Has anyone heard of a rolling block discharging when the block is closed? (A stuck firing pin that hits the primer.) I had heard this some where. I always close the block slowly on my '67 danish in 50-70 when I shoot it.
john
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Has anyone heard of a rolling block discharging when the block is closed? (A stuck firing pin that hits the primer.) I had heard this some where. I always close the block slowly on my '67 danish in 50-70 when I shoot it.
john
I've not heard of it happening but I do recall reading that the the firing pin can freeze in place. Some guns were made with no means to retract the firming pin; some were made with coil springs around the firing pin & some have a cam that retracts the firing pin as the block is opened. See DeHass' Single Shot Rifles & Actions.
DeHass's book is excellent, and well worth the price for single shot fans.
Jim
This is an interesting thread. I have 2 comments to add.
A friend of mine had one of the 7mm RRBs. He loaded and fired a single round which blew the breech open. The expanded case was left in the barrel and the primer was impaled on the firing pin in the open the breech block. He took his damaged case back to the gun shop and they produced a 7X57 case they had fired that looked normal. I know the shop well. They are honest but not particularly special gunsmiths.
My friend checked his chamber with a cast and showed it to me. The casting showed the chamber had a slightly shorter neck and sharper shoulder than a normal 7X57 case.
When his cartridge was fired he theorized that the heavy hammer blow drove the case mouth in to the throat causing the high pressure and pierced primer. The pierced primer blew the hammer back and the residual pressure opened the breech block. This may offer a clue to how the breech block opens. A high pressure gas leak may be able to blow the hammer back. It sure blew his open though his primer was pierced to enable it.
In regard to oiled cases. I had read of lightly oiled brass fire forming and stretching less and I began trying it with a 40-65 High Wall. This is low pressure ammo in a massively strong action. The case fire formed well and there were no issues. Next I tried a CZ 527 in .22 Hornet. Then reformed .303 WW and R-P brass in a 6.5X53R Dutch M95 Steyr Mannlicher rifle. The cases fire formed perfectly. Since then I have made it a practice wipe a very thin film of oil on each case as I fire form new brass. All my experience with this had been positive.
I don't plan using this for normal shooting of fire formed brass in a rigid bolt action. For this application it only slows down shooting as my existing brass life is nearly infinite with failures being neck or body splits. I will definitely use this technique to prolong case life in the springy Lee-Enfield rifles and reduce the extraction load on my Hakim extractor.
I absolutely believe that a pierced primer could vent through the firing pin hole and unlock the hammer.Quote:
A high pressure gas leak may be able to blow the hammer back. It sure blew his open though his primer was pierced to enable it.
I recall firing Iraqi Ball in a 303 British rifle. The stuff I had was awful, over pressure and it pierced primers. The gas venting would blow the firing pin all the way back. I had to remember to place my thumb out of the way as the cocking piece snapped hard.
Then I had some awful 8 mm ammo. That pierced primers and blew the firing pin back.
If pierced primers can blow a firing pin back to the stops under spring tension, I have no doubt that it could unlock the hammer.
Incidentally, last weekend I shot some 30-06 in a push feed rifle. I was shooting 169 Lapua with 48 grains of Pat's surplus AA2520. This lot of powder is one grain slower than the other AA2520 I have had. The first five shots all had case head separations. It was my reloads, and I figured I had oversized the cases (Which proved true when I got home and measured loaded ammo.) So, I got out a bottle of 10W-30 and coated the remaining cases with oil. Fired twelve more rounds. One round had a case head separation mark. Eleven rounds did not.
Funny thing is, the groups with oiled cases are tighter. Significantly better clusters.:madsmile:
From looking at an exploded view of the action parts, The block is only secured by the hammer on firing. If the hammer spring is weak, it can allow the action to open under pressure. The action would close again as the pressure returns to normal. This would happen very quickly, giving the impression that the action remained closed. The use of a reload with the slightest amount of sizing lube on the case would add to the problem. That is why the factory ammo works OK.
Compare the spring strength to your other action and check the cases for sizing lube.
The RRB is a self locking action. That is as the hammer rolls under the breech block it locks and any firing forces create more friction that helps keep it locked. However if a huge gas leak blows back against the hammer the gun may unlock as the pressure drops.
My chamber neck is short also.:confused: I trim the cases about 1/16" to avoid an unsightly ring around the fired cases. I cut my own chamber with a reamer I bought off eBay. I have refused to sell it even though I now have no use for it because I think it is improperly ground (brand name reamer too).:dunno:Quote:
Originally Posted by ireload2
My problem was a very light mainspring that I thinned to reduce that awesome RRB trigger pull. It would appear I went too far.:eek: Trigger pull is great, but evidently the recoil of the firing pin is forcing the hammer back and opening the block. I have experienced no pierced primers. That picture if the blown case is the actual case head that hit me above my left eye. It was not a light blow. I found it in my shirt pocket after I got home. The blown case came right out with no problem.:cheers:
I am now trying to perfect a coil spring setup (ala DeHass) to stop the breech block from opening and simultaneously improve trigger pull.:super:
Oiled cases make me nervous. I will try that as a last resort. I think I read Hatcher too many times. This is a plot of 1903 Failures I deveoped from Hatcher's and SRS data. The receiver failures have a yellow center. A lot of those failures were attributed to greased rounds.:slap:
Jim:cool:
Jim, I believe the "greased round" problem was the fact that the troops would slather grease on the bullet/neck of the case. At that point the neck/chamber clearances were hydraulically reduced to "zero," the neck could not expand to release the bullet, and the rest (was) history.
Do a little Googling and see if you read it the same way....
MEH,
I do read it the same way. I used to know the name of the grease they used, and it was heavy grease vs oil.
Will glycerin work?
Jim