How to determine "Max-Trim to Length" with a custom chamber?

Discussion in 'Reloading Forum (All Calibers)' started by BD100, Oct 27, 2014.

  1. BD100

    BD100

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    I know reloading manuals always give a max case length dimension for each cartridge listed, but how would you determine this if you have a custom chamber? I have a 6-06 and have been using 2.494 as my max case length before I trim. This is based off the 25-06 saami spec in my Nosler Loading Manual. So far this number seems to work ok, but if I really wanted to determine what the max is for my chamber, how would I go about doing this?
    Could the gunsmith who built the gun provide it based on the reamer he used?

    Thanks guys. I'm a little new to the custom stuff, so trying to increase my knowledge base. :)
     
  2. MFG_BOP

    MFG_BOP

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    I think you need one of these:

    http://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/sinclair-chamber-length-gage-prod32925.aspx

    My Vartarg is 1.412" and manual says cut to length at 1.395"

    Hope that helps
     
  3. devildogandboy

    devildogandboy

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    yep, I use these also. good tool to have for chamber length checking.

    Bruce
     
  4. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    The reamer print has it listed in the specs
     
  5. Gene66

    Gene66 Gold $$ Contributor

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    I to use the Sinclair gauges,works great ,fast and accurate.
     
  6. fdshuster

    fdshuster

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    I also use the Sinclair chamber length gauges, but, it's sometimes tough to order that little gauge only, (when that's all you need), without spending $6 shipping for a $7 item.

    The pictured gauge can be homemade with everything you already have.

    I used a Dremel cut-off wheel to cut the front half of the case neck off. A jewelers needle file to de-burr both rough cut edges. The cut-off surface needs not to be perfectly square, because you are using the original straight mouth to make contact at the front of the chamber. Seat any old bullet to the approx. normal seating length, apply just a tiny drop of oil on the ogive of the bullet, slide the "collar" over the bullet & chamber the dummy round. I've compared length dimensions doing it this way and with the chamber length shown on my chambering reamer drawings, and the Sinclair gauge, and they are all within .001" or so.

    Note: Another time when this homemade gauge may be needed, especially with a custom chamber, is when the major diameter on the front of the Sinclair gauge is larger than the chamber neck diameter. Ex: A 260 Remington may have a chamber neck diameter of .299" and the gauge could be .295", but what happens when your custom chambering has a .294" neck diameter, as my 6.5x47L ? The homemade gauge remains an alternative choice.
     

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  7. artbosco

    artbosco

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    If you have a customer chamber you should be able to easily obtain a drawing of the reamer's specs that was used to cut it. Your gunsmith or the reamer manufacturer can provide you with a copy of the print. The max trim to length should include a .010" reduction for safety and another .010" reduction for case neck growth. In other words if the max on the drawing is 1.520", trim to 1.500". :)
     
  8. fdshuster

    fdshuster

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    Outdoorsman: Yes, the reamer print drawing ( I have them for most of my custom chambers/ I buy my own reamers most times), but some will insist that the dimension shown is not necessarly correct. I don't happen to agree with them, but there you have it.

    And while you may be satisfied with trimming .020" shorter than chamber length, some of us work to closer tolerences, in my case to .005" with the ppc's and BR's, and .010" with conventional cartridges like the 223 and 308's that do stretch more.

    Case length's are measured after every sizing.
     
  9. fguffey

    fguffey

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    I make gages for determining the length of a chamber from the mouth of the chamber to the bolt face. It is easier if the reloader has a forming die in '243" or 6mm for the 6/06.

    F. Guffey
     
  10. brians356

    brians356 Gold $$ Contributor

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    That doesn't tell him how deep the barrel was chambered using the reamer, or how the gunsmith headspaced the barreled action. Each gun must be gauged to really know how long the chamber is. "Trust - but verify."
     
  11. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    I guess so. I often take for granted the gunsmith knows what hes doing and with as many lathes are out there in basements and garages thats a bad thing to assume.
     
