.380 case neck tension

stephensackro · December 17, 2018, 01:53 PM

While loading some .380 ACP FMJ bullets, it always seems that the bullets go in the case too easily. There is just not much of the bullet that goes inside the case and I know it is the neck tension that actually holds the bullet firmly in. Also, I believe that the case thickness for .380 is relatively thin. If my bullets measure .355 OD and the inside of the expanded case (not belled out) measure .352 ID, That leaves only .003 " (actually .00015 on each side) to provide for the tight fit. What would the recommended fit be? I do have a metal lathe so I could take a thousands or two off of the case expander if need be.

My Kahr CW 380 barrel slugs out at .353 ID. Seems a little undersize to me? Are .355" OD FMJ bullets safe to shoot in this barrel? Typically shouldn't the FMJ bullet be the same size as the bore or maybe .001 over at most?

jag2 · December 17, 2018, 02:38 PM

This may be over simpliying it but put your calipers away and start tinkering with your die. Back to basics. Flare your brass enough to easily insert your bullet, adjust your seating die to crimp the bullet enough so you can’t push it in. I usually do that with a little thumb pressure, you will learn how much thru trial and error. Just use some of your unprimed brass (and of course no powder) and go at it. It sounds like you are over flaring so start there.

stephensackro · December 17, 2018, 05:19 PM

I always try to flare the absolute smallest amount that I can, just so the bullet will barely sit on the case. Just not much of the bullet in the case on this small cartridge.

jag2 · December 17, 2018, 06:28 PM

But your first line says the bullet goes in too easy. Even with over flaring that should be resolved with a proper crimp.
I know your problem, I've loaded .30 Mauser which is a bottleneck round and a nightmare to get right.
What bullet are you loading? I've used a 100 grn. plated (Ranier), it is .465 long. What is your OAL, could you make it shorter? Its been years since I loaded 380 but I don't remember any problems with that bullet. Always hard to diagnose others problems but I guess keep working with the crimp, that's the obvious next step.

stephensackro · December 18, 2018, 07:46 AM

I load 45 acp, .357, 9mm and others and for me .380 seems to be the hardest to get right. I think proper neck tension is what actually is supposed to hold the bullet in. I am loading Magtech 95 gr (.354) FMJ bullets with a overall length of .966. They seem to shoot fine so maybe this isn't an issue but I do like to experiment and get it right. That's half the fun for me. I think I'll try using some .355 FMJ bullets and see if I can notice a difference. My Kahr CW380 slugs out at .353 ( a little small? ) so I hope the larger dia bullet will be safe?

Lexspeed · December 18, 2018, 10:00 AM

Steve, I shoot a lot of 380acp with a variety of my vintage and new auto loaders (i.e. Sig p238, Femaru M37, Beretta M1934, etc). I've used Berry's 380 RN .356 without any issues such as you have experienced. I am a novice reloader but so far Berry's has worked for me.

kmw1954 · December 18, 2018, 12:17 PM

Stephen I also load 380 acp using a Lee Turret press with Lee 3 die pistol dies, Xtreme 100gr plated bullets and a mishmash of assorted brass. I shoot these in a Witness Pavona and a S&W 380EZ. I have not experienced any problems so far with reliability or accuracy.

If you Kahr shoots factory ammo then I wouldn't worry about the diameter of your hand loads.

TailGator · December 18, 2018, 12:27 PM

Are you having any functional problems? Can you move the bullet after the round is finished?

buck460XVR · December 18, 2018, 07:15 PM

Are you using Lee dies? I had issues with poor neck tension using Lee dies with .380 and when I contacted Lee, they admitted to having a problem with their standard sizing die and recommended I buy their .380 "U"(undersized die). I did since I didn't trust the regular sizing die to produce safe ammo. It cost me as much as the whole 4 die set. It does give me the proper neck tension tho......

dgang · December 19, 2018, 01:19 AM

I too had problems with .380's using Lee dies with both JHP and plated bullets. Had to resort to a very firm crimp to hold the bullet at .970", not possible with plated bullets. Upgraded to a Dillon RL500 and have not had a problem since. Now loading 100gr. X-treme bullets (plated) and using a very light taper crimp. Cannot move the bullet even with heavy thumb pressure. X-treme bullets measure out to .355" Might be your forming die?

stephensackro · December 20, 2018, 03:59 PM

I have been using RCBS dies but I think I might switch to the Lee undersize die. That should give me more neck tension. With the RCBS die's it almost seems that the expander die is loose and doesn't even expand the case very much at all. Maybe my RCBS sizing die is out of spec?

dgang · December 20, 2018, 09:52 PM

Sounds like you've nailed it. Neck tension and sizing the most important part, crimp not so much unless you are using a roll crimp on a revolver cartridge. On my .380s a very slight bulge shows on the case where the bullet is seated.

December 17, 2018, 01:53 PM	#1
stephensackro Member Join Date: January 4, 2015 Posts: 25	.380 case neck tension While loading some .380 ACP FMJ bullets, it always seems that the bullets go in the case too easily. There is just not much of the bullet that goes inside the case and I know it is the neck tension that actually holds the bullet firmly in. Also, I believe that the case thickness for .380 is relatively thin. If my bullets measure .355 OD and the inside of the expanded case (not belled out) measure .352 ID, That leaves only .003 " (actually .00015 on each side) to provide for the tight fit. What would the recommended fit be? I do have a metal lathe so I could take a thousands or two off of the case expander if need be. My Kahr CW 380 barrel slugs out at .353 ID. Seems a little undersize to me? Are .355" OD FMJ bullets safe to shoot in this barrel? Typically shouldn't the FMJ bullet be the same size as the bore or maybe .001 over at most?

