s491 6ppc neck diameter

Discussion in 'Sako Short Actions' started by longrange223, Jun 22, 2011.

  1. longrange223

    longrange223 Member

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    was wondering what the neck diameter of a factory chambered s491 in 6ppc was? any help would be appreciated

     

  2. jburke832

    jburke832 Well-Known Member

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    Longrange,

    Sako S491 necks vary but I'll SWAG that it's around .273. My friend has a Sako BR that's .272. The custom competitive chamberings are generally in the .263 range.

    Any factory cartridge chambering will vary based on the number of times the reamer has been used. A good indication of chamber neck diameter is to "mike" a fired case. This will be very close to the true dimension, though not as accurate a ferrocasting the chamber.

    John
     
  3. longrange223

    longrange223 Member

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    my fired brass measures .2705,using lapua brass & was gertting ready to make some new & was trying to figure out what to turn the necks to
     
  4. jburke832

    jburke832 Well-Known Member

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    Longrange,

    As a genral rule the case neck thickness should about .0125. That being said the target boys generally suggest about .003 - .004 clearance between the case neck and the chamber. Doing the math, .243 +.006 = .249 .2705 - .249 = .01075

    I would go with a neck thickness of .010 to .011.

    Check out www.6mmbr.com There is a lot of great info there.

    John
     
  5. sakotex

    sakotex Well-Known Member

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    lr223-
    I may be wrong, but if you don't want to turn the necks, it sounds like your chamber's neck is .2715 to .2725 given your measurement of a .2705 fired case plus .001 to .002 springback...
     
  6. longrange223

    longrange223 Member

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    talked to accuflite today & jb told me it should have a .269 neck from the factory,told him about my brass &he didn't know what to think,making new brass because i want to be sure,i'm getting powder residue down onto the shoulder of my brass & that doesn't seem right,gonna try another sizing die instead of the redding small base bushing die also & see if that helps
     
  7. jburke832

    jburke832 Well-Known Member

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    LR223,

    I have never fired a round that did not show powder residue on the neck. The entire case expands to obturate (seal) the chamber to prevent gases from expanding. Without ferrocasting the chamber you, nor JB at accuflite, nor Sako, have a clue as to what your actual chamber neck dimensions are. Should you have used a custom reamer you would know precisely, however due to wear on the reamers in manufacturing the dimensions will vary, as long as they are within the SAAMI specs.

    Same is true with reloading dies. The neck resizing diameters will vary. The only way you can know preceisely what is going on is to ferrocast the chamber, measure the neck diameter, and then purchase bushing dies wiht the appropriate size bushing for your chamber dimensions.

    What you will probably find out, however, is that the bushing dies are designed for custome chambered competition rifles and you my not find the proper size bushing because you mass produced neck is too large.

    All of that brings back to the primary reason for neck turning; chamberability, neck concentricity and bullet tension. I think you will find my previous recommendation will provide you with an accurate load, short of re-barreling with a custom reamer.

    Next question, why in the world are you using small base dies? The only time you should use small base dies are for single shots and automatics to ensure the round has been full length resized to SAAMI minimum specs for ease of chambering.

    If you are bent out of shape on neck turning and neck dimensions you should be neck sizing only. Using small base dies, or even full length resizing. completly defeats your concern about neck dimensions. You seem to want a precise fit in the neck of the chamber, but are allowing the entire case to rattle around in the rest of the chamber. This seems more than a bit contradictory.

    Neck sizing a fired case allows the pre-fired case to naturally conform to the chamber dimensions.

    I do hope this helps.

    John
     
  8. longrange223

    longrange223 Member

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    i may go with a wilson neck sizing die,the only reason i want to neck turn is to use lapua brass,it's what i use in my custom ppcs & i find it very hard to beat,guess i'm using benchrest thinking on reloading for thjis gun,i like to have my loaded round .002 below the actual neck size of the chamber with a bushing .003 below the loaded round size when using n133 powder,it's always worked for me & i was thinking it should work in this gun as well,don't get me wrong,this gun soots great! just trying to get a little more accuracy out of it & i think it will do it,never had a factory gun shoot like this one! thx for all your help
     
  9. jburke832

    jburke832 Well-Known Member

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    LR,

    Ya can't beat Wilson, and you are dead on with your neck sizing thoughts. The only issue is figuring out the actual neck chamber diameter. I think we're both close to where you want to be as far as neck turning. A cast of the chamber is the only thing that will bring you to the actual tolerances you desire for the neck sizing bushing, but it may be a bit over kill for a factory chamber.

    Good Shooting!!

    John
     
  10. longrange223

    longrange223 Member

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    may start by slowly turning down the neck of a lapua case .001 at a time & use some ink to see when it barely fits the chamber,not precise but it will give me an idea & it's cheaper than having a cerrocast done,you're right about being overkill on a factory chamber!
     
