Advice needed ... bolt opens on firing!

[303Guy]

Right, here it is.[IMG][/IMG]

From your photo which is not as zoomed in as this one, it looks as though that cam face is worn.

[Son]

I would like to know the accurate weights of the mainspring, and an accurate measurement of headspace. Also a measurement of rim thickness of what are obviously commercial and therefore most likely undersized case rims. Check the striker protrusion as well...

Please humour me a little here... we seem to be entering uncharted territory...
If the mainspring is significantly weak, it may have enough momentum to ignite the primer. But at full travel, indenting the primer, I wonder if a weak spring and the primer backing out/ case expanding rearward into the head gap is off- seating the striker and therefore the cocking piece in the long cam groove enough to allow the bolt to lift unopposed when "bounced" under the handle by the receiver.


Just another thought... how far does the bolt handle lift before the cam stud engages on the ramp between the long groove and the short groove... the adjustment of the striker and bolt head relationship determines this...

When screwing the bolt head in with the striker in the fired position, the rear of the bolt head should contact the collar on the striker a few degrees before the bolthead rotates to the position it is in to fire. At this point the cocking piece begins to move back from the bolt body. If it engages well before, then the cam stud has much more free play to allow bolt lift and much less ramp to prevent it.

Might be onto something here... From your pics, the cocking piece doesn't seem to be moved very far back to get into the short cam groove, indicating it may not be very far into the long groove when fired. If this is the case, then the bolt handle would have a lot of free play "lift" before it engages the cam.

Look at the gap between the cocking piece and rear of the bolt body here, with the bolt handle lifted.... yours looks a lot less than that to me.. gladly stand corrected if not
Attachment 46008

[Peter Laidler]

Ain't looked at this in any depth but the ONLY mechanical explanation that there can be is this. Excess CHS is causing an undue amount of inertia to be exerted upon the bolt. The locking cams of the bolt and body are worn to such an extent that instead of FLAT surfaces bearing hard against each other on recoil, you have rounded surfaces acting on each other and these rounded surfaces are in effect no more than a thread - albeit an interrupted thread of course. This is acting no differently than a loose hub nut. The looser it gets, the more 'hammer action' or cyclic inertia you get against it and thereafter, the faster it unwinds itself.

In this case, there is a massive initial drive against the bolt, the surfaces try to unwind and there's onloy one way to go............

Worn body and bolt. ZF/BER. But the ZF route was always on the cards in any case.

ZF is the UK Military equivalent of scrap

You could try to replicate this by putting a brass .3" or so dia rod down the bore against a spent case and hammering the case backwards. No good using a press. The explosive and instantaneous action of a cartridge exploding doesn't happen like that. You need to replicate it using an immediate instant load such as a big heavy hammer blow

Am away for a few days. Look forwards to the comments and all have a good time. I will!

[browningautorifle]

I sure thought they looked like bullet holes

Recycled roofing. The holes are at the top of the ribs where we used to nail the tin down.

---------- Post added at 08:59 AM ---------- Previous post was at 08:58 AM ----------

Excess CHS

Sounds about right...

[spentprimer]

Right, here it is.http://<a href="http://s388.photobuc...a0.jpg</a></a>

From your photo which is not as zoomed in as this one, it looks as though that cam face is worn.

Comparing to the photo you posted, the one in my rifle is quite worn in that area of the bolt. The camming surface is actually quite polished and the edges seem to be "rolled over" a bit. Seeing your photo makes me believe this rolled over wear or perhaps better described as peening is not normal and certainly not wanted. Additionally, given the marks on the stock socket and bolt handle as well as Peter's CHS thoughts, I will start looking for a bolt and a cocking piece. It seems as though someone was selling some NOS one's in an internet surplus site somewhere. In the meantime, I will continue to look for a usable means of measuring cocking force of the mainspring and see if anything there seems to be incorrect.

As to the cartridge rim thickness. The surplus ammo with headstamp: GB1944 VII . (1) .059", (1) .062", (4) .063".
The rims on the reloads are: (1) .058", (2) .059", (1) .060", (2) .061".

So far there have been 13 rounds fired downrange. Scott has the case head of one round that is not included in the rim thickness measurements and it was a reload. None of the surplus ammunition had case head separation.

