5.56 Neck Tension / Setback Question - Barnes 55gr TSX

[SmokyJoe]

I've been working on a new load for a 5.56 semi-auto and have come across a possible neck tension / setback issue. With my other loads (308 / 45 / 223) I have typically tested for sufficient neck tension by pressing against the side of the bench. Not really a lab test, but until now, all have held tight.

After seating the Barnes 55gr TSX without a taper crimp, I was able to press the bullet back into the case with ~15lb of force. After adding a taper crimp, I could still set it back although with ~20 to 25lb of force.

Details:
COAL: 2.218"
Once fired LC brass, full length sized. Case trimmed and chamfered to 1.75"
Neck tension: .002" to .003". Inside of neck was cleaned to remove sizing lube
Taper crimp with Redding taper crimp die (you can see the limits of this in the photo)

When I push on it and the bullet sets back, the reduced COAL is 2.15". The taper crimp prevents further setback as it engages the edge of the groove. I should also note this is with an empty case, ie, no powder.

Does anyone have experience with similar tension / setback issues with the Barnes TSX and/or suggestions?
Is ~20 lb resistance relatively OK, or should I be trying for the M193 milspec of 35 lb?

Thanks in advance for any guidance.

JD

 

[KUSA]

Have you considered a Lee factory crimp?

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[SmokyJoe]

KUSA, thanks for the suggestion. I think the Redding taper crimp die I use is sufficient for crimping. I am going to try cycling rounds a few times to see if there is any setback induced by that.

JD

 

[KUSA]

The Lee factory crimp is different. You can squeeze the shit out of the neck if you want to. Just depends on how much tension you want.

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[pawprint2]

I'm looking at your photos, my old eyes may not be seeing what your trying to show us, are you saying the round on the right is 6/100s of an inch shorter than the one on the left? It looks a little like it has moved a "snug" more than 6/100th of an inch. In any case, bullets moving around can and do cause catastrophic problems. Google: Damaged guns do to bullet set back, you'll be shocked. IMHO KUSA's has given you very good advice, Lee factory crimp die, will give you a crimp, like no other. In any case always be as safe as you can! Good luck.

 

[SmokyJoe]

Thanks for the thoughts and recommendations. The differential is .068". The Lee Crimp die would be better, but my sense is that a crimp for this round may be more beneficial if it were in a groove as opposed to where I have it now. If I squeeze the shit out of it in a location outside of the groove, the bullet may deform and I'd rather not get into that if possible.

I am going to revise my plans and set this up at 2.19 COAL, with a taper crimp that goes into the groove. This length is per Barnes recommendation with a case trim length of 1.75". If my Redding taper crimper does not keep it in place at this OAL, I'll give the Lee FCD a try.

I am presuming that this issue is related to the fact that the TSX grooves decrease the amount of surface area in contact with the case, thereby decreasing the amount of force required to move the bullet.