Effect of crimp on pressure

BoogieMan · November 21, 2015, 11:28 PM

Effect of crimp on pressure.
I loaded mix headstamp for my 460, I won't do again. Anyway, the crimp on the longer brass is visible dealer on the longer brass. COAL is still longer than min. Basically I loaded 20 rounds and set 5 aside that have a very heavy crimp. These are hunting rounds so the 15 will get me through the season without trouble, but I don't want to pull them if I don't need to. But, these loads are on the hotter end of things and I don't want to take any chances either. The 460 already opporates at very high pressure.

Kosh75287 · November 22, 2015, 12:25 AM

All else being equal (and it never is, as .44 AMP likes to point out), I'D expect a heavier crimp to raise pressures SOME, but whether it would raise it from slightly below maximum to discernibly over maximum, I'm not so sure.

The effect of heavier crimp is that the projectile is held in place slightly longer, as the propellant burns more completely resulting in higher chamber pressure before the projectile moves from the case mouth, on its way through the cylinder and down the barrel. I often suggest slightly increased crimp on reloads if cases are sooty after firing, and if the powder burns more completely I'd expect chamber pressure to be a little higher.

I'd be more concerned about changes in overall length (shorter) causing pressure excursions, than crimp. It's usually a really big deal only in small cases, but given the pressure involved with the .460, a little could mean a lot.

hartcreek · November 22, 2015, 02:47 AM

Post some photos. I am not going to tell you the loads that I worked up with virgin brass for my 624. Lets just say that it was way over and I use a good crimp. I had no problems with extraction and no over pressure signs other then flattened primers. From what I have loaded I can tell you that your heavier crimp isn't going to make enough difference in the pressure.

Jimro · November 22, 2015, 03:18 AM

There are going to be a lot of qualifiers in my response.

Generally, for revolvers, a heavier crimp produces more consistent pressure curves and bullet velocity without a significant increase in max pressure.

The cylinder gap is an immediate "relief" valve that bleeds off pressure the moment the bullet leaves the cylinder, and for heavy hunting magnum revolver cartridges the powder is slow enough that some of it is still burning at this point. Once the bullet is in the bore, or forcing cone, of the barrel, the effects of a crimp have an effect rapidly approaching zero on that portion of the powder burn and pressure produced.

So IF you have a heavy charge of a relatively slower burning powder, I expect the heavier crimp will give you more consistent velocity numbers without any other difference than the lighter crimped bullets of the same charge.

You'd have to chrono them to find out.

If you have a light charge of a fast burning powder, where the powder is all burnt before the bullet leaves the cylinder, a crimp can increase max chamber pressure. But, if you aren't loading above max published charge you should be OK unless there is something wrong with the firearm.

Jimro

Clark · November 22, 2015, 04:55 PM

If you want to see a difference in pressure:
45 Colt 21 gr H110 250 gr XTP no crimp, bullet stuck in forcing cone, 0 fps
45 Colt 21 gr H110 250 gr XTP roll crimp, 1000 fps

BoogieMan · November 22, 2015, 08:32 PM

Clark- your saying that the lack of a crimp gave the same results as no powder at all?

Clark · November 22, 2015, 11:19 PM

The powder did not seem to burn. It was still in there.

The Hodgdon load books say no reduced H110 loads.
I contacted them and asked that had anything to do with detonation.
I was told it did not.
It has to do with stuck bullets.

That could be bad in the bore, but for me, they stick halfway in the cylinder and half way in the forcing cone. The cylinder cannot swing out. That is a hard to clear jam. After that happened some old guy told me he always carries a tinker toy stick to pound out bullets like that.

F. Guffey · November 22, 2015, 11:50 PM

Difference and effect? I do not wonder and have no curiosity. There are factors, I am the fan of bullet hold, I want all the bullet hold I can get. What is the difference in pressure with a little bullet hold and a lot of hold? Then there is time and distance, I am thinking there is not much time wasted between the bullet leaving the case with a light crimp and a heavy crimp.

I am the fan of the jump start, I want my bullets to have that 'running start'.

F. Guffey

November 21, 2015, 11:28 PM	#1
BoogieMan Senior Member Join Date: April 4, 2012 Location: South Jersey Posts: 2,217	Effect of crimp on pressure Effect of crimp on pressure. I loaded mix headstamp for my 460, I won't do again. Anyway, the crimp on the longer brass is visible dealer on the longer brass. COAL is still longer than min. Basically I loaded 20 rounds and set 5 aside that have a very heavy crimp. These are hunting rounds so the 15 will get me through the season without trouble, but I don't want to pull them if I don't need to. But, these loads are on the hotter end of things and I don't want to take any chances either. The 460 already opporates at very high pressure. __________________ Concentrated power is not rendered harmless by the good intentions of those who create it. Milton Freidman "If you find yourself in a fair fight,,, Your tactics suck"- Unknown

