2500 thread hits to my search for this. Do crimps increase chamber pressure on .357?

[Tallbald]

I can't find definitive factory guidelines with my die sets for measuring crimps on my revolver loads. All I find is "if more crimp is desired, turn X amount further in". I sometime wonder if too heavy a crimp with my FCD could raise chamber pressure significantly or even dangerously. How does one "measure" a crimp? I work to mimic what I see on a factory load but there must be a way to quantify it that I haven't seen discussed. I'll apologize for asking a basic question. But several tries of the search feature yield thousands of threads to search through.... Thanks. Don

[mannyCA]

I believe that crimping does increase pressures and allows for a more complete powder burn. Another way I could think of pressures increasing would be when applying a roll crimp and your using brass of unequal lengths, the brass can be caught between the bullet and the throat.

That being said, during initial setup you should pull a round after crimping and see if it deformed the bullet in anyway, if so it could be too much crimp. A light crimp could be defined as just enough to remove the bell from the mouth. A medium crimp could be somewhere in between, of course, its all subjective to the loader.

[Blackwater]

With the slower burning powders, say from about AA9 and slower, it sure seems to increase the load's consistency. Whether it increases peak pressures a bit or not isn't, at least to me, nearly as important as the consistency question. Another way to look at it, and maybe more valid with respect to creating good loads, is that while a heavy crimp may increase pressure, that pressure also creates higher velocity, so you're getting something of potential value for that pressure increase, along with the aforementioned increased consistency, and that's a pretty darn good tradeoff. This is especially true when you consider that the lighter crimp will likely produce lower velocity.

If you're thinking about trying to get more velocity by using lighter crimps so you can add in a little more powder, it's very unlikely that would work because the lighter crimp wouldn't produce quite the velocity that a load with a good, heavy crimp does. You'd also be creating the possibility of not having enough crimp to keep the bullet in the case during recoil, and having it be pulled out of the case by inertia, and in a revolver, tying up the gun and making it useless.

FWIW, I like light crimps in stuff like .38 Spec. WC's, but always use a good crimp with heavier loads, especially in the magnums. This seems generally to be about the optimum. Crimps have a purpose, and we can't really adjust from light to heavy just because we want to. They're to keep those bulllets in the case until they line up wiht the cylinder and it's their turn to fire. Ignoring that purpose can create a very aggrevating gun problem at the range when a bullet pulls out and the cylinder can't turn. Not a lot of fun.

[Tatume]

You will not find any solid advice on how much crimp to apply, because it depends on the bullet and the application of the ammo. Some bullets have deeper crimp grooves, some shallower, some have a nice bevel, some don't, etc. You will have to tailor the crimp to the bullet. That said, and paraphrasing Brian Pierce, apply as much crimp as possible without damaging the bullet when loading high-pressure hunting style ammunition. For target ammo, you can use less so long as your bullets don't migrate under recoil.

[44man]

Case tension is the control for a better burn, crimp only aids that to keep boolits in under recoil. The amount of pressure increase from over done crimps is not much and can actually ruin tension as you force brass to bulge.
Each boolit will have a different groove, like the Lee with chicken scratches so the die must be adjusted as you change boolits. Easy way is a shim stock washer under the die ring.
Only fold to the bottom of the grooves.
Revolver tests from shooting no crimp, one at a time to full profile did not show a difference worth a hoot.
Crimp is always a problem with soft lead that can ruin a boolit or not open fully to scrape a boolit. The boolit opens the crimp, it does not jump off the boolit from case expansion. If you have any crimp left on fired brass, you need to harden the boolit.
Where you see changes in velocity or pressures is when not enough tension is used, boolits creep out from recoil and that changes airspace. No crimp will hold if there is not enough tension.
I proved that when I shot factory cast loads with full profile crimps like factory jacketed loads in the .454. Two shots tied up both the SRH and a Freedom.
The most even readings come from every case having the same grip on a boolit and crimp will NOT aid that. To shoot dead soft from revolvers and expect accuracy is folly. The lever gun that needs a crimp works the same as does any with a magazine full of rounds that can not resist recoil.
Use crimp as an aid, not a solution.

