To Crimp Or Not To Crimp, That Is The Question?

[Shooter375]

To crimp or not to crimp, that is the question? I tried a little experiment to examine the effects on accuracy of crimping. I shot six identical rounds with one exception. The exception being that three were crimped with a Lee Factory Crimp die and three that were left uncrimped. These are the results.

There is a significant difference in accuracy.
1.274 MOA (crimped) vs. 0.557 MOA (uncrimped)
Other differences include a decrease in velocity for the uncrimped rounds. 2480 fps (crimped) vs. 2448 fps (uncrimped).

Uncrimped

Crimped

Uncrimped

Crimped

Fired from my Kimber Caprivi in 375 H&H.
I think, based upon these results, I will use an uncrimped round for the first round and fill the magazine with crimped rounds which will hold up better under recoil. Is a 1/2 inch of accuracy worth it? What do you guys think?

 

[deewayne2003]

Try backing off the crimp some, I use LFCD for almost all my rifle ammo and I’ve never seen a decrease in accuracy.

Remember the petals of the Lee FCD don’t have to close all the way to get a good crimp.

 

[PHOENIX PHIL]

I wonder if you don't need to tweak the load for crimped cartridges. Maybe bump the load down in 0.1 or 0.2 grain increments to match the uncrimped velocity. Worth a try.

 

[Alistair]

With respect, and I hate to be that guy, but your experiment is not able to make any claims about comparative accuracy and especially isn't able to claim 'significant' differences either way. As a guy with a decent working knowledge of experimental design and statistics it physically pains me when people make statements like this.

All you can conclude from this test, is that the rifle is more or less zeroed with either ammo type and that crimping probably yields a significant velocity difference. That's it.

Three rounds of each is not nearly enough of a data set to draw conclusions on relative accuracy even if it were done under controlled conditions from a machine rest, which I'm betting it wasn't, and is nowhere near enough to claim that any difference that you saw is 'significant'.

That being the case, I'd crimp the lot. At least all the rounds will be the same, you won't have to try and remember crimped and not crimped in the field, and you're less likely to have bullets moving in the magazine and cocking up feeding, which is far more important. More energy too, which won't do any harm.

 

[ARHinAK]

I’d crimp them but I’d back it off a little bit.

 

[TucsonFX4]

Thanks for sharing your results. Data is data. Though, I agree with @Alistair.

If you want to crimp, build up a load where you are crimping. Don’t build a load uncrimped and then crimp and compare (which is what seemed to have been done). That’s ok, but just don’t look at it as black and white.

BTW, gorgeous rifle!

 

[Shooter375]

I developed the load crimping all the rounds since this is a 375 H&H which is used as a dangerous game rifle. I shot 1 and 1/2 to 2 inch groups at 100 yards with it. I am happy with that accuracy. I thought I would just see what not crimping would do. Interesting results. I also agree with Alistar who is correct in noting that only 3 rounds is not a statistically significant experiment.

 

[R eight]

Interesting. But I think that you’d really need to fire off a few more rounds to get an accurate picture of what is happening. A batch of just 3 rounds may give an indication but not a reliable/ accurate picture.

Maybe a test batch of at least 20 in each would give a better indication.

 

[Shooter375]

Interesting. But I think that you’d really need to fire off a few more rounds to get an accurate picture of what is happening. A batch of just 3 rounds may give an indication but not a reliable/ accurate picture.

Maybe a test batch of at least 20 in each would give a better indication.

Agreed! But those Swift A-Frames are expensive. Ha Ha! I will give it another try sometime in the future and post those results. I would be interested to see if others have similar results.

 

[Doug Hamilton]

To crimp or not to crimp, that is the question? I tried a little experiment to examine the effects on accuracy of crimping. I shot six identical rounds with one exception. The exception being that three were crimped with a Lee Factory Crimp die and three that were left uncrimped. These are the results.

View attachment 572526View attachment 572527There is a significant difference in accuracy.
1.274 MOA (crimped) vs. 0.557 MOA (uncrimped)
Other differences include a decrease in velocity for the uncrimped rounds. 2480 fps (crimped) vs. 2448 fps (uncrimped).
View attachment 572532
Uncrimped
View attachment 572533
Crimped View attachment 572534Uncrimped
View attachment 572535
Crimped View attachment 572536Fired from my Kimber Caprivi in 375 H&H.
I think, based upon these results, I will use an uncrimped round for the first round and fill the magazine with crimped rounds which will hold up better under recoil. Is a 1/2 inch of accuracy worth it? What do you guys think?

