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| Fitting a SMLE Bolt Body http://www.yesterdaysweapons.com/phpBB3/viewtopic.php?f=23&t=8684 |
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| Author: | Gun Nut [ Mon Dec 28, 2009 12:19 pm ] |
| Post subject: | Fitting a SMLE Bolt Body |
After finding my numbered to the rifle bolt had a bit more sideplay at the Bolthead than I could put up with I finally decided to try a new bolt body and bolthead. I ordered both because I wasn't sure where the problem lay. Also surprisingly a new old stock unissued replacement bolt body turned out to cost less than a used bolthead. The Bolt Body I ordered is a BSA 1950's manufacture according to the vendor, and by all evidence the BB had never been fitted to a action body before, though it bears a Birmingham Nitro Proof stamping on the bolt knob. I suspect these were from the Austrian contract that ran out about 1956, and 1956 is stamped under the handle root along with M/470 (possibly a C rather than 0). Heres what I found out about fitting a new Bolt Body. First off the rear ends of the lugs are very roughly milled, and the angle where lug meets the body required quite a bit of careful hand filing and polishing to allow the bolt to turn home and lugs to sit back far enough to make contact. Till those angles, especially at the corners, were cleaned up the bolt fitting could not proceed. Due to the rough milled surface spotting wasn't easy. Mostly I proceeded by guess and by golly. I managed to obtain a pretty good fit but not perfect. Wear to the seats in the body required putting slight rake to the mating surfaces. Some rake of the surfaces is normal , and allowed for. Due to the unsupported open end of the resistence shoulders a very slight rake resulted on proof firing and was considered beneficial to ease opening when a cartridge expanded. Some No.1 rifles show very little rake at the shoulders, but every older SMLE I've examined displayed some. I found to achieve a good mating of the surfaces I had to stone the lugs at a slight angle to match the setback. I stopped at a hair over 50% contact on each lug , tesfiring will begin the final seating process. By the time its settled in headspace may be a thousandth or so more than it is now. I'll check headspace after test firing with some fairly hot Mk8z MG ammo I'd set aside not intending to use in the rifles. The Mk8 can be hard on a SMLE if used much, but should make a reasonable minimum proof and begin the seating process. If the bolt holds up to remote firing with several of these MG rounds then it should be fine with my lighter handloads. Perfect fit by stoning is nearly impossible, and lapping would only wear the action body shoulders un-necessarily. Advice on accuracy with the bolt actions says that 80% contact on each lug is necessary for good accuracy. At 50% before test firing firing I expect around 80% contact by the time the lugs settle in. PS Just examined the lugs again and compared them to the actual effective contact surface area of the seats and find I'm alread very near the 80% contact point after all. Due to the beveled section at the begining of each resistence shoulder the lugs when in full contact have nearly 25% of their surface free from any contact point. |
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