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Thread: Slugging new barrel blanks?

  1. #61
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    Quote Originally Posted by MilGunsmith View Post
    Our .30cal test barrels requirements are .3000" to .3005" on the lands and .3080" to .3085" on the groove. We have had lots of barrels that were outside those numbers. They still shot accuratly, but didnt pass pressure or velocity requirements. We shoot everything with referance ammo to confirm.
    OK, you seem to be stating categorically that a barrel a few tenths out "won't pass your pressure/velocity requirements."


    Am I understanding you correctly?

  2. #62
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    The test barrel requirements , that were written back at Frankford Arsenal, are for uniformity in test equipment. The test barrels are used for ammunition testing during manufacturing, so some uniformity between different test locations is necessary. We have seen barrels that were outside the dimensions shoot well, but the pressures and velocities might be off.

    At one time all the barrels were made at Springfield Arsenal, gauged, chambered and shipped to the different test centers as needed. Now all the barrels are bought from outside vendors, so the dimensions are checked before use. The barrels are inspected with an air gauge, for both groove and bore diameters, width of lands and grooves, and chamber dimensions.

    The difference is that you build a rifle, then tune the load to shoot in that one barrel. We have to build ammo that shoots within a tight parameter of requirements, so that it shoots the same from lot to lot and in different rifles. When a soldier is handed ammo in the field, he needs to know that it will shoot the same as the last batch he was given.

    All new ammo lots are tested using reference ammo to ensure consistency in the setup and test results. The reference ammo lots are tested at multiple locations using the same batch of barrels to establish a set of pressure and velocity numbers to compare new ammo lots to. The test procedures are similar to that in the SAAMI manual https://saami.org/technical-informat...ami-standards/
    We use the SCAT-P and TECP-700-700 ORD Test Manual

  3. #63
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    I on the other hand have custom match barrels of 20 descriptions, some discard "rifling setup" barrels as much as a FULL THOU undersized, 6MM's, 338's and 30cal's in all sorts of configurations, from different numbers of grooves (3gr, 4gr, 5gr, 6gr, ratchets from 3mfgrs etc etc), to different bore/groove diameters, land hts and rifling profiles...I even take old factory barrels and re-cut to match the chambers and throw them into the mix as I use'em for fireforming or brake testing, and basically my long term testing, weighing charges down to the single kernel-even on cases of 100gr capacity, has shown.....

    they all make pressure about the same.

    Of course this goes against EVERYTHING I'VE EVER READ, HEARD, OVERHEARD AND INTUITED, (except the opinions of Harold Vaughn and another ballistician not currently working)

    but game don't lie.

    I hold highly suspect any opinion where "dirty bores raise pressures" or "different bullets" or even meloniting or coating with the current crop of monkey-poo...... cuz I can't find repeatable evidence of it.

    And I shoot everything with ES down in the dirt, under 10fps mostly.....I don't even acknowledge the validity of SD.

    It's very easy to see trends when I don't have to "average" nor "find means" nor bend the numbers around nor make graphs...... It's wikkid easy to just READ THE RESULTS straight from the notes.


    XX chamber/throat/COAL/temp/hum/powder.... in other words IDENTICAL COMPONENTS, CHAMBER AND ROUND
    XX bullet WEIGHT
    XX powder charge
    XX barrel length

    Yields very predictable results...

    I've even gone back and rechambered barrels marked as "fast" or "slow" or whatever and am reformulating all my thoughts in regard to bore diameter/configuration

    And all the years of work I did and notes I took while throwing powder charges.....burnt and gone forever along with all my "good group" targets LOL

    IN MY CASE..... learning to cut identical chambers and learning to weigh charges down to the kernel has completely reset everything I ever "knew" about reloading for consistency.

    And about the velocity of different barrels.

    It's a great time to be alive...

    al


    PS...... I remember vividly one time back in the 90's I posted on this forum that "deep-seated boattail bullets hanging 'wayyy down into the case on a .243AI would cause pressure spikes"

    Now I'm talking half the friggin' bullet hanging below the shoulder..... .243AI chamber with .000 freebore and 105 Starke's and 108 Eubers.....

    This guy comes on name a' Boomer and sez.... "I wish you would quit stating stuff like that as fact"

    And I leapt up "But My Testing Shows!!!"

    And he came back with "then your testing sucks"

    And I sez "Well the tell me why I have these velocity spikes over my chronograph!!"

    And he sez "because you're ignorant?"

    I said it then, and I'll say it today ....... "THANK YOU BOOMER!!"

    each day I try to lessen my ignorance

  4. #64
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    Rereading this thread, I see a lot of opinions and damn little experience. I have watched my friend cast laps and measure them several times, I have also seen the results of mismatched bullet and barrel dimensions by comparing targets shot before and after remedial lapping. Just to be clear, I have discussed the whole issue of an air gauge compared to slugging with one of the owners of one of the two biggest producers of the highest quality cut rifled barrels, because I have zero experience with an air gauge, and he has used both. HE told me that you can feel things using a slug that you will not detect with an air gauge. As far as verifying what you are feeling goes. if your have a barrel that has choke in the muzzle and cast a lap there, and measure its diameter, and then pull it back to where it feels loose and use a flat tipped jag to tap on it to slug it up, to a the same feel as the muzzle, pull it out through the breach and remeasure it, you will be able to tell what kind of dimensional difference you are dealing with. Differences in diameter that are well under .001 are easy to detect. The fellow that casts the laps once spent a lot of effort trying to get a 6PPC barrel to shoot before casting a lap to see if he could find a problem. When he did he found that there was a definite loose spot that was several inches long up toward the muzzle. Before he did that he had put in a lot of time trying to get that barrel to shoot. The maker replaced it and confirmed what he found. It does not take long for my friend to cast a lap and as he calls it " map" a barrel. His customers can afford top quality work, and they evaluate that quality by looking at their targets and the color of their cleaning patches. Mapping barrels helps protect his reputation. No one who has used one argues with the usefulness of a bore scope. Slugging or casting a measuring lap is just another way to look at a barrel to see things that cannot be otherwise detected using the resources that a gunsmith would have available to him.

  5. #65
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    Quote Originally Posted by HiWall View Post
    Hi-

    How do you get the slug to swell up sufficiently?

    If the barrel has choke do you slug it from both the breech end and also the muzzle end and only then drive the slugs to say, the middle of the barrel in each case?

    Also, is it possible to slug a gain-twist barrel?
    Hi Hi (I mainly answered because Tad got to say Hi Wall)

    This is a big subject and now that laps are also involved.... even bigger so I'll opine a couple times then pull back

    #1, FOR ME, I "swedge up" (swage up, tighten, obturate, smash, upset) my slugs using steel rods wrapped with masking tape

    #2, "barrels with chokes" is a lapping issue, not a slugging issue IME so I'll just withdraw into my foreskin on that one and

    #3, no, it is not feasible to slug a gain twist, it's _possible_ in the sense that yes, you can push the slug thru but....why?

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