On my first safari I did not reload. My .458 WM is a vicious kicker and there seemed to be some forward movement of the bullets in the factory loads. I took up reloading and determined that I could do better than factory loads. So before going back to Africa I worked up some stout 500 grain loads. I crimped every round. The accuracy is very good and I don't have any bullets moving around to make cycling the bolt difficult. On my next trip I fired a grand total of one round at a buffalo bull. He went about 25 yards and piled up dead, so it really didn't matter whether I had crimped the loads or not.
The first bull I killed required several shots to.put down and I would have felt better about not having the last shell in the magazine being hard to cycle through because the bullet had moved. When I wasn't having to shoot I was topping off the magazine so it was only the last round that stuck, but why do that?
As a side note, I also had some movement in 300 grain bullets in my .44 mag revolver, so I always crimp those as well.
Bottom line, I would always crimp any heavy bullets in hard recoil firearms.

 

[Alistair]

I developed the load crimping all the rounds since this is 375 H&H which is used as a dangerous game rifle. I shot 1 and 1/2 to 2 inch groups at 100 yards with it. I am happy with that accuracy. I thought I would just see what not crimping would do. Interesting results. I also agree with Alistar who is correct in noting that only 3 rounds is not a statistically significant experiment.

I would say that 1.5-2" is more than good enough for your use case and thanks for being a good sport about my post. No offence intended and sorry if it came off a bit snarky, just a personal bug bear of mine!

You've actually inspired me to do a thread in the reloading forum on this topic, so thanks for that. I'll tag you and I'd be interested in your critique!

 

[Safari Dave]

Back off a little on the crimp and you will be fine.

 

[fourfive8]

On my first safari I did not reload. My .458 WM is a vicious kicker and there seemed to be some forward movement of the bullets in the factory loads. I took up reloading and determined that I could do better than factory loads. So before going back to Africa I worked up some stout 500 grain loads. I crimped every round. The accuracy is very good and I don't have any bullets moving around to make cycling the bolt difficult. On my next trip I fired a grand total of one round at a buffalo bull. He went about 25 yards and piled up dead, so it really didn't matter whether I had crimped the loads or not.
The first bull I killed required several shots to.put down and I would have felt better about not having the last shell in the magazine being hard to cycle through because the bullet had moved. When I wasn't having to shoot I was topping off the magazine so it was only the last round that stuck, but why do that?
As a side note, I also had some movement in 300 grain bullets in my .44 mag revolver, so I always crimp those as well.
Bottom line, I would always crimp any heavy bullets in hard recoil firearms.

Actually in guns, actions like doubles and revolvers, recoil has the potential for "pulling" bullets of the unfired cartridge(s) out of the case. Actions with stacked and tube magazines have the potential for "pushing" bullets of unfired cartridges back into the case. Correctly crimping some semi-auto cartridges is especially tricky and specific. Paying attention to that difference is a critical safety concern. For most other cartridges, roll crimping during the bullet seating process is also tricky and many times reloaders mess up the process, paying little attention to the detailed specs and mechanics involved. Using the roll crimp shoulder incorrectly in the bullet seating die many times actually decreases tension or causes variable neck tension round to round. There is no reason not to crimp most cartridges but it has to be done correctly. Certain semi-autos that headspace on the case mouth's rim require a specific taper crimp and die. For most other applications, the Lee Factory Crimp Die (FCD) is by far the best method. For the process, simply turn out the bullet seeing die body a couple of turns and re-lock the set ring to avoid using the internal roll crimp shoulder during the bullet seeing process. Then re-set the bullet seating stem for proper seating depth. The Lee FCD is used in the last step of the reloading process. Also, keep cases trimmed to consistent and correct length for any crimping process and to also prevent the dangerous condition of "crimping" the case mouth rim into the bullet at the chamber leade during chambering. That condition can create extremely high pressure during firing.

 

[B0MBOY]

Generally I thought it was known that for superior accuracy you don’t crimp your bullets. Most long range shooters i know don’t crimp their bullets.

But crimping is necessary if you’re concerned about recoil moving the bullets in the cases under recoil. I crimp the snot out of my 45-70, 44 magnum, and 375 h&h handloads for that reason.

 

[CoElkHunter]

Very interesting and informative thread. So far, I've only loaded .458WM and .416 Taylor big bore cartridges. I tapered crimped them and used moderate loads with 450gr Barnes and 350gr.Speers in the WM and 400gr Barnes Originals (no cannelure) in the .416. I haven't noticed any movement of the bullets in the cases yet, but maybe I SHOULD roll crimp them? For a novice big bore reloader like me, the bullets just seem so long and heavy that my perception is that it would take a lot of recoil to move them in the case when taper crimped? I'm probably naive but that's been my limited experience to date.

