Primer bullet push & primer setback

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TexasMac
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Primer bullet push & primer setback

Post by TexasMac »

I was reading an old internet link this morning on testing the power of various primers. I use Federal GM150M match large pistol primers in .40-65 & .45-70 BPCR cartridges. So, being somewhat bored, I decided to determine how far a primer along would shove a 540gr Paul Jones Creedmoor bullet (16:1 alloy) down the bore of my Browning. As the photo below displays, the bullet was shoved almost completely into the lands. The land impressions stop just short of passing the driving band. No doubt a rifle primer would have pushed it much further into the bore.

BTW, on a related subject, in an article I wrote some time ago titled, Firing a Black Powder Cartridge - Progression of Events (http://www.texas-mac.com/Firing_a_Black ... vents.html), I made the following comment:

“As the primer ignites, the force from the primer alone is more than sufficient to drive it backward out of the primer pocket until it contacts the breechblock resulting in primer setback unless the case stretches back, contacts the breechblock and reseats the primer flush with the rear of the case head.”

The above is the main reason the softer breechblock face of some older 19th and early 20th century rifles can experience peening around the firing pin hole when firing cartridges with pistol primers which are not as tall as rifle primers & can gain more momentum prior to striking the breechblock face.

Later on in the article I commented on what happens to the primer when firing a full power load. “Although the case locks against the chamber wall the pressure is sufficient to stretch it back enough to reseat the primer flush with the rear of the case. By the way, if you doubt the case is stretching back to reseat the primer, fire an unloaded case with only a primer. If the primer remains slightly backed out of the primer pocket but is flush after being fired in a full powder load, it’s a clear indication the case is stretching back slightly, but it’s minimal and is not a reason for concern assuming the headspace and/or head clearance is not excessive.”

In today’s little experiment the primer was certainly setback the amount of the head clearance in my Browning.

Image

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
mdeland
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Re: Primer bullet push & primer setback

Post by mdeland »

Interesting experiment Wayne. How hard was it to push the bullet back out of the barrel? We have had that happen a time or two at our monthly events and one time a disaster was averted by one of our more experienced ,heads up shooters, who stopped the fellow from loading up another round before checking the bore and torching it off.
He was shocked to see the bore was plugged with the previous squib loaded bullet. He didn't even think the primer had detonated. The bullet was far enough up bore to except another loaded round.
TexasMac
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Re: Primer bullet push & primer setback

Post by TexasMac »

mdeland wrote: Fri May 29, 2020 3:07 pm Interesting experiment Wayne. How hard was it to push the bullet back out of the barrel?
Mike,
It was stuck in the bore pretty good but dropped out after dropping a .45 cal drill rod on it from the muzzle 3 times.
Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
beltfed
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Re: Primer bullet push & primer setback

Post by beltfed »

Wayne,
I wonder if the case slides back as much or moreso than "stretching" back over the primer
before full pressure.
beltfed/arnie
beltfed
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Re: Primer bullet push & primer setback

Post by beltfed »

Also, I imagine that the practice of setting up loads to crush fit into the lands
will help to Keep the case back against the breech block and so minimize or eliminate
the (pistol) primer from backing up (much) more than to bring it to flush with case head
beltfed/arnie
beltfed
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Re: Primer bullet push & primer setback

Post by beltfed »

Also, I imagine that the practice of setting up loads to crush fit into the lands
will help to Keep the case back against the breech block and so minimize or eliminate
the (pistol) primer from backing up (much) more than to bring it to flush with case head
beltfed/arnie
Clarence
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Re: Primer bullet push & primer setback

Post by Clarence »

Wayne,

How much neck tension with that load?

Clarence
TexasMac
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Re: Primer bullet push & primer setback

Post by TexasMac »

Clarence wrote: Fri May 29, 2020 7:48 pm Wayne,
How much neck tension with that load?
Clarence
Clarence,
Essentially none. The bullet easily slipped into the neck.
Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
TexasMac
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Re: Primer bullet push & primer setback

Post by TexasMac »

beltfed wrote: Fri May 29, 2020 6:52 pm Wayne,
I wonder if the case slides back as much or moreso than "stretching" back over the primer
before full pressure.
beltfed/arnie
Arnie,

I think what actually happens depends on how the cartridge is loaded. If the bullet is slip fit with little or no tension and/or the nose is not contacting the leade, when the firing pin hits the primer it pushes the case forward to contact the rim seat while igniting the primer. When the primer fires it setsback the amount of the head clearance. Then under full pressure the case stretches back some re-seating the primer flush.

