Crimp on semi-auto loads

S

Stats Shooter

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I am looking for advice on crimping AR-15/AR-10 loads.

I recently made, and fired a lot of 200 rounds achieving a terrible 2.5 moa with .003 crimp.....i then used the same load with no crimp, single shot it and got 1/4 inch groups at 100 yards in my .308. I am now trying a .001 crimp.

My question is: Do any if you guys have a standard crimp for bullets with/without cannalures in semi-auto autos?
In my bolt loads I do not crimp at all.
 
I do not crimp any of my AR loads , There's no need as long as you have antiquate bullet hold which most dies will give you .

I'm just starting a 308 build and have never loaded for 308 semi's before . I to am interested in what guys do with there 308 semi loads .

I will say this , Only crimp rifle bullets that have a crimp groove , in the crimp grove and absolutely do not crimp match bullets . All your doing when you crimp match bullets that don't have a canelure is crushing the core which unbalances the bullet pretty much turning that high end match bullet into cheap plinking bullet .
 
You are getting into the- crimp, no crimp debate
Very strong opinions on both sides

I only crimp-- pistol rounds ( only to get the bell out of the case )
rounds used in a tubular magazine
some magnum calibers ( not all ) with very, very high recoil

I load with no crimp ( even if the bullet has a crimp cannalure )
223, 308, 3006, 6.5X55, 7.62X54R, 303, 7MM Mauser, 8MM Mauser

In all these calibers I tested with a crimp and it only degraded
accuracy
No bullet creep or set back with no crimp when used in semi auto rifles
 
No crimp on gas gun ammunition. The brass neck tension is more than enough ...and if ever found to not be enough, toss the case.
 
I've been reloading both 5.56 and .308 for AR's for many years. I've found that if you have proper neck tension then there is no need for a crimp and bullet setback isn't a problem. I've also found that I get better accuracy and lower SD's with no crimp in both AR's and bolt guns. I think part of the problem with a crimp is it deforms the body of the bullet changing its ballistic coefficiency enough to effect accuracy.
 
Neck Tension — Not Just Bushing Size is a pretty good read on the subject. When I load for example .223 Remington or .308 Winchester for either my gas or bolt guns I rely on neck tension. Many years ago I did try the Lee FCD (Factory Crimp Die) and never saw any improvement and in some cases accuracy degraded. Others have had better luck. When loading cartridges like 444 Marlin or 45-70 for my lever guns I like a nice uniform roll crimp and that also applies to 44 Magnum used in my Ruger 44 Carbine.

As to a taper crimp or neck tension? Enough so when a loaded cartridge is pressed bullet end against my bench the bullet remains in the case and does not move. Anyway, with a focus on only .223 Remington and .308 Winchester I rely only on neck tension and how much neck tension depends on the brass neck thickness, bullet diameter, and seating depth.

Ron
 
http://www.exteriorballistics.com/re...sgunreload.cfm

Excerpted from the Sierra article, quoted below (link re-copied above) about bullet movement. This is my view of it. I have run similar tests on Sierra's match bullets in reloaded ammo with the calipers at the range. For me with competition FL sizing dies, the movement of the bullet has not been significant after cycling, nor has function or accuracy suffered from not crimping. For reloads that will be put through practical shooting or more demanding conditions, crimping may be more necessary.

"To counteract this tendency, the semi-auto shooter is left with basically two options: The first option, crimping, brings up some other issues that can be troublesome. In general, crimping degrades accuracy. Most match bullets are not cannelured (which also seriously damages accuracy potential), a requirement for correct application of most crimps." (they go on to talk about factory crimp dies as an option)

"That having been said, crimping is still, at best, an occasionally necessary evil. Avoid it if at all possible."
 
I started reloading for my Garand and used a crimp (Lee collet crimp). Aster a few hundred, I tried skipping the crimp step. I saw no "push backs" and no differences in accuracy/function. Most of my brass is HXP and a few Hornady. I'm using mostly Hornady and Nosler bullets. Works for me...
 
Worth mentioning, many of us use a neck lubricant, either wet (a bit of case lube) or dry (motor mica or graphite or moly) during resizing. This makes bullet movement on feeding a greater possibility, so when loading for a self-loader, you want to remove the lube completely after resizing. One way is to use light cleaning (vibratory tumbler) to remove dirt and grit for resizing, then do the main cleaning after resizing.

Moly bullets will self-lube no matter what you do to the case. You may want to avoid them in self-loaders, but that lube does tend to make bullet pull consistent. So do your own testing to see what shoots best in your rig.

Also note, if you are measuring bullet length on extracted cases to see if the bullet moved forward, you want to measure the head-to-shoulder dimension on the case body before and after, as well. Hatcher observed long ago that chambering can size a case down a little in the chamber, and the extra brass will flow forward to lengthen the neck. So if you see a change in cartridge length, as Sierra did, you might be fooling yourself about whether or not bullets actually pulled out inertially or if the case shoulder was set back. Check both so you are sure which one is actually happening.

