Sticky Bolt on 7mm mag

Discussion in 'Reloading' started by jsimonh, Mar 17, 2011.

  1. jsimonh

    jsimonh Well-Known Member

    Messages:
    89
    Joined:
    Jul 27, 2010
    I decided to try a different load for my 7mm rem mag with 68gr of Retumbo and the Berger 180 Hybrids. Velocity was good averaged around 2980~ with ES around 25 with the exception of one low and one high round. Accuracy was really good at 850yds, probably the best I've had, but on about 5 rounds out of the 20 the bolt wouldn't open easy. It would "rise" as easy as it ever has, but wouldn't slide open easily on the 5 rounds. It didn't take much at all to get it open, but definatly a little sticky. I didn't recognize any other pressure signs but I typically don't press the envelope to much. The nearly 3000fps with a .674bc bullet is very appealling, but I don't want to risk anything that could be dangerous.

    I guess I'm just looking for opinions on what my next step should be. I was thinking about just dropping down .3 to .5 grains and not worrying about it.
     
  2. mountainman

    mountainman Active Member

    Messages:
    38
    Joined:
    Jan 14, 2011
    check the lenght of your brass, if OK, then drop down .2 grs and try again. If it's pressure your not high by much. I would go down .2 grs at a time. If the bullet is against or close to the rifling back it out a little. Berger bullets like a jump to the rifling, .020 to .080 off the lands isn't uncommon and they shoot best for me around .050 to .060 off the lands and I can now add more powder for more FPS.
     

  3. jsimonh

    jsimonh Well-Known Member

    Messages:
    89
    Joined:
    Jul 27, 2010
    Thanks for the reply. Brass was all trimmed to 2.490 and the bullets are seated .020 off the rifling. I'll probably give it another go with a slightly lower amount as you suggest.
     
  4. cowboy

    cowboy Well-Known Member

    Messages:
    1,058
    Joined:
    Jul 14, 2007
    Question for you - are you FL resizing and moving the shoulder back at all?? Any idea how many times brass has been fired totally? And last question is - did you notice any resistance when you were chambering a round?

    If none of the other suggestions fit - your easiest solution to try is to reduce powder as suggested but summer is coming and so is the heat and you may/maynot be right back to the same problem later on.

    I shot a belted 7mm rem mag for years and ran into the same problem after using brass beyond 4-5 times even with FL resizing.

    If your brass has had a number of uses you might want to take a look at Larry Willis' belted mag collet die and see if the explanation fits into what you are running into. Innovative Technologies - Reloading Equipment

    Good luck------
     
  5. jsimonh

    jsimonh Well-Known Member

    Messages:
    89
    Joined:
    Jul 27, 2010
    I shot 30 rounds today loaded with 67gr of Retumbo. I had about 5 stick pretty bad, so we got to tinkering and noticed that some of the loaded unfired cases would stick pretty bad if I chambered them and then immediatly tried to extract them.

    This is new Win brass trimed to 2.490 and sized in a Redding Body die and Lee Collet Neck die.

    I'm not sure why it would go in easy then extract hard with it being unfired, but thats what it was doing.

    Any ideas?
     
  6. kk alaska

    kk alaska Member

    Messages:
    13
    Joined:
    Nov 24, 2010
    My 6.5 X 284 does the same thing with soft Lapua brass. Switch to Win brass
    (same capacity) and bolt is fine. Soft brass will some times show those symptoms.
     
  7. jsthntn247

    jsthntn247 Well-Known Member

    Messages:
    661
    Joined:
    Jan 14, 2009
    Try bumping the shoulder back some with a FL die.
     
  8. Ackley Man

    Ackley Man Well-Known Member

    Messages:
    98
    Joined:
    Mar 21, 2009
    Normally new brass has been sized at the factory to SAAMI minimum specs. Accordingly there probably was not a head space or case measurement problem with the brass that you bought. You indicated that you body sized the virgin brass before loading which may have moved the shoulder forward on a few pieces depending on your die dimension. Properly head spaced rounds should exhibit slight bolt lift resistance but not usually extraction resistance. There are a few things that may be causing the extraction resistance: bullets are actually seated out and engraving the lands but there is enough neck tension that the bullets are not being pulled from the cases, the cases have a severe concentricity issue, the cases have a diameter measurement issue, the rifle chamber is fouled or the loaded round neck diameter is tight in the chamber neck. I don't understand why you body sized the virgin cases and then did not chamber a few empty cases to check to see if the case shoulder to case base dimension was a good fit with the rifle chamber. Measure run-out on one of the rounds that you indicate is sticky when you chamber it. Particularly bullet run-out, case neck run-out and case body run-out. Compare a sticky round to a not sticky round by taking several case diameter measurements. Inspect the bullet ogive to be sure the bullet is not engraving the lands, clean and inspect the chamber, throat and follower. You should find your problem somewhere in the process. Hope this helps.
     
  9. kc

    kc Well-Known Member

    Messages:
    970
    Joined:
    Jan 7, 2003
    Take a felt marker to the brass and you can see the area that is sticking.
    somtimes a company makes a chamber thats to short, I have had that problem once, I was lucky it was a new rifle. they gave me a new rifle after they found it would stick with new amunition also. The chamber was to short, and I just bought the rifle and went to there range.
    I hope your 7 Mag will be fine.
     
  10. jsimonh

    jsimonh Well-Known Member

    Messages:
    89
    Joined:
    Jul 27, 2010
    I'm getting great info from you guys, thanks!

    I use a RCBS precision mic every time I reload. I sized the brass because it comes in a bag and had necks that were visibly out of round. Normally I'd just lee collet neck size them, but for some reason I decided to body and neck size.

    As I stated earlier it was only about 5 out of 30 that had this problem. When I resize fired brass I only bump the shoulder back about .003, this new brass was a lot furter back then that. I don't have the numbers in front of me, but I think it was someting like .020 shorter then my resized fired brass.

    This particular set of shells had the bullets set back .020, and I measured everyone at the ogive to make sure.

    The first time I shot and had this problem (68gr) I never tried to extract a loaded round back out. Thats why I was assuming I was having pressure problems. When I had the same problem at 67gr I began chambering and then extracting each shell, then re-chambering it to shoot. Only a hand full were hard to extract, and they were equally tuff to extract after firing (the 5 that stuck not all of them).
     
  11. Ackley Man

    Ackley Man Well-Known Member

    Messages:
    98
    Joined:
    Mar 21, 2009
    I am not sure where your load data came from but Hodgdon lists a max load of 68.0 grains with a 175 Nosler Partition producing 51,200cup pressure. The 180gr long ogive Bergers that you are using differ from the Noslers in a couple of ways - they reduce the case capacity due to the amount of bullet seated into the case and the long ogive causes more resistance. Thus the pressure will increase. The max load that you should be safely using is 66.4 grains which will yield 2849fps from a 26" barrel with a case fill ratio of 101%. You may indeed have a pressure problem but it is strange that it is isolated to only a few cases. Again, you need to take a series of measurements from the problematic cases. Here is a link to the SAAMI spec drawings of the chamber and case for comparison purposes.
    http://www.saami.org/PubResources/CC_Drawings/Rifle/7mm Remington Magnum.pdf