Shimming a CVA QRBP with Rubber O-Rings

[Bluedevil]

Hey guys!

I finally got ahold of some rubber o-rings from McMaster-Carr in the size of 1x4.5 (buna). I would like to try the rubber o-ring method for my CVA Accura V2 QRBP I was just wondering how many o-rings would it approximately take to achieve 0 headspace/primer crush using CCI 209M shotshell primers? I don’t have my muzzleloader with me so I can’t try it out till the weekend but was looking for an estimate. Thanks again!

 

[HC]

1

Sent from my ME301T using Tapatalk

 

[Busta]

You only want to use 1 o-ring at a time. You may also need to adjust your firing pin bushing for best results.

If you have a caliper, first measure the OAL of your breech plug without a primer, with a primer, and with a primer with the o-ring installed in the bottom of the primer pocket.

You will want more crush on the primer using an o-ring, than you would with just a bare primer. This can all be controlled with the firing pin bushing.

An easy way to determine what you have now for headspace is to measure a primer length before and after firing. Just a primer, with no powder or bullet. This will determine your base line, and then you can adjust from there.

The o-ring will measure 1mm thick, which is roughly 0.039". You need enough headspacing without an o-ring installed to account for roughly 0.030" of that o-ring when installed. That would give you roughly 0.009" crush on the o-ring when installing your primer of choice. CCI 209M usually are in the 0.297" - 0.298"ish ballpark.

The above crush example Is just an example. You may desire slightly less or slightly more crush on your o-ring for your particular primer and load.

This is not as hard as it sounds, and can be completed in under 5 minutes easily. If I lost you anywhere along the line, don't be afraid to ask for clarification. I'm heading off to work, so you might not hear back until later today.

Good luck!

 

[Muley Hunter]

If you're going to use shims on the firing pin housing to adjust the headspace. You don't need to use the o-rings. My Accura V2 only needed .022 of shims to give me .002 crush on a federal 209a primer. That's just right. It's still easy to close the action and I get zero blowback.

I've never liked the o-rings because it makes the primer stick out of the pocket too much and falls out easier.

Too much crush on the primer can make the gun fire when closing the action. It happen to Jon. (FrontierGander) So, be careful. If you're not sure. Just use one o-ring and nothing else. It will be enough to stop blowback and give reliable ignition.

 

[MrTom]

I was having fits with dirty primers after firing but just changed from the CCI primers to Winchester primers in the blue box and that alone solved the problem. Using the O-rings you'll know if the fit with any primer is ok because while you may be able to close that action you may not be able to cock the hammer if combination of o-ring and primer length is too long.

I'm not a fan of having anything in the primer pocket except the primer and think that the firing pin shim kit that can be gotten from CVA for free is maybe the best option outside of trying different primers brands. I dinked around with half a dozen different primers by brand and by ML compatible but as soon as I did the Winchester primers the problem was solved. The two guns at issue were one identical to the rifle you mention and a CVA Optima Pistol. Both cleaned up using the Winchester product. I'd just try the Winchester primers....blue box.

 

[Travis299]

One of the rubber O-Rings in the primer pocket & you can seat the O-Ring with a primer. The only problem that I have had is you have to be sure that the primer does not fall out when closing the action by pointing the action down when closing with a firm snap. We use the O-Ring on our Accuras and the fired primers are squeaky clean which eliminates the firing pin assembly fouling.

 

[Muley Hunter]

I was having fits with dirty primers after firing but just changed from the CCI primers to Winchester primers in the blue box and that alone solved the problem. Using the O-rings you'll know if the fit with any primer is ok because while you may be able to close that action you may not be able to cock the hammer if combination of o-ring and primer length is too long.

I'm not a fan of having anything in the primer pocket except the primer and think that the firing pin shim kit that can be gotten from CVA for free is maybe the best option outside of trying different primers brands. I dinked around with half a dozen different primers by brand and by ML compatible but as soon as I did the Winchester primers the problem was solved. The two guns at issue were one identical to the rifle you mention and a CVA Optima Pistol. Both cleaned up using the Winchester product. I'd just try the Winchester primers....blue box.

That's because the Winchester primers are the longest primers. It's important when shimming the firing pin housing to set it for the primer you're going to use and stay with it. I like the federal 209a primer because it's the hottest primer and has never failed me.

You got lucky that you needed no shims to have no blowback.

