Headspace: Rimless vs Revolver cartridges

Discussion in 'Reloading Room' started by ex_isp, Apr 11, 2015.

Thread Status:
Not open for further replies.
  1. There have been several questions I've seen regarding setting up new reloading systems.
    I thought this an appropriate time to bring up headspacing as it relates to "rimless auto cartridges.

    In a revolver cartridge, headspace is set by the rim of the cartridge resting on the back of the cylinder.
    [​IMG]

    In a semi-auto example I'll use .45 ACP. Extra crimp does NOT hold the bullet in place and in fact can be dangerous. Rimless cartridges headspace on the case mouth. The chamber is cut to allow insertion of the cartridge only so far in. OVER crimping can allow the cartridge to lisp further into battery resulting in pinching off and severely restricting the bullets traveling down barrel when fired. This can result in KABOOMS.

    See rimless pic below
    [​IMG]

    This is the one of the reasons for the "plunck test" for handloads. On rimless cartridges like 9mm, .40, .45, 10mm, the "bell" or "flare" the press introduces into the prepped brass should be only enough to allow insertion of the bullet without shaving copper from it. The taper crimp should be only enough to allow for the finished cartridge to chamber smoothly.

    When ever I set the press up for a new caliber (ie changing from .40 to .45) I inset my toolhead already set up with the correct dies. Even though my .45 toolhead should be still set form the last time I used it, I still check it. I take 1 piece of brass, resize it without putting a primer in it. i next check the "flare in the next station. Don't want too much as this prematurely wears out the brass. I then make check the seating die to ensure correct seating depth. Lastly, I check the crimp. After applying the crimp, I take this "dummy " bullet and drop it into the barrel. It should go "plunk".

    I should probably mention I'm using a 4 stage press, but the steps are essentially the same. Again, examine the .45 diagram above and notice the area in the chamber where the case mouth sit next to the "shoulder" in the chamber. That is were the round "headspaces" against in a rimless cartridge.

    Hope this makes sense!

    Ex
     
  2. Proper neck tension is what holds auto caliber bullets in place and keeps them from suffering setback. No amount of proper taper crimp will fix poor neck tension. Period.

    On top of that, the auto case headspaces on the case mouth, so if you push it in too far it can cause problems. The taper "crimp" on an auto caliber should remove the bell and maybe .001 more, and that's it.

    Anyone who says differently is simply wrong.

    Rimmed cases like .38spl and .357 mag are a different story and use a roll crimp, not a taper crimp. Different crimp dies entirely.

    If you can push an auto bullet further into the case after seating it and removing only the flare with the crimp die, your brass is weak.
     

  3. Here is a photo with dimensions (dementia?) showing a properly taper crimped .45. Only .001" less the the rest of the case where the bullet is pressed into. But there is still a definite rim for headspacing in the battery.
    Note that the rim has just been "touched"to take the flare down and ensure proper feeding.

    [​IMG]
     
  4. The throat on my 1911 45 acp is .452. That is before the rifle lands start, while I agree one should not over crimp, a person would have to put an extreme crimp to allow the case to be in the throat, to the point of deforming the bullet. A good crimp is necessary for proper ignition, and to avoid bullets stuck in the barrel. It's either that or buy a cannelure tool because no matter what the bullet WILL set back, it is just a matter of how much. Even if you have a .455 bore, which I doubt, it would still be a stretch to over crimp.

    I measure everything, every loaded case is the same case length and OAL. I usually get below 50fps deviation, most times below 30fps. No signs of overpressure at all, and extreme accuracy. My 1911 gets 2 inch groups from just a weaver stance at 10 yards. I have gotten 1.5 inch groups from a rest at 25 yards. My crimp is .002 below the case diameter. I expect the rim to leave a light cannelure in the bullet.

    Also keep in mind the taper crimp on a 45 acp and similar rounds is NOT roll crimped, no matter how hard you try. If pushed hard enough it will push the case to the bullet diameter, but it will not be roll crimped. At least not on my dies. And yes my rounds are checked for seating depth, they are the same with a sized trimmed case, as a loaded case.

    If you can move your bullet with your thumb, you do not have enough crimp, or the case is bad, or the sizer is not the proper size. If you want to run with a minimum crimp I suggest a cannelure tool, or a undersize sizing die. Both are a tad expensive. But less than lost fingers from a hot round following a squib.
     
  5. Not implying that a .45 is roll crimped... photo shows taper.

    Have seen LOTS of people new to reloading (and using soft plated bullets for cost) taper crimp to where there is a dangerously low amount of rim left to headspace on. They, in their new to reloading beliefs, tend to overcrimp to ensure smooth feeding.

    And you are right that a taper crimp will help to retain the bullet a pico second longer on ignition, helping to build pressure for proper combustion... especially with slower powders.