  12. artbosco

    artbosco

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    FD, I shoot the 6PPC & 30BR competitively and have never found the need to neglect safety.

    If you've had a chance to view Jack Neary's training videos on the 6PPC cartridge you will have noticed that accuracy wasn't compromised when trimming in excess of .020".

    Even though Jack used a 1.525" chamber length he found that trimming back to 1.490" had no effect in preventing him from being inducted into the NBRSA Hall of Fame. He does say that once his brass grows to 1.492" or 1.493" he trims back to 1.490".

    I the absence of viewing the videos, here's an article where he discusses his chamber length and his trim to length: http://www.targetshooter.co.uk/?p=1024

    To keep things in perspective I always ask folks to pull out a piece of copy paper and turn it on its edge. What you're looking at is approximately .004". I need a strong magnifying glass or a microscope to see that dimension.

    For me, .005" is not enough for safety, it might be in vogue in some circles, but .035" did not prevent Mr. Neary from being inducted into the BR Hall of Fame. [1.525" - 1.490" = .035"]

    Here is part one of Jack's multiple videos: http://www.youtube.com/watch?v=7SZWvn68bRU :)
     
  13. fdshuster

    fdshuster

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    Outdoorsman: With all due respect to Jack Neary, my concern about the formation of a ring of carbon at the chamber mouth is one of my considerations when keeping the gap between the case mouth and the front of the chamber to a minimum. There just is no empty space available for the buildup of carbon to form.

    The carbon ring was pointed out to me by a local, very well known match competitor & builder of custom benchrest rifles, when I had my first look thru a Hawkeye borescope, many years ago. I immediately bought my first one then. PM me if you are interested in his identity.

    The rifle in question was (and still is), a factory Remington 700 BDL chambered in 222 Remington. I reported signs of high pressures with the same load I had been using for a few years, and the borescope inspection followed. There was a massive buildup of carbon, much time and effort was spent in removing it, (JB bore paste & a new bronze brush), and I then took measurements using the Sinclair gauge. What I found was a chamber length of 1.742" for a cartridge with a length of 1.700". Yes, I was following the "advice" of the one size fits-all loading manuals ( the same manuals that tell you to adjust your sizing die down 'til it touch's the top of the shell holder, then back it off a turn), so I was creating a gap of over 1/32" that filled with the accumulated carbon buildup.

    That was about 15 years ago, and to this date I have never had a ring of carbon in any of my chambers.

    I'm comfortable working with the clearances, keep a very close check on case lengths, and have never had a problem. Others may not be willing to spend the additional time in measuring case length's after every sizing, some are happy to over-trim, and some have even admitted to me they "never bother to check case length's since I keep them real short".

    And finally, Jack Neary's winning performance(s) were based on much more than his case trimming versus chamber length's, I'm sure. Question? If he would have kept the cases within, lets say ten thousandths, would his scores and/ or groups have taken a nosedive? I doubt it very much. I don't believe it has much if any effect on accuracy.

    Not saying my way is the only way, and if someone decides to trim with more space between the case mouth and front of the chamber, that's their decision, as it is mine to keep them closer.
     
  14. BoydAllen

    BoydAllen

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    Gentlemen,
    If I may...the carbon that sometimes bites us, that is in the very front of the chamber is just powder fouling that a bore sized brush has missed.