December 17, 2018, 05:19 PM	#3
stephensackro Member Join Date: January 4, 2015 Posts: 25	.380 neck tension I always try to flare the absolute smallest amount that I can, just so the bullet will barely sit on the case. Just not much of the bullet in the case on this small cartridge.

December 18, 2018, 07:46 AM	#5
stephensackro Member Join Date: January 4, 2015 Posts: 25	.380 Neck tension I load 45 acp, .357, 9mm and others and for me .380 seems to be the hardest to get right. I think proper neck tension is what actually is supposed to hold the bullet in. I am loading Magtech 95 gr (.354) FMJ bullets with a overall length of .966. They seem to shoot fine so maybe this isn't an issue but I do like to experiment and get it right. That's half the fun for me. I think I'll try using some .355 FMJ bullets and see if I can notice a difference. My Kahr CW380 slugs out at .353 ( a little small? ) so I hope the larger dia bullet will be safe?

December 19, 2018, 01:19 AM	#10
dgang Senior Member Join Date: April 14, 2000 Location: Colorado Posts: 204	I too had problems with .380's using Lee dies with both JHP and plated bullets. Had to resort to a very firm crimp to hold the bullet at .970", not possible with plated bullets. Upgraded to a Dillon RL500 and have not had a problem since. Now loading 100gr. X-treme bullets (plated) and using a very light taper crimp. Cannot move the bullet even with heavy thumb pressure. X-treme bullets measure out to .355" Might be your forming die? __________________ I shoot, therefore I am.

December 20, 2018, 03:59 PM	#11
stephensackro Member Join Date: January 4, 2015 Posts: 25	.380 neck tension I have been using RCBS dies but I think I might switch to the Lee undersize die. That should give me more neck tension. With the RCBS die's it almost seems that the expander die is loose and doesn't even expand the case very much at all. Maybe my RCBS sizing die is out of spec?

December 17, 2018, 02:38 PM	#2
jag2 Senior Member Join Date: June 30, 2009 Location: dallas Posts: 773	This may be over simpliying it but put your calipers away and start tinkering with your die. Back to basics. Flare your brass enough to easily insert your bullet, adjust your seating die to crimp the bullet enough so you can’t push it in. I usually do that with a little thumb pressure, you will learn how much thru trial and error. Just use some of your unprimed brass (and of course no powder) and go at it. It sounds like you are over flaring so start there.

December 17, 2018, 06:28 PM	#4
jag2 Senior Member Join Date: June 30, 2009 Location: dallas Posts: 773	But your first line says the bullet goes in too easy. Even with over flaring that should be resolved with a proper crimp. I know your problem, I've loaded .30 Mauser which is a bottleneck round and a nightmare to get right. What bullet are you loading? I've used a 100 grn. plated (Ranier), it is .465 long. What is your OAL, could you make it shorter? Its been years since I loaded 380 but I don't remember any problems with that bullet. Always hard to diagnose others problems but I guess keep working with the crimp, that's the obvious next step.

December 18, 2018, 10:00 AM	#6
Lexspeed Senior Member Join Date: November 18, 2015 Location: Southern IL Posts: 152	Steve, I shoot a lot of 380acp with a variety of my vintage and new auto loaders (i.e. Sig p238, Femaru M37, Beretta M1934, etc). I've used Berry's 380 RN .356 without any issues such as you have experienced. I am a novice reloader but so far Berry's has worked for me.

December 18, 2018, 12:17 PM	#7
kmw1954 Senior Member Join Date: June 11, 2016 Location: SE Wisconsin Posts: 1,524	Stephen I also load 380 acp using a Lee Turret press with Lee 3 die pistol dies, Xtreme 100gr plated bullets and a mishmash of assorted brass. I shoot these in a Witness Pavona and a S&W 380EZ. I have not experienced any problems so far with reliability or accuracy. If you Kahr shoots factory ammo then I wouldn't worry about the diameter of your hand loads.

December 18, 2018, 12:27 PM	#8
TailGator Senior Member Join Date: May 8, 2009 Location: Florida Posts: 3,787	Are you having any functional problems? Can you move the bullet after the round is finished?

December 18, 2018, 07:15 PM	#9
buck460XVR Senior Member Join Date: December 28, 2006 Posts: 4,342	Are you using Lee dies? I had issues with poor neck tension using Lee dies with .380 and when I contacted Lee, they admitted to having a problem with their standard sizing die and recommended I buy their .380 "U"(undersized die). I did since I didn't trust the regular sizing die to produce safe ammo. It cost me as much as the whole 4 die set. It does give me the proper neck tension tho......

December 20, 2018, 09:52 PM	#12
dgang Senior Member Join Date: April 14, 2000 Location: Colorado Posts: 204	Sounds like you've nailed it. Neck tension and sizing the most important part, crimp not so much unless you are using a roll crimp on a revolver cartridge. On my .380s a very slight bulge shows on the case where the bullet is seated. __________________ I shoot, therefore I am.