Large Rifle Primer--QRBP

[ronlaughlin]

To me, the dimensions of the Blackhorn QRBP are better suited to using rifle primers, not shotgun primers. A couple of days ago a rifle, and a couple of breech plugs came in the mail, so yesterday morning the flash hole of the Blackhorn plug was enlarged to 0.035", and a dutchman was put into the mortice along with some red loctite. The dutchman was made by cutting a small piece off the QRBP fitment tool. Using JB Weld to fill the mortice was considered, but in the end, the dutchman was used instead.

This morning the loctite had hardened, so the plug was turned in a lathe till the dutchman was flush. Then the primer socket was enlarged in a mill, so the Precision Rifle large rifle primer adapters could be used. The socket was also made deep enough so that an o-ring would fit, and allow the rifle to go into battery, and the hammer be cocked.

The shooting set today, was just about the same as yesterday, except the truck was parked one foot further away, and it was 4 degree, instead of 6 degree. Five shots were taken at 85 yard plus 1 foot. The scope setting was the same as yesterday' final setting.

The Blackhorn QRBP didn't fit the barrel as nicely as the QRBP used yesterday, but ignition was perfect, even though there is some blow by. Turning the plug in the lathe to flush the dutchman was more difficult than i envisioned, so now i am wishing i would have used JB Weld to fill the mortice..

 

[Busta]

Ron,

looks like the flange got dinged or rolled in a bit on the front of that plug?

You might be able to expand that flange back out with something like a 5/8"-11/16" bolt with a chamfer on it, then re-seat the plug back to the barrel? Since you already filled in the slot for the tool, you would have to wrap some leather around the back end and use something like vice grips to re-seat it.

Looks like you may have problems at the other end as well? Too deep? Too wide? Leaking through the adapter?

 

[ronlaughlin]

Took your advice, and pressed a 5/8" bolt into the end of the plug. First pass had no effect, so the second time i really got on it. After that, with the plug in place, the rifle wouldn't go into battery. Some muscle work using a pipe wrench three times, which wasn't easy; the rifle will now go into battery. We won't know if this fixed the seal on the muzzle end until the next trip. The other end leakage isn't from between the primer, and the adapter for sure. Doesn't seem like it is drilled too deep, because it takes a brisk closure to get the hammer to cock. It could be the socket is too wide, and that is possible. What it could be, is soot/carbon deposits on the nose of the adapters; they have been fired dozens of times, and i have been remiss in keeping the end clean. My concern was making sure the inside of the adapter was clean, so the primers would fully seat.

Thank you for your help, and thank you for forcing me to have go up and shoot some more..

 

[Busta]

I guess I forgot to say, "go easy"?

My Blackhorn plug seals completely on the front. Absolutely nothing gets past that flange.

Is it possible that the plug was dropped on that flange, or maybe it got bumped. It looked like it had a flat spot front and center in your pics. A flat spot would definitely let that blowback past the flange.

I hope that works out.

 

[ronlaughlin]

Yep, i did go easy, but there was zero change. When the 5/8" bolt was pressed enough into the breech plug so that when the tension was released, they stayed together, that did the job. Perhaps i should have mentioned the pipe wrench used to marry the breech plug to the barrel was kinda miniature; about 5" long.

The seal between the front of a QRBP, and the barrel, if all is right, is perfect. Twice before, this has been. Possibly, after using your suggestion, the seal at the front of the Blackhorn plug, will be so. Too bad the nose of these plugs is so fragile.

If the work i did to the rim of the plug makes it worse, i may consider switching the other plug over to rifle primers. Perhaps i shouldn't do that; perhaps i should just purchase a new Blackhorn QRBP and modify it to use the rifle primers.. No, tax time cometh, and insurance premiums due, and..

 

[ronlaughlin]

Ron,

looks like the flange got dinged or rolled in a bit on the front of that plug?

You might be able to expand that flange back out with something like a 5/8"-11/16" bolt with a chamfer on it, then re-seat the plug back to the barrel? Since you already filled in the slot for the tool, you would have to wrap some leather around the back end and use something like vice grips to re-seat it.

Looks like you may have problems at the other end as well? Too deep? Too wide? Leaking through the adapter?

