Crimping for Accuracy

[500Stroker]

Can I gain accuracy by crimping the case neck, commonly found in factory ammo?
The theory would be that crimping adds consistency to the neck tension.

 

[jonbearman]

If you are truly trying to reload for accuracy , then crimping will do nothing but deforming the bullet you wish to be consistent. You can figure out what your neck tension you have by measuring , then measure your bullets pressure ring if it has one or the bearing surface. Then measure the inside of the neck and subtract the neck diameter from the bullet and you should end up with .003 to .004 thou neck tension which is more than adequate.


Measure the neck ID for clarity. What cartridge and gun are we talking about?

 

[500Stroker]

I am posting this for a friend.
He is shooting a custom model 70 with a Shilen barrel, chambered in 243wssm. Yes, I said 243wssm. He has been loading for a looooong time and declares he see's tighter groups after crimping.
I think it just increases cup pressure/velocity. I have never crimped anything that was not tube feed.

 

[people]

What Jon said. I will add this. In the 223rem shooting 69 and 77gr SMK bullets a very light crimp will help. I bought a tool to measure run out and found out crimping them some how made them have less run out. I was using a standard die and rotated the casing to help align the bullet.

Fast forward to using a competition setter I had very little run out and they shot as good as the old way. I tested crimping with the straight ammo did not get an improvement in run out. I did however get slightly better groups.

So to recap 99% of the time crimping will not help.

 

[jr600yd]

Well let's think about this crimping thing?
Benchrest shooters shoot EXTREEMLY small groups. Do they crimp? (NO)
High power shooters have stages of rapid fire. Do they crimp (NO)
F class shooters (some call belly bench rest) do they crimp? (NO)
Hunters? I doubt it
So who does?
Well the military uses crimped ammo, not for accuracy but to avoid ammo malfunctions in automatic weapons.
Factory ammo has a crimp, again not for accuracy, that ammo has to function in ALL rifles of a specific caliber.
Crimping may help a piticular firearm but that is not the general rule. If it was believe me the bench rest guys would have been doing it a long time ago.

 

[joshua43214]

If there is any chance of bullet walk, you should crimp.
I don't have a semi-auto .223, but I doubt the recoil is enough to walk the bullet out, it certainly feels very mild in my Contender.
I would probably do a light crimp on hunting rounds for reliability if nothing else. Ammo you take into the field gets abused, I don't like the idea it getting pushed in deeper from manhandling/dropping or walking out from recoil. Always (Always) crimp tube magazine ammo.

Who crimps?
Silhouette shooters, and folks who shoot .44mag

For any kind of accuracy I would play with crimping last after everything else. Some gun/load combinations seem to like a light crimp. My old 700 in .308 liked a light crimp until I switched to a slightly faster powder. I don't like to crimp because it adds and extra step to ammo making and can knock stuff out of alignment, and it shortens case life.

To do this right, you will want to go through the whole process of neck turning so you get a proper match to your chamber, then use bushing style dies so you can adjust neck tension. With a match barrel this should be no problem, but you might not get a good fit with fancy brass like Lapua on a factory barrel. You wanted an excuse to wait 6 months on a new Hart barrel right?
On my really old 700, I used military surplus brass to get the thicker case walls, and honed out an RCBS die to get good neck tension. It fit my budget at the time, and made a pretty good shooter out of a cheap gun.

 

[mac86951]

Interior Ballistics would suggest that a crimped round would have a higher 'pressure to start' This might allow for a change in velocity as well. I'll go further to say that I don't crimp anything but my SASS .38 special and .44 mag rounds. I wonder how much different the 'pressure to start' could be with crimps and doing it consistently is unexpected.

Military crimps are to assist in weather resistance for the ammo. Primers sealed is along with it.

I can see how crimping could affect run-out, but as previously stated so do better seating dies/methods.

Can crimping increase accuracy? Possibly, can it assist consistency? If you aren't consistent in reloading before crimping, I certainly wouldn't expect consistency after crimping especially neck tension, but I could see that with an increase in starting pressure uneven neck tension might become less of a factor, but it would make case length and trimming more of one.

-Mac

 

[LHSmith]

This theory most likely has roots in advertising claims, and the die makers have different opinions on this one. Speaking specifically to bottleneck rifle cartridges....Lee Precision is the only die manufacturer that claims "even bullets with no cannelure ( crimp groove) WILL shoot more accurately if crimped in place with a Lee Factory Crimp Die". However, they only offer this die in a limited number of cartridges -most of which are typical chamberings in lever, semi- auto, or pump rifles. All the other die manufacturers specifically advise against crimping any bullet with no cannelure. About 20 years ago, Speer had a massive ad campaign warning consumers NOT to crimp any of their bullets without a cannelure. The warning was in each box and plastered in all the shooting mags at that time.
IMO, knowing the inconsistency of neck wall thickness on most new brass, I would think crimping would have an adverse effect on accuracy, and though one can turn necks to gain consistency, the thinner the neck the less effect crimping has on tension.

 

[Joe Salt]

LHSmith you are right about LEE FACTORY CRIMP DIE! Back in the 1980's there was a shooter at or club in PA. that was using a LEE CRIMPER and almost broke the 1000 yard record at the time. I myself never believed in Crimping other than my pistol rounds. But needless to say he didn't set the world on fire after that. So no I'm not for it! And if I remember right it done a hell of a job on the necks!

Joe Salt

 

[Larryh128]

I have never seen a bullet walk in a case YET from recoil on a hunting rifle without crimping. Certainly not in an ar -223. If I was hunting Africa big 5 then I would probably crimp for peace of mind, nothing else. The 243 WSSM is a different cat because of the very heavy neck walls and it could have a different effect on his accuracy. Raise initial pressure? Yes. Velocity, I doubt it.