The Third Option: Ignore the problem. Berger did some good work to show that changes in group size with seating depth aren't large over short distances. They advise testing in 0.030" and 0.040" steps for target and hunting accuracy, respectively, with the secant ogive VLD bullets. The tangent ogive target bullets will be more sensitive, so I use 0.020" steps with them these days. A 0.007" change is not significant within those step ranges. Indeed, I've measured the bullet base-to-ogive length and the ogive-to-tip lengths on 30 Cal SMK's varying that much, and the base-to-tip lengths varying twice that much. So that 0.007" number is within normal variation. Just select a bullet and powder combination that behave well in your gun without having to seat too close to the lands, and the chambering changes will never be visible on paper, IME, though YMMV, so test in your gun rather than just take this on faith.
 
I do both and have had good results both ways.

If either is not giving you the results you desire, do the other. If that makes it even worse, switch back.
 
I do things differently than most, so take this for what its worth...

When I NEED a crimp, I use a factory crimp die.
Rolled or tapered crimp dies press STRIGHT DOWN on the mouth of the brass,
ALWAYS effecting the shoulder bends in the brass.

Unless the brass are trimmed to EXACTLY the same length, every crimp will be different.
Trimming AR brass to EXACTLY the same length serves no purpose in an AR (or any military semi-auto chamber) other than trying to uniform length for the seating/crimp die.

A factory crimp die presses 'IN' on the mouth from the sides, while supporting the shoulder, so you get a much more uniformed crimp pressure on the bullet.

The next way to do things is to think about the neck size/tension itself.
You simply UNDERSIZE the sizing ball a little, that gives you more neck tension on the bullet without any crimp.

This is easy to do with about any commercial sizing die,
You simply pull the decapping rod, tape over the threads, spin it in a hand drill motor/chuck, and use a fine abrasive on the sizing ball...

GO SLOW, and be careful, measuring often, you can take too much off quickly!

With the neck expanded less, the grip on the bullet is tighter, and crimping isn't always nessary.
 
Unclenick said:
Also note, if you are measuring bullet length on extracted cases to see if the bullet moved forward, you want to measure the head-to-shoulder dimension on the case body before and after, as well. Hatcher observed long ago that chambering can size a case down a little in the chamber, and the extra brass will flow forward to lengthen the neck. So if you see a change in cartridge length, as Sierra did, you might be fooling yourself about whether or not bullets actually pulled out inertially or if the case shoulder was set back. Check both so you are sure which one is actually happening.
Click to expand...

Interesting you say brass will flow forward . It's been a couple years now but I did a test that in fact showed shoulder set back on 223 cases being chambered in an AR . I don't have my notes in front of me but I sized the cases to have .002 case head space and chambered them by loading in a mag with the bolt locked back . I then released the BCG and let it fly home loading the round . If memory serves I'd get about .0015 of set back each time I did the test . If I chabered the same cartridge again in the same way I'd get an additional .001 to .0015 shoulder set back each additional time . This would continue until i would have a total cumulative set back of about .004 to .005 . These test were done using multiple cases and 3 different rifles with pretty much the same results regardless of the rifle or cases .

I even did a couple limited test where I sized cases that should not have chambered by a couple thousandths but the inertia of the BCG flying home set the shoulders back enough for the bolt to close .

I believe it was BartB that brought up the possibility that the extractor or ejector in the bolt could be causing the case to hit the chamber shoulder hard before the case sat in place in the bolt causing the set back . That to was interesting so I also ran the test with multiple bolt configurations . Complete bolt , stripped bolt as well as bolt with only the extractor and bolt only with ejector . This had NO effect on the cases having shoulder set back when chambered . In each configuration the shoulders were set back pretty much the same .

How ever the one thing I never did in those tests was check the COAL before and after each chambering :( . I was only looking for shoulder set back , looks like a new test is in order .

I'm interested in seeing if I get brass flow forward or the shoulders are just pushed/crushed/smashed back . Yes I completely understand how brass flow happens when you're sizing a case but not sure I see that happening in a chamber . Only because your chamber has no case wall support pushing on the walls of the case forcing any displacement forward like a sizing die does . So I'll run more test and see what I come up with .
 
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Crimps are needed in hot loads and for lever actions. Not required for a semi. Neck tension should be sufficient.
Crimps don't get measured. The amount of crimp is measured as 'enough', 'not enough' and 'too much'. Highly unscientific thing, so it is.
You can forget the cannelure altogether.
 
I've never crimped a gas-gun round, and that's the bulk of what I shoot.

The Sierra article notes some movement; the amounts they report are on par with measurements I've taken (in the 0.005" neighborhood). Chump change. But someone who publishes load data with a lawyer on retainer is going to default to the conservative side on everything, regardless of it's significance.

But if you do crimp, do it so you just barely tell. Less is best.
 
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Well, I brought this whole thing up because I have made many loads for my ak and AR's and not done a "real" crimp, like a factory crimp or used a crimp die. I do roll crimp my 40 s&w rounds. Then when I tried to crimp my accuracy suffered. So I guess I'm now in the "I don't crimp " crowd
 
" I do roll crimp my 40 s&w rounds."

How's that working out? Roll crimping semi-auto pistol rounds is generally a no-no.
 
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