Large pistol primers in 45-70 for Trapdoor?

[pima4440]

Hi guys,

I found through google search that some people here are using Large Pistol Primers in their 45-70, because it gives better consistency than rifle primers.
Is this a problem if I use them in my trapdoor? I don't have any large rifle primers because of the shortage, but I have CCI large pistol primers.

I've tried a few and some of them show signs of piercing. It's not a dramatic crater, but enough that some gas is escaping from the rear so the primers appear darkened.

This is with trapdoor loads (~17,000 psi) using 4198, as well as black powder (55gr goex and 70 gr goex) as well.




How have other people done it? And are there any disadvantages besides the primers piercing?

Thanks!

[Abilene]

Howdy Pima4440.

Welcome to the forum!

Bottom line: I've never owned a Trapdoor and have no experience with its lockwork/action, but I'll throw a couple random thoughts out there.  Do Trapdoors ever suffer from excessive headspace, and if so could that cause this?  Is it possible to lighten the hammer spring tension a tad?

I'm sure those that know these rifles will be along shortly.  Good luck!

[pima4440]

Bottom line: I've never owned a Trapdoor and have no experience with its lockwork/action, but I'll throw a couple random thoughts out there.  Do Trapdoors ever suffer from excessive headspace, and if so could that cause this?  Is it possible to lighten the hammer spring tension a tad?

It headspaces on the rim, so I don't know how that could be measured or corrected.
And the hammer springs are very heavy, i don't know of any way to correct that.

The hard part is I don't have any large rifle primers so I can't do a side-by-side comparison to see if that will immediately correct the issue. But reading posts of people using large pistol primers in 45-70 - and even preferring them to rifle primers - tells me it has been done successfully in the past.

I'm sure those that know these rifles will be along shortly.  Good luck!

Yes hopefully especially those who PREFER pistol primers over rifle primers. I would really like to hear what they do and if they have any of these issues!

[Abilene]

The headspace issue would be the distance between the rim of the chambered round and the bolt face.  If that is excessive then the shell can go further rearward when firing. 

Where are you located?  If you were in central Texas, I could swap you some LRP for your LPP.  Maybe somebody close to you could do the same?

[Ranch 13]

 Rifles of that time period have large firing pins, chances are pretty good that the primers will look the same even when using large rifle primers.

[Drydock]

The problem is that Large pistol primers are shorter than large rifle primers.  When fired they tend to slam back into the breechface, often damaging it around the firing pin hole.  This has been noted on modern rifles, the older steel in a trapdoor would be more problematic. 

Large pistol primers can help with standard deviations, but mostly in smaller cases like 32-40 and 38-55.   Once you get to the 70 grain calibers it's harder to see, especially if using compressed charges.  Those that do use them often use some sort of spacer in the primer pocket to prevent the damage mentioned above.

In a Trapdoor I simply would not do this.  Unless you're looking for single digit standard deviations in velocity to limit vertical stringing at 1000 yards, it's just not worth it.

[pima4440]

The headspace issue would be the distance between the rim of the chambered round and the bolt face.  If that is excessive then the shell can go further rearward when firing. 

Where are you located?  If you were in central Texas, I could swap you some LRP for your LPP.  Maybe somebody close to you could do the same?

I'm in PA, i wish i could swap but shipping hazmat would be too expensive...

Rifles of that time period have large firing pins, chances are pretty good that the primers will look the same even when using large rifle primers.

I'm curious because a lot of people say they've done it successfully, some even for trapdoors

https://www.cascity.com/forumhall/index.php?topic=39471.0
https://www.cascity.com/forumhall/index.php?topic=64966.0
https://www.cascity.com/forumhall/index.php?topic=55238.0
https://www.cascity.com/forumhall/index.php?topic=64944.0
https://www.cascity.com/forumhall/index.php?topic=54079.0

Is it possible that I have the wrong firing pin? Mines is an 1884 but running with a Type 2 firing pin with the squared retaining screw recess




Should I pick up a type 3 firing pin with the oval recess? Maybe there is firing pin overtravel from mismatched firing pin?

The problem is that Large pistol primers are shorter than large rifle primers.  When fired they tend to slam back into the breechface, often damaging it around the firing pin hole.  This has been noted on modern rifles, the older steel in a trapdoor would be more problematic. 

Large pistol primers can help with standard deviations, but mostly in smaller cases like 32-40 and 38-55.   Once you get to the 70 grain calibers it's harder to see, especially if using compressed charges.  Those that do use them often use some sort of spacer in the primer pocket to prevent the damage mentioned above.