 

[lpreddick]

i help a friend load a .223 9 twist with almost no freebore. if we load a flatbased bullet the bullet's base goes through the neck and if we try to seat the bullet into the lands, it gets pushed back further. the pressure ring of the flat base expands the neck as it passes through and the remaining tension on the bearing surface is not enough to hold the bullet when it engraves the lands. if we use the lee crimping die the bullet stays put. currently we're working on loads with flatbased bullets. since boat tail bullets don't seem to have a pressure ring, they tend to stay put when seated into the lands . if we jump bullets, they all have to be seated into the case, taking up space. not really sure why a 9 tw would have so little freebore as i would think the twist is to shoot heavier, and longer, bullets. not sure crimping will improve accuracy in this factory gun but this is an ongoing experiment.

 

[amlevin]

Interior Ballistics would suggest that a crimped round would have a higher 'pressure to start' This might allow for a change in velocity as well.

Richard Lee covered this in his "2nd Edition" showing that the crimped ammo he submitted for testing showed increased pressure. The amount for the tested ammo was low, only a couple hundred psi.

For me, rather than crimping and damaging the bullet, I'd rather just use a larger bushing and increase neck tension.

Other than removing any flare in a straight walled case, pushing the case mouth back against the bullet, I don't crimp. Even with a cannelure on my "AR food" I don't crimp.


This is another one of those questions that will never produce unanimity in the answers.

 

[4xforfun]

If you are truly trying to reload for accuracy , then crimping will do nothing but deforming the bullet you wish to be consistent. You can figure out what your neck tension you have by measuring , then measure your bullets pressure ring if it has one or the bearing surface. Then measure the inside of the neck and subtract the neck diameter from the bullet and you should end up with .003 to .004 thou neck tension which is more than adequate.




Measure the neck ID for clarity. What cartridge and gun are we talking about?

You are forgetting one critical element here. The thickness of the brass. I have a .264 calaber that has a loaded measurment of 298 (.301 neck, wall thickness of .017) and another that measures .289 (.292 neck .0125 neck thickness). If I use .003 smaller bushing on each than the loaded measurment on both, do I have the same same "neck tension"?

How about my 300 wby tubes. I have .338 loaded rounds , .332 loaded rounds, and .328 loaded rounds (.340, .334 , .330 chambers). If I use a .003 smaller bushing than the loaded rounds do I then have the same "neck tension"?

 

[mac86951]

Interior Ballistics would suggest that a crimped round would have a higher 'pressure to start' This might allow for a change in velocity as well.

Richard Lee covered this in his "2nd Edition" showing that the crimped ammo he submitted for testing showed increased pressure. The amount for the tested ammo was low, only a couple hundred psi.

For me, rather than crimping and damaging the bullet, I'd rather just use a larger bushing and increase neck tension.

Other than removing any flare in a straight walled case, pushing the case mouth back against the bullet, I don't crimp. Even with a cannelure on my "AR food" I don't crimp.


This is another one of those questions that will never produce unanimity in the answers.

Thanks for the reference, I'll check that out.

I mentioned a possible velocity change in a half-brained manner, It hit me after I submitted it. We have a local AR guy who really enjoys short barrel 1:7 twists, and wants to shoot at 600y with us 24" barrel guys. Absolutely doable but wind is hard enough for us, that with the 16" barrel some careful reloading is in order. He found a good powder selection to achieve 2650fps consistently he claims, and in that case I think crimping could only help velocity in the shorter barrel. As you say its only a few hundred psi, so mostly negligible, but might be 2660 instead of 2650. Blah blah, excuse me for ranting, but its piqued my interest enough for more research. Again, thanks for the reference!

-Mac

I do crimp for my 55gr .223 remington loads in my carbine (6.5lb rifle). I'm using slop brass and cheap dies, but with neck tension at 0.002-0.003" my starting load will be 2.210" and if I measure the last unfired round out of the 30-round mag it'll be 2.260 (hmm that also happens to be the max allowable in my AR magazine). Still shoots, but doesn't stay put.

I won't crimp any bullet that does not have a cannelure.

Cheap AR food, fun plinking and no worries. Accurate? uhm, not by my definition.

 

[amlevin]

I won't crimp any bullet that does not have a cannelure.

Cheap AR food, fun plinking and no worries. Accurate? uhm, not by my definition.

Try some Hornady 55 gr A-Max bullets with a light crimp. Work fine in an AR and are far more accurate than the FMJ-BT's. Don't cost a fortune either.

 

[2506]

I did some extensive testing of crimped verses non crimped using the Lee Factory Crimp Die in a number of different old military rifles. Most of these rifles have throats that are a mile long. My finding was that the use of the crimp die DID increase the accuracy in most of these rifles. The only one I could tell no difference in accuracy was in 5 different M-96 Swede 6.5x55 Mausers. At the time I was shooting matches with these old STOCK military rifles we called old mans military rifle matches because most could not get down into those positions. We shot from a bench for score at 100 yards with 20 shot strings shooting 10 shots on two targets to facilitate easier scoring. There was some died in the wool bench rest shooters that used all their bench rest tricks in loading for their rifles and told me that if I used a Lee Crimp I was just wasting my time and I was ruining the bullets etc. I never did tell them what I was doing but I kept walking away from these matches with most of the best scores leaving them red faced and scratching their heads. ;D So for SOME situations crimping DOES increase accuracy.

 

[artbosco]

Can I gain accuracy by crimping the case neck, commonly found in factory ammo?
The theory would be that crimping adds consistency to the neck tension.

Crimping is not a substitute for neck tension which is applied with a F/L Bushing Die. Various size Bushings apply different amounts of neck tension for fine tuning a load. Crimping is not associated with accuracy, only for keeping a bullet in place.