Crimp

[DogmaDog]

Hey all,

I just set up my new 550b (thanks Brian, I got it!), and loaded about 50 rounds just for the purpose of function checking them before real "load development"

I feel pretty confident that I got all the dies adjusted pretty well except for the crimp die, because I'm not sure how to properly measure crimp, or how narrow a tolerance there is for variance in crimp.

Some factory ammo I have measures 0.470", using digital calipers at the case mouth.  Some reloads I did on another guy's machine before I got my own measure 0.471" to 0.473", but the casing doesn't have a straight contour...it looks like there's a bulge just below the case mouth.  Several of these rounds wouldn't slide easily into a Midway MAX-spec case gauge, but they all functioned just fine in my gun.

I tweaked the die around a bit, and finally settled for the point at which the case just begins to show that bulge below the mouth, because thats the first visual sign that the crimp die is actually doing anything more than just removing the bell to the case mouth.  The calipers read 0.471"  

The thing that's confusing me is that the further down I screw the die (more crimp, right?), the larger diameter I get right near the case mouth, because of that bulge.  

How do I make sense of all this?

Thanks,

DogmaDog

[TBF]

45acp should crimp to .469 measured at mouth. As for the bulge that sounds ungood. measure the case EXACTLY at the mouth. Be sure brass is of good quality, AMERC is notorious for being too thick at the mouth, PMP is pretty thick too, PMC is inconsistant and S&B is pretty thin, but useable. Most major AMERICAN brass is very good. If you measure too far back from the case mouth by the time you resize to .469 its really too much ( might be the source of your bulge? )As always this is IMHO and mileage may vary. What is your brass length? ( 45acp wont change much with one firing, but its worth checking if there is a problem like this )         Good luck                                Travis F.

[TBF]

I had to come back, dont really think of "crimp" on auto rounds . Think of it as removing the " bell " and returning the case to its original straightness.        Travis F.

[DogmaDog]

TBF,

I reloaded some more last night, and took a closer look at the crimp.  Measuring as close as possible to the case mouth, the "bulged" rounds were about .460.  Rounds like that worked fine in my gun when I fired them a couple weeks ago, but some wouldn't pass a case gauge.

I readjusted the crimp die, and now it sits at .466", and the rounds look better. I may have to back off just a bit more, eh?

My Speer manual shows 0.473" as the outside diameter of the case mouth.  I couldn't find where it specifies whether this is a maximum crimp diameter, or optimum, or before crimping...thoughts?

Anyway, thanks for your help!

DogmaDog

[TRG65]

When I'm setting up my dies for a semi, I follow Travis' advice I don't think of a crimp.  I use a separate crimping die and tighten it down until it touches the case mouth (with a case in the station and the ram raised the die will stop turning when the resistance from the case mouth is encountered) then tighten 1/4 turn more.  I check a round in a case gauge and if the case sticks on the case mouth, I tighten another 1/4 turn.  This same procedure can be used with a seating and crimping die just remove the seating stem.

[DogmaDog]

HighTech,

Hmmm.  Part of my confusion may stem from Dillon's instruction manual--they say to screw the crimp die down until it just touches the case RIM.  I guess they probably mean the rim around the mouth, not the rebated rim at the base of rimless cartridges.  

Oops.  

So I guess that bullets getting pushed into cases during feeding, or backing out of cases during recoil isn't any big concern, and even just a very light crimp is sufficient to prevent it??

Groovy,

DogmaDog

[TRG65]

DogmaDog,

Yes, getting bullets pushed back into cases is a concern.  A quarter turn puts more crimp on than what you might imagine.  

A good test without using the firearm is to measure the OAL of the loaded round with your chosen crimp.  Place the bullet against your loading table nose down, primer up, and push for all your worth (better yet do this with an unprimed round).  Measure the OAL again.  If the bullet has been pushed back, tighten the crimp die another 1/8th or 1/4 turn and repeat.  If not you are ready to rock.

I have never had a semi-auto round back out from recoil.  When I first started loading I did have some problems with bullets being pushed back.  Wierd things happen when those rounds ignite.  Then I started using the above "crimp test" and haven't had any problems with rounds being pushed back since.

[Flexmoney]

DogmaDog,

I haven't been paying too much attention to this whiole thread, so forgive me if this isn't really the question...

So I guess that bullets getting pushed into cases during feeding, or backing out of cases during recoil isn't any big concern, and even just a very light crimp is sufficient to prevent it??

In an auto round...don't think of the crimp as holding the bullet in place within the case.  The job of holding the bullet in place should be placed on the larger surface area of the bullet and brass.

I don't know if this is a good example or not...but, it comes to mind...

Think about trying to climb a rope, hand over hand.  Now, think of having to climb the rope using just your index finger and thumb (crimp).  

Now, think of wrapping all your fingers around the rope and making a firm fist.   Nice, even pressure with all the fingers means that you don't have to grip as hard with just the index finger and thumb to get the same holding power.

[bhg]

Dogma,

    I beleive the bulge that you are seeing is actually the case deforming form excessive crimp.  I like to set the crimp die by leaving it backed out.  Fully raise a cartridge with a bullet seated to the correct OAL.  Now screw the die down just until you feel it contact the case.  Lower the case just enough to allow you to turn the die about a quarter-turn.  Inspect the case, usually the quarter turn will actually leave a slight bell.  Continue this adjustment in quarter to eighth turn increments until the case walls are straight.  Any additional adjustment will be the actual crimp.  Just remember an eighth of a turn will do more than you may think...

bhg

[Alan550]

You seem concerned about outside case-mouth diameter, and I'm wondering about brass thickness at the mouth.  If you set the crimp with thin brass, then some thicker stuff gets used, you'll be crushing the bullet if you use the same crimp-to diameter.  