In a Trapdoor I simply would not do this.  Unless you're looking for single digit standard deviations in velocity to limit vertical stringing at 1000 yards, it's just not worth it.

Well this is concerning, do you know what kind of spacer they are using?
What's interesting is the primers are not backing out or flattening though -- I've gotten flattened primers from excessive headspace in a revolver before (low pressure 15,000 psi target loads, but it was a revolver with recessed chambers and the headspace was excessive leading to primers backing out and being flattened, despite the low pressure). But in my picture you can see they're nice and rounded, which tells me they're not slamming back into the breechface with that much force. Do you have links to threads with pictures of breechface damage from using LPP in 45-70? 
Not that I doubt you, I just want to check the pictures of the breechface damage to make sure I'm not damaging my rifle.

Unless you're looking for single digit standard deviations in velocity to limit vertical stringing at 1000 yards, it's just not worth it.

Funny enough 11 gr of Unique and 405 bullets with CCI pistol primers did achieve single digit standard deviations!
5 shots at 1049, 1056, 1051,1048, and 1055.

[pima4440]

Update: I stoned the roughness off my firing pin and ended up shortened it a few thou in the process.

Then I loaded up 5 primer-only blanks and tested them out. It looks like these are not showing any signs of piercing (look at the top row only. The ones in rows 2 and 3 are from before, and you can see some are darkened and others are intact)



Did shortening the firing pin and smoothing out the roughness solve the problem? Or will they start being pierced again when there is greater recoil force from a full load?

[Ranch 13]

 You may have solved part of the problem. Only way to know for sure is load some up and give them a try.
Trying a different firing pin may help, but the one problem with these original rifles is the hole in the breech block may be worn and that will eventually break a firing pin..
I have 4 original rifles and they all will put massive dents in the primers. My regular shooting partner shoots a sharps with the original style and size firing pin and he has to recheck the hammer and drop it on a fired case to keep the large rifle primers from sticking to it, and even at that has to drop the block pull the firing pin and clean the shavings from the primers at the end of every day of shooting.
On the "shim" under pistol primers the shooters that do that usually seat the primer thru a sheet of paper. The literally dozens of shooters I know first hand and in my own experience that use pistol primers in large bpcr cases don't use the paper shim under the primer and have no problems. Federal 150 match and RP 2 1/2 are the most commonly used pistol primers by competitors, and they're used in everything from midrange and sillhouette to creedmoor and the gong matches. The difference in height between the 2 isn't all that great, but as in all things shooting some rifles show a definite preference in primer choices.

[pima4440]

On the "shim" under pistol primers the shooters that do that usually seat the primer thru a sheet of paper. The literally dozens of shooters I know first hand and in my own experience that use pistol primers in large bpcr cases don't use the paper shim under the primer and have no problems. Federal 150 match and RP 2 1/2 are the most commonly used pistol primers by competitors, and they're used in everything from midrange and sillhouette to creedmoor and the gong matches. The difference in height between the 2 isn't all that great, but as in all things shooting some rifles show a definite preference in primer choices.

Thanks for this first hand info, this is very reassuring! Which rifles are you shooting these 45-70 loaded with Large Pistol Primers?
Are they modern guns with better-toleranced firing pins/chambers, or are they old originals as well?
I'm glad I won't need to do the shim approach, that sounds like trouble for ignition consistency.

You may have solved part of the problem. Only way to know for sure is load some up and give them a try.
Trying a different firing pin may help, but the one problem with these original rifles is the hole in the breech block may be worn and that will eventually break a firing pin..
I have 4 original rifles and they all will put massive dents in the primers. My regular shooting partner shoots a sharps with the original style and size firing pin and he has to recheck the hammer and drop it on a fired case to keep the large rifle primers from sticking to it, and even at that has to drop the block pull the firing pin and clean the shavings from the primers at the end of every day of shooting.

Well at least it's reassuring to hear that I'm not the only one running into this issue with originals, and that people are running into this even with Large rifle primers. It makes sense since the early 45-70 cases were fully enclosed in a folded head cartridge. Even trying to replicate the original loading is tricky because primers back then were a lot harder.

Funny thing, everyone talks about oversized bores and casting oversized bullets at.459"-.461" but the originals were loaded with .456" bullets!

[LongWalker]

The problem is that Large pistol primers are shorter than large rifle primers.  When fired they tend to slam back into the breechface, often damaging it around the firing pin hole.  This has been noted on modern rifles, the older steel in a trapdoor would be more problematic. 

