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Thread: Pressure signs in rimmed cases?

  1. #1

    Pressure signs in rimmed cases?

    I'm in the process of working up a load for my 7x65R drilling, with a bit of help from various users of this calibre here and in Germany. The published load data isn't a huge help as it is all for bolt actioned rifles able to withstand higher pressures, rather than for an elderly breech-loading rifle.

    Even though I'm being very cautious, it occurs to me that the pressure indicators I'm used to in bolt actions with cases spacing off the head will possibly be different to a rimmed cartridge spacing off the rim and essentially immobile in the chamber, therefore no flattened primers. Is there anything specific to rimmed cases that I should be looking for as I work up to near maximum loads for this kind of rifle?

    Thanks,

    Adam.

  2. #2
    Hi Adamant,

    I have 3xdrillings the 7x57R is my favorite.
    The factory ammo is produced at 10% less energy levels than for the bolt action 7x57.
    I would begin at 12% less energy than a 7x65 bolt load to be on the safe side.

    martin

  3. #3
    get your self, beg, borrow, buy or steal, a micrometer graduated in tenths and learn to read it I you cannot do so now and measure case expansion at the web where the case head meets case wall this is the weakest spot and where the pressure expansion rings shows. This was the method of keeping a check on pressure rises that Ken Waters used. He fired factory ammunition then measured the expansion ring and had a amount that he would not allow the ring to grown more than when developing his loads. A digital caliper is just not good enough for such accurate measuring it has to be a micrometer. Luckily as they are out of fashion one can acquire one quite cheaply nowadays.

    Norma Lists the 7x65R for break actions but only with Norma powders of course. Hornady say to reduce their data by 10-15% for break action rifles like drillings.

    Now you might like to go to some other forums like Nitro Express where you will likely find other fans of such rifles and cartridges. GBO is another forum that has a drilling forum where you might find some better guidance.

  4. #4
    Brithunter, thanks for that. I have a Mitutoyo 1" / 0.0001" micrometer - I'll dig it out. Before I start hammering Google, do you happen to know what kinds of tolerances Ken Waters regarded as acceptable as I haven't been able to source any factory ammo to use for comparison person?

    The Hornady data was my starting point but I'm not getting anywhere near their velocities with comparable loads, even using H4350.

    Adam.

  5. #5
    I'll pull his books out later and have a look. Now I know where they are unlike the screws I was hoping to find for jase . Just stopped for a cuppa.

  6. #6
    For best results it needs to be a blade type micrometer so you only measure a local area.
    There is a section in the Speer reloading manual that explains exactly how to do this, and some suggested tolerances.


    Neil.

  7. #7
    There's a vernier type blade in the micrometer's box IIRC, which I've never used but which should do what you describe. I must have missed that in the Speer manual - I have a not very recent copy here somewhere, so I'll drag it out and have a look...

    Just when I thought reloading was getting a bit humdrum and routine, along comes something new to keep me interested.

  8. #8
    Actually because you just measuring the pressure ring which of course will be the largest part of the case wall a normal micrometer is just perfect for this. Now as your working with a break action gun Waters suggests allowing no more than 0.001" increase for top loads at the pressure ring. 0.0005" would be better still but he is comparing with factory loads which we do not have in this case or do we?

  9. #9
    Quote Originally Posted by Brithunter View Post
    Actually because you just measuring the pressure ring which of course will be the largest part of the case wall a normal micrometer is just perfect for this. Now as your working with a break action gun Waters suggests allowing no more than 0.001" increase for top loads at the pressure ring. 0.0005" would be better still but he is comparing with factory loads which we do not have in this case or do we?
    That's really helpful, thankyou. I will have some factory ammunition shortly c/o Alan Wey but until them I'll err on the side of caution - I'm working up from a very conservative load using once fired brass (as Speer advise over new or work hardened brass) so I should get clear early indications of pressure using this method.

    Thanks,

    Adam.

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