[Tallbald]

I see your folk's points. When I load and adjust the crimp, I carefully watch the slug (I only use cast slugs , either commercial of of my own creation) for deformation. The retraction move out of my FCD after the crimp is formed should, If I understand function, eliminate any bulge that may have occurred with crimping. ***As a side note (and comments are appreciated here), I at times have found that the OAL specified for a load in a manual is not possible if I align the crimp with the cannalure of the cast slug----I haven't figured that one out yet and try to hit a happy medium).
So is the general idea that a crimp just sufficient enough to retain the slug at recoil or prevent pushing it into the case at chambering, not going to affect pressure dangerously? I don't want to paint with too broad a brush, but I do want to learn and practice safe loading . Thanks for your input folks. Don

[10mmShooter]

44man is the man very well stated,

I would only add as other have mentioned you have to consider the load and firearm, for my .44 Henry, I load "lite" loads of SR-4756 or Green Dot with a 240 LRN-FP that only generates 1050fps out of the 9 pound Henry, it barely moves under recoil, so although its a 10 rd tube feed gun, I use only the slightest of roll crimp on the rounds, since the firearm and load generate very little recoil there is no projectile set-back(projectile being pushed back in the case due to recoil in tube feed rifles)

Same applies to my revolver loads in my 6 inch 629PC Competitor, I load Green Dot and SR-4756 with a 255gr K-SWC at 950 fps, again a "lite" .44 load, in a big heavy revolver, for it I apply a very light taper crimp just enough to knock of the case mouth flare. Again with the combo of gun and load, I have no issues with bullet pull(projectile slipping forward under recoil)

obviously as .44man stated above....proper neck tension is holding the projectiles....not the crimp.

[MtGun44]

The neck tension is the primary factor, crimp is for recoil or magazine forces. I have never
seen any damage from a full normal roll crimp in revolver boolits, even at 8 BHN - at least
any effect on accuracy. I am not persuaded that the crimp, even for very soft boolits has any
bad effect on the boolit. Perhaps there are situations, but my testing has not shown any
effect on accuracy.

Bill

[44man]

Check fired brass Bill. Any crimp left means you sized the boolit leaving brass. Soft lead will be sized when seating so tension is not the same as harder boolits.
Tallbald, never worry about published OAL stuff. Only thing to avoid is a boolit nose sticking out the front of the cylinder.
This is ideal, the fired 30-30 case that was crimped allows me to start a boolit in by hand. Crimp has been ironed out fully. 121403

[44man]

Very heavy guns need less crimp to hold a boolit. A wimp hold can promote more inertia as do those real light guns, what is it? The S&W 329 I think.
I can take that problem to real short barrels too. Too much recoil and barrel rise. Just harder to hold boolits. Any that move before shot will change velocity and accuracy.

[Char-Gar]

The question is too broad for an easy answer. But the amount of crimp won't make the difference between a safe load and an unsafe load it that is the question. Will a crimp have an effect on accuracy? A uniform crimp will be an aid to good accuracy. If the crimp is not uniform then accuracy might suffer.

As a general statement, I agree that the principal function is to keep the bullet where it belong until shoved forward by the pressure of the expanding gas. The above two sentences refer to handgun rounds.

I would not recommend the use of a crimp on a cast bullet rifle round, unless it is used in a tubular magazine under spring pressure, which might shove the bullet back in the case.

[Char-Gar]

I see your folk's points. When I load and adjust the crimp, I carefully watch the slug (I only use cast slugs , either commercial of of my own creation) for deformation. The retraction move out of my FCD after the crimp is formed should, If I understand function, eliminate any bulge that may have occurred with crimping. ***As a side note (and comments are appreciated here), I at times have found that the OAL specified for a load in a manual is not possible if I align the crimp with the cannalure of the cast slug

Forget about those book numbers. Crimp the bullet in the groove provided. If the round will chamber and the bullet not stick out of the front of the cylinder, you are good to go.

[williamwaco]

With normal loads, I crimp no more than a couple of thousandths.

With heavy recoiling loads like .44 Mag and up, I crimp a little more.
Never what "they" would call a heavy crimp.

I mark one of these with a felt tip marker on the primer and load it in the revolver.
I fire five shots then reload keeping the marked cartridge.
Then fire five more being sure to not fire the marked cartridge.
Repeat one more time.

