Headspace on an M1917

[Patrick Chadwick]

Dear Edward,
I was delighted to see your photos of the 308 cartridge fired in a 30-06 chamber. But your comment "One half inch of excess headspace ..." seems to be a trifle misleading.

From your contributions, I deduce that you have the CIP or SAAMI data to check this out: The shoulder diameter of the 308 case is actually slightly larger than the diameter of the 30-06 case at the same distance from the base. So if you feed a 308 case into a 30-06 chamber it will jam. I have mentioned this before, in describing how a clueless person next to me at the range was cursing because it was so difficult to close the bolt. There will,in this situation, be actually zero head clearance on the 308 case.

A genuine 1/2" of clearance would make it impossible to fire a cartridge - the firing pin would not be long enough!
The jamming/camming effect will obviously be highly sensitive to chamber size and degree of resizing applied to the case. I suggest you try it out.

Patrick

[Chuckindenver]

Patrick?
your are correct, the .308 is a little fatter then the 30-06, and is a little tough to feed into a bolt action 30-06, and for years thought it might be tough...untill it happened to me.
last summer, at the range, my son mixed up the .308 with the 30-06.. i reached in the 06 can, grabbed a round, tossed it in my A3, and touched the switch, heck, it even hit the steel target i was aiming at, ejected the case, and to my suprise it looked exactly like the one pictured,
i felt nothing different when i went to close the bolt,
however, in the past, iv tried with the fring pin assembly removed, on other 03,s and the bolt would not close on a .308 round.
could have been just me, closing the bolt in a hurry, a slightly oversized chamber , who knows for sure, i still have the case someplace, as a dummy reminder, to never get in a hurry, and look at what you feeding your rifle.

[jmoore]

Haven't done this trick , yet, myself, but I have picked up a few at various ranges. It's rather shocking the first time you see one.

[Chuckindenver]

first, and only time for me ,,i hope. it was like a WTF...momment.

[Innovative]

How about this one?

This shows a 300 Win. Mag. round fired in a 300 Weatherby rifle. Notice the unusual fired case. This could easily have been a real disaster.

[Weatherby round on the left, the 2 on the right are both Win. Mags.]

[jmoore]

Yup, complete w/ longitudinal splits in the case neck. It's in my odd dead brass collection somewhere, along w/ something like a .30 Carbine round fired in something WAY too big in diameter. There was enough pressure to swell the entire case forward of the web to a surprising degree.


The belted mag example isn't really a "bad or excess" headspace problem since technically the Win Mag did have proper headspace in the Weatherby mag chamber as it nominally headspaces on the belt. This time it's like what they did to the .303 Ross rifles in WWI- enlarged chamber.

[jamie5070]

Earlier this summer I mixed up some ammo when I took one of my 1917 enfields and an 1891 argentine out. I had a stripper clip with tree rounds on it and loaded them into the '17 and fired away. As I ejected the third round I saw that the cartrige was missing its neck (i thought). Then I noticed that the first two looked the same. I got off easy but it rattled me. I couldn't shoot a rifle for the rest of the day and hit any thing. The '17 is fine.
Maybe I should start a thread titled "Stupid things I did and survived."
john

[Chuckindenver]

actually, last year i had a guy bring me a Weatherby with a case stuck in the chamber...guess what...it was a .300 mag, stuck in the .300 Weatherby.
after i got the case out, and asked the guy to bring all his ammo in,,it was all ..300 Mag..when i asked why he was doing this...
said the salesman told him he could shoot .300Mag in that rifle....and it was 20.00 a box cheaper...i just stood dumbfounded.
and said..whay dont you sell this rifle, and get the cal, you want?? his wife had got him the Weatherby for a gift, and he didnt want to hurt her feelings..
sooo, the rifle was free right???yes....then buy the right ammo for the rifle..and dont blow the gift up, and kill yourself being cheap...he agreed, and got the right ammo..
another note...he had been shooting .300mag, in that rifle for 10 years, and had 4 empty boxes, with stretched out cases in them...
had one not finally stuck so bad he coudnt get it out,,he still wuld have shot that rifle, with the wrong ammo..another note...screwdriver marks were all over the breach of that rifle..
some so bad, i had to clean and lap them so the bolt would work smooth again..
i had to put the barreled action in a freezer over night to get the case out..even a case extractor wouldnt get it loose.

[OlManDow]

Good and thorough posts already. Note that the M1917 bolt moves forward several thousandths of an inch when rotating it closed, due to the slanted locking recesses and bolt lugs. Headspace is measured when the bolt is all the way down, or at least far enough to apply the safety. US SAAMI 308 standards are 1.630 GO and 1.634 NOGO. NATO 7.62 is 1.6355 GO and !.6415 NOGO. Note that the NATO GO exceeds the SAAMI NOGO; and the NATO tolerance range is amazingly sloppy. Other standards exist, mainly due to the limitations of the intended rifle - e.g. reliable functioning in the L1A1; action (body in UK terminology) stretch in the No.4 variants. I don't know what the excuse is for the Italian BM59's - most I have seen exceed the NATO NOGO.

Note the RCBS case mike in the other posts - inexplicably, it shows most of the NATO ammunition inside SAAMI specs - a really sloppy fit situation.

[COLTMAN1]

I have a sporterized 1917 Enfield. When I close on the FORESTER NO_GO the bolt easily closes. I added a shim to the No-go gauge that was .011 and it is where I would like the bolt to ideally sit. (with the square corner in the middle of the bolt handle 45`)

With the FORESTER Field gauge, the bolt almost closes.. It is just about 1mm short of closed with a little finger pressure. It might close if I press harder. (Corner is at about 75`) Would this be safe to shoot?

NOTE: This is an Eddystone rifle and I don't want to mess with cutting the barrel. It looks great as is but just don't want myself of someone else to get a face full of gas. or brass.