    Personally, I use nothing but real JHPs which are more forgiving of tight crimps. But then, I use almost exclusively, slow powders for maximum velocities. Have same issue in .40 with LongShot. Ran fine in my G22 but in my partners SR40, the SAME round would leave unburned powder in the barrel. Slightly tighter crimp solved that.

    Additional, In the SR40, the cases were ejecting heavily sooted down one side of the brass. From the G22, they were clean. Assumption: Sr40 has slightly looser chamber, taking more initial pressure to seal.
     
  6. It is also true that every gun is a little bit different. That's one reason why reloaders like to build their own ammo and tune it to their own weapon.
     
  7. Even IF a person tapered crimped that much, the case is lighter than the bullet. Upon ignition the case is firmly against the breech before the bullet has moved significantly. So much so that in SAMMI tests ammo ignited in a fire had little force, because the case was the projectile. Once fired the case will form to the the chamber fully, this is why with hot loads there is a glock bulge. It is the primary cause of blowouts, that the thicker area of the case becomes weak and blows out at the unsupported area of the chamber where the loading ramp is. It would be next to impossible for the case to become lodged in the throat after the primer is struck. Unless the case is very much over length.

    It is just simple physics. But again overcrimping deforms the bullet, which may lead to leading and poor accuracy. Over time leading could be dangerous unless removed. It is pretty hard to have a crimp on bullets close to the case size, as most bullets the ogive does not start abruptly, it is gradual. In the case of my hard cast LRNFP at the start of the ogive the bullet is only .450, though the cylinder is .452. Pretty much makes a .001 difference a non crimp on those bullets. It will keep the bullet from moving forward, but nothing to keep the bullet from moving back except for the friction of the inside case walls against the cylinder of the bullet. And in the case of cast bullets, they have less friction than jacketed. That is why they have higher fps for the same load, and bullet weight.

    My advice is to not worry so much about overcrimping and worry about consistency. But that is just my opinion.

    ETA If you are not seating to depths recomended by bullet manufacturer, the bullet jump is more important than the crimp. You do not want the bullet resting on the lands. You can find this by just barely seating a bullet, then measuring how far it did not seat fully in the chamber. You want a little more than that distance.
     
    Last edited: Apr 11, 2015
  8. From Ranier
    Quote:
    We, at Rainier Ballistics, recommend using lead bullet load data when loading our bullets. There is no need for adjustment when using lead bullet load data. Our bullets are jacketed using an electroplating process and are softer than traditionally jacketed bullets; hence the recommendation to use lead bullet load data. If you only have access to traditionally jacketed load data, we recommend a starting powder charge directly between the listed minimum and maximum load. A roll or taper crimp may be used with our bullets; do not over crimp.


    If the case mouth is closed too much during the removal of the belling step, the entire loaded round can chamber too deep in the chamber which would allow the mouth to get pinched in the throat. When the mouth gets pinched, it can't expand during discharge, thus delaying or preventing the gases and bullet from escape freely from the case, the result is a KB. There are other undesired effects less catastrophic, yet still potentially dangerous, or damaging to the firearm.


    Watch this whole video. And don't tell me this is "the unsupported Glock barrel issue". I as well have seen the HP bolt-in-barrel video and agree the HP is much more resistant to this kind of failure. This info however, extends to MOST modern semi autos.
    Again, watch the whole video and you will see the danger in over crimping. I have not yet re-found the article where an HP carbine suffered the SAME fate. But I will.

    https://www.youtube.com/watch?annotation_id=annotation_879286&feature=iv&src_vid=_q9O-wVfQ-s&v=u5oa3D4SDzs
     
  9. Here was his load data

    Load Data:

    Case: Federal (once fired - bought rounds and fired myself)
    Primer: CCI 500
    Powder: x.x grains of Titegroup
    Bullet: Rainier 165 grain HP

    Video description explains exactly what happened. Over bell removed all neck tension as the die wasn't a under-sizing die. Over crimp turned the mouth inward, impeding the barrel throat as well as causing setback ... pressure had only one way to go before it could overcome the resistance. Round landed on target lower left @ 7-8 o'clock position.

    Mod Edit: No grain counts when posting data. ~Rachgier~
     
  10. They recommend not over crimping for two reasons. The plating is thin and may fracture, causing separation upon leaving the barrel. Second the lead that is plated is soft lead, and deforms more easy than hard cast lead. I use Berry's bullets, and I use a crimp that leaves a light cannelure. I have had NO problems and fantastic accuracy, and consistancy.

    I used to use ranier bullets in 38 spl, and learned very quickly that without a tight crimp with target loads the bullets would get stuck in the barrel. Keep in mind this was published lead load data. With a revolver this is not a big deal, because they do not fire usually as rapid as a semi auto. If this happened in a semi auto during rapid fire, bye, bye fingers, hand, and possibly eyes. NO thank you. Put a good crimp, and I have never had another squib.

