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Post by stevepodleski on May 3, 2019 11:54:05 GMT -8
Hi I have a 243LBC AR with a 40deg shoulder. I've read that BlackHole developed the 243LBC. I don't know who developed the 243LBC with the 40deg shoulder. I bought the rifle second hand. The bolt is a JP Grendel bolt. It had around 2200 rounds fired.
The load is 28.5gr. of Varget with a Nosler 105gr CC bullet loaded to 2.28 OAL that will fit the mags. The bullet seating is at least .020"of the lands or more. The barrel is 8twist 26" Krieger. The lug near the extractor failed.
Any help is appreciated as to why this lug failed?
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Post by GLSHOOTER on May 3, 2019 12:07:52 GMT -8
I think that's a Whitley deal. Call JP. Bolts break. That's a fact that often times has no rhyme nor reason.
Greg
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Post by stevepodleski on May 3, 2019 13:31:22 GMT -8
I have shipped the bolt to JP.
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Post by GLSHOOTER on May 3, 2019 14:55:09 GMT -8
I have shipped the bolt to JP. Is this a Grendel bolt or a 7.62X39 bolt? Greg
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Post by stevepodleski on May 3, 2019 15:39:41 GMT -8
It is a Grendel bolt.
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Post by GLSHOOTER on May 3, 2019 16:04:25 GMT -8
Then it not a 243 LBC. Maybe a 6MM TURBO IIC. The Grendel bolt gets lots of praise for its design but realistically it is weaker than the 7.62X39. Ask a REAL engineer and not some fool wit the back of and envelope pie in the sky idea. Two or three causes of breakage. Bil Alexander built a Grendel that broke bolt sin under 10 shots consistently for one guy. The upper was out of square on that one. In all the thousands of rounds we have shot with 7.62 bolts in all these variants we have never broken a bolt yet. Luck? YMMV Greg
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Post by stevepodleski on May 3, 2019 18:55:20 GMT -8
Yes, I should have said Grendel bolt failure. Don't know why is titled this thread: "243LBC Bolt Failure"!
Are you saying that a 7.62x39 bolt is stronger than a 6.5 Grendel bolt? Will it work with 6.5 Grendel case?
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Post by GLSHOOTER on May 3, 2019 19:35:08 GMT -8
Yes, I should have said Grendel bolt failure. Don't know why is titled this thread: "243LBC Bolt Failure"! Are you saying that a 7.62x39 bolt is stronger than a 6.5 Grendel bolt? Will it work with 6.5 Grendel case?
I'll fix the title The all BHW LBC cartridges use a 7.62 bolt. It to use one the chambering is run in 0.010 deeper, nominal, to adjust for less bolt face depth. Yes the 7.62 bolt is stronger. Think about it. Bolt face on the G. Is 0.010 deeper. That means the part sticking up has more potential flex vs. the 0.125 depth on the 7.62. The old story was the 7.62 bolts were weak because originally many were just opened up. 233's and this impacted the heat treatment drastically. New bolts are purpose built and don't suffer from that. Currently the strongest bolts on the market that work in standard barrel extensions are from Young Manufacturing. I personally had input in them and did the Beta testing for them. The walls on the bolt are thicker surrounding the case and the lugs are thicker also. The engineering math says 22% stronger. They are chromed and MPI tested. I'm shooting them in LBC and 6.8 Wildcats. I'm running them hard and they are letting me step up in pressure levels. The LBC/GRENDEL can finally be loaded up and not be so concerned about breakage. Greg
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Post by GLSHOOTER on May 4, 2019 6:47:14 GMT -8
BTW I meant to ask. How do you form your brass?
I see the guys from ARFCOM are lining you out with the same reasoning I gave you on bolt design and receiver/barrel alignment.
I looked over Whitley's site and I see the only 40 degree shoulder is the 6mm Improved Turbo 40. Is your shoulder blown forward ahead of a standard Grendel height besides having the angle massaged or is it merely a 40 degree change?
Greg
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Post by stevepodleski on May 4, 2019 10:00:04 GMT -8
I compared my case to my friend's Fat Rat and my shoulder is shorter. I think the Fat Rat is similar to the 6AR Turbo 40deg?
The 243LBC shoulder is .048 forward from the 6AR shoulder.