 

[Bluedevil]

Thanks everyone for the replies that’s awesome! I haven’t been to the range yet and I’m hoping to make it out there tomorrow but just out of curiosity I decided to measure primers with my calipers (Starrett). I took 10 primers from each of the following manudacturers:

CCI 209M (Magnum) -

1) 0.296
2) 0.296
3) 0.297
4) 0.294
5) 0.295
6) 0.294
7) 0.298
8) 0.296
9) 0.300
10) 0.295

Total = 2.961 / 10 = 0.296 (avg)

CCI 209 (Non-Magnum)

1) 0.297
2) 0.297
3) 0.296
4) 0.296
5) 0.295
6) 0.296
7) 0.296
8) 0.297
9) 0.296
10) 0.297

Total = 2.963 / 10 = 0.296 (avg)

Federal 209A -

1) 0.295
2) 0.296
3) 0.296
4) 0.297
5) 0.296
6) 0.296
7) 0.297
8) 0.297
9) 0.297
10) 0.295

Total = 2.962 / 10 = 0.296 (avg)

Winchester W209

1) 0.301
2) 0.302
3) 0.301
4) 0.302
5) 0.301
6) 0.302
7) 0.302
8) 0.302
9) 0.301
10) 0.301

Total - 3.015 / 10 = 0.302 (avg)

Fiocchi 616 (.209 Type)

1) 0.297
2) 0.297
3) 0.297
4) 0.298
5) 0.298
6) 0.297
7) 0.299
8) 0.297
9) 0.299
10) 0.297

Total = 2.976 / 10 = 0.298 (avg)

To be continued.......

 

[Busta]

You never mentioned what powder you would be shooting? If you intend on shooting Blackhorn 209, do you have the Blackhorn Breech Plug?

Another primer that is as long or longer than the newer Winchester W209 is the European made NSI (Nobel Sport). They are a little larger in diameter, and fit the metric primer pockets of the CVA breech plugs well. I use them in my Optima Pistol.



As you now know, there can easily be up to 0.005" variation in the same lot of primers. The manufacturers have to allow for the longest primers, for both fitment and liability issues. This leaves you with excessive headspace. The o-ring can safely help take fitment issues and excessive headspace out of the equation.

Using static shims either behind the firing pin bushing (or in some rifles in the primer pockets) can also work, but if you set your primer crush headspace for -0.002" at the mean (0.296") when you have a length spread of 0.005" in your chosen primer (CCI 209M), not all will be happy. You will have a 0.001" crush on your 0.295" primers, and 0.006" crush on your 0.300" primers. So instead you'll have to set it up for the worst case -0.002" crush @ 0.300", leaving any primers between 0.295" and 0.298" (your majority) with no crush and between 0.000" to 0.003" excessive head space.

This is where the o-ring really shines. You can compress the o-ring instead of crushing primers, and have a cleaner breech and receiver. This also allows you to shoot different length primers as well. The o-rings will usually last for a full range session of around 40 shots before needing replaced.

Another added benefit of the o-ring is once a primer is installed for hunting, it makes your breech end of your powder completely waterproof. No rain will migrate beyond the slightly compressed o-ring like it can on a bare primer. This also keeps the business end of the primer completely dry as well.

Pretty cheap insurance when you think about it.

Just some things to think about.

 

[Muley Hunter]

The Federal primers have a .002 variance. So, with a .003 set crush with shims will give you a proper headspace all the time without having to use an o-ring that causes primers to fall out too easily.

 

[Busta]

Some might want to go back and read the original post? He said he would like to try the o-ring method with CCI 209M primers. Why not let him come to his own conclusion? I was merely trying to help him in his quest.

The only precautionary measure that needs to be considered, is getting fitment right with just primers before even considering loading the rifle.

I've been using o-rings in several breech plugs for 10 years now. Even kept it a secret for 6 months testing Blackhorn 209 in several rifles and breech plugs, before giving the idea away. They work great in a tip-up (break open) rifle that has the headspace to allow it. I've even modified several breech plugs primer pockets to accommodate them.

I have also experimented with them in the bolt action Knights back in 2008-2009. They can be made to work in those, however the camming action of the rotating bolt has to be taken into consideration. The headspace needs to be perfect, or the primer will turn the o-ring out when opening the bolt. Static shims work better in that application because of the leverage the rotating bolt and camming action provide. Either way, it still needs to be headspaced.

Good luck to the original poster. I hope you find what you are looking for! If you have any questions, just ask here, or send me a PM.

I will say, if you are intending on shooting Blackhorn 209, you will want a Blackhorn 209 breech plug (either CVA or Western Powders), or have your current OEM plug modified with a larger diameter flame channel, vent liner, and powder pocket.

Here is a refresher on the original post for those that may need it.

Hey guys!

I finally got ahold of some rubber o-rings from McMaster-Carr in the size of 1x4.5 (buna). I would like to try the rubber o-ring method for my CVA Accura V2 QRBP I was just wondering how many o-rings would it approximately take to achieve 0 headspace/primer crush using CCI 209M shotshell primers? I don’t have my muzzleloader with me so I can’t try it out till the weekend but was looking for an estimate. Thanks again!