Large pistol primers can help with standard deviations, but mostly in smaller cases like 32-40 and 38-55.   Once you get to the 70 grain calibers it's harder to see, especially if using compressed charges.  Those that do use them often use some sort of spacer in the primer pocket to prevent the damage mentioned above.

In a Trapdoor I simply would not do this.  Unless you're looking for single digit standard deviations in velocity to limit vertical stringing at 1000 yards, it's just not worth it.

This--LPP being shorter than LRP--is the problem.  Over the years I've seen a number of trapdoors with damage to the breechface due to the use of pistol primers (and damaged 2 myself, more on that to follow).  The damage caused is fairly consistent: the metal around the firing pin hole gets peened, creating a recess around the hole.  Trapdoor breechblocks are case-hardened; the softer metal under the case moves on the impact of the primer. 

Since the only place the metal can go is into the firing pin channel, eventually you get a situation where the firing pin is locked in place.  If you are lucky, you have ignition problems.  If you aren't lucky, the pin sticks forward during a timed-fire match so when you flip the breechblock closed on a new cartridge, it fires before the breechblock is locked in place. 

At best, this guarantees that EVERYONE on the firing line is awake.  Worst case. . . well, I've never heard of anyone dying, but when a trapdoor fires out of battery it can get messy.  (On the bright side, this does sometimes create an opportunity to acquire a trapdoor at a really really good price.)

I did some experiments with back around 2005, after seeing a gun fire out of battery due to this problem, and came to some tentative conclusions.  "Tentative" because I just didn't have enough data points.  (Over the course of about 2 years I burned up ~2,000 rounds and ruined 6 "orphan" breechblocks.  I couldn't afford more at the time.)  I basically took my "new" very cheap 1884 trapdoor and a selection of breechblocks and set up test loads with different primers. 

The peening seemed to occur earlier with early (high arch) breechblocks.  Using later (low arch) breechblocks, the damage would still occur.  It just didn't seem to happen as fast. 

Firing pins seemed to stick forward sooner when the breechblock used a firing pin spring.  I think this is because the spring effectively reduces the diameter of the firing pin channel/increases the diameter of the firing pin.  My impression was that the aluminum-bronze pins may be slightly more prone to sticking in damaged breechblocks if the gun is fired rapidly ("mad minute" rate of fire).  I have a hunch this was due to the alloy expanding more/more rapidly. 

Use of LPP with paper shims seemed to result in smaller standard deviations in velocity, but at a slightly reduced average velocity (ca. 20 fps).  I could see no difference on the target, shooting from a bench out to 500 yards. 

Damage occurred more rapidly when using LPP in smokeless loads.  It happened in BP and duplex loads at about the same rate. 

Looking at the OP's primers, I suspect the primer piercing will resume when full-power loads are fired.  He might want to remove the breechblock from the rifle and put a straight-edge across the face to see if there has been any previous damage.

[Ranch 13]

 Pima I have two original Sharps Borchardts, and my neighbor has an 84 trapdoor and carbine, that I accuse him of breaking down and stuffing in his barracks bag when he mustered out. LOL
The large pistol primer thing is something that a rifle might get along with really well, and the next rifle might not like them worth a flip.
But in this supply train thing we find ourselves in currently it just really boils down to run what you got, and hopefully things will turn around someday.

Some claim the paper between the powder and primer ,either punched in with the primer or a separate wad in the case before charging help with accuracy. I've tried both methods, and haven't really seen enough benefit to make it worth the effort. If a person were shooting just a few rounds at a setting it might pay off, but I seldom find myself loading for anything less than a couple hundred rounds at a setting, except when load testing a new rifle/powder/bullet etc.

[Sedalia Dave]

No experience with the LPP in brass designed for LRP.

Where I do see a serious problem is punctured primers. Whenever the firing pin punctures a primer is provides a way for an extremely hot jet gasses to escape to places not designed to handle them. This gas jet WILL damage the firing pin and the bolt face and it doesn't take very long to do so. Think of that gas jet as a very tiny high pressure cutting torch.

One reason that the firing pin is puncturing the LPP is that the material thickness is less than that of LR primers. A firing pin that is a little too long or has a tip that is borderline may puncture a large pistol primer but not necessarily a large rifle primer.

