Why all the fuss about consistent rimfire ignition?

B

Bill Calfee

Gun Fool
Why all the fuss about consistent rimfire ignition?


CYA friends:


When we have to deal with rimfire ammo with uneven amounts of priming compound, and uneven amounts of powder, why should we need to worry, so much, about the action producing extremely consistent ignition?


I'll answer this with a question:


Why would we want to compound the issue of uneven priming and powder with uneven ignition?


We can't control the consistency of the priming compound or powder.


All we can humanly do, is to produce the most consistent ignition possible so that what is reflected at the target, is only what we have no control over.


Your friend, Bill Calfee

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PS:

If we had perfect ammo, every round the exact same velocity, with all else being equal, the actions that produce the most consistent ignition would produce the best accuracy.


So why would anyone want to handicap their potential accuracy, by not using the actions that produce the most consistent ignition?


Robert Oates finding General Lee and putting it in Fred Sears' hands, has been an eye opening history lesson about SAP rimfire ignition.



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Something to ponder

Hi Bill

When a case is loaded into a chamber there is a clearance gap so you can safely load a case.

Gravity means the case sit on the bottom of the chamber until the bullet contacts the lead, now it is crocked in the chamber.

The ignition part, you then smack it with a pin off center.
This causes the barrel to vibrate as I have measured it at the muzzle.

If I can measure the barrel moving with just the firing pin doing it's thing then sorely it must move the case and bullet around at a critical time.

The consistency of this then must be very important including the consistency of the inertia it imparts on a firing case.

Therefore the important thing is consistency how ever it is achieved.

Also do you think the clearance between the bolt and action and how the operates closes the bolt has an effect as this would affect how the case and bullet end up sitting in the chamber.

If this is the situation with an erratic operator even if it is just very slight differences swinging on the bolt handle could this open a door to an opportunity to improve accuracy buy isolating / reducing somehow operator inconsistency in moving the bolt.

Regards
Graham
 
Friend Deveng

Deveng said:
Hi Bill

When a case is loaded into a chamber there is a clearance gap so you can safely load a case.

Gravity means the case sit on the bottom of the chamber until the bullet contacts the lead, now it is crocked in the chamber.

The ignition part, you then smack it with a pin off center.
This causes the barrel to vibrate as I have measured it at the muzzle.

If I can measure the barrel moving with just the firing pin doing it's thing then sorely it must move the case and bullet around at a critical time.

The consistency of this then must be very important including the consistency of the inertia it imparts on a firing case.

Therefore the important thing is consistency how ever it is achieved.

Also do you think the clearance between the bolt and action and how the operates closes the bolt has an effect as this would affect how the case and bullet end up sitting in the chamber.

If this is the situation with an erratic operator even if it is just very slight differences swinging on the bolt handle could this open a door to an opportunity to improve accuracy buy isolating / reducing somehow operator inconsistency in moving the bolt.

Regards
Graham
Click to expand...

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Friend Deveng:


This is the reason I developed parallel, straight, sided chambers, no taper.


With a .2240" diameter case and a .2250" diameter chamber, gravity doesn't have much to work with.


We do have to get the case in the chamber, and that bullet is covered with wax, so there is a certain amount of "slop" between the OD of the case and the ID of the chamber, that is, if .0005" can be a fair definition of "slop".



For years when I used 12 ignition, I laid the firing pin tip back at the top.


What this did was to pin the case to that side of the chamber, every round that was fired.

Therefore, that .0005" of "slop" was always in the same location.



I no longer do that with 6 ignition......after testing thoroughly I found it wasn't necessary.


But laying the pin tip back at the top most certainly is a benefit for 12 ignition.




Yes, when we close the breech bolt the barrel vibrates......


And when the trigger sear breaks and the cocking piece over rides the transfer bar, the barrel starts to vibrate, well before ignition takes place.



There's another factor involved with this consistent ignition stuff.


If the case head isn't penetrated consistently to the same depth, then yes the barrel's initial vibrations are inconsistent too.


So uniform, consistent ignition, all else being equal, is the difference in the accuracy potential of a rimfire accuracy gun.


This is why I've created such a fuss about consistent rimfire ignition these last 20 years, ever since I built my first MD-PAS Turbo actioned gun.



The first MD-PAS Turbo gun I ever built opened my eyes to the difference consistency of ignition makes in rimfire accuracy.


Your friend, BC
 
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