November 22, 2015, 12:25 AM	#2
Kosh75287 Senior Member Join Date: October 15, 2007 Posts: 820	All else being equal (and it never is, as .44 AMP likes to point out), I'D expect a heavier crimp to raise pressures SOME, but whether it would raise it from slightly below maximum to discernibly over maximum, I'm not so sure. The effect of heavier crimp is that the projectile is held in place slightly longer, as the propellant burns more completely resulting in higher chamber pressure before the projectile moves from the case mouth, on its way through the cylinder and down the barrel. I often suggest slightly increased crimp on reloads if cases are sooty after firing, and if the powder burns more completely I'd expect chamber pressure to be a little higher. I'd be more concerned about changes in overall length (shorter) causing pressure excursions, than crimp. It's usually a really big deal only in small cases, but given the pressure involved with the .460, a little could mean a lot. __________________ GOD BLESS JEFF COOPER, whose instructions, consultations, and publications have probably saved more lives than can ever be reliably calculated. DVC, sir. انجلو. المسلحة. جاهزة. Carpe SCOTCH!

November 22, 2015, 03:18 AM	#4
Jimro Senior Member Join Date: October 18, 2006 Posts: 7,097	There are going to be a lot of qualifiers in my response. Generally, for revolvers, a heavier crimp produces more consistent pressure curves and bullet velocity without a significant increase in max pressure. The cylinder gap is an immediate "relief" valve that bleeds off pressure the moment the bullet leaves the cylinder, and for heavy hunting magnum revolver cartridges the powder is slow enough that some of it is still burning at this point. Once the bullet is in the bore, or forcing cone, of the barrel, the effects of a crimp have an effect rapidly approaching zero on that portion of the powder burn and pressure produced. So IF you have a heavy charge of a relatively slower burning powder, I expect the heavier crimp will give you more consistent velocity numbers without any other difference than the lighter crimped bullets of the same charge. You'd have to chrono them to find out. If you have a light charge of a fast burning powder, where the powder is all burnt before the bullet leaves the cylinder, a crimp can increase max chamber pressure. But, if you aren't loading above max published charge you should be OK unless there is something wrong with the firearm. Jimro __________________ Machine guns are awesome until you have to carry one.

November 22, 2015, 04:55 PM	#5
Clark Senior Member Join Date: December 4, 1999 Location: WA, the ever blue state Posts: 4,678	If you want to see a difference in pressure: 45 Colt 21 gr H110 250 gr XTP no crimp, bullet stuck in forcing cone, 0 fps 45 Colt 21 gr H110 250 gr XTP roll crimp, 1000 fps __________________ The word 'forum" does not mean "not criticizing books." "Ad hominem fallacy" is not the same as point by point criticism of books. If you bought the book, and believe it all, it may FEEL like an ad hominem attack, but you might strive to accept other points of view may exist. Are we a nation of competing ideas, or a nation of forced conformity of thought?

November 22, 2015, 08:32 PM	#6
BoogieMan Senior Member Join Date: April 4, 2012 Location: South Jersey Posts: 2,217	Clark- your saying that the lack of a crimp gave the same results as no powder at all? __________________ Concentrated power is not rendered harmless by the good intentions of those who create it. Milton Freidman "If you find yourself in a fair fight,,, Your tactics suck"- Unknown

November 22, 2015, 02:47 AM	#3
hartcreek Junior member Join Date: April 22, 2014 Location: Washington Posts: 1,549	Post some photos. I am not going to tell you the loads that I worked up with virgin brass for my 624. Lets just say that it was way over and I use a good crimp. I had no problems with extraction and no over pressure signs other then flattened primers. From what I have loaded I can tell you that your heavier crimp isn't going to make enough difference in the pressure.

November 22, 2015, 11:19 PM	#7
Clark Senior Member Join Date: December 4, 1999 Location: WA, the ever blue state Posts: 4,678	The powder did not seem to burn. It was still in there. The Hodgdon load books say no reduced H110 loads. I contacted them and asked that had anything to do with detonation. I was told it did not. It has to do with stuck bullets. That could be bad in the bore, but for me, they stick halfway in the cylinder and half way in the forcing cone. The cylinder cannot swing out. That is a hard to clear jam. After that happened some old guy told me he always carries a tinker toy stick to pound out bullets like that. __________________ The word 'forum" does not mean "not criticizing books." "Ad hominem fallacy" is not the same as point by point criticism of books. If you bought the book, and believe it all, it may FEEL like an ad hominem attack, but you might strive to accept other points of view may exist. Are we a nation of competing ideas, or a nation of forced conformity of thought?

November 22, 2015, 11:50 PM	#8
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	Difference and effect? I do not wonder and have no curiosity. There are factors, I am the fan of bullet hold, I want all the bullet hold I can get. What is the difference in pressure with a little bullet hold and a lot of hold? Then there is time and distance, I am thinking there is not much time wasted between the bullet leaving the case with a light crimp and a heavy crimp. I am the fan of the jump start, I want my bullets to have that 'running start'. F. Guffey