[Trailrider]

Drydock, et al, is absolutely correct! The difference in length between LPP and LRP is, IIRC without looking it up is about .009". I do know that using LRP in cases intended for LPP's in pistols, as well as in rifles can cause cylinder lockup in the revolvers, and possibly magazine explosions in tubular magazine rifles! This includes cartridges that are so-called dual-purpose, including .44-40 and .44 Magnum. Using the LPP in large rifle cartridges including .45-70 can result in pieced primers and other problems. Unless it is an absolute emergency, don't do it!

[Ranch 13]

 The guy that owns all the national records in BPTR in the military rifle class (original unmodified trapdoors etc) uses nothing but rp 2 1/2 primers not only in his trapdoor, but all his bp loads except for a 40-65, 1886 he shoots in lever gun sillhouette. That rifle just doesn't like large pistol primers.
There are bunches of other shooters in bpcrs and bptr that use large pistol primers in their rifles, with and without the paper under the primer....

[pima4440]

Ahhh this is why it's so tough.

On the one hand you have people telling you never to do that or you'll damage the gun:

This--LPP being shorter than LRP--is the problem.  Over the years I've seen a number of trapdoors with damage to the breechface due to the use of pistol primers (and damaged 2 myself, more on that to follow).  The damage caused is fairly consistent: the metal around the firing pin hole gets peened, creating a recess around the hole.  Trapdoor breechblocks are case-hardened; the softer metal under the case moves on the impact of the primer. 

Drydock, et al, is absolutely correct! The difference in length between LPP and LRP is, IIRC without looking it up is about .009". I do know that using LRP in cases intended for LPP's in pistols, as well as in rifles can cause cylinder lockup in the revolvers, and possibly magazine explosions in tubular magazine rifles! This includes cartridges that are so-called dual-purpose, including .44-40 and .44 Magnum. Using the LPP in large rifle cartridges including .45-70 can result in pieced primers and other problems. Unless it is an absolute emergency, don't do it!

And on the other hand you have people who have done it all their life with both antiques and reproductions -- and even champion shooters using LPP instead of LRP in their antiques!!

Pima I have two original Sharps Borchardts, and my neighbor has an 84 trapdoor and carbine, that I accuse him of breaking down and stuffing in his barracks bag when he mustered out. LOL
Some claim the paper between the powder and primer ,either punched in with the primer or a separate wad in the case before charging help with accuracy. I've tried both methods, and haven't really seen enough benefit to make it worth the effort. If a person were shooting just a few rounds at a setting it might pay off, but I seldom find myself loading for anything less than a couple hundred rounds at a setting, except when load testing a new rifle/powder/bullet etc.

The guy that owns all the national records in BPTR in the military rifle class (original unmodified trapdoors etc) uses nothing but rp 2 1/2 primers not only in his trapdoor, but all his bp loads except for a 40-65, 1886 he shoots in lever gun sillhouette. That rifle just doesn't like large pistol primers.
There are bunches of other shooters in bpcrs and bptr that use large pistol primers in their rifles, with and without the paper under the primer....

Who's a man supposed to listen to in these kind of situations?

[Ranch 13]

 Pima if you can get ahold of the last 2 issues of the Black Powder Cartridge news, and look at the match reports with equipment lists, that may go along way to helping sort things out.
Are Large pistol primers the best thing to use? I don't know at times they are and at times they might not be, but the sheer number of matches won and top contenders at those same matches by shooters shooting lp in big blackpowder cases, certainly shoot holes in some of the nay sayers theory...
Run what you have and don't look back, when large rifle primers come available to you grab a brick or two and see if there's a difference.

[Drydock]

There were some threads showing the damage on the Shiloh forum a few years back, but I cannot find them.  In my defense, the search function on that forum sucks!   

One thing to keep in mind.  Those folks using LP primers and winning matchs with them, are usually using modern made rifles, with far better steels and heat treatment than an original trapdoor.  And if you talk to them they will tell you they check their breechblocks after every match.  Many of them now swage the primer pockets of their brass for these primers.  Kirk Bryant has manufactured new breechblocks for original rifles damaged in this way.  He expects his breechblocks to stand up to this practice, and will replace under warranty any that don't.  I would also caution that there is a great deal of variation in the quality and thickness of case hardening in rifles of that era.  It's luck of the draw as to what you have.

In addition to peening, the softer cups of LP primers can lead to gas cutting of the block from gas escaping past the primer.  Something to watch for.

I would at least Shim the primer cup.  Maybe nothing will happen, but no one out there is making new Trapdoor breechblocks should this one become damaged.

[Drydock]

https://www.blackpowdercartridge.com/large-pistol-primers-in-black-powder-loads