Rimfire Central Firearm Forum banner

504 firing pin issue

449 Views 6 Replies 4 Participants Last post by  Picher
Since adjusting my headspace so that my bolt would not close on a .0425" no-go gauge, I have been noticing deep firing pin impressions and wondered whether I was inducing extra barrel vibrations during discharge that could be causing slight inaccuracy at 50 yards. What I speak of is that since the distance from the firing pin to the breechface has lessened, the crush distance is also less, and the 22 brass will only compress so much between the firing pin and breechface, which may be sending an unwanted impulse into the breech end of the barrel, causing a condition not condusive to top accuracy? I have noticed that standard velocity ammo accuracy has not been what I expected, and actually high velocity Aquila has been more accurate. Another thing I have noticed is that the firing pin may have acquired a minutely slight bend in it due to the shortened headspace. Now the firing pin tip definitely does not make contact with the breechface when dry firing, so that is not the issue, BUT the distance between tip and barrel is very small during discharge, and probably too small. I am thinking of stoning down the tip of the firing pin, as it does seem to have a distinctive 'M' shape and impression on the brass, and making it a flat tip, like you would think a 22 firing pin should be. Any thoughts Picher, or others more knowledgeable than me?
1 - 7 of 7 Posts

· Registered
Joined
·
680 Posts
The M shape firing pin is supposed to increase rimfire ignition performance. Much like the Swiss 1867 Vetterli 10.4 Swiss rimfire forked firing pin rifle. I would look elsewhere for the problem. Are you using a torque wrench on the action screws? Amount of Torque on action screws can have a large impact on group sizes it pays to experiment but 25, 26, and 27 inch pounds is a good area to start out on.
 

· Registered
Joined
·
1,239 Posts
Discussion Starter · #4 ·
Educator, flat with a slight angle, with the longer edge toward the center of the cartridge was what I had in mind. Like this:
http://www.snipersparadise.com/tsmag/june04/Picture4.pdf

Smoky, I have the action screws torqued to 24 in/lb on the front and 22 in/lb on the rear. I think it's a firing pin clearance-to-breechface after firing issue with the tighter headspace.
 

· Registered
Joined
·
680 Posts
I guess why I don't think it is the problem is I have a stock 541T sporter barrel that the firing pin will hit the chamber if it is dry fired. It really hits the case head hard and leaves the rim somewhat mangled. It shoots 1/2 inch 50 yard groups (five shot) with 3 loads regularly. And will shoot SK target ammo well below that most groups with SK are in the .270 to .420 range.

Remington tends to use alot of spring pressure for the firing pin springs in their bolt guns. Not all guns like this accuracy wise. Have you thought about getting an extra firing pin spring and "adjusting" spring pressure?

Have you tried experimented with any SK, or Eley ammo?

The firing pin issue is an interesting one and it may indeed be part of the problem because the average 504 does not seem to shoot with average 541 so you never know. Your experiment may work. I sure would like to see it work for you. Because it may help others.
 

· Registered
Joined
·
1,066 Posts
There are three keys to the proper firing pin strike.

1. Note that the ideal firing pin shape does not strike the fold of the rim, but just inside. A heavier than normal strike does no damage at that location. If the pin strikes the rim, it sets up unwanted vibrations that can affect POI.

2. The lower portion of the pin is forward of the upper portion, resulting in the dent in the case that re-directs flame toward the rim on both sides of the strike.

3. The pin should be rounded on the edges to allow flame to exit around the strike and to prevent case perforation.

Hope this helps.

Picher
 
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top