Crimp Your Cartridges! (The Factory Secret For Better Loads)

A worrisome thought occurred to me as I pulled the last .300 Winchester Magnum cartridge from my rifle’s magazine after a successful whitetail hunt in Montana.  The rounds looked odd, not right in the least.  Good news–bad news.  Good news, a yummy buck lay at my feet in peaceful repose.  The .300 Win. Mag. had dropped him like a 100 pound potato sack from a tenth story window.  Straight down, done.  Bad news, the cartridges I had assembled the month before appeared off in some way.

To start with, the plastic tips on the 180 grain Nosler AccuBond bullets were bent over a bit.  They had more in common with a Smurf’s cap than a bullet nose.  I had not seen this before with these, although it’s common with lead soft-point bullets.  The AccuBonds in the Boss’ .300 WSM Browning A-Bolt, and the 260 grain version I run in my Winchester Model 70, chambered in .375 H&H, don’t do this.  Something different–something definitive–had occurred.

I worked a fresh round loose from the Uncle Mike’s cartridge wallet on my belt.  If you don’t have one, by the way, get one. They are a great way to tote extra ammo in the field.   Unlike a standard cartridge keeper with loops, the cartridge wallet encloses the rounds in a nifty double flap, which holds up to ten and protects them from the elements.

I put the odd cartridge next to the fresh one which had never been in the gun.  The new one stood taller than the veteran.  At first, I attributed this to the fact the tip had been peened over.  I compared them further.  The line where the tip meets the gilding metal bullet jacket didn’t line up on both rounds.  This discrepancy bore mute evidence to the fact the bullet had been pushed back a few thousands of an inch into the case.  Examination with a micrometer confirmed this when I returned home.

I checked the other rounds I had run through the gun at various times during the hunting season but not fired.  Six neat, little Smurf hats greeted me.  Same story with the micrometer–all pushed back.  As far as I could determine, they had either been beaten hard in the magazine under recoil, and or, had been hammered when I cycled them through the action.

Operator error?

My Savage 111 rifle has a detachable magazine, but I don’t trust the gimcrack plastic latch.    To insure the mag doesn’t take an unplanned, and unwanted, trip from the rifle while in the field, I secure it with some camo duct tape and treat it like a blind magazine.  In other words, when it’s time to unload the gun at day’s end, I cycle each round through the action with the bolt.  Sometimes, in a lazy fit, I short-stroke the bolt to just “pop” the rounds free from the magazine lips.  This seemed an acceptable procedure until I found those flogged rounds.  What to do?

For more on the rifle used in this test read, Are Affordable Hunting Rifles Any Good? LocaCarnivore Test and Review: Savage 111 Package Rifle

This is the first time I’ve had this problem with ammo.  Neither my hand loads, nor the factory ammo I’ve used, have done this.  Several factors prevented it.  Factory bullets have cannelures, a narrow band engraved around a bullet’s shank with small, vertical grooves much like a washboard.  The softer brass case mouth is pressed, or crimped, into the cannelure so the ridges hold the bullet secure in the case.  The 180 grain PPU soft-points I once ran in the Savage, and the factory AccuBonds, are all crimped.

Cannelures on .357 Magnum cartridges.

I have fired hand loads without a crimp in the .375, but it has a hinged magazine floor plate so I don’t cycle the rounds to empty the mag.  Plus, the Model 70 has proper, Mauser-style, controlled-round-feed which glides the cartridges into the chamber without the bump and bash inherent in push-feed guns..  The Savage and the A-Bolt are both push-feed, but the A-Bolt’s detachable mag has a reliable and sturdy floor plate system to keep it in place, so the Boss removes the mag to empty it.  Just the Savage gets the blind mag treatment.

Regardless the cause, this had to stop.  Never mind the effect on accuracy, this could get dangerous.  One round I examined had been pushed back almost to the ogive’s base.  If I attempted to fire it, it may have blown up due to excessive pressure.  Not good.  I had two choices: bag the hand loads and get factory ammo, or find a way to crimp them.  I chose the latter.