That cartridge has now sustained the efforts of 15 firings to dislodge the bullet. If the bullet moves, crimp it a little more and try the test again.

For photos, see:

You can also see a photo here of what severely excessive crimping can do to your bullet.

[gwpercle]

A little.
But in the overall scheme of things not enough to be concerned about. A heavy crimp is not going to raise pressure to any dangerous level. Crimp as much as required to hold the boolit in place.
A boolit that is dislodged by recoil or magazine spring pressure is of far more concern than a heavy crimp. If the crimp is excessive the case will buckle or bulge and they will have a problem chambering.
Gary

[DougGuy]

I just got finished with a little bench testing two styles of crimps. These were Lee C430-310-RF boolits sized .432" in PMC brass over 17.0gr LilGun, WLP primers, all charges weighed to the .0 of a grain. Boolits are 50/50+2% with a BHN of 10 or so. I can dig a thumbnail into them.

The crimp on the left is a collet style formed by a modified uncataloged Lee collet style factory crimp die. There is a thread here that I detailed what modifications were done to a .45 Colt die of the same style, this .44 die was done the same way. http://castboolits.gunloads.com/showthread.php?201449-Question-about-type-of-crimp-required&p=2239315&viewfull=1#post2239315

The cases on the right have the roll crimp, done by the seating die in a Lee set.

The aim of using this modified collet crimp die is to provide a little more resistance to the initial travel of the boolit so the burn time is increased and this can bring better consistency to the velocity and lower the standard deviation, which translates to more even recoil impulses on the gun in the shooters' hands which -should- mean a little bit better groups, all things given. It also serves to further prevent any movement of the boolit in the adjacent chambers during firing. This allows a softer alloy boolit to be held steadfast at it's seating depth, again removing the variable of growing case volume if a boolit jumps forward during firing of adjacent chambers.

Bottom line, in a bad situation with dangerous game, the very last thing you could want is a gun locked up from a boolit jumping crimp, and this is merely added insurance.

Now, for the surprise. I fired these loads over a chrony 5' from the muzzle, the roll crimped rounds on the right were running right in the 1170 - 1185f/s range, and the ones on the left with the collet crimp were some 20 and 25f/s faster! With half the SD of the roll crimped rounds, they were running right up in the 1196 - 1200f/s range.

http://i1202.photobucket.com/albums/bb374/DougGuy/Reloading/DSC03150_zps2fffcc0c.jpg (http://s1202.photobucket.com/user/DougGuy/media/Reloading/DSC03150_zps2fffcc0c.jpg.html)

As you can see, the crimps are fully unfolded, and these loads shoot better than any other load I have EVER fired in this old SBH in the 25yrs I have owned it. There is a decent amount of case neck tension but the softer alloy will fool the eyes in that it does not distort the case in the same manner a hardcast boolit does, and so you think there is less tension because you don't see the ripples. Not so. A soft .432" boolit pushes into the case with the same resistance as a hardcast .432" boolit but the edges of the lube grooves aren't as pronounced as a hardcast so you see distortion from the hardcast much easier.

Does the style of crimp affect pressure? In my findings, the answer is yes. Why? Because as a stiffer crimp provides more resistance to movement of the boolit, more of the powder burns before the boolit clears the case mouth, OR the powder that burns, burns slightly more efficiently. All of us big bore gunners know that slow burning powder NEEDS some neck tension to hold the boolit back, it NEEDS a good healthy crimp, this is just my own way of crimping these big softer alloy boolits and it works.

In closing this post, I'd like to say thank you to the entire castboolilts patronage, many of you helped me develop my sense of bearing in learning and loading cast boolits, special thanks to 44man for his volume of posts and his expertise. Jim, we don't always agree on everything, but just goes to show that there is generally more than one way to perfect a process to the point of acceptable excellence. I have a great deal of respect for your methods and the methods of some of the other old heads here, some things I do my own way for my own reasons, this crimp being one of them, using a little softer alloy than you favor is another, but it's working very well here. Still, hats off to you sir.

[DougGuy]

Hmm.. Dbl post somehow.. OP to answer your original question, the answer is yes. As described in the post I made before this one. The fact that your question was for .357 and not .44 makes zero difference, the answer would still be yes.