If the COAL is such that the nose is pressed into the leade than head clearance is eliminated and the primer has no room to setback.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
TexasMac
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Re: Primer bullet push & primer setback

Post by TexasMac »

beltfed wrote: Fri May 29, 2020 6:54 pm Also, I imagine that the practice of setting up loads to crush fit into the lands
will help to Keep the case back against the breech block and so minimize or eliminate
the (pistol) primer from backing up (much) more than to bring it to flush with case head
beltfed/arnie
Arnie,

I certainly agree. After posting the following I realized you had made a similar comment. So, to paraphrase your comment, if the COAL is such that the nose is pressed into the leade than head clearance is eliminated and a large rifle primer has no room to setback. If shorter large pistol primers are used the primer will still setback the amount of the difference in height between a large rifle and large pistol primer.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
mdeland
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Re: Primer bullet push & primer setback

Post by mdeland »

This is the main reason I am a stickler for extractor fit along with tight head spacing. Usually I ask for three cases from the lot that will be shot and , measure the rim thickness at four point around the clock on all three ,take the average and cut go plus .002. This almost always will account for the case production variance and still keep the head space and extractor tight to the rim underside thus limiting case stretch and primer back out. This tolerance in conjunction with short pistol primers can give the primer quite a run at the block face if not kept to a minimum.
I suspect also that on occasion there is some gas leakage from pistol primers as I have at times noticed a circular erosion pattern around firing pin holes in breech faces and wonder if it was rifle primers that is actually the cull-pert.
Many times a tight extractor fit will hold the case head against the block or bolt face from firing pin impact when long head space would allow it to move forward in the chamber.
Another variable that is important to consider here as well is if the block face is square to the bore and does not allow the case head to be bent out of square from back thrust which then requires the case to be indexed the same each time to maintain a consistent head space.
Rolling blocks are really bad about this but I have also found it in low and high wall Winchesters. I just make it a habit when chambering any rifle now to square the bock face to the action hole and fit the extractor just as tight as the head space to the brass that will be used.
Glen Ring
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Re: Primer bullet push & primer setback

Post by Glen Ring »

I read most of what's posted here and it's good info for sure. My 40-65 had been shot by the former owner using Pistol Primers and I had to replace the block. I had read all the info about using Pistol primers to get a more complete burn and a lower SD. I understand all that and I do not own a chronograph any more. I do shoot a LOT though. I use pyrodex because of the slower burn rate, but use magnum Rifle primers. I test the loads at 500 meters and Pyrodex shoots flatter and with better accuracy than any black powder I have used in THAT rifle.My 45-70 will shoot anything pretty darn good...But i use Pyrodex in it also with a taper crimp. I know I'm using smokeless magnum rifle logic...but all that seems to work out very well in the 40-65 and well in the 45-70.
There are those that talk, and those that act. Make a choice.
mdeland
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Re: Primer bullet push & primer setback

Post by mdeland »

Paul Mathews was a proponent of Pyrodex loads as well and had good success with it. He authored at least four small books on all aspects of BPCR's. I have four of his books and have used quite a bit of his information repeatedly. I still have not found a better lube than his recipe for black powder as well as smokeless loads.
I have not tried it in cartridges but did so with muzzle loaders and found it's performance dismal in cold weather. It is also more corrosive and needs cleaning attention as soon as possible after use.
I could not get it to reliably ignite in temperatures below about 20 degree F. The fouling was easier to deal with for me.
Woody
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Re: Primer bullet push & primer setback

Post by Woody »

I tried it in the 70's when it was introduced and found it wanting. I finally burned the remainder of that one lb. container and have no desire to revisit.

Sorry Glenn, but in my opinion, black powder is more appropriate for these rifles.

Woody
Richard A. Wood
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TexasMac
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Re: Primer bullet push & primer setback

Post by TexasMac »

My experience is similar to Mike (mdeland). In the mid-80's I used it for a while in a caplock muzzle loader in competitive matches. It did not work out well, plus the problem with corrosion. I used what I had left to blow a tree stump out of the ground for fun & switched to Goex at the time. After using Goex 2Fg for a while when I started BPCR then switched to Swiss 1.5 several years ago.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
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