Overclocking barrel

[andym79]

Hi guys,

I have changed a couple of barrels before no drama.

Wound the old one off, took a bit of force, went to wind the new one on. It over clocked easy, like 180 degrees. I know that as the barrel has sight groves and an extractor groove etc

The action is a Win 94BB.

If I were to try and file the shoulder to clock in the next 1/2 turn so that it lines up, how much forward motion would the shank experience (its a .875 shank with 28tpi).

I assume I would also need to file the end of the shank for correct headspacing on the rim.

Depending on how far the forward motion is, I may need to be careful of a slightly reduced chamber.

Can someone please help me with the maths. I want to know what the forward motion i.e loss in headspace and chamber size will be from advancing the barrel in another 1/2 turn.

Gut instinct tells me this might be too much to file. At a ball park I guessing 180 degrees could loose 20 thousandths?


Thanks in advance

[ascast]

at 28 tpi, 1 turn would be 1 / 28 th of a inch. 1/2 turn in would be 1/2 that.

if you are running windows, you have a calculator a few clicks away.

1/28th inch equals 0.03571 inch. 1/2 turn in would be 1/2 that or 0.01785 inch or just under 18 thousands.

[andym79]

Thats the problem with be raised on the metric system. Maths is generaly logical but not when it comes to metric threads.

Is it do able without a lathe? I guess headspace is the biggest issue, if enough material is taken off the end of the shank where the rim headspaces between the end of shank and bolt and headspace is checked I guess that it isn't a concern.

[Der Gebirgsjager]

I think a careful worker could do the job with a file, but you must be careful to remove about the same amount of metal all the way around the barrel's shoulder to obtain a snug, even fit, and not have a visible gap somewhere around the circumference. Another thing to consider when installing a barrel, the last 1/8 turn should be very snug to prevent the barrel from being loose or becoming loose in use, so you want to remove less metal than the full half turn. It should be what they call a "crush fit". You might or might not effect your headspace. So really, you want to remove somewhat less than the full indicated amount, and it's kind of a "cut and try" operation. Looking at the rifle from the muzzle end and using your slight dovetails as being top dead center, ideally you'd want the barrel to stop at about 11 o'clock when screwed in as absolutely tight as you could do so with your hands, and then bring it to 12 o'clock with your barrel wrench. A word of caution on these Win. '94-type receivers--you have to be careful not to collapse them. If you're clamping the barrel and turning the receiver, or clamping the receiver and turning the barrel, either way you need a spacer block inside the receiver. There is another way to go, less to be recommended, which is to use a very thin steel shim, like a thin washer, which slips over the thread shank and against the barrel's shoulder which prevents the barrel from screwing in quite as far, and you get where you need to be by screwing it in half a turn less rather than half a turn more. This could also effect your headspace. In theory, cutting back the shoulder might result in the necessity of removing the same amount of metal from the face of the breech and then cutting the chamber the same amount deeper; whereas using a shim might give you excessive headspace. But you won't know for sure unless you try, and either way you're not that far off and headspace might not change significantly. '94-type actions are more springy than bolt actions and often there's a little play in the action which makes things not quite as critical. I think you can do it, but worse case scenario, if you screw it up it can be straightened out by a good gunsmith without too much trouble. Good luck.

[shaggy357]

Should be able to find the right shims at Brownells or Numrich..only .017" in barrel shims should be cheap.....just an idea...

Steve :)

[flounderman]

put a washer on it and file the washer. If it is a rimmed case, you could get some headspace.

[JSnover]

+1 on shimming it back to position. Much faster and easier than cut-and-try to time it just right and then have to worry about headspace.

[Geezer in NH]

Old trick is to peen the barrel edge at the shoulder to make it lock up earlier. Trick has been done for years or go the washer route.

[Ballistics in Scotland]

Have you actually measured the barrel threads at the dimensions you quote? The sticky thread on barrel threads gives these dimensions, and the one for the ordinary 94 is about the same as in various books going back to the 1960s. Books do parrot one another mistakes sometimes, but one is Roy Dunlap's with a dimensioned drawing, and I can't see why the Big Bore would be smaller instead of bigger.

"Win 94 .809x20
Win 94 BB .875x28?"

Would .785 be a typo? That sort of accident happens to me a bit. If it is .875 (or 7/8in.) x 28 you can get a threading die to use, not for threading, but as a guide to evenly file the shoulder back. Just use feeler gauges between the die and the barrel shoulder. In the UK and no doubt in Australia it is a lot of money to pay for a die you won't even thread with. But here is one from China on eBay, which is a lot cheaper than a messed up barrel.

http://www.ebay.co.uk/itm/1pcs-HSS-Right-Hand-Die-7-8-9-10-12-14-16-18-20-24-27-28-32-Threading-Tool-/291421584986?var=&hash=item43da147e5a&autorefresh=true

Incidentally for anybody in the same situation with the standard 94, its thread is probably 13/16in. It is where the flanks of a V-thread are that counts, and the crests can easily be that .0035in. smaller with no harm at all done.

Alternatively if you know someone with a lathe, he could thread a piece of steel to use in just the same way. Why not just have him turn the barrel shoulder? It is the best way, but you might have a law, as we do, against firearms repair without a license, and this would only be making a tool.

The shim method can be good, but the shoulder on a 94 barrel is likely to be a narrow one, and there is a chance the barrel will spit it out as you tighten it. Various techniques, some of them mutually exclusive, could avoid this. You could file the shoulder forward and use a thicker shim. You could make one of spring steel and harden and temper it. You could indent the shoulder surface all over with a centrepunch. You could soft solder the shim to the shoulder.

Whatever you do, the hole in the shim should be so small that you have to screw it over the threads.

.01785in. extra on the shoulder is about at the outside limit for peening, and liable to look ugly. For a round barrel I would use a plumber's pipe-cutter with a bluntened wheel to emboss a narrow ring around the barrel. I think you would need a metal band temporarily epoxied onto the barrel threads to keep the cutter from slipping out of line. For an octagonal barrel press hard steel wires into two opposing sides, repeated four times in all, with an engineering press or a large vice.

Do the shoulder job or verify where the new barrel puts the case-head before your lay out money on ways of dealing with the headspace. It might be that if the maker has messed up the shoulder, he has still put the chamber and rim exactly as deep as they ought to be, and you won't have to do a thing after adjusting the shoulder. The class act for determining this is a depth micrometer, used from case head to barrel shoulder before assembly, but a reloader's caliper should be good enough.

The 94BB's cartridges aren't made for benchresting, and there is a pretty good chance that the .375 won't require extending for the case-neck, or the .307 or .356 for the shoulder. The last two would be the annoying one if it does, as you need an expensive chamber reamer to correct it.

[andym79]

Hi guys, firstly thanks for all the help!

I went the file route as Scotland said "but the shoulder on a 94 barrel is likely to be a narrow one, and there is a chance the barrel will spit it out as you tighten it." There is almost now shoulder below the barrel!

I used my micro files and went round and round. It was wrench tightening at 6oclock before but slow by filing it I got it to clock up. I also had to file about 5 thousandths of the face to give correct head spacing. As to the chamber well it took without a resistance on bolt close the cartridge I put through it. Fired it remotely in a remote area and all seems fine!