BP Percussion Question????

[Old Time Hunter]

Maybe somebody can answer this question: Has anyone had enough blowback to clear the spent percussion cap and throw the hammer back to half-cock? If so, what can be causing this.

Scenerio:

Today I went on a antlerless early season herd control hunt and decided to use my Lyman Great Plains Hunter percussion rifle in .50 caliber. Used 30-1 Lee R.E.A.L bullets that were cast last year, caked with SPG and loaded over 85 grains of Fg. A few weeks ago I came to the conclusion after multiple different loads, that this gave me the best accuracy from 50 to 100 yards with that particlular bullet, but none of loads, even when loading 100 grains of FFg gave me any indication of blowback. So I was quite surprised when I cleared my gun after coming out of the woods, that the hammer was thrown back to half-cock and the spent cap blown off. So I went to the range and blasted off about twenty more, changing my loads from 70 grains all the way back to 100 grains...it did not seem to matter, as only three of the twenty did NOT blow the hammer back and all three were with different charges. One with 75 grains of Fg, one at 80 grains and the other at 90 grains. I then went to my round ball and patch, shot ten rounds with charges from 70 grains to 90 grains....there wasn't any that blew the hammer back. Cleaned the gun out, and loaded sabots using 110grains of Fg, absolutely no problems.

Can it be the bullets?

Can it be the temperature difference between when I practiced a couple of weeks ago (mid-70s) and today, high 30's when I went out and about 45F early this afternoon?

[Chuck 100 yd]

Your nipple vent hole is too big I bet. My dad had a hawken style rifle that did that. It also would on occasion misfire, due
to I believe a whimpy hammer spring and caps not fully seated.

[Griff]

Your nipple vent hole is too big I bet. My dad had a hawken style rifle that did that. It also would on occasion misfire, due
to I believe a whimpy hammer spring and caps not fully seated.

Yep, whimpy mainspring, nipple holes too large &/or caps noy fully seated. Nipples can get burned out with repeated firings. Need replacin' from time to time.

Just like a cartridge with too large a flash hole, part of the main charge will escape to the rear.

[Rusty]

Replace the nipple with a stainless one and it will last a lot longer.

[Old Time Hunter]

Your nipple vent hole is too big I bet. My dad had a hawken style rifle that did that. It also would on occasion misfire, due
to I believe a whimpy hammer spring and caps not fully seated.

Yep, whimpy mainspring, nipple holes too latge &/or caps noy fully seated. Nipples can get burned out with repeated firings. Need replacin' from time to time.

Then why does it not do that when I use round ball w/patch or the sabots?

Also, it has a brand new stainless steel nipple on it...just put it on a couple of weeks ago.

[Griff]

Your nipple vent hole is too big I bet. My dad had a hawken style rifle that did that. It also would on occasion misfire, due
to I believe a whimpy hammer spring and caps not fully seated.

Yep, whimpy mainspring, nipple holes too latge &/or caps noy fully seated. Nipples can get burned out with repeated firings. Need replacin' from time to time.

Then why does it not do that when I use round ball w/patch or the sabots?

Also, it has a brand new stainless steel nipple on it...just put it on a couple of weeks ago.

Weight. That REAL bullet weighs alot more'n a RB. Are ya also usin' a heavier charge?

[adirondakjack]

Heavier bullet means moire chamber pressure, and more "venting" through the nipple.

Once upon a time I had a '61 Navy clone revolver that when loaded stout would "self cock" (semi-auto if you will). Though mine never did, I've heard of revolvers going "full auto" with heavy loads and beat up nipples.

[Hobie]

Your nipple vent hole is too big I bet. My dad had a hawken style rifle that did that. It also would on occasion misfire, due
to I believe a whimpy hammer spring and caps not fully seated.

Yep, whimpy mainspring, nipple holes too latge &/or caps noy fully seated. Nipples can get burned out with repeated firings. Need replacin' from time to time.

Then why does it not do that when I use round ball w/patch or the sabots?

Also, it has a brand new stainless steel nipple on it...just put it on a couple of weeks ago.

Could be the pressure is sufficient to do so with the conical but not with the rb or sabots. Generally it does this with a new nipple because you've got too much powder in there (too high pressure) but a too large flash hole in the nipple can do the same thing as that increases the pressure on the hammer face. It is a balancing act.

[Old Time Hunter]

Weight. That REAL bullet weighs alot more'n a RB. Are ya also usin' a heavier charge?

Hmmm....approximately 390 grains to 177, the sabots are 325...this might be an issue.

Hobie the flash hole seems to be about the same.

[Nath]

I have experienced it OTHunter! I like a flash hole no larger than .040" (or 1mm).

The nipple shape internally could be having an influence, do you have the old one to try?

Nath.

[Old Time Hunter]

Nath, yes I do..heading outside within the hour to play around with it.

[Nath]

Any change with the old nipple?

Nath.

[gamekeeper]

I had a .58 Buffalo Carbine that came with monster size nipple, every time I upped the powder charge it would push the hammer back to half cock.
When I shot it in the evening the flash from the nipple was a little off putting.

[KCSO]

If the hole in the nipple is anywhere close to say a #51 drill bit it is too big and you need a new nipple. Also the mainpring should be fairly stiff, most of the new repro's are a tad weak to start with. A GOOD lock will have a crisp and stout hammer pull.

[Griff]

...the flash from the nipple was a little off putting.

Is that ALL??? I think I'd develop a MAJOR flinch!!!!

[gamekeeper]

Yup!

[aragornelessar86]

If you changed the nipple between your original tests and when you began noticing the blow-back then I can guarantee it's either the hole size or the channel shape. Also when you say that you can vary the load as much as 40 grains and you still get blowback that tells me it's an issue with the nipple or maybe the mainspring, though I can't see why the mainspring would go bad all of a sudden unless it broke. Did you buy the new nipple from the Mfg. or is it an aftermarket part? If it's aftermarket I'd try a new factory nipple and see what you get.

As a reenactor I've drilled out the nipple on my Springfield, and if I put live rounds in there it will frequently blow back.

Good luck!

[Old Time Hunter]

Any change with the old nipple?

Nath.

Nope, no change...it too has blowback with the REAL bullets, but not the sabots or RB w/patch, just like the SS nipple. Which by the way I got from Lyman the mfg of the rifle.

[aragornelessar86]

Interesting. Sounds to me like the mainspring. Now, you did say that with the the exact same setup you did a bit of load testing and didn't have this problem right?

[Old Time Hunter]

Interesting. Sounds to me like the mainspring. Now, you did say that with the the exact same setup you did a bit of load testing and didn't have this problem right?

Yep! Even went to a 110 grain Fg charge on the sabot's...no mis-fires, no blow-back.

[Nath]

Perhaps the REAL bullets obturate alot more! Take a look at the main spring would my next inspection.

N.

[Griff]

I hesitate to ask, although I do anticipate an affirmative responsel, but must, for clarities sake; you ARE lubing those REAL bullets, eh?

[Old Time Hunter]

I hesitate to ask, although I do anticipate an affirmative responsel, but must, for clarities sake; you ARE lubing those REAL bullets, eh?

Yep, quite heavily with SPG

[Nath]

I hesitate to ask, although I do anticipate an affirmative responsel, but must, for clarities sake; you ARE lubing those REAL bullets, eh?

We calls that dancin' round the bush

N

[aragornelessar86]

I can't imagine why the mainspring would just go out like that, but it could happen.

OTH, do I understand that while the gun was set up the same in your tests, you were not using the REAL bullets until you actually got out into the field? Did you happen to change powders between your testing and your field experiences?