    Recently, to address this, I followed some advice that I have known about for some time, but due to being in somewhat of a rut, I had failed to follow. After doing a normal cleaning on a well broken in, but un heat cracked 6PPC barrel, that had only been fired a few rounds since its last cleaning, I put a fairly fresh 6.5mm bronze brush on one of my chamber rods, shoved it to what felt like a fraction of an inch past the front of the chamber neck, and gave it a couple of dozen partial turns, switched to a 6mm brush, shoved it a mite farther, and repeated the same thing, then I wiped out the chamber and leade area with a strip of paper toweling wrapped to a loose, oversized cone shape, over the 6MM brush (my usual chamber wiping method at the end of a barrel's cleaning). What I saw on the paper toweling was evidence that the brushing had dislodged some powder fouling at the front of the neck, that my regular cleaning with a new bronze brush had missed. This motivated me to make a change in my decades old cleaning procedure. I ordered an inexpensive one piece stainless cleaning rod using Amazon Prime (for about $9 delivered) and plan on cutting it off to a length such that it will extend past the butt of all of my rifles' stocks when a brush that is mounted on it is at the front of which ever chamber I am using it on. The plan is to use my cheap, somewhat slow, cordless drill to spin a brush for perhaps five seconds, at the front of the chamber. Others have reported doing this with good results, and I do not think that it should hurt anything if done carefully. Due to the fact that most of my shooting in this caliber has been with 133, I have not had problems with a hard carbon ring a little farther forward, but I have seen one or two trying to get started in one or two of my other rifles, something a little very careful work with IOSSO remedied. I have the use of a bore scope, but do not use it every time that I clean. Generally, when I have scoped my barrels, they have passed inspection with flying colors, but I am going to modify my procedure anyway, just to see if it changes my results in any way.

    I think that the main thing that we need to do to get away from fliers caused by powder fouling buildup at the front of the case neck, is to trim often so that cases will be of uniform length, not just to maintain some clearance (Neary speaks to this.). and to manage and monitor shoulder bump, because cases are blown forward at the beginning of the ignition/firing cycle, with the result that those with more bump will extend farther than those with less, even though they are trimmed to the same length. Recently, when returning some Lapua brass that has some life left in it, but was from an estate, and was probably of mixed usage, I found that because of the variance of work hardening, that my bump, with the same die setting, varied quite a bit, and that that resulted in a variance in trim length using a trimmer that indexed off of the shoulder. At first the variance in trim length bothered me, but then I realized that at least until I had a chance to fire and retrim before sizing, that this was not such a bad thing, since the extension into the chamber neck as the cases were fired would actually be more uniform. In the future, I plan on using these types of trimmers on fired cases to see if the trim length is more uniform. I sorted the cases that were not by amount of bump, using that as an indication of work hardening differences. Within the group there was a large subset that were uniform, and lesser numbers that varied by various amounts. In the past, I have not looked at the uniformity of case bump within sets of cases, I may change that.
     
  15. artbosco

    artbosco

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    I make it a routine part of my cleaning to always clean carbon build up in the end of my chambers with slightly over sized brushes and JB bore cleaning compound. I then cleanse the chamber of all reside then proceed with normal barrel cleaning. My Hawkeye confirms the absence of carbon build up in the end of the chamber and barrel. High tech gadgets are great, aren't they? No more guessing. :)
     
  16. rvn1968

    rvn1968

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    FDShuster,I love your homemade gage.The cartridge in your pictures would have a COAL of 2.035".correct ??
     
  17. brians356

    brians356 Gold $$ Contributor

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    Boyd, is that the LCGW WFT trimmer?

    I don't see why we need to be satisfied with using brushes and rags to remove carbon from the corner at the end of the chamber neck. I wonder if a tool couldn't be made, which has a squared-off brass (or ?) cutter head, shaped not unlike the plug in the Sinclair chamber length gauge, but with a serrated edge. The cutter head would have to be be a close fit for the chamber neck diameter, and you would insert it until it stops at the end of the chamber neck, then turned a few times to scrape out any crud there.

    Thoughts?
     
  18. brians356

    brians356 Gold $$ Contributor

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    Not COAL (cartridge over-all length) - that's to the bullet tip. It is the chamber length he's measuring.
     
  19. fdshuster

    fdshuster

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    rvn1968: As already answered by brians356, it's the chamber length, at 2.035". This on a Tikka barreled 308. I never let the cases get any longer than 2.025".

    I cannot take credit for the idea: saw it here on this site about a year ago, and also thought it was a great suggestion.
     
  20. rvn1968

    rvn1968

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    I meant brass overall not COAL,sorry brainfart. Tom
     

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