BCM middy short strokeing


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HOLY DIVER
March 12, 2011, 03:31 PM
trying 2 figure out why my BCM mid length is short stroking the load is 21.6 grains of imr4198 55fmj bt thats not an underpowered load i don't think? its what i allways loaded for my AR'S kinda lost not sure what the problem is

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68wj
March 12, 2011, 03:42 PM
I am not familiar with that loading, but lets start with the usual suspects. Make sure that you gas tube is installed correctly and not bent. Your gas key should be tight with no sign of leaking gas between the carrier. Your gas rings should have a firm fit in the carrier and ideally be staggered. Have you had this issue before with factory ammo? What buffer are you running?

Chris Rhines
March 12, 2011, 03:50 PM
21.6 grains of IMR 4198 is 1.2 grains OVER the book max for a 55grn. bullet. That's pretty hot, and could be the cause of your problems (overpressure gas system, magazine spring can't keep up.)

Try some factory ammo. I bet the problem goes away.

-C

HOLY DIVER
March 12, 2011, 03:50 PM
running a carbine buffer gas key is on there a staked well by BCM going to get regular pmc bronze and try that will report back soon

Mags
March 12, 2011, 04:21 PM
Do you have a BCM auto carrier? Semi carriers and carbine buffers sometimes don't work so well.

Whoops seen you do have a BCM carrier, I would try an H-buffer before calling BCM.

HOLY DIVER
March 12, 2011, 06:18 PM
well i'm glad 2 say the middy is running fine now...figured i'd clean it and try again...(before i took it down 2 clean it i tried xm193 still short stroked) anyway i took the bolt down......3 of the gas rings were perfectly lined up i'm almost %100 sure i off sett them last time i cleaned it anyway i went ahead and cleaned everything the lubed it made sure the gas rings were off sett and she is running great now. i put about 100rds through it to make sure.about 70rds of xm193 30 or so of my reloads.


Chris my Sierra book has that load well under the max what book are you going by?

Quentin
March 12, 2011, 06:22 PM
The gas rings lined up shouldn't make any difference. Maybe cleaning and lube were the ticket.

M1key
March 12, 2011, 06:28 PM
Could be pressure curve not appropriate for your system.

try some xm193


M

HOLY DIVER
March 12, 2011, 07:24 PM
M1key, tried xm193 before i cleaned it...short stroked.after cleaning xm193 and my reloads ran fine. it was a windy day maybee the bcg got full of grit?heck i dono

kwelz
March 12, 2011, 07:35 PM
Could have been any number of things but it wasn't the gas rings. Guys have taken out all but 1 ring before to prove that the gap lining up means nothing.

Glad it is working for you.

You shouldn't have to keep it clean. Chances are there was something in there gumming up the works and it came out when you disassembled it for cleaning.

MrCleanOK
March 12, 2011, 08:32 PM
LUBE was the answer to your problem. AR-15s like to be wet. They will run with one gas