The right crimp in your style

I researched the subject both on the internet and with people who know more about reloading than me.  Turns out, several companies make crimp dies.  They come in three flavors: roll crimp, taper crimp, and factory crimp.  I chose a factory crimp die from Lee Precision for the simple fact the Redding dies recommended by a gun store clerk I know and trust were not available at the time.  The literature Lee includes with the die states one can anticipate improved accuracy as well as bullet security because a factory-style crimp creates more uniform case neck tension.  This tension plays a crucial role in how a round builds pressure when fired and how fast the bullet leaves the neck.

Frustration washed in waves over me once I made this decision.  It meant I had to redo all my load development for two guns.  If you change any one variable with a load–bullet, powder, case, primer–you have altered the experiment and must start from the beginning.  This would also cut into my limited bullet supply, not to mention my prized H4350 powder stash.  Just my luck I standardized all my hunting guns on this powder just as the 6.5 Creedmoor craze hit and those shooters gobbled up all the H4350 on the planet.  According to all available sources, this is the Holy Grail powder for the 6.5 CM and the true believers who run this cartridge use powder like most people use air.  Sigh.

Die(ing) to start

The dies arrived within a week from Midway USA.  I say dies because I decided to get one for the Three-Seven-Five so I could solve the one reservation I had using my hand loads for dangerous game hunting (ie, bears).  The dies were well finished and had what seemed complete instructions included.  I sat down at the loading bench and dived in.

Lee Precision factory crimp die

Once eighteen rounds had been assembled per the Nosler manual, two per each half-grain step up in charge weight from 66.0 grains to 70.0 grains, I set up the crimp die.  Lee’s instructions are quite explicit on one point.  Do not, under any circumstances, jam the collet leaves tight together.  They state this will damage the die beyond repair (and, I assume, void the warranty).

Crimp die’s business end. Note the gaps between the collet leaves. Lee warns to avoid crunching the leaves together too hard.

This led me to use much caution.  I set up the die per Lee: run it into the press until the base touches the shell holder, then one half turn more.  I sent a cartridge up the die with the press ram, then lowered it and took a look.  Nothing had happened as far as I could determine.  I compared it to a factory round.  The case neck on my hand load didn’t seem crimped at all.

Per the instructions, I gave the die a quarter turn and repeated the process.  Still no obvious crimp.  Another quarter turn.  This time the collet leaves seemed tight, and you remember what Lee said about too tight.

Quick, the Bat Phone…

I called Lee.  They assured me I’d see a small (0.004-inch) groove in the case mouth if I had done things right.  I went back to the bench and mulled the situation for five or ten minutes.  Then inspiration struck.  If I had a feeler gauge, I could measure the gap between the collet leaves and know for sure if I risked damage to the die.  Now, if only such a thing existed in my shop, but I had nothing which would reach down into the tiny space inside the die.

Lee’s tech boffin had told me the minimum leaf clearance: a sheet of paper’s width.  I fiddled about with some note paper and after a trial and error origami session with some scissors, I had my go-no go gauge.  Turned out the die had room to spare.

Crimping scene–take two

I worked the die tighter about an eighth-turn at a time until the press arm found the same resistance as when I use a sizing die.  I pulled the guinea pig round free one last time and there, just discernible, sat a definite crimp mark on the case mouth.

Uncrimped case (left) vs. crimped. 0.004-inch wide crimp groove is just visible around case mouth.

I know what some out there are thinking at this moment, “Wait, those Nosler AccuBonds he’s using don’t have cannelures.  You can’t crimp a bullet without a cannelure.”  I thought the same thing until Lee assured me their die presses the case mouth into any bullet, ie. creates its own crimp groove.  Further, Nosler informed me such a groove did not affect their bullets’ aerodynamics or terminal performance.

Prove it

The crimp mark still didn’t look too robust, so I brought out the dial caliper and measured a uncrimped round and the test article.  I had indeed made a dent, so to speak, in the problem.  The finished case measured 0.005-inches narrower at the mouth.  Both Lee and Nosler confirmed this should prove sufficient.  In fact, Lee’s boffin called it a “heavy crimp.”  Who knew?

Range time

After a two-week wait for my schedule and the weather to align, I drove out to the local range.  While I can shoot at LocaCarnivore’s palatial corporate headquarters, this test required a rock-solid shooting bench and known, measured distances.  You can read about my load test protocol in detail here: Develop Your Hunting Loads for Less (LocaCarnivore DIY Series).