Only had 4 vials of powder left, but pressing the 5/8" bolt into the breech plug, and redoing the marriage of the plug to the barrel, did help. The fit isn't perfect, but far less soot got past the rim of the breech plug. As expected there is no change to the leakage at the primer end. Perhaps adding a 0.005" shim or so, behind the firing pin bushing will cure the leak, maybe..

Wow, the point of impact sure changed this morning. Temperature was a way warmer, 36 degree, is that why? In order to fit the plug to the barrel using a little pipe wrench, i had to remove the fore end, and barrel from the breech, is that why? Seems the removal and replacement could have changed the impact. The screw holding the fore end seemed kinda loose when i removed it, and i am sure it is tighter now than it was.

 

[Busta]

That forend screw will definitely change things. It looks like it wants to group now? Bump your powder up or down 5 grains to see what direction it wants to go.

I actually float almost all of of my forends on my tip-ups, and it is as simple as an o-ring between the forend and the barrel. I index the barrel screw so it goes back to the same torque each time. This can really help some rifles, others, not so much. My Optima Pistol has nothing, and it will shoot 200 gr Shockwaves over 80 grains of Blackhorn 209into one hole off the bags/bench @ 50 yards. I have a few rifles that can't do that.

Are you getting any primer/o-ring compression when you close it up? If you lay a straight edge across the back end of the breech plug with a primer installed, the primer should be a little proud of your firing pin bushing is flush with the standing breech. The breech plug should lock up and hold a 0.001" feeler guage or shim stock.

Tried zooming in on your o-ring, but I'm on my phone. Best I can tell, it looks like you are leaking between the primer adapter and the o-ring? IIRC, you said earlier that you opened the flash hole up to 0.035"? I would shoot for 0.010"-0.015" compression on the o-ring to start and may require adjustment in/out of the firing pin bushing to find the sweet spot.

 

[ronlaughlin]

...it looks like you are leaking between the primer adapter and the o-ring? IIRC, you said earlier that you opened the flash hole up to 0.035"? I would shoot for 0.010"-0.015" compression on the o-ring to start and may require adjustment in/out of the firing pin bushing to find the sweet spot.

Yes, i agree the leak seems to be between the adapters, and the o-ring. Today, after this morning' shoot, i juggled the shims on the firing pin bushing some. My goal was to get a few more thousandths of compression of the o-ring, even though the primer is proud of the breech plug rim, indicating there is definitely already compression of the o-ring, since the firing pin bushing was alreadly proud of the breech. Have also loaded up more vials with only 80g of Blackhorn for the next trip out.

Yes, i did open the flash hole to 0.035". When using rifle primers, the flash hole never grows larger.. Rifle primers can handle much more pressure than shotgun primers too, and they aren't at all erosive like shotgun primers. When using shotgun primers, it seems wise to start about as small as possible for flash hole size, because it will grow with each shot, and because the smaller flash hole holds back the pressure on the primer from the powder burn. Shotgun primers also seem to benefit from a longer larger flame channel, which absorbs some pressure from the powder burn, but rifle primers seem to work great with a small short flame channel, and that is why i modified the Blackhorn QRBP to use rifle primers.

Using the chamfer of the 5/8" bolt to expand the rim of the plug back towards new, worked good.

 

[ronlaughlin]

What a beautiful morning this was. Bright blue skies, very little breeze, but just 2 degrees. The cold temperature once again had me shooting with the rifle, and my left hand on the window rest; my right elbow in the steering wheel. Shot 3 times up close, and then moved to where i could make a 200 yard shot, and shot 3 more times. The powder load was reduced to 80g so for to save dinero.

To shoot at the longer range the elevation dial was twisted up 32 clicks--8 moa. There was an light intermittent breeze from left to right.

Reticle wobble is more noticeable at the longer range, but it wasn't too bad. When using the Federal 215 primers, the flame channel doesn't get caked with the hard hard carbon. Upon returning home, the soft soot in the flame channel i removed by spinning the naked 1/8" drill in my finger tips.

 

[JStanley]

That looks great Ron. Is that with the low power scope?

Just curious if the primer pocket is centered well on the flash channel. You said you made the pocket in a mill vs in the lathe. Maybe if the pocket is a little off center, the fire leaks a little :huh?:

 

[ronlaughlin]

This rifle has a 4X scope. Yes, it is very possible the socket isn't perfectly centered.

