This is 300 blk in a CMMG barrel powder coated blue bullets sized to 0.309.
This is at the end of the case neck and the beginning of the throat picture taken with a boroscope.
Could this be caused by excessive crimping or is there something else i should check? I use a taper crimp but i have a lee factory crimp die on order.
Last edited by almar; 01-30-2024 at 05:31 PM.
“It is not enough that we do our best; sometimes we must do what is required.”
― Winston S. Churchill
Not caused by crimp. If in front of case mouth, case too short. Else soft lead and high pressure load that expands before the bore and then gets shaved.
Whatever!
So, the gun won't chamber shells anymore, or won't cycle?
It cycles just fine which means that i could have excess clearance, Thanks ill check case length. These are low pressure subsonics with lead hardness that matches pressure rating at about 15-16ksi.
Last edited by almar; 01-30-2024 at 07:32 PM.
“It is not enough that we do our best; sometimes we must do what is required.”
― Winston S. Churchill
wow great pic. Just a curiosity question, were just looking and checking or were you seeing barrel leading and eventually found this?
It may be interesting to chamber an empty case just to see how short the brass looks in there, not that you could measure it though.
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Sinclair International/Brownells sells caliber-specific chamber length gauges that allow you to measure your chamber length and compare it to your brass length. They're only $5, but the .30 gauge is currently out of stock.
https://www.brownells.com/reloading/...?sku=749000804
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Thats a good idea. My cases are per spec. So maybe ill check with a case in it. I was aligning the gas block and i saw this.
“It is not enough that we do our best; sometimes we must do what is required.”
― Winston S. Churchill
i took more pictures after cleaning it out and after firing one round through it. This is with a sized case in it and you can see the slight clearance and more build up. my cases measure at 1.366 case spec is 1.368
“It is not enough that we do our best; sometimes we must do what is required.”
― Winston S. Churchill
It can also be caused by the case mouth step being too sharp. I run into this often with straight walled wildcats. If you can polish it slightly and break the edge it'll stop shaving the bullet. These solid copper bullets started obturating around 50Kpsi and leaving rings. A slight polish of the case mouth step stopped it and allowed the load to be increased without leaving any more rings.
How would did you polish it? Lead and lapping compound? I'm wondering if sizing down to bore would fix it.
“It is not enough that we do our best; sometimes we must do what is required.”
― Winston S. Churchill
Felt bob and red rougue to break the edge. The slightly rounded edge will allow the bullet to conform down in size v/s the edge trying to shave it. You might be able to use a fine neck sized ball hone running in in/out over the shoulder several times. It doesn't take much. I put a tight fitting patch/barbless jag in the bore to keep it from touching the leade.Originally Posted by almar
Last edited by Moleman-; 01-30-2024 at 10:11 PM.
That's why the bullet should not be larger than the throat diameter at the case mouth. Or the alloy is too soft for the load allowing it to swage into the clearance between the throat entrance and the case neck and then some getting shaved/scraped off the bullet as it is forced into the throat.
Larry Gibson
“Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
― Nikola Tesla
What about a little light judicious fire lapping? I have not seen a <$200 AR barrel that a little smoothing would hurt, shut the gas off and bang away.
Pour some acetone on a paper towel then take one of your bullets and rub it vigorously on the wet part of the paper towel for 30 seconds. If there is even the slightest hint of color transferring into the paper towel from the bullet then the bullet has failed this coating Integrity test.
Place a bullet on a metal plate and hammer it flat into a coin. Look for paint chips and failures. Now Hammer that coin into the cube and recheck for paint chips and failures. Metal fatigue or failure is normal the metal can crack with this test and that's okay. What you are looking for is paint failure and if there is even the slightest paint failure the bullet has failed this second coating integrity test.
Why? This torture test proves nothing and isn't his problem.
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I'm sorry you feel that way.
The torture test is to verify if the coating was done correctly. I am sure you already know that incorrectly done bullet coatings can cause barrel leading.
That's quite a test! I'm intrigued enough to try that on my own! Thank you for the suggestion.
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