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69gr SMK good for AR15 semi not bolt?

Biff2

Private
Minuteman
Mar 31, 2017
31
2
I know are some old threads on crimping but after doing some tesing with new starline brass and two different brands of 69gr 223 bullets I think having that crimp ring that the 55gr have is best.

I have two Newer Colt 6920s ARs that I tested with.
I have new starline brass that I only did a light camfer to each case mouth.

I load up a few rounds (no power or primers) And cycled them.
The violent slamming shut of the BCG acts like a kinectic hammer.
The rounds did move after I carfully extract them
And they can move both ways
- Sometimes the round became longer from 2.252 to 2.259 (kinetic hammer effect)
- Sometimes the round became shorter from 2.252 to 2.230 (This is due to when the bullet hits the feed ramp)
They might be moving both ways a little. 1. When the bullet hits the feed ram it moves in some, then when it suddenly stops it moves the bullet out. So the net result can be +- in length

I did a light crimp and found while less they still moved.

BTW the 55Gr Hornday FMJ with the tamper crimp ring on the bullet never moved in my tests.

So not sure I want to trust these rounds in semi auto. They would be find for bolt 223 or if I gently one at a time feed into the my AR. But how can I trust my load development on these two ARs if the bullets are moving?

I know some people say "I never crimp not in 40 years" but have they actually tested the ammo if it moves or not? If they are just shooting for fun they might not ever know why their groups or fps go up and down. 2 MOA is good enough so its possible in 40 years they had a issue that never was noticed.

I have like 80 69gr loaded to test none of them have been crimped. I did this testing after originally seeing how much the feed ramps scratched up the bullets then found some moved.

I shot some using range brass a few months back and was not impressed with the accuracy of the 69gr. So ordered the new starline to see if it would improve groups.
I think they were 1.5-2.0 MOA using range brass. They were probably moving some too.

Im thinking 69gr with a crimp ring (Not sure if anyone makes these) might be best for AR 15 semis.
 
used the black hills blue box 69g in my jp ctr-02 with zero issues and nice accuracy. when they stopped making them, i started handloading with mixed brass and 69smks and also got nice accuracy and reliability. can't say how lightly or heavily crimped, but it's working for me.
 
used the black hills blue box 69g in my jp ctr-02 with zero issues and nice accuracy. when they stopped making them, i started handloading with mixed brass and 69smks and also got nice accuracy and reliability. can't say how lightly or heavily crimped, but it's working for me.
I guess I could run them all through the crimp die and just guess as to how much crimp I need.
Next time at the range maybe I can hand load the non crimped ones and compare to ones I crimped to see if there is any differance. I worry a little of bullet set back where it goes from 2.250" to 2.15" length. Probably would not hurt anything but give slightly higher pressure and velocity.
 
i'm just using a redding small base full length sizing die and then a rcbs matchmaster competition seating die. i started reloading back in late 2020 and perhaps just got lucky with the setup. no crimp die. but i agree you don't want set back esp if loaded hot, which mine aren't.
 
i'm just using a redding small base full length sizing die and then a rcbs matchmaster competition seating die. i started reloading back in late 2020 and perhaps just got lucky with the setup. no crimp die. but i agree you don't want set back esp if loaded hot, which mine aren't.
I think I figured out some of the issue on setback

Its the feed ramp on my newer LE 6920. It has a sharp edge someplace because it leaves a long scratch on the bullets. This is not an issue with typical NATA 5.56 ammo 55gr they have bullets with a canicular they don't budge.
Feed ramps can have burrs that are so severe the cause failure the feed because the friction of the burr is more than the action/buffer can overcome so it just stops with a round 1/2 way in.
I don't have those issues but to produce a full length scratch on the bullet it will produce more friction that say a feed ram that was polished smooth no sharp edges.
While its true my rounds do grow in lenght from 2.252 to 2.258" The setbacks when they occur are more severe from 2.252" to 2.20" I tested my 55gr bullets and they do not move.

At least with new starline brass the 69gr smooth projectiles from Sierra and RMR bullets will have a tendancy to move some, either with kinetic hammer effect or worse feed ramp sharpness causing some set back

I think if I can smooth out the feed ramp so it does not scratch the ammo it will fix set back. Wonder if that is a warranty issue?
 
Regardless of brass mfg, the amount of neck tension you’re realizing with specific bullet diameters can definitely affect setback or length variation. If mixed brass, almost certainly. Annealing can mitigate the issue, but still need to sort brass by mfg to assure a consistent process. If not annealed, at min bring number of variables in check by segregating headstamp. Bushing dies are a definite option as a preferred workaround, and potentially eliminate need to crimp.
 
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This is what I'm dealing with, one of my three LE 6920 seems to scratch up the rounds a bit more. It feeds fine just mars up the bullets and seems to set back some of the non canicular 69gr bullets. The 55gr bullets don't move at all but they have a canicular crimp ring.

colt feed ramp LE 6930.png
 
This is what I'm dealing with, one of my three LE 6920 seems to scratch up the rounds a bit more. It feeds fine just mars up the bullets and seems to set back some of the non canicular 69gr bullets. The 55gr bullets don't move at all but they have a canicular crimp ring.

View attachment 7905525
I know your asking about loading. But the link I'm gonna add will have some info in what to do, to smooth out the ramps to not gouge your projectiles like that.

 
Fake news.
The 69 SMK is great in semi autos. Maybe even the best.
 
Fake news.
The 69 SMK is great in semi autos. Maybe even the best.
Ditto , 69 SMK are legendary in the AR/Semi auto platform . They have won a lot of competitions , in bolt guns also .
 
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