    It is free choice, if you don't want to use a firm crimp, then don't. For safety I will continue to use a crimp that will insure a consistent burning of powder.

    BTW what lab determined it was overcrimp and not setback or weak case from reloading. As I said before physics beat out a amateur video.

    Did you even look where the blowout was? On the unsupported case as most are!

    Again you can do what you want, but that kid is full of doo doo. He had blowout, as I have explained repeatedly the throat, or he calls lead is just the barrel diameter without rifling. On a 45 acp that would have to crimp the case until it was smaller than the bore diameter, and still the case will move to the breech before the bullet moves. Check out SAMMI testing for fire departments. Plus if the round was that far forward it would cause a light strike and likely not fire.

    Do not use cases that fail a case gauge check!

    [ame="https://www.youtube.com/watch?v=3SlOXowwC4c"]https://www.youtube.com/watch?v=3SlOXowwC4c[/ame]

    You need to skip to the bonfire to see just what SAMMI has proven. During combustion the case is lighter than the bullet, bullet stays put, case flies.
     
    Last edited: Apr 11, 2015
  11. Sorry Rach.

    Suffice it to say that the charge was below book maximum.
     
  12. To give you an example one of my 45 acp weighed total 241 grains. The bullet itself is 200 grains. With less than 10 grains of powder, I won't give actual data. That leaves the case weighing between 30, and 40 grains. Which do you think will move first in the chamber? The case or the bullet?
     
  13. Rachgier

    Rachgier Administrator Staff Member

    The projectile doesn't always stay put. Equal and opposite and all that. The case will fly farther than the round does, but the rounds do fly and with sufficient force to be consider lethal if you're silly enough to be too close.
     
  14. I have no doubt it moves some, just like the cylinder on a revolver moves to the rear upon firing, even though it is heavier than the bullet. Excessive pressure will cause a reaction. But just like a rocket at NASA, the ground vibrates, but it is the rocket that moves.

    This has long been known on forensics that the breach face will leave impressions in the head of the brass that can be seen by a microscope. All I had to see in that video was the blown out head to know what happened. It happens with Glocks, and most brands. Glocks get more attention for it.

    People are reminded all the time, do not load weak cases, do not be lax about powder charges, do not shoot bullets with excessive setback.

    While it is possible to over crimp, that chamber would have to be in very sorry shape for a case mouth to fit in the lead. The lead is the same diameter as the barrel, without the lands.

    That video does help to vindicate Glock though...
     
  15. moona11

    moona11 King of you Monkeys Lifetime Supporter

    WW I like berry bullets to but have you tried extreme bullets. They have a lot of sales and shipping ain't bad. I also use RMR site a lot free shipping.
     
  16. I haven't tried them yet, though they bombard my inbox with spam. That does not make me want to purchase from them. If I would just buy new barrels for my Glocks I would quit using plated or jacketed bullets.

    I have been a fan of cast bullets most of my life.

    Another issue that striker fired shooters must watch is out of battery discharge. I am not sure how much of a problem it is now, but it was a problem. Pay attention to make sure your gun is in battery.
     
    Last edited: Apr 11, 2015
  17. MXGreg

    MXGreg Supporting Member

    I picked up some .45 cases down at the range last summer that show what happens with an over crimp. The person who shot these also dropped one unfired round so I know they were loaded with LSWC bullets, guessing 185 or 200 grain. The spent cases in the picture (sorry its crappy) show that even after firing, the case mouth is still rolled in. The case on the left even has a brass "hair" curling out from just above the blow-out.

    [​IMG]
     
  18. moona11

    moona11 King of you Monkeys Lifetime Supporter

    Which site? I think you would like extreme bullets. Rmr has good deals on pulled hydro shok some times or other kinds. Next time I find 380 deal I'll pm you.
     
  19. I have seen that wayyyyy more times with reloaded revolver cases. Mostly because they can be relaoded so many times. That is from brittle cases.

    Brass becomes brittle when it is worked, that is why it has to be annealed to be formed or bent. It has only happened twice to me in my life, and that is why I inspect every single case. It is also the reason I do not reload 40 S&W YET. High pressure round with a unsupported chamber. If I do it will only be 1 time reloads, then the scrap yard.

    http://bisonballistics.com/articles/the-science-of-cartridge-brass-annealing

    They explain why those cases split.
     
    Last edited: Apr 11, 2015
  20. X-treme bullets. I don't have a link because I moved them all to the spam list and deleted them. I don't mind once a month, but I was getting emails daily, sometimes several a day.
     
Thread Status:
Not open for further replies.