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Blown top straps

jonlowerjonlower Member Posts: 41 ✭✭
edited September 2011 in Black Powder and Cowboy Action Shooting
Thought it would be good to discuss this problem. Colt SA's and other clones have been known to blow up on occasion. Several explainations have been given, from squib loads to not enough powder laying against the primer and so on. As I have reparied at least 20 blown SA's over the years, I have found one common denominator in all of them: weak trigger/bolt springs and improperly fit cylinder bolts. This causes the bolt to jump out of the notch during rapid or hard cocking. If the cylinder rotates about 3/32nds off center, there is still enough primer surface under the firing pin to allow a detonation of the primer. Bullets, especiall Keith style types with a shoulder below the ogive, will fire and catch on the rear barrel breech. If it's a hard bullet, chances are it will not enter the chamber and a catostrophic detonation of cylinder and top strap will occour. To make it easier to understand, cylinder "throw by" will cause you problems. Refrain from using lightened springs and make sure your bolt is fitted properly by a gunsmith who knows SAs'

JP
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Comments

  • Wolf.Wolf. Member Posts: 2,223 ✭✭✭✭✭
    edited November -1
    This is an interesting topic.

    Why not post it in the "Ask the Experts" forum here in the GB Forums as well and ask the question, "Have any of you SAA users experienced or seen much of this and what is your opinion of the causes for these failures?"

    It sounds like you have isolated the probable cause and I think it would be interesting to read through the replies of others as well.
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  • v35v35 Member Posts: 12,710 ✭✭✭
    edited November -1
    That's interesting. I thought barrel throating would funnel out of time bullets into the barrel and shave the rest off.
    I don't like to beat up my SAAs' cylinders with heavy lock springs. I make sure cylinders are properly timed.
    when a leg of the lock or lock spring breaks, and they break not that infrequently, I can see an out of time firing problem.
    I am surprised you can do a proper top strap repair that will hold up.
    You must be very skilled.
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  • jonlowerjonlower Member Posts: 41 ✭✭
    edited November -1
    Yes, they hold fine for blackpowder or smokless shooting if the loads are kept at cowboy velocities. As for the light springs, I'd rather have a little missing blue from my cylinder than a blown up gun or damage to my shootin' hand. Besides, if the timing is right, the bolt falls into the notch approach. If the bolt head is polished, it seldom leaves any deep drag gouging or scratching. It is something to think about.
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  • GatofeoGatofeo Member Posts: 230 ✭✭✭
    edited November -1
    Very interesting topic. Never thought of the weak springs and poorly fit cylinder bolts.
    I wonder if this could also be verified by comparing the primer of the , off-center from the pin, this may show.
    However, with heavy loads, this offset hit of the firing pin may be obscured.
    I'm with you on the cylinder ring. I've never found it unattractive unless it was very wide and deep. A slight ring doesn't bother me, but some people just freak out at any evidence of a dragging bolt past the cylinder notches.
    I'd rather have the ring, instead of a topstrap in my forehead.
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  • cbyerlycbyerly Member Posts: 689 ✭✭
    edited November -1
    It is my understanding that minumum or below minimum smokeless powder charges have a tendency to detonate rather than burn. The cone on the barrel should prevent any top strap from blowing if the cylinder is mis-aligned. When a top strap blows, the cylinder is also blown. It cannot rupture from over pressure if the bullet has left the ctg case.
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  • machine gun moranmachine gun moran Member Posts: 5,198
    edited November -1
    A bolt spring at full torque may cause the bolt to snap into the notch-lead with considerable force, but it does provide for non-skipping, and for very secure locking when it drops into the notch. The same force will cause the bolt to gouge a nice deep groove around the periphery of the cylinder if the gun is not at all timed, or even if it is properly timed and the shooter allows the bolt to pop up against the surface of the cylinder. The latter is caused by lowering the hammer from the half-cock position when the cylinder is out of index, and this usually occurs after only semi-knowledgeable people have checked the gun for a loaded condition.
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  • v35v35 Member Posts: 12,710 ✭✭✭
    edited November -1
    Note top straps on S&Ws don't blow and their locking bolt springs are feather light compared to the SAA.
    I suspect a broken cyl lock bolt leg or cyl lock bolt spring can in a properly timed gun precede a gross out of time condition and a blown top strap.
    The only way to be sure an SAA cylinder is locked is to check it every shot or hear four clicks.
    At one time I shot SAA Colts a lot and broke a number of lock bolt legs and lock bolt/trigger springs. Bullets were keith 255 gr SWC & 185 gr RNSWC.
    I guess I was lucky when the parts broke.
    Using an unaltered lock spring a lock bolt will beat up a cyl lead-in even when highly polished. It's really a very heavy spring.
    For that reason and to reduce breakage, legs are tapered & polished.
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