Thank you to everyone that took the time to follow this saga, examine the video and photos, interpret my mis-labeling of parts and trying to understand my written description of the problem at hand. And most importantly added your insight and expertise! I really do appreciate it.

As parts show up and I have more questions or updates I will post back here on this thread. Hopefully, we can get this tired old warhorse back in the fight after curing her ailments.

I really appreciate your help with this matter.
Bill

[srtolly1]

Umm,,yah forget the duct tape!! Even though I have no clue what's going on with this rifle,,, I just have to say Fatman is a animal.!!,,My man is fearless.

Not fearless, not real bright either. The Marine Corps sucks the fear out of you.

Almost forgot I was on this forum, lost all my bookmarks.

The bolt handle was most definitely all the way down. As stated in an earlier post, the pressure would have to be down before the handle could come up. The first round I fired on this rifle popped the bolt handle up.

[David TS]

Are those bullet holes in the overhead cover at the range in the video?

LOL at Brian

Tell you what, there's no way you'd ever get me to fire that rifle............

[jmoore]

Right, here it is.http://i388.photobucket.com/albums/o...ps072ae0a0.jpg

From your photo which is not as zoomed in as this one, it looks as though that cam face is worn.

A couple of thoughts since I was on last:

303Guy's photo made me wonder if either the cocking cam cut is rather too wide or is off postion. That or the stud on the cocking piece is small.

But the second thought that occurred is that maybe the firing pin isn't screwed fully into the cocking piece. Which would imitate the issues above, i.e., too much rotational slop.

Combined with a loosish bolt or one that needs relieving on the underside of the bolt handle, the combination might be enough to create that much bolt unwind. Normally, you would expect the cocking cam faces to move the handle back down, so...

I think the test at the bottom of Son's Post #62 would be most helpful.

Might be onto something here... From your pics, the cocking piece doesn't seem to be moved very far back to get into the short cam groove, indicating it may not be very far into the long groove when fired. If this is the case, then the bolt handle would have a lot of free play "lift" before it engages the cam. Look at the gap between the cocking piece and rear of the bolt body here, with the bolt handle lifted.... yours looks a lot less than that to me.. gladly stand corrected if not

[Bruce_in_Oz]

A couple more things:

With the bolt in the rifle, the safety stud on the cocking piece should NEVER "bottom out" in the "firing side" of the cam track of the bolt. Continuous "bottoming-out" will cause a fracture of the HARDENED carbon-ally steel / "special" iron. The collar on the "mild steel" striker is where any "impact" should be taken.

SMLE strikers (should) have a qualified / indexed thread.

On drawing C-583 (13 August 1920, it states:

"30 Thds. (threads) per inch R.H.
Position and figure of thread and keeper screw recess B (ref. to drawing) to be in accordance with gauge."

Of course, one needs the spec for the gauge to establish the "start point" of said qualified thread.

On C-587 ( the drawing for the earlier (1920) cocking piece, we read:

".25 diam. 30 thds. per inch R.H. Position and figure of thread to agree with gauge.

Good luck with that!

SO, the striker and cocking piece threads are QUALIFIED and thus expected to assemble the same way EVERY time, more or less.

The cocking piece has very fine tolerances on the location of ALL working surfaces. The length of the safety stud is specified at 0.244" High and 0.240" Low. There is a 0.007" TOLERANCE on its overall position on the tongue of the cocking piece.

The length of the main parallel body of the striker is an ABSOLUTE 5.377", i.e., ZERO tolerance.

The "collar" has a 0.005" tolerance on its thickness and the tolerance for the distance from the front of the collar to the tip of the striker is 0.002", i.e. 1.368"Accept", 1.366"Reject.

No wonder these things were time-consuming and expensive to make!

And don't forget that these components were made on late-19th century machines; ONE operation (cut, grind etc) per set-up / jig, and all powered by steam-driven overhead shafts and leather belts.

[303Guy]

Two bolts I looked at will bottom out on the bolt body/cocking piece faces before the safety lug but one doesn't have the minimum half turn on the bolt head. But it does bottom out on the bolt head.