I recently resolved an ongoing ignition problem with a newer CPA rifle.  After reading the "Inconsistent Ignition" thread in the General Forum, I believe this information may be helpful both specifically and generally.

The problem was that the rifle (.32-40) would print two groups at 200 yards - one group approximately 1.5" above the other.  Tightening screws, changing firing pins; changing powders, charges, primers, cases, and even the scope had no effect on this condition.  I even used different front and rear rests - the condition persisted.

The source of the problem turned out to be the roll pin used to secure the Niedner bushing and firing pin to the breechblock.  This roll pin had very slight bow that introduced a wee bit of drag on the fore and aft motion of the firing pin.  I don't how the pin acquired that bow but, oddly enough, I found the same bow in a another used CPA roll pin that was kept as a spare.

When the offending roll pin was replaced with a properly sized solid pin, the drag on the firing pin went away as did the vertical stringing. 

JackHughs

   

  That is a most interesting inquire into the subject of "casual connection".  With that being reported, the next inquire in the sequence would be the subject of "frequency".

C.M.M.

Quote:


  Would you care to be a tad bit more specific regarding the replacement retaining pin that was used, i.e., the diameter, length, material spec. in the event another Forum reader should decide to follow your recommendation for correcting "vertical stringing" of a series of consecutive shots ?

Thanks,
C.M.M.

UtahDave wrote on Aug 7^th, 2013 at 10:16am:


I use a Weber-style breech seater.  I don't think the plugged case would put much load on the pin - particularly in relation to the load imposed on the Niedner bushing (and retaining pin) each time the rifile is fired.

JackHughs

I have also seen a roll pin deformed, the mortise in the firing pin did not go back far enough and the firing pin was slamming into it. For those of you who have a roll pin it is a real pain in the arss to get it out, the solid pin is a slip fit and I am not sure why they went with the roll pins on the newer rifles?

Roll pins just don't have a place in firearms construction in my book and all it does is to cheapen the quality substantially. One the actioned is indexed to spot and drill the hole the reaming process is just a simple extra step to insure quality. What ever the reason, possibly a slightly over sized holes it was a huge step backwards and it turns a simple firing pin replacement into an arduous task requiring a punch, hammer and bench block. Not items typically found in ones shooting bag and it could ruin ones day at a match. Mine has the slip pin and I can change the firing pin in well under 5 minutes.

I am going to have to look at mine. Have noticed one breech block takes more main spring pressure than others to pop primers. Have 5 blocks between 3 CPA's Might be some drag.

When replacing roll pins best if you have the right punch. If switching to solid pin it will need hand fitting.

Reason for the roll is to avoid hand fit's They work OK when they work OK

Boats

In my book that sounds very much like #41 drill rod. Easy to get but usually comes annealed. Field expedient would be a dremel to part off a #41 drill bit.  Of course a drilled hole will not be as accurate as a reamed hole so one may have to fit.