The photo shows some soot is getting through between the primer adapter, and the o-ring. The soot just wipes off with a finger, or a paper towel. On a white paper towel, the soot barely shows; it seems insignificant. Decreasing the headspace by shimming the firing pin bushing further out, reduces the soot to zero, but it was some more difficult to put the rifle into battery. The head space the way it is now does allow some leakage, but the rifle is easy to put into battery, and the leakage is minimal. Next time i hope to make the socket smaller, and and shallower. Maybe that will work better stopping blow by, around the primer.

 

[JStanley]

Next time i hope to make the socket smaller, and and shallower. Maybe that will work better stopping blow by, around the primer.

That would probably help. Sometimes I use an end mill chucked up in the tailstock of a lathe (after centering) to bore nice smooth & centered holes with flat bottoms like you need. Especially if using a boring bar that small isn't possible.

 

[ronlaughlin]

Yes, i will use an end mill, and it will be held in a collet, not a chuck, which should make things better. Also, the plan is to use a dial test indicator to get the plug very very centered.

 

[bestill]

Have you found any performance gains or accuracy with lrp vs 209?
Or is advantage just effects on breech plug?

 

[ronlaughlin]

Initially, i was interested in using rifle primers so i could shoot heavy loads of Blackhorn, without having blow back soot coming right back through the shotgun primer. Then black rifles became cheaper, and i had great fun shooting them, and spotting for myself, because of little recoil. Now, that phase has passed. The by product of using the rifle primers was learning how erosive the shotgun primers are.. i had no idea. Now i am using the rifle primers because it so fun to clean the flame channel of soft soot, and having to clean the flash hole, because it gets smaller..not larger.

What i am planning to try with this rifle in the spring, is shooting 140g loads of Blackhorn using the rifle primers, because they won't leak soot, like shotgun primers do. What i am hoping for is better accuracy at 300 yard, because the bullet won't be going transonic out there, with the heavier powder loads. Time will tell if i actually pursue this idea.

Rifle primers don't seem to be any more accurate than shotgun primers.

Thank you for your advice on the tooling for my mill, for removing the brazed Knight vent liners.

 

[bestill]

I spent alot of effort trying to use pr. Lrp adapters also and struggled to make them seal.
I shoot a custom knight with a brux barrel and shoot100 gr by weight of blackhorn and push 327 mh bullet at 2400 fps. I use a custom breech plug that has a tungsten carbide bushing installed with a .031 flash hole and flame channel is .187 diameter x .625 long. When i set headspace i like to compress 209 primer by .003 with this setup i get no leakage and flash hole will last way past 1000 shots.
I did similar setup to a flat faced cva breech.
This is what most smokeless builds are using with very hot loads.

 

[ronlaughlin]

Well, one thing is the adapters are made from stainless, and don't seem to compress, whereas shotgun primers are compressible, so can be made to seal. The o-ring in the primer socket under the adapters seems to work OK for me.

Most of my shooting in the past couple year has been with Omega rifles. There is a large span of the primer unsupported in these rifles, and that very well may be why i am experiencing so much blow by right through the primer. One thing i have tried is making a neck on the Omega breech plug to hold the shotgun primers further up; this worked better.

Obviously, if the shotgun primers hold up to smokeless pressures, and your 100g Blackhorn load, there is a way for me to use them, without the blow by right through. Using the bushing eliminates flash hole wear, so it seems i have no logical reason not to use shotgun primers. However, right now i am kinda having fun using the rifle primers, and plan to continue..

 

[bestill]

Tinkering is what its all about and thats wear innovation comes from.. push on.
Have you tried opening up your flame channel ?

 

[ronlaughlin]

Yes, for shotgun primers the flame channel is normally increased to 5/32". Never have tried the near 6/32" you are using. For rifle primers, the flame channel has been left 1/8".

Now you have me thinking.. with the longer flame channel of the QRBP, and a larger diameter, one should be able to use more powder, without blow by going through the shotgun primer..

 

[bestill]

You got it. Ive found a flame channel volume of .0175 cu in. Works
Example.187x.625 or .160x.750 or
.140x.875 flame channels.
When i do a custom breech in a new build. I start small with flame channel then slowly open up until i get primer swell reduced to a acceptable level then increase channel.010 extra to allow multiple shoots before channel gets carboned up. Hope this helps.