[cbrick]

The crimp won't add pressure or velocity. As 44man said, case tension holds the bullet or not for proper powder burn. Crimp aids in preventing the bullet from moving under recoil and you don't need any more crimp than necessary to hold the bullet under recoil with your load in your gun. Excess crimp only serves to shorten brass life. Here are the results from a crimp test I did with my FA 357 ranging from NO crimp to a heavy crimp.

Crimp Tests

FA 357 Mag 9”
RCBS 180 GC Silhouette @ 192 gr. (WW+ 2% Sn HT @ 18 BHN)
16.0 gr.H-110
Winchester brass
CCI 550 primer
Temp 700 Humidity 38%


All chrono tests 10 shots



1>

My normal profile crimp, second firing of WW brass, Carbide die sized




E.S. 30




A.V. 1518




S.D. 9







2>

Roll crimp, second firing of WW brass, Carbide die sized




E.S. 30




A.V. 1520




S.D. 9







3>

No crimp, second firing of WW brass, Carbide die sized, very slight bell




E.S. 30




A.V. 1528




S.D. 9







4>

Light profile crimp, virgin WW brass, not sized, not expanded, slight bell only




E.S. 26




A.V. 1532




S.D. 8







5>

My normal profile crimp, virgin WW brass, not sized, not expanded, slight bell only




E.S. 26




A.V. 1536




S.D. 8




I hope this helps explain the roll of crimping.

Rick

[fredj338]

It will vary with the powder you choose. Slower powders will benefit with a slight pressure increase to help burn the powder more efficiently. Faster powders will show less pressure affects by little or a lot of crimp.

[cbrick]

It will vary with the powder you choose. Slower powders will benefit with a slight pressure increase to help burn the powder more efficiently. Faster powders will show less pressure affects by little or a lot of crimp.

The crimp test in post #17 not only used H-110, fairly slow powder for the 357 and not only that but a snoot full of it too. There were no variations due to crimp. In another test (didn't find the chart in this computer) using 1680, an uber slow powder in the 357 showed very similar results. Case tension determines how well the powder burns.

Rick

[DougGuy]

The crimp won't add pressure or velocity.

That may be true between a roll crimp and a profile crimp as your findings suggest. It may make a difference in both pressure and velocity in comparing the type of crimp, collet vs. roll, as my findings suggest.


As 44man said, case tension holds the bullet or not for proper powder burn. Crimp aids in preventing the bullet from moving under recoil and you don't need any more crimp than necessary to hold the bullet under recoil with your load in your gun.

A true statement that is, however if you are using a collet crimp such as the one I like, it may have an added benefit in that not only does it prevent the boolit from moving, it seems to benefit slow burning powder by offering enough resistance over neck tension and roll crimp to allow for a better burn of the powder. IF this is the case, then this is reason to employ this style of crimp with heavy for caliber, soft alloy boolits in the .44 Magnum, moreso than -just- holding the boolit from moving.




I hope this helps explain the roll of crimping.

Rick

If you can show variables that can be attributed to a certain style and amount of crimp, I think it's fair to say that there is more than one purpose gained by the choice of crimp. This is what I am finding with my efforts.

[cbrick]

If you can show variables that can be attributed to a certain style and amount of crimp, I think it's fair to say that there is more than one purpose gained by the choice of crimp. This is what I am finding with my efforts.

Doug, explain the results of test #3 in the chart.

Rick

[DougGuy]

Doug, explain the results of test #3 in the chart.

Rick

I think you missed what I was trying to say. Your chart shows no discernable difference between a roll crimp and no crimp in test #3.

What I said was I think there very well -could- be a difference in comparing crimps by style and not by how much or none at all. I am saying the collet crimp provides enough resistance to boolit movement to make a measurable difference, whereas the roll crimp does not offer enough resistance to make a difference. This is also verified by your results.

Let's look at the two styles from a different angle.. One, how much effort would it take to pull a boolit from a non-crimped case, as compared to how much effort it takes to pull a boolit from a roll crimped case? You and I both know to expect -some- difference in how much work is required to do this task.

