bullet creep forward on chambering in 300 BLK AR

[Bgd]

I know this topic has come up on numerous occasions. I thought I had this problem solved by using converted LC brass. Today I tried loading 150 grain Speer GD bullets and they are moving forward in the case .1 each time they are chambered. This was in converted LC brass that I have not had a problem with before. it is not compressed charge and I tried a light crimp.

I may need to just stick to bullets like the cannelured 115 Lehigh CC that you can crimp the crap out of.

Has anyone found a solution to this problem?

Thanks

[Bgd]

I just had an idea that maybe I got some case lube inside the neck. I am going to clean the cases in the sonic cleaner and try again monday.

[plant.one]

define "light crimp"

[rebel]

Carbon build up in your neck can be your friend. Try not cleaning a few, 0000 steel wool the outside of the necks and load them for a test.

[Bgd]

define "light crimp"

Just enough to put pressure on the bullet but not enough to dent the bullet since it has no cannelure.

[Bgd]

Carbon build up in your neck can be your friend. Try not cleaning a few, 0000 steel wool the outside of the necks and load them for a test.

dang i cleaned them all.

[plant.one]

define "light crimp"

Just enough to put pressure on the bullet but not enough to dent the bullet since it has no cannelure.

ok couple more questions if you dont mind


how far from contact did you screw the FCD in for your crimp? 1/8th turn? 1/4?

are you using same headstamp brass or mixed?

how many times has this brass been fired?

are you belling the case mouth before seating (either via a universal expander, a M die, or a powder through die?)





additionally lets take a couple actual measurements and see what exactly you're working with.

i would suggest the following

measure the ID and OD of the case mouth prior to seating
measure the case wall thickness in the neck
measure the OD of the neck at the case mouth - or as close as you can get - after seating but before crimping
measure the OD of the neck at the case mouth - or as close as you can get - after crimping


the more info you can provide the better chance that someone will be able to help you.

[Bgd]

define "light crimp"

Just enough to put pressure on the bullet but not enough to dent the bullet since it has no cannelure.

ok couple more questions if you dont mind


how far from contact did you screw the FCD in for your crimp? 1/8th turn? 1/4? 1/8th with a RCBS TC die

are you using same headstamp brass or mixed? LC

how many times has this brass been fired? converted 223 second firing after conversion.

are you belling the case mouth before seating (either via a universal expander, a M die, or a powder through die?) no belling





additionally lets take a couple actual measurements and see what exactly you're working with.

i would suggest the following

measure the ID and OD of the case mouth prior to seating ID .301 OD .324
measure the case wall thickness in the neck .11
measure the OD of the neck at the case mouth - or as close as you can get - after seating but before crimping .331
measure the OD of the neck at the case mouth - or as close as you can get - after crimping .330


the more info you can provide the better chance that someone will be able to help you.

[plant.one]

other than your pre-seating neck ID being a bit tight - i think most folks are looking for -0.003 to -0.004 under bullet dia and you're at -0.007 - your numbers seem about right.

i wonder if seating a bullet into a neck that small is actually forcing the bullet to act as a neck expander mandrill and losing any grip you might have gained with a properly sized neck ID.

or if you're possibly getting some kind of bullet/jacket deformation seating into a neck that tight that hasnt been annealed - have you pulled a bullet after seating to check both pre and post crimp? might be worth a look to know for sure.



i'm not familiar with the RCBS TC die... but from a quick google it appears to be a seating AND crimp die combo... is that accurate?

most of us are using a LEE FCD to taper crimp.

i dunno how much a difference it will make, but i recall plenty of times in the past (not necessarily with the RCBS die you're using) that taking the seating and crimping step into two different processes often can be the catalyst for success.

[Bgd]

other than your pre-seating neck ID being a bit tight - i think most folks are looking for -0.003 to -0.004 under bullet dia and you're at -0.007 - your numbers seem about right.

i wonder if seating a bullet into a neck that small is actually forcing the bullet to act as a neck expander mandrill and losing any grip you might have gained with a properly sized neck ID.

or if you're possibly getting some kind of bullet/jacket deformation seating into a neck that tight that hasnt been annealed - have you pulled a bullet after seating to check both pre and post crimp? might be worth a look to know for sure.



i'm not familiar with the RCBS TC die... but from a quick google it appears to be a seating AND crimp die combo... is that accurate?

most of us are using a LEE FCD to taper crimp.

i dunno how much a difference it will make, but i recall plenty of times in the past (not necessarily with the RCBS die you're using) that taking the seating and crimping step into two different processes often can be the catalyst for success.

When I first started loading blackout I ran into this problem so I sanded one of my expander buttons down to see if it would solve the problem. I was using the expander that I sanded. I swapped out the expander for one that measures .305. I loaded a round and it only moved .0005 out, the second time I chambered it moved an additional .0004. without being crimped. big improvement. I can probably live with that. I will load a few more and make sure this round is not just a fluke. The things i changed were cleaning the cases, used the expander button that measured .305, I also cleaned the inside of the neck with alcohol and let them sit overnight.

I had this problem when i first started loading blackout and the problem went away when i switched from FC cases to converted LC cases. I was surprised to see it show up again. just goes to show we should never stop checking our rounds.

I have a LEE FCD die and i love it for putting a full crimp on my 30/30, 45/70 rounds, and blackouts that have a cannelure. i have trouble putting a light crimp on with it.

Thanks for your suggestions everyone. Any other pointers are welcome!!