I cam over to this website when I read that Black Hole was the originator of the 243LBC cartridge.
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Post by stevepodleski on May 4, 2019 10:12:33 GMT -8
Yes, I should have said Grendel bolt failure. Don't know why is titled this thread: "243LBC Bolt Failure"! Are you saying that a 7.62x39 bolt is stronger than a 6.5 Grendel bolt? Will it work with 6.5 Grendel case?
.. .The all BHW LBC cartridges use a 7.62 bolt. It to use one the chambering is run in 0.010 deeper, nominal, to adjust for less bolt face depth. Yes the 7.62 bolt is stronger. Think about it. Bolt face on the G. Is 0.010 deeper. That means the part sticking up has more potential flex vs. the 0.125 depth on the 7.62. The old story was the 7.62 bolts were weak because originally many were just opened up. 233's and this impacted the heat treatment drastically. New bolts are purpose built and don't suffer from that. Currently the strongest bolts on the market that work in standard barrel extensions are from Young Manufacturing. I personally had input in them and did the Beta testing for them. The walls on the bolt are thicker surrounding the case and the lugs are thicker also. The engineering math says 22% stronger. They are chromed and MPI tested. ... I would need to resize and push the case shoulder back .010" and possibly trim. If I can't do that, I will throw the old brass out since it has already many firings.
Thank you very much for that info. I did not know that the manufacturing technology for the 7.62x39 bolt has improved. My next new bolt will be a Young bolt.
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Post by GLSHOOTER on May 4, 2019 10:14:21 GMT -8
I compared my case to my friend's Fat Rat and my shoulder is shorter. I think the Fat Rat is similar to the 6AR Turbo 40deg? The 243LBC shoulder is .048 forward from the 6AR shoulder.
So are you saying your case is shorter in the shoulder than the true 243 LBC? Is the barrel stamped 6AR? How are you making brass? What dies are you using? Greg
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Post by stevepodleski on May 4, 2019 10:42:42 GMT -8
I compared my case to my friend's Fat Rat and my shoulder is shorter. I think the Fat Rat is similar to the 6AR Turbo 40deg? The 243LBC shoulder is .048 forward from the 6AR shoulder.
So are you saying your case is shorter in the shoulder than the true 243 LBC? Is the barrel stamped 6AR? How are you making brass? What dies are you using? Greg I don't have a print for the 243LBC. I have a print for the 243LBC AR and 6AR. My case is longer at the shoulder than the 243LBC AR and 6mm. The beginning of the shoulder is 1.1909"
I don't know if I have a stamp on the barrel. I would have to take off the handguard. I use Redding 6AR dies to Lapua 6.5 Grendel brass and fire form. The final die is a custom made die.
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Post by GLSHOOTER on May 4, 2019 11:18:26 GMT -8
So are you saying your case is shorter in the shoulder than the true 243 LBC? Is the barrel stamped 6AR? How are you making brass? What dies are you using? Greg I don't have a print for the 243LBC. I have a print for the 243LBC AR and 6AR. My case is longer at the shoulder than the 243LBC AR and 6mm. The beginning of the shoulder is 1.1909"
I don't know if I have a stamp on the barrel. I would have to take off the handguard. I use Redding 6AR dies to Lapua 6.5 Grendel brass and fire form. The final die is a custom made die.
A chamber for the 243 LBC shoulder starts at 1.150. Have you done a case capacity on fired brass check on yours? In mine using Lapua brass I get 35.2-36.17 depending on what batch of brass I am using. Greg
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Post by stevepodleski on May 4, 2019 11:47:58 GMT -8
I don't have a print for the 243LBC. I have a print for the 243LBC AR and 6AR. My case is longer at the shoulder than the 243LBC AR and 6mm. The beginning of the shoulder is 1.1909"
I don't know if I have a stamp on the barrel. I would have to take off the handguard. I use Redding 6AR dies to Lapua 6.5 Grendel brass and fire form. The final die is a custom made die.
A chamber for the 243 LBC shoulder starts at 1.150. Have you done a case capacity on fired brass check on yours? In mine using Lapua brass I get 35.2-36.17 depending on what batch of brass I am using. Greg I measured one case=36.3 (flat meniscus).
The shoulder for the 243LBC AR without the 40 deg shoulder starts at: 1.150 which is the same your 243 LBC.
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