Nonstandard proof marks

Discussion in 'Shooting, Hunting and Fishing' started by stoatman, Feb 25, 2009.

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  1. Second one of the morning!

    Has anyone here seen nonstandard proof marks from one of the British proof houses before? I'm thinking, for instance, of a chamber, throat, or barrel which deviates from the CIP specification.

    If you seen them, what do they look like?

    For instance, would an American 7.62 x 39 barrel be marked up as:

    7.62 x 39 mm (.308")
    7.62 x 39 mm (.300"-.308")

    Or what?

    I vaguely remember seeing nonstandard 7.62 NATO proof marks on target rifle barrels years and years ago, but I can't quite remember what they looked like.
  2. Looking at an M10A1 (the AIA version of the No5), the calibre "7.62mm x 39" is simply sandwiched between the "NP" and and inspection code of some sort. I can't see anything odd on any of the other non-standard rifles I have.

    I wasn't aware that the Proof houses actually made any attempt to detect "non standard" barrel or chamber features - the most I've seen them detect (or miss, in several cases) are obvious physical flaws such as bulges.

    I don't know what non-standard 7.62mm marks you may have seen. Were they British marks, or European? The old (1960-70s) British 7.62mm proof used to include the case length in Imperial - ie 2.0154" instead of 51mm - but I've never seen anything denoting deviation from standard.
  3. I think that last one you mentioned is what I have seen.

    Anyway, this is all to do with the fact that I am having my M10A1 re-barrelled and may get a custom chamber conformed exclusively for .308 projectiles. I had a chat with the proof house and they said that they would have to mark it as nonstandard, "with all dimensions".

    The proof house don't check for nonstandard barrels, however if you admit it to them then they say that they are obliged to mark as nonstandard (and an American spec 308 barrel counts as nonstandard since the CIP "Z" measurement is 7.92 mm instead of 7.82 mm for 308).

    I asked them "hypothetically, what if I didn't tell you", and the reply was "hypothetically, if the headspace gauged okay and it passed proof then we hypothetically wouldn't care".
  4. It is now a moot point anyway: Dutch firearms licensing don't care what the proof mark says, so long as the serial number on the rifle is the same, and the same cartridge goes in it.

    So, custom throat here we come!

    Now, do we go extreme at .3085, or a little looser...

    Something which had crossed my mind was the whole issue of what if someone accidentally loaded/chambered a cartridge with a .311 projectile, something which is not an issue in the SAAMI chamber, since the freebore is enormous at a little over .313. My view, and the view of my gunsmith, is that it shouldn't be an issue ( CIP peak pressure is only 3350 bar compared with 4150 bar in 308 Winchester, for which the action is designed.)
  5. If you don't tell the proof house then they will proof it with a 311 dia bullet which may answer your question!
  6. If I have a .3085" freebore, they might not be able to chamber a cartridge loaded with a 311 bullets if the parallel section protrudes from the case!

    I have just been studying two chamber reamer diagrams:

    Pacific Tool --.3085 freebore, .080" long. thereafter 1.5° taper.
    Clymer -- .3138 freebore, 0.000 long, entering straight into a 1° taper.

    I did the geometry on the Clymer one, and the effective freebore is .166!!!!! A 311 projectile will touch metal after .080, but won't actually hit the throat until the .166 mark.

    I am starting to think that the reputation for inaccuracy of this cartridge is actually due to the bullet rattling into the rifling due to extremely generous throating rather than anything inherent to the shape of the cartridge or its capacity.
  7. Oh, and finally: I'm thinking that I will admit to the proof house that it is nonstandard since I'm strongly leaning towards the .3085 throat, and although the chances are that a 311 proof round will not produce any problems (it is, of course, an action intended for 308 Winchester), I don't really want to take the risk.

    If I am mad enough to change my mind and go for the Clymer reamer, then I just won't tell them.
  8. The Clymer figures don't make any sense to me. Can you post the drawings up for comparison?
  9. If you have a custom chamber (let's say a tight neck) then they will define that measurement on the proof stamp. Your 7.62x39 with a .308 calibre bullet has been done numerous times (the rebarrelling of the CZ carbine makes a fine woodland stalking rifle with .308 available NBTs) and will read like '7.62x39 (.308)'. It is a while since I worked in the trade and I have forgotten exactly how they write it, but it's no drama.

    It won't affect the condition to acquire on your FAC, so long as somewhere on the proof stamp it says '7.62x39'. I usually go for the bare minumum definition of what I want to enable me to be flexible (7.62, 6mm, .22 CF etc). If you get a bargain offered in between you are more likely to have the slot for it!
  10. Not got access to DII at the moment but have a look in AESP 1000-A-003-013 should be some info in acceptable proof marks there.

  11. I forgot, it's not Clymer, it's JGS, and they say it's SAAMI minimum!

    Drawing not to scale...

    clicky to enlarge

  12. This is perhaps easier to visualise (not to scale; diagrammatic only):

    Attached Files:

  13. ugly

    ugly LE Moderator

    Take bore sizes seperately it doesnt seem to matter if the bullet is either .308 or .311, if it chanbers it will fire with no perceptible impact on either pressure or accuracy. If you make the chamber tighter by shortening it then it may be an issue for proofing. Why submit to proof if you are doing the work yourself? It really only needs doing if done for sale! Cant the Dutch proof it?
  14. 1. work being done by gunsmith in UK, cannot legally transfer back to me w/o valid proof marks
    2. Dutch have no proof law; what little is made here is not proofed (unless the owner wants the warranty to be valid on a Lothar-Walther tube)
    3. .308 IS less accurate in .311 barrels - done it before... results not good.
  15. ugly

    ugly LE Moderator

    Read the work done by Sierra using both sets of bullets in the other barrels and although it was weight dependant it certainly seemed to show no major differences. That said Sierra bullets are good quality!