Now, if you ever go to use a kinetic boolit puller on one of these collet crimped rounds?? LOL pack you a good lunch, and maybe order a new boolit puller, because you will have to exert 4x the amount of beating to pull one of these..

When it gets to this ^^^^^^^^ the difference becomes very clear, and this style crimp is in a whole 'nother ball game..

I will document this collet crimp a bit more, I didn't have but 10 rounds put up of each type crimp and I only fired half of those. I waited to see chrony results of this load before I committed to loading 50 or 100, which I am very satisfied with the velocity the load produced, so now I can load a bunch of them and do a proper comparison with multiple strings.

[cbrick]

Was the roll crimp the only crimp used? Was the amount of crimp varied between tests?

Not only is proper case tension responsible for consistent powder burn but you cannot make up for improper/inconsistent case tension with any amount or type of crimp.

Rick

[DougGuy]

Was the roll crimp the only crimp used? Was the amount of crimp varied between tests?

Not only is proper case tension responsible for consistent powder burn but you cannot make up for improper/inconsistent case tension with any amount or type of crimp.

Rick

Oh I am by far and away not making up for the absence of case tension, there is case tension and a goodly amount of it. Just because you don't see rings around the case doesn't mean there isn't tension. I can feel case tension at the press handle.

I'm saying the collet crimp AIDS powder burn where a roll crimp (by your chart) does not do so. And if I am correct, then yes a crimp CAN raise pressures. That explains my 25f/s bump over the roll crimped rounds I chronied.

[cbrick]

How old is your brass?

Rick

[DougGuy]

Age of this brass is an unknown. I know you can say the case neck is softened, annealed, etc but again there is plenty enough life in it to hold the collet crimp and make you work like a dog to pull one of them, so I don't think age is a factor. I don't see any of them stretching or thinning above the web so they can't be but so many firings on them. They looked really good when I got them, possibly they were once fired and I have only fired them once.

[cbrick]

They don't have to stretch. Work hardening will cause variation in case tension.

Rick

[44man]

I suppose there is a difference with a FCD but tests showed reduce case life. Seems to be about the same as a full profile.
Now I can't say what crimp the double tap loads had but they were drastic, hard to tell between a profile and a FCD, yet they pulled from recoil. I would never take them for bear protection. My gentle roll crimps did not pull.
I have many profile crimp dies, some are Redding but I rarely use them. I adjust so they look like my roll crimp anyway. The reason I don't use them much is because a lot of my boolits are larger and will not pass through the top of the die. I never felt like lapping them.
I had to watch my Hornady seater dies too, found one caliber where the boolit would not go through the floating part and had to lap it out.
With my Hornady dies I seat and crimp all at once, never a separate operation unless I use jacketed with the profile crimp die and still only make a roll with it.
You all know I shoot the big guns more then any, the .475 and .500 JRH and boolits will not move from recoil. The inline seating of the Hornady dies are about the best to keep boolits straight.
Soft lead with a profile or FCD just has to be sized trying to open a crimp so the boolit can come out smaller then groove. Maybe a drastic "slump" will iron the case. But the crimp marks are still there and eventually will crack.
I am cheap as dirt and am shooting .44 cases since the early 80's, fired over 40X. I still have Midway and Fed brass. I finally had one case split!

[stephen m weiss]

I built a spreadsheet doing internal ballistics. One feature I put in was a crimp that requires a specific amount of force to overcome, but does not use up much energy to remove. I also built a rig to test the peak force to overcome actual crimps. Note that I did not independently test neck tension versus crimp. I found that: with a very low pressure load, crimp force increases chamber pressure causing a more complete burn, and higher velocity. For a high pressure charge, crimp force has NO effect whatsoever on the velocity. With over a 50% case fill, just the primer going off nearly overcomes the crimp, and the very initial burn pops it out. Velocity values didnt change even 1%.

I tested force to remove the bullet for a 308 cast not quenched and fmj, as well as 223 fmj. They were 80, 110, 100 lbs respectively. The value was independent of the depth of the crimp. It was most likely controlled by coefficient of friction, brass thickness, circumference and yield strength.

I use light crimps on all cast bullets to take out the seating flair. I also want the crimp to do an airtight seal against the lube to keep moisture out since I use cereal filler.