  Just food for thought..........

[shaughn leayme]

I do this for both rifles and pistols (auto's) I take the loaded round after setting or while setting the crimp and then put a metal plate on a scale (bathroom type is sufficient) and put 40 pounds of pressure against the round and hold for about 20 seconds and then reverify the OAL, it it changes then reset the crimp and try again.

You have to do this everytime or you should. whenever you switch to a different lot of brass, since some can be thicker or thinner as the case may be.

I have not suffered set back even when the same round has been chambered a few times and I have also checked them after they have been loaded into battery during shooting.

I also use a SAAMI ammunition guage to check for any other variance.

[TBF]

Alan550 has food for thought, remington brass is thinner than win. amerc is too thick, pmc can go either way. This is why  I sort my brass. Recently I relearned an old lesson, I somehow ended up with mixed brass in a batch I thought I had sorted, during loading the pressure needed to seat bullets was very low on some cases ( bullet just about fell in ) fortunately I felt it while loading and upon inspection it was pmc brass, just a slight push of the bullet against the bench pushed bullet in about .250 needless to say this could have been a slight problem if fired. Alot of loaders do not sort brass and never seem to have a problem, a local commercial loader uses mixed brass ( thier ammo is crap but its due to more than just brass quality )So I guess you could go either way, but I wonder how many blown cases blamed on the dreaded double charge are actually due to bullet set back from innadequate bullet grip? As for the crimp thing I got my measurement from Bill Wilsons book and it seems to work fine, not to say that slightly larger may not also work equally well. You wont see much of a "crimp" on 45acp as was said in a previous post its really the brass that holds the bullet. Until you get really familiar with auto rounds its a good idea to push the nose of the bullet against the bench good and hard to check it. If it moves you have a problem. Hope I am not talking too much.....        Travis F.

[benos]

Sounds like definite over crimping.

Like has been stated - in an auto, when you think of crimp, instead of the word crimp, think of the concept of ONLY removing the flare and returning the case mouth to it's original dimension. Which, measured at the very edge of the case mouth with the thin, end part of the caliper jaw, should be the sum of the bullet diameter plus two times the case wall thickness, measured right at the case mouth. On a 45 with typical brass, this should be real close to .470". (.450 + .010 + .010) And the best way to achieve that is to do exactly as bhg said. If I remember correctly, I cover this and other topics typically not found in manuals fairly well in the Competition Reloading video I did for Dillon using the 650. Even though the video was shot with the 650 as the machine example, the video contains quite a bit of valuable info for the competition shooter, no matter what press you are using. I've got some good feedback on it over the years.

be

It's HERE.

[DogmaDog]

Thanks BE, and everyone!

I shot some of my handloads last weekend, and they seem to work fine, so 0.467 isn't hurting anything, but I may back it off to 0.469 anyway.  I was able to push a bullet further into the case by about .003 on my desk with the 0.467 crimp on it, though.  

Anyway, thanks again,

DogmaDog

[TBF]

What type of brass? bullet setback is not good. The real test is whether it gets pushed back during chambering, chamber a round several times if it gets shorter you could have a problem                   ( with more short = more problem ) brasswise, some pmc , not all its very inconsistant, and remington brass is pretty thin, s&b is fairly thin also  ( at case mouth ) that combined with jacketed bullets can make for a fairly loose fit.             Travis F.

[DogmaDog]

TBF,

I'm using once fired S&B brass with hardcast lead bullets.  I'm also loading them somewhat long (1.260), so I may seat them to 1.25--the additional bearing surface may allow for a tighter hold on the bullet by the case.

Thanks all,

DD

[Guest Steve Harris]

It is important to keep in mind that, in straight walled cases, the mouth of the case determines the headspace. Too heavy a crimp can result in too much headspace (that is dangerous), can deform the bullet and may also result in failed primer ignition. If you are loading heaver bullets seated with ample contact within a sized case then the crimp may not be needed to retain the bullet until fired. Try just running the crimper onto the case to just enough to ‘repair’ the belled edge. Use calipers to measure the overall length of one of your loads. Load that round first in your mag and fill the rest of the mag. Fire all but the last round and again measure the overall length of that round. If it hasn’t changed then your crimp die is set correctly.

[Robjk]

Dogma,

Measure your bullet .452 Measure your case wall thickness and double it .010 x 2 = .020

Add the bullet and case thickness = .472

You want a crimp of .002 to .004  

A crimp of .002 would measure .470 at the tip of you crimp. A crimp of .004 would measure .468 at the tip of your crimp.

If you had .460 and .466 at the tip of your crimp, your crimp is .006 and .012 ouch… A tighter crimp will change the case pressure. If you shoot your .466 crimps check for signs of over pressure. (primer backing out or bulged case)  Let us know!!!

Rob

[TBF]

      Just food for thought, brass springs back when crimped, lead and copper do not. Supposing excessive crimp is applied, at some point the fit may become looser than if crimped less? I have not experimented with this but it seems possible...Though it is doubtful that would account for being able to push a bullet further into case, crimp on auto rounds is not responsible for bullet grip.                  Travis F.

[DogmaDog]

I've shot pretty much all my "eratic" ammo (early experimental lots just to learn how to operate the press...variable OAL and crimp).

Anyway, most of those loads were mild 200 gr. bullets at 740 to 800 FPS, and I didn't see any high pressure signs at any crimp or OAL. I was pretty much unable to detect any difference resulting from OAL or crimp in those loads, though I didn't exhaustively test for such.

For the time being, I've settled on a 200 gr LSWC loaded to 1.255" with a 0.469-0.470" crimp, over 4.6 gr WST to make major.  

Actual bullet wt. is 202.5 gr on average, and measured velocities put the power factor from 166 to 173 or so.