The results were mixed.  I didn’t see an overall improvement in accuracy.  The chart below tracks the results from two test rounds for each half grain step in charge weight.  The average accuracy decreased compared to the uncrimped rounds.   Although, I had good news on the velocity front.  I gained about a 100 fps increase across the board with the crimp.  This is a problem I have chased for the past few years.  My hand loads did not come close to the velocities advertised in the loading manuals.  No matter what I did, they always lagged behind and caused me significant frustration.

Powder Charge Vel. (No Crimp) Vel. Spread MOA (No Crimp) Vel. (0.005″ Crimp) Vel. Spread MOA (0.005″ Crimp)
66 2718_2728 10 0.5 2831_2844 13 1.2
66.5 2735_2752 17 1.5 2863_2859 4 0.92
67 2771_2774 3 0.25 2880_2898 18 0.62
67.5 2801_2804 3 0.75 2906_2898 8 1.54
68 2827_2826 1 1.0 2927_2918 9 2.08
68.5 2834_2834 0 1.0 2946_2945 1 1
69 2859_2849 10 1.5 2973_2972 1 1.04
69.5 2884_2891 7 0.25 2913_3010 97 0.90
70 2946_3000 54 0.5 2979_3042 63 2.86
Average: 2824 12 0.81 2922 24 1.35

The creep back problem appeared cured, as well.  I put one crimped round in the magazine while I fired other test rounds, then measured it with the micrometer.  Zero deviation, and the tip remained undamaged.  I chalked the tip problem up to my ham-handed unloading technique.  I solved this issue with a change in procedure.  Now, I pull the magazine and unload it by hand.  Hey, duct tape is cheap.

Final Results

After range test number one, I had two loads which promised the best accuracy, and both had acceptable velocity, as well.  Another week ensued while I waited upon the weather gods.  Once I got back to the range, I fired two, three-shot groups for each semi-finalist.  In my experience, the three shot groups open up a bit compared with the two shot development groups.  In this case, they opened up more than anticipated.  The more accurate lower velocity load promised 2890 fps and 0.6 MOA averaged 2860 at just a tick under 2.0 MOA.  The faster, but less accurate, one hinted at over 2970 fps and 1 MOA but delivered 2950 fps at 2.7 MOA.  My original, creep-prone loads had delivered 2960 fps and 1.0 MOA.

I know some out there would slash their wrists if they had this happen to them, but there are several factors which eased my disappointment.  The 1.0 MOA for the original load had been derived after just one, three-shot group fired at twenty-five yards due to budget and facility constraints.  Not a realistic test.  Add in the fact they are useless due to the creep back, the accuracy and velocity become moot.

2.0 MOA is just fine for shooting deer and elk out to 400 or 500 yards–the farthest I dare shoot at the moment with my gun, optics, and skill.  Would I like more accuracy?  Sure, but I won’t lose sleep over the issue for now.  For more, read Hunting Rifle Accuracy: How Much Do You Need? (The LocaCarnivore Expert).

Bottom Line

Should you crimp or not?  Despite my results, rifle rounds should get crimped to ensure they are safe and will resist damage from the rough and tumble treatment they can get in the field.  This is more imperative for magnum cartridges due to their stiff recoil, in my opinion.

I agree with the theory crimps should improve accuracy.  My test methodology with the uncrimped rounds did not have enough consistency to draw a clear conclusion.  At some point, I need to run a definitive test with a control group and a test group under standardized conditions.  I am pleased I solved the velocity problem which has vexed me for so long.  I plan to discuss this issue further with Lee and Nosler to see if I could do things better and improve accuracy as well.

In the meantime, I have a good load which duplicates the classic .300 H&H Magnum’s ballistics.  A cartridge which has slain every game animal on the planet at one time or another with few, if any, complaints from those who’ve used it.  It’s accurate enough for my present needs, and thanks to the high BC AccuBond, still delivers over 2000 ft-lbs. at 500 yards.  As a bonus, it’s well-mannered–for a magnum–even in this eight pound rifle.  It doesn’t hammer my shoulder too bad and I can track my shots through the scope.  If I decide I can’t live without those other 90 fps from the other semi-final load, and I have the time, bullets, and powder to spare, I might play around with bullet seating depth a bit just for giggles.  Stay tuned.


Other helpful stories you’ll like:

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