Neck Dings

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Rick32
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Neck Dings

Post by Rick32 »

Greetings all, I'm new to the forum and to the 300. I bought a new PSA AR platform rifle W/ 18" barrel and from the factory and it was dinging the case necks during extraction (see pics) Sent it back and PSA put a new barrel on it, does the same thing. Note the last borescope pic, you can see where the brass is accumulating on the locking lugs at about 7:00. Pics are a mix of hyper and sub sonic handloads. Any help would be appreciated!

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rebel
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Re: Neck Dings

Post by rebel »

A 1/2 inch piece of self adhesive velcro on the ejection guard will fix this. Does the case mouth have kind of a d-shape to it looking down at the mouth?
Also what brand of brass is it? Those almost seem to be sharp feed ramp marks.
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ReadyAimDuck
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Re: Neck Dings

Post by ReadyAimDuck »

These look like marks from the feed ramps to me too. If you look at the dings on the brass and look at the feed ramps, do you see how the space between the marks on the brass appears to be the same size as the space between the edges of the feed ramps?
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dellet
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Re: Neck Dings

Post by dellet »

Neck hitting the backside of the locking lugs on the way out after firing.

You should be able to match the width of the marks to lugs. To polish that side you probably need to have the barrel off, or try an AR chamber brush and pull it back against the lugs. It will get better in time on its own with waar.
300 Blackout, not just for sub-sonics.
Rick32
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Re: Neck Dings

Post by Rick32 »

Thanks for the replies! I'll try the velcro trick, that would be cheap and easy. Note in the pix that the brass looks like (to me anyway) it's being pushed from the shoulder towards the neck, if this was happening during feeding I'd expect the opposite. I shucked some rounds thru the chamber, no dings. Next range trip I'll hand feed a dozen rounds to prove or disprove feed ramp damage. Pics 1 and 3 (in original post) are hyper sonic and #2 is sub, note the position of the dings in relation to the mouth, the slower moving bolt put the dings closer to the shoulder. Brass is once fired LC 556, cut to size, induction annealed, trimmed on a Dillon RT1500, sized, tumbled again W/O media, neck turned on a Forster and loaded on a Dillon XL750. I also bought some made for 300 Starline brass, no difference. I get a slight "D" on some of my sub rounds, none on hyper. Bought some factory Winchester sub rounds, in addition to shooting a 10" group, the case mouths were nothing short of mangled. The folks here are more helpful than PSA customer service who told me my handloads are the problem and I need a new buffer spring. Should I try snipping a coil off of the extractor spring?

Sub "D" neck
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Close up ding on Starline brass that was not neck turned

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ReadyAimDuck
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Re: Neck Dings

Post by ReadyAimDuck »

The "D" Shaped dent you are getting is the result of the case mouth hitting the brass deflector on the upper receiver after the case is ejected. That occurs on the 300AAC brass because the case is a shorter case than the .223/5.56 cartridge that the deflector on the receiver is designed for. So the mouth of the 300AAC case hits where otherwise the shoulder of the 5.56 case would hit. The mouth is more prone to denting as you are seeing. Thats not abnormal. Different loads are going to increase/decrease this effect, as will buffer/spring combos. Unless they are dramatically dented, it shouldnt be a problem for the sizing die to correct. I'll also mention that the D shape dent you have in the picture is minimal compared to many that I have seen, and I would not worry about that. Or, you can install the pad/velcro trick if you like.

The two scratches occur from the locking lugs, as dellet mentioned. I was incorrect when I stated it was the feed ramps. When the brass is being extracted it is catching the locking lugs and being scratched at the sharp edges. I also don't believe this is much of an issue and in my experience it will go away after enough rounds have kind of worn the sharp edges down a bit.
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dellet
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Re: Neck Dings

Post by dellet »

It’s not being pushed from the shoulder toward the neck, it’s being pulled.

The reason that it won’t do it with Feeding loaded rounds in and out is that the bullet is in contact with the chamber and holds the case neck off the backside of the locking lugs.

If you mark a neck with a sharpie, drop an empty case in the chamber and extract it, it will leave a mark. But you’re not likely to generate enough force by pulling on the charging handle to duplicate the marks.

You could also do a search for “fang” or “snake bite” and come up with a few threads. The reason it’s more promenade with Blackout than 223 is the shorter case length changing the geometry. What normally would be on the shoulder of a 223 is on the neck of a Blackout case.
300 Blackout, not just for sub-sonics.
Rick32
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Re: Neck Dings

Post by Rick32 »

Thanks dellet and all who responded! I already have velcro applied and I'm going to try the chamber brush/deburr trick, maybe a little lapping compound applied. I would think the gouges would be stress points on the neck which could cause cracks? I guess this should be posted in reloading.
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plant.one
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Re: Neck Dings

Post by plant.one »

you'll probably end up scraping your brass due to primer pockets getting loose before those fang marks will bite you with neck splits.
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