Bulged 209 Primers

[ElDiablo]

I was sure that you were going to have a huge flash hole too. Im really surprised that its only .029”.
Did these bulging primers just recently start? Start around the same time you started using those o-rings? Or has this been happening a while?

First two I’ve ever seen. Been running o-rings in this rifle and another Omega for 1-2 years. Can’t say for sure which plug was in which rifle as they get moved around though. Generally using a 300 ish gr bullet and 110-120 grV BH209. Maybe it was just an issue waiting to happen.

 

[ElDiablo]

Pic of the difference in seating depth of the o-ring plug vs no o-ring. Quite a bit of unsupported primer there (of course there is some compression upon closing the action).

 

[ronlaughlin]

One might try a shorter primer, like the STS, or making the primer socket a little deeper, say about 0.015" deeper. Either might cure the issues.

 

[bronko220002]

I first was going to say to check your flash hole but you already did. That pic does not look right. I believe that the primer should be fully encased by the BP. Why is it sticking out so far? Its almost like the BP is seated in too deep. Do you have the correct BP in the rifle?
I'm pretty sure the BP for the Omega and Impact are different. (Omega and Encore are the same)

 

[ElDiablo]

I first was going to say to check your flash hole but you already did. That pic does not look right. I believe that the primer should be fully encased by the BP. Why is it sticking out so far? Its almost like the BP is seated in too deep. Do you have the correct BP in the rifle?
I'm pretty sure the BP for the Omega and Impact are different. (Omega and Encore are the same)

Yes, the plug is correct. The plug on the right in the pic above is the factory Omega plug with no o-ring. The plug on the left is the factory plug with an o-ring.

 

[bronko220002]

Yes, the plug is correct. The plug on the right in the pic above is the factory Omega plug with no o-ring. The plug on the left is the factory plug with an o-ring.

I never owned an Omega but have Encores and other inlines and none have the primer protruding like that. That's why it seems odd to me.

 

[smokeeter]

[I first was going to say to check your flash hole but you already did. That pic does not look right. I believe that the primer should be fully encased by the BP. Why is it sticking out so far? Its almost like the BP is seated in too deep. Do you have the correct BP in the rifle?
I'm pretty sure the BP for the Omega and Impact are different. (Omega and Encore are the same)]




the primer should protrude somewhat from the BP to enable extraction.

 

[alternate]

That primer appears to have too much unsupported wall. You can't just eliminate the O-ring because you still need to maintain .003 - .005 crush fit. I don't know how a factory rifle would get like that. On rifles that I build I spend a lot of time ensuring the crush fit is maintained without excess primer protrusion. I use the crush fit for sealing and never tried an O-ring. To use that plug in that rifle shimming the breech plug and eliminating/reducing the O-ring seems to be the best solution.

 

[ElDiablo]

I appreciate all the feedback on this. Seems that this is confusing to a lot of members who don’t own an Omega. I should have been more clear in the original post.

The o-ring is an aftermarket from McMasterCarr placed in the primer pocket of the OEM plug to eliminate blow by. Which it does very well. But, the rifle shoots just fine (with a slight amount of blow-by) without the o-ring and I still get a little primer crush.

After considering all the comments and thinking about this further, I think this is simply an issue of not enough support on the walls of the 209. The primer pocket needs to be deeper to reliably use an o-ring. So I’m going to go back to shooting it without the o-ring. It’s still not clear to me why this issue is just now showing up though.

 

[scratcherky]

Pic of the difference in seating depth of the o-ring plug vs no o-ring. Quite a bit of unsupported primer there (of course there is some compression upon closing the action).

View attachment 34883

This picture certainly indicates much more than .003 to .005 compression on the oring. Something is amiss right here.

 

[ElDiablo]

This picture certainly indicates much more than .003 to .005 compression on the oring. Something is amiss right here.

I don’t follow.

 

[ronlaughlin]

I’m going to go back to shooting it without the o-ring.

If you are interested in trying a plug with a deeper primer socket, one can be mailed to you, if you reimburse me the postage. PM your address.

 

[ElDiablo]

I’ll send you a pm Ron!

 

[Ninering62]

First time I’ve seen this. I’m using a .035” thick o-ring in an OEM TC Omega plug which causes the 209 to sit fairly proud of the plug.
Using Fed 209As.
Plug was clean to start (reamed).
Headspace did not seem overly tight. Crush with o-ring measured at about .003-.004”.
Flash hole measured at .029”.
Temps were warm - about 80 degrees.
One 209 to foul then two shots.
First shot 400 gr bullet with 110 grV BH209. Second shot 260 gr bullet with 120 grV BH209.

Two shots yesterday showed that the primers bulged on the unsupported sides. The lower half of the sides are clean so no leakage past the o-ring, but there is slight cratering on the firing pin impression, some flattening and some carbon on the primer face indicating leakage around the primer cup.

Thoughts on what is going on here guys?

View attachment 34756
View attachment 34755

Dangit dude, I've never had that happen. From reading your post, it looks like you had checked all the boxes, done & covered every aspect properly & everything is in the parameters of where it should be. I, unfortunately, don't know what to tell you. I'm perplexed over that too.

 

[Ninering62]

Combination of pressure and the unsupported portion of the primer is the theory.

That makes sense.

 

[Ninering62]

Looks like fully half of the primer is outside the pocket. Even if you could reduce head space a lot you would still get leaking past the cup.

Yep

 

[bronko220002]

If you are interested in trying a plug with a deeper primer socket, one can be mailed to you, if you reimburse me the postage. PM your address.

Ron, a deeper primer pocket move the primer further from the firing pin? I would suggest that also for better seating of the primer (less exposed) and a spacer in the breech below the breech plug.
It appears to me that the BP is too short which is why I asked in my first response if the OP had the correct BP installed. The Omega and Impact look the same but are not interchangeable.
If this were my rifle I would deepen the primer pocket and see what thickness spacer I would need under the BP. Or at the very least buy an Omega BP just to be sure.

 

[ElDiablo]

Ron, a deeper primer pocket move the primer further from the firing pin? I would suggest that also for better seating of the primer (less exposed) and a spacer in the breech below the breech plug.
It appears to me that the BP is too short which is why I asked in my first response if the OP had the correct BP installed. The Omega and Impact look the same but are not interchangeable.
If this were my rifle I would deepen the primer pocket and see what thickness spacer I would need under the BP. Or at the very least buy an Omega BP just to be sure.

This is an OEM Thompson Center Omega breech plug. It fits. It works.

Deepening the primer pocket by .015” just allows the use of an aftermarket o-ring in the primer pocket.

Ron has figured this out and confirmed that it works.

 

[bronko220002]

This is an OEM Thompson Center Omega breech plug. It fits. It works.

Deepening the primer pocket by .015” just allows the use of an aftermarket o-ring in the primer pocket.

Ron has figured this out and confirmed that it works.

I trust Ron but deepening the primer pocket and installing an O-ring will still have the primer protruding the same amount and the problem will persist.
I'm not sure why the Omega leaves so much of the primer exposed. My Encore, which uses the same BP, fully encases the primer with a small amount of primer crush.
I stand corrected. My primer is not fully encased in the primer pocket.

 

[ElDiablo]

A perfect Omega breech plug solution is in the works that will solve all the issues in the OEM and aftermarket plugs. Hopefully more to report soon…..