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Old 11-13-2006, 04:07 PM
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Izhmash Biathlon Basic Modifications

Fuzzy's Projects . . . !
Bryan "Mick" Knight and others

Izhmash Biathlon Basic Rifle Modifications

Quote:
This rifle . . . a relative newcomer to the American shooter, and intended as one of several "sporterised" versions of the original Russian Baikal/Izhmash Biathlon match rifles . . . is proving to be one of the best acquisitions on the market for the smallbore rimfire shooter desiring good accuracy and reliability at a relatively low cost. Other variants of the BB, as it's becoming known to the American shooter, are equipped with barrel-mounted open sights, or storage for extra magazines in the butt. Like much of the inexpensive Russian equipment it will not win any prizes for superb aesthetic finish, but the actual important parts - the receiver, trigger mechanism and barrel - are well made and appear to offer the reliability of the proverbial brick outhouse ! The stock, is of some unknown hardwood, and might even have been whittled out of a convenient 2x4, but overall this rifle will outperform the vast majority of the current American crop of smallbore rifles right out of the box !

The action - a toggle bolt type - will be somewhat strange to the average American shooter. Borrowed from its' Biathlon parent, ( I suspect that the actions actually used are those from the high-end Biathlon Rifle production line that didn't "quite make the cut" in quality control ), and designed primarily for speed, and ease of usage when wearing gloves, it offers re-loading times much faster than the typical bolt action, and approaching those of a semi-automatic. It offers an alternative approach to that used in the more sophisticated Forstner action of the very expensive Anschutz biathlon rifles. Here are full views of the stock BB from both sides:



Quote:
Overall the lines of the rifle are pleasing . . . it offers good balance in the hands .... points naturally . . . and has a heavy enough barrel to offer considerable stability in the hold. The trigger, as delivered does exhibit some creep and over-travel, but typically has a pull-off weight of approximately 2#. The trigger mechanism offers some facility for adjustment to suit personal needs . . . some rifles, apparently randomly, are even fitted with a fully adjustable mechanism similar to that on its' big brother, the more expensive, Izhmash Biathlon used in formal competition.

If you are considering using one of these BB's for current CMP Rimfire Sporter competition in the 'Scope-Sighted "T" Class, as many of us are, it will almost certainly have to undergo some minor modifications. When fitted with anything other than the simplest fixed-magnification scope, the overall weight will probably exceed the CMP 7.5# maximum limit . . . so some "dieting" is required ! Secondly, with that 2# trigger pull, a little exploration of the trigger mechanism will be needed to bring it up to the CMP 3# minimum. Finally, and again probably due to the "quality control considerations" noted above, you may have to do a little adjusting/polishing of action components.

Stage 1 - 'Scope Installation and Preliminary Weighing

So . . . . let's get started ! Assuming that you've decided on a suitable set of Weaver-style rings and a 'scope, install them and check the correctness of 'scope location, fore and aft, for correct eye relief in all three shooting positions - (Prone, Sitting/Kneeling and Offhand). & Now weigh the rifle, using an "accurate scale". I have found the Rappala digital fish scale sold in the Sporting Goods department at Walmart to be accurate enough within, say, +/- 0.1# for the purpose. (Ref: Topic #11 on the Projects Index page).

If you meet weight limits - Fine ! If not, then consider your options . . . switch to a lighter scope/rings combination and try again . . . or start whittling on the stock ! Some ideas for "stock whittling" are shown in Project #9, including my own "Tatiana", the slinky city lady in 'basic black' that we created from the original peasant gal BB. For reference I found that it was possible to remove almost 0.5# of weight from the original stock in that transformation process. Always keep in mind that the rifle "MUST FIT YOU" if you want to shoot your best !

Stage 2 - Checking the Action for Smoothness

Before starting on any modifications or general tuning, first find out what the rifle can do . . . how smooth is the original OOB action !

Referring back to the "possible quality considerations" how smoothly does each round feed from the magazine to the chamber, when actuating the toggle bolt, as compared to the smoothness when actuating the bolt without any rounds in the magazine ? From first-hand examination and trial of several examples of the BB action, it has been observed that there can be a distinct "end-of-travel" hang-up in the feeding operation. If this is observed, take a closer look at the way the incoming round is gripped by the face of the advancing bolt, particularly with regard to it "sliding freely" into the bolt face pocket, and under the claws of the two extractors. If the extractor claws exhibit insufficient clearance from the bolt pocket face, then the round does not fully enter the pocket and tends to hit the chamber entrance at too steep an angle. There is a tendency for the extractor claws to show a little skewness in their pockets, and to have rather sharp, burry edges.

To remedy this problem start by removing the bolt . . . Depress the pawl at the rear and after lifting out the rear toggle pin, slide the complete bolt block and toggle linkage out to the rear of the receiver. Now take a round of ammo, and test insert it into the bolt face pocket by lightly sliding it upwards as if it were being fed from the magazine. In all probability it will only go about 1/2 to 2/3 of the way in before becoming "tight". The remedy is to examine the extractor claws for skewness and/or burrs . . . if found a LIGHT filing or stoning is recommended . . . keep those under-surfaces of the claws basically parallel to the bolt face, with just a slight relief on the lower leading edges. Remove just enough material to remedy the problem . . . NO MORE ! . . . and keep testing with the re-assembled rifle/bolt and a round of ammo as you go. I'd suggest using an old style ignition point file, or better yet, one of the "el cheapo" diamond-coated Chinese ones now available, for the operation, which can then be done without removing the extractors from the bolt.

Clean the bolt and toggles thoroughly after this adjustment and re-lube the complete assembly with a suitable product . . . I have used either Shooters Choice High-Tech grease, or Primis Lube Gel with good results.

Stage 3 - Trigger Mechanism Adjustments and Modifications

For the purposes of this article I'll assume that we're going to "heavy up" the trigger for CMP competition . . . if you want a lighter match or bench-rest pull-off, then some operations will need to be "reversed".

Let's start by removing the barreled action from the stock . . . first a single screw at the rear of the trigger guard must be removed and the moulded plastic guard lifted out . . . it has a lip at the front that engages in a recess in the stock. Then undo the the two captive screws holding the barreled action to the stock, and separate the two pieces. Lay the stock to one side and let's take a look at the barreled action, and particularly the trigger mechanism

Fig A - Left-Hand View


Fig B - Right-Hand View


Fig C - Bottom View


Fig D - Trigger Mechanism Bits

Last edited by aom22; 12-22-2007 at 04:38 PM. Reason: Update Links
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