 

[fourfive8]

Very interesting and informative thread. So far, I've only loaded .458WM and .416 Taylor big bore cartridges. I tapered crimped them and used moderate loads with 450gr Barnes and 350gr.Speers in the WM and 400gr Barnes Originals (no cannelure) in the .416. I haven't noticed any movement of the bullets in the cases yet, but maybe I SHOULD roll crimp them? For a novice big bore reloader like me, the bullets just seem so long and heavy that my perception is that it would take a lot of recoil to move them in the case when taper crimped? I'm probably naive but that's been my limited experience to date.

The potential problems with roll crimping are many. The roll crimping shoulder in most bullet seating dies pushes down the axis of the wall of the case neck while at the same time attempting to swage the rim (mouth) inward. A common outcome is that while the roll crimp may form and yield a crimp with satisfactory appearance, the case walls of the neck are slightly and variably wrinkled thus lessening neck tension. Using this method , it’s nearly impossible to end up with consistent neck tension and consistent results.

By contrast the Lee Factory Crimp Die imparts no force down the axis of the case wall. A fingered collet simply squeezes the neck rim (mouth) inward to form the crimp at the desired location on the bullet’s shank as determined by the seating depth and seating operation already completed. The neck tension the sized case neck imparts on the shank of the bullet remains unchanged.

 

[Joker12]

I used to think that with a few exceptions crimping wasn't necessary. Then on my probably once in a lifetime hunting trip in S.A. I had a problem with bullets moving so much that I decided to finish the trip using my backup rifle. The ammo that was problematic was for my #1 Ruger 338wm using 250gr Noslers and it was from the rough ride of the vehicle. Some moved in and some moved out but the result was no longer reliable. My old reliable 30'06 was fine with no problems. Since then I have become a believer in crimping for reliability and the Lee FCD is a wonderful tool for that. If I'm range shooting or hunting deer very close to home its not always crimped but otherwise I crimp and particularly when using heavier bullets. Reliability is more important than fine tuned accuracy in hunting rifles and ammo.

 

[Nevada Mike]

i use the Lee FCD for most of my ammo reloading - from 25-'06 to 404J. Especially with the larger bores it seems to improve variance and allows much lower ES. In my 404J, for instance, I have seen ES in my hunting loads as low as 10 pfs over three shots. But I have not proven this by extensive testing of bullet pull, etc.

I did find that roll crimping with the seating die was not consistent or satisfying and sometimes got case necks that were slightly deformed and would not chamber in my rifles. I quit roll crimping my cartridges and use the Lee FCD exclusively. The Lee FCDs are very inexpensive and they work very well.

 

[fourfive8]

Three pics show sequence using a Lee FCD

 

[Doug Hamilton]

Actually in guns, actions like doubles and revolvers, recoil has the potential for "pulling" bullets of the unfired cartridge(s) out of the case. Actions with stacked and tube magazines have the potential for "pushing" bullets of unfired cartridges back into the case. Correctly crimping some semi-auto cartridges is especially tricky and specific. Paying attention to that difference is a critical safety concern. For most other cartridges, roll crimping during the bullet seating process is also tricky and many times reloaders mess up the process, paying little attention to the detailed specs and mechanics involved. Using the roll crimp shoulder incorrectly in the bullet seating die many times actually decreases tension or causes variable neck tension round to round. There is no reason not to crimp most cartridges but it has to be done correctly. Certain semi-autos that headspace on the case mouth's rim require a specific taper crimp and die. For most other applications, the Lee Factory Crimp Die (FCD) is by far the best method. For the process, simply turn out the bullet seeing die body a couple of turns and re-lock the set ring to avoid using the internal roll crimp shoulder during the bullet seeing process. Then re-set the bullet seating stem for proper seating depth. The Lee FCD is used in the last step of the reloading process. Also, keep cases trimmed to consistent and correct length for any crimping process and to also prevent the dangerous condition of "crimping" the case mouth rim into the bullet at the chamber leade during chambering. That condition can create extremely high pressure during firing.

You are right. I said that wrong. In the .458, the bullets appeared to "push in" flaring the case mouth, which made it stick on extraction.
In any event, I use the Lee FCD to crimp the the cases of heavy kickers. Bullets moving around in the case is never a good thing. I've never seen the problem, and don't crimp, on my 7mm's or 30 cal's.