do with my BB 7-2 (rifle #2's) barrel. Also, I doubt I could have gotten the ejector out undamaged if he had not offered some guidance. I needed to remove the ejector for the barrel lapping operation, as it will chew up a cleaning rod in short order. I cannot thank Marc at Altius enough. Hope he does not mind my mentioning his name.... Anyway, the ejector is pressed/driven into position by the way, and is driven completely INTO the receiver for removal after you remove the magazine well (for clearance). If one looks at the ejector from the outside of the 7-2's receiver, there is what I thought was a slot for a screwdriver. WRONG! This slot is merely a visual alignment aid for use when installing the ejector. As you indicated, Altius does remove/install barrels on the Izhmash rifles. I may avail myself of their services if rifle #2's barrel does not perform and I decide to rebarrel. For now though, I need to test more at 50 yards before making that decision.
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Old 05-22-2020, 08:49 AM
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Doing it.

My 7-2-KO always strings vertically. Bought it new and spiffed it up quite a bit, pillar bedding, made the trigger adjustable, refinished the stock, fabricated a full length one piece scope rail from a Nightforce steel picatinny blank, installed a checkered metal butt plate. Still not fun to shoot, and discovered a possible culprit with a bore-scope... the transition of the chamber to the lands was mangled somehow, and knew the barrel at a minimum needed to be removed and trimmed/rechambered. Problem is all my .22 LR reamers have .216 solid pilots, and the Izzy has a .215 minor i.d. grrrrrr.

Pressed out the barrel and to my dismay discovered very little epoxy holding the ensemble together. Turns out the design incorporates a sleeve within the receiver that captures the forward action screw post (which was wobbly/loose) and has a slight interference fit at either end, relying heavily on its own epoxy which was lacking as well. The barrel in turn is epoxied into this sleeve, and similarly has an interference fit only in the vicinity around the extractor cuts, with epoxy securing everything from there forward. Keep in mind the voids were about 70% air, and 30% epoxy on mine, which might have compounded the marginal performance attributed to the shoddy chamber???

The sleeve had to go. Came up with a crazy idea for an indexable barrel arrangement, that will permit barrel/caliber changes for different .22's and a Mach 2 barrel down the road. Going to single point a new chamber on the factory barrel since I doubt I'll ever need a .215 pilot after it's done, as even my tight bore Lilja's accepted a .216 pilot. In the future I might get a PTG premium reamer with interchangeable pilots. The latter task (rechambering the stock barrel) will tell me if the chamber and/or more secure barrel fitting improves the grouping with the previously poor performing barrel. I might add that aside from the chamber, the original bore appeared to be exemplary!!

As it stands, last night the receiver got clamped into the band saw, and lopped off everything from the aft edge of the forward action screw hole forward. The new arrangement will be grafting on a new receiver nose that borrows a lot from a BR50's design, which will make barrel adaptations quick and painless. By the way... got a chuckle as the saw was running... the receiver sang like a wind-chime due to the inner sleeve's epoxy voids allowing the sleeve to resonate... it was at that moment I knew things could only get better

Will post updates.
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Old 05-23-2020, 06:33 AM
Triggershoe
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Quote:
Originally Posted by Ziabeam View Post
My 7-2-KO always strings vertically. Bought it new and spiffed it up quite a bit, pillar bedding, made the trigger adjustable, refinished the stock, fabricated a full length one piece scope rail from a Nightforce steel picatinny blank, installed a checkered metal butt plate. Still not fun to shoot, and discovered a possible culprit with a bore-scope... the transition of the chamber to the lands was mangled somehow, and knew the barrel at a minimum needed to be removed and trimmed/rechambered. Problem is all my .22 LR reamers have .216 solid pilots, and the Izzy has a .215 minor i.d. grrrrrr.

Pressed out the barrel and to my dismay discovered very little epoxy holding the ensemble together. Turns out the design incorporates a sleeve within the receiver that captures the forward action screw post (which was wobbly/loose) and has a slight interference fit at either end, relying heavily on its own epoxy which was lacking as well. The barrel in turn is epoxied into this sleeve, and similarly has an interference fit only in the vicinity around the extractor cuts, with epoxy securing everything from there forward. Keep in mind the voids were about 70% air, and 30% epoxy on mine, which might have compounded the marginal performance attributed to the shoddy chamber???

The sleeve had to go. Came up with a crazy idea for an indexable barrel arrangement, that will permit barrel/caliber changes for different .22's and a Mach 2 barrel down the road. Going to single point a new chamber on the factory barrel since I doubt I'll ever need a .215 pilot after it's done, as even my tight bore Lilja's accepted a .216 pilot. In the future I might get a PTG premium reamer with interchangeable pilots. The latter task (rechambering the stock barrel) will tell me if the chamber and/or more secure barrel fitting improves the grouping with the previously poor performing barrel. I might add that aside from the chamber, the original bore appeared to be exemplary!!

As it stands, last night the receiver got clamped into the band saw, and lopped off everything from the aft edge of the forward action screw hole forward. The new arrangement will be grafting on a new receiver nose that borrows a lot from a BR50's design, which will make barrel adaptations quick and painless. By the way... got a chuckle as the saw was running... the receiver sang like a wind-chime due to the inner sleeve's epoxy voids allowing the sleeve to resonate... it was at that moment I knew things could only get better

Will post updates.



Z-- Please do! That's very interesting about that "sleeve" you mentioned.. I was not aware of that. I knew the barrels were glued/pinned, but as has been mentioned, the glue job is not well executed and the voids are there (evidenced by oil seepage from the barrel receiver interface) for sure. That's funny about the receiver "singing" in the bandsaw---would like to have heard that! Sounds like you have taken on quite a project there, my friend. Going where no man has ever gone on the 7-2! I wish you success with this, and by all means keep us informed with your progress.
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