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Very Hot Topic (More than 25 Replies) Mucho blowback on case used breech seating (Read 1179 times)
Cbashooter
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Mucho blowback on case used breech seating
Feb 22nd, 2021 at 1:04am
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I have a 32-40 Stevens that's having issues.ive tried different cases, bullets ?powders,breech seater depth etc.after about 10 shots the front. 1/2" of the case is coated with powder carbon and crud.so much so its causing the case neck to get smaller after each firing.I've used annealed cases with no change.
Ideas?
  
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westerner
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Re: Mucho blowback on case used breech seating
Reply #1 - Feb 22nd, 2021 at 1:14am
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Use a tapered pointy tool to bell the case mouth out every couple shots. I use a 50 caliber jacketed bullet.† Annealing the necks should help too. Standard 32-40 necked chambers tend to do this more compared to a breech seating straight taper chambers.
  

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argie1891
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Re: Mucho blowback on case used breech seating
Reply #2 - Feb 22nd, 2021 at 1:45am
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when i first got my CPA 32-40 i loaded a few cases with some really light loads of powder i had used in fixed ammo. the speed of the bullet really isnt important to me as all it needs to do is penetrate both sides of a sheet of paper.. anyway i actually had a couple cases crumple. the pressure was so low the powder gas came back and crushed the case. after losing 2 cases i decided that super light loads and breach seating might not be a great idea. that may or may not be your problem but too low pressure can cause the case to not expand to fill the chamber. an extra grain of powder might fix your issue.
  

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boats
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Re: Mucho blowback on case used breech seating
Reply #3 - Feb 22nd, 2021 at 7:09am
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Aggregate of the good advise above. Little bit of flare mouth of the case & higher pressure. 14.5 4227† 20O gr bullet & breech seated pretty much a standard load. At times I went little bit more. 14.7-14.8

Depending on ambient temperature and is the target† at 200 yards or 200 meters bullet could go sub Sonic at the target. Holes showing unstable, seemed to have little effect on accuracy happens just before impact. Bump the charge up they would go round.

Even so 14.5 was always my starting load. Now use that barrel fixed 170 gr bullet. Still use 14.5 4227 cases show no sign of blow back.

Boats
  
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Cbashooter
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Re: Mucho blowback on case used breech seating
Reply #4 - Feb 22nd, 2021 at 9:28am
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"14.5 4227  20O gr bullet & breech  seat:

That's one of the loads I was using. 

I'll try a flared case.

Thanks a for the input.
  
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Premod70
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Re: Mucho blowback on case used breech seating
Reply #5 - Feb 22nd, 2021 at 9:46am
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If breach seating is the way you shoot the rifle expand the case neck until it just drags the chamber. My 32-40ís chamber is cut way over size in the neck area and there is no way one can shoot fixed rounds but a custom expander spreads the case neck out leaving a thousandth or so clearance in the chamber and all is well. A flare at the case mouth is marginal at sealing the neck for a consistent powder burn, better to expand the case neck back to at least the transition from the case neckís parallel sides to the case body. Good luck.
« Last Edit: Feb 22nd, 2021 at 9:52am by Premod70 »  
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marlinguy
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Re: Mucho blowback on case used breech seating
Reply #6 - Feb 22nd, 2021 at 10:30am
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Breech seating results in a much larger case capacity than fixed, so often have to increase the powder charge to get the same results you'd get with fixed ammo. I do slightly bell cases using my M die to bell just enough to allow easy chambering. But also use hotter charges to help seal too.
  

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Cbashooter
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Re: Mucho blowback on case used breech seating
Reply #7 - Feb 22nd, 2021 at 10:51am
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Thanks everybody for the input. I'll try.the flared case. I've done all the other tricks.
  
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Re: Mucho blowback on case used breech seating
Reply #8 - Feb 22nd, 2021 at 10:54am
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Here is one solution to the problem of case mouth collapse. This is not my concept but was used by a couple of California shooters I knew back in the 80s. I had one of my Simmons re-decappers modified as shown in the illustration.
Set the expander plug to just kiss the case mouth to ensure it's round and VERY SLIGHTLY flared. 
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Re: Mucho blowback on case used breech seating
Reply #9 - Feb 22nd, 2021 at 11:03am
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My 32-40 Hiwall did the same thing.  Upon the advice of the members of this board I started flaring the end of the case slightly using a tapered punch about 8" long as I am not a machinist by any stretch of the imagination.  I just push it in a tad so that the case chambers with a slight resistance.  I wipe the neck off when I decap just out of habit.  Tom
  
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Re: Mucho blowback on case used breech seating
Reply #10 - Feb 22nd, 2021 at 11:06am
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I'm not sure if anyone mentioned this:

(You need to Login or Register to view media files and links) $17 MSRP

And for portability...
(You need to Login or Register to view media files and links) $55 MSRP

  
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Cbashooter
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Re: Mucho blowback on case used breech seating
Reply #11 - Feb 22nd, 2021 at 11:08am
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Thanks RSW I can make one if those for my Simmons tool on my little Unimat.

  
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JLouis
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Re: Mucho blowback on case used breech seating
Reply #12 - Feb 22nd, 2021 at 11:10am
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Brass cases have quite abit of spring back and I have never had one fully blow out to the correct fit. If you have the means to make a neck expanding button. You can then over expand it to where it will spring back to the correct size for your chamber. This is actually what I do myself and you do want the neck to drag going in as has been mentioned above. They way I do mine is I make an expanding button basically the same as the ones on a resizing die. Then drill and tap it 8-32 unscrew the one on the die off and then screw the new one on. Doesn't matter what the die might before just adjust it down far enough to just size the neck of the case being used. If you happen to have a guage pin set it makes it allot easier to find the correct size. Just keep going up and expanding it one size at a time until you find the correct spring back fit and then make the expander button the same size as it. Now you have one you can use on multiple cases on an as needed basis. Screw it off when done and put the one that came with die back on. I keep mine in that same sizing die case for future use so I don't have to go looking for it. I hope this all makes sense and that it might be helpful for your own personal use. Below is the original with decapping pin and two of different sizes I have made to use on the same sizing die.

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Cbashooter
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Re: Mucho blowback on case used breech seating
Reply #13 - Feb 22nd, 2021 at 11:11am
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CajunRebel wrote on Feb 22nd, 2021 at 11:06am:
I'm not sure if anyone mentioned this:

(You need to Login or Register to view media files and links) $17 MSRP

And for portability...
(You need to Login or Register to view media files and links) $55 MSRP


I have a Decker/Huntington press i use for some bench work already.the lee expander tool works good but NOE makes specific expanders for those that are like the m die

  
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JLouis
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Re: Mucho blowback on case used breech seating
Reply #14 - Feb 22nd, 2021 at 11:28am
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I clean my primer pockets quite allot because my rifle is chambered having Zero headspace on the back of the primer and case. Any slight primer carbon buildup in the bottom of the primer pocket that has been cut to minimum LP primer size specs has to cleaned up. So I made the below primer pocket scraper and on the other end it is turned to down maintain my case neck size as was expanded in my prior post. I really like the way you have yours setup. I might need to give it a try but mine would not be tapered but to the correct size and not sure how easy the case would slide back off. Case is a 25-35 so I actually size the depth of the straight neck quite a bit deeper. This to insure the neck is always central to the bore / square to the base of the bullet the best that I can. 

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« Last Edit: Feb 22nd, 2021 at 11:50am by JLouis »  

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