 

[Bluedevil]

Sorry I forgot to add I am shooting Blackhorn 209 through a CVA Blackhorn 209 QRBP. The QRBP shown in that pic is the stock breechplug that came with the CVA Accura.

I would like to try the rubber o-ring method first, McMaster-Carr doesn’t ship to where I live (Canada). I had to get them shipped to a US address and then brought back to Canada. I’m not sure if CVA ships ships to Canada either I’ll have to double check. Thanks again for all your help and opinions greatly appreciated.

 

[Muley Hunter]

Busta.........He's free to do as he pleases. I'm just explaining another option if he doesn't like the o-ring. Using an o-ring doesn't need much explanation. Put one in the primer pocket and go shoot.

 

[Busta]

Muley, it's all becoming crystal clear now. It's obvious you've never done it, or at least never done it right?

Bluedevil, if you need any help, just give me a PM.

 

[Muley Hunter]

Done what? Use an o-ring? Sure I have. I wouldn't be talking about it if I hadn't of tried it. Have you shimmed one? You don't think that's a better way? Once it's done you don't have to mess with it anymore and the primers stay in the pocket better.

We were shimming the FP housing long before anybody used o-rings and before the BH breech plugs came out. We got BH 209 to fire reliably by just setting the headspace with shims, using hot primers like the Federal and keeping the flame channel clean. As a side effect, the primers stayed squeaky clean with no blowback.

The first thing I noticed when using an o-ring was the action had to be slammed shut. It has to be that way for the o-ring to be compressed the proper amount and i don't like it. I've heard others complain about that along with the primers falling out to easy. When the proper setting is made with shims the action closes as easy as having no primer installed. As it should be.

As I said. I was just offering another option in case he doesn't like the o-ring. I'm not looking to argue about it.

 

[NewlyMinted]

I’m wondering if I did this all wrong. I tried the McMaster Carr rubber o-rings on my CVA plugs because both my black horn QRBP and the standard QRBP have blowby/ blowback. And it just melted, there was an awful melted rubber smell. I tried seating it a couple of different ways and after firing off a few primers, I just went back to not using the o-rings.

The plugs are new and only have about 50 shots through each. I tried CCI 209, 209M and the Federal 209A and all have 4/5 sooted out primmer. Every now and again the primer comes it shiny.

I clean it well, the flash hole fits a #70 bit.

What have I missed?

 

[Busta]

I’m wondering if I did this all wrong. I tried the McMaster Carr rubber o-rings on my CVA plugs because both my black horn QRBP and the standard QRBP have blowby/ blowback. And it just melted, there was an awful melted rubber smell. I tried seating it a couple of different ways and after firing off a few primers, I just went back to not using the o-rings.

The plugs are new and only have about 50 shots through each. I tried CCI 209, 209M and the Federal 209A and all have 4/5 sooted out primmer. Every now and again the primer comes it shiny.

I clean it well, the flash hole fits a #70 bit.

What have I missed?

What rifle? Unless you have the Apex, you can adjust/shim your firing pin bushing in the standing breech. That is where you want to start.

The flash hole itself is not a problem. You need a 1/8" drill bit to cut the carbon out of your flame channel between the primer pocket and the flash hole. That is where the carbon builds up and causes blowback.

 

[GM54-120]

A #70 bit is .028
1/8" is .125 or roughly a #31 bit
The regular QRBP (not BH09) takes a 3mm bit

If you are cleaning with a #70 you are doing next to nothing. The flash hole wont shrink from carbon but the flash channel will.

 

[Jisonhood1023]

You only want to use 1 o-ring at a time. You may also need to adjust your firing pin bushing for best results.

If you have a caliper, first measure the OAL of your breech plug without a primer, with a primer, and with a primer with the o-ring installed in the bottom of the primer pocket.

You will want more crush on the primer using an o-ring, than you would with just a bare primer. This can all be controlled with the firing pin bushing.

An easy way to determine what you have now for headspace is to measure a primer length before and after firing. Just a primer, with no powder or bullet. This will determine your base line, and then you can adjust from there.

The o-ring will measure 1mm thick, which is roughly 0.039". You need enough headspacing without an o-ring installed to account for roughly 0.030" of that o-ring when installed. That would give you roughly 0.009" crush on the o-ring when installing your primer of choice. CCI 209M usually are in the 0.297" - 0.298"ish ballpark.

The above crush example Is just an example. You may desire slightly less or slightly more crush on your o-ring for your particular primer and load.

This is not as hard as it sounds, and can be completed in under 5 minutes easily. If I lost you anywhere along the line, don't be afraid to ask for clarification. I'm heading off to work, so you might not hear back until later today.

Good luck!

I am having this issue with a new cva optima. In adjusting the firing pin bushing are you just unscrewing it a little to protrude out of the breech face?