  11. jburke832

    jburke832 Well-Known Member

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    That's a good idea, however don't you think that it would be more important to have concentric necks with consistent bullet tension that a tight fit in the chamber. Lapua is good stuff, but I'll bet you will still find some variation in neck wall thickness. I believe you would want to hit that happy medium of all of your case necks concentric with the minimum gap between loaded round neck to chamber tolerence.
     
  12. longrange223

    longrange223 Member

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    that's what i'm shooting for,don't necessarily want tight,usually like around .002 total clearance,would like to get that with concentric necks & consistant tension
     
  13. longrange223

    longrange223 Member

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    nearest i can tell by turning lapua down in small increments my neck diameter is between .271 & .272,loaded round is measuring at .2685,will have to test fire & see how it works
     
  14. stonewall2

    stonewall2 Member

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    Sako rifles are chambered for 6 P.P.C. USA not to Benchrest specs.
    So you need the 6 P.P.C. USA dies ie Wilson special oversize seater to load this properly.

    The same ^ P.P.C.USA spec is required for your F.L. die .

    Sako 6 P.P.c. brass has a thicker head on the case and the capacity is slightly reduced.

    Try Sako brass, AA-2015 and 68 Berger bullets in this rifle as that combination has worked very well in a Sako hb single shot.

    You will be jumping the bullets -in this case .101 to the lands becase I used my Br dies set for my Pindell 6 P.P.C. with out changing the adjustments.

    Do a search on Benchrest .com as this subject comes up a lot.

    Do a chamber cast with cerrosafe to be safe .

    There are a lot of neck turning tools on the market.

    Some actually work........


    If I can help -not a problem.

    Glenn
     
  15. longrange223

    longrange223 Member

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    got a new wilson seater & redding full length bushing die this past week,all set up with new lapua brass & 28.1gr of n133 behind an arnette 68 gr bullet,can reach the rifling but bullet isn't in the case much,have to try it out this weekend since i'm shooting it in the ubr nationals next week in the factory class,will let you know how it goes
     
  16. Sagewind1951

    Sagewind1951 Member

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    Hello. I'm Norm, and have a question (or series of them) related to this thread. At the root, it's about the Sako USA standard or spec case neck or chamber neck specification. I recently bought a pre-owned (reportedly not used) A1, SN5xx single shot 6mm PPC that is apparently going to take some sorting out. The factory heavy barrel is marked 6mm PPC USA, the action Sako 6PPC A5xx, which as I understand it should be a non-neck-turn chamber. Factory 6mm PPC cases are currently made of unobtanium, apparently, so I have Lapua 220 Russian cases hydraulically formed. Necks measure .269 OD as formed in RCBS full-length sizing die and neck expanded, .270 OD with a Barnes 68 gr. Match Burner bullet seated. Neither will fully chamber. Cases sized but NOT neck expanded with a neck OD of .260 will chamber easily. The indicator "ring" in the tapered portion of a partially neck sized case (using die-makers blue) appears to be .262. A case neck-turned to .265 will also not chamber. I thought I understood that the Sako chamber neck was a larger diameter than the "benchrest" .262-neck specification. Any enlightenment would be appreciated!
     
  17. dgeesaman

    dgeesaman Well-Known Member

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    Have you scoped the chamber to see if there is carbon buildup in the forward part of the neck?

    My Sako 6PPC-USA chambers measure .272 in the neck.
     
  18. Sagewind1951

    Sagewind1951 Member

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    I don't see anything that looks like carbon buildup. I'll know more when I get the chamber cast done. The neck area (using a Lyman bore camera) looks rough. No significant fouling evidence with a patch and Shooter's Choice. I'll post again after the chamber cast.
     
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  19. Sagewind1951

    Sagewind1951 Member

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    Well, it wasn't carbon buildup. Three chamber cast attempts failed (would not come out at 1/2 hour) and had to be melted out with a heat gun; messy, don't recommend it. However on the last attempt I did get a small unmelted piece about 1/4" wide of the area from the neck/shoulder juncture to a bit ahead of the beginning of the throat. It confirmed what the Lyman Bore Cam hinted at: a groove about .005 deep at the very front of the neck of the chamber. I did also eventually get a .259 plug gauge into the neck (but I'll have to de-Gauss the gauge, as I did it on the end of a pocket magnet). I ultimately rented a chamber reamer from 4D Reamer Rentals (6mm PPC Sako) and reamed the neck. Headspace is unchanged, it touched the throat lightly too. Now an un-neck-turned case formed from a .220 Russian with a 68 gr. Barnes Match Burner bullet seated will chamber without interference (OD .270). I don't have an explanation for how the neck got that way, nor how it escaped the Sako factory in that condition. It'll probably be next week before I can get some loads put together and get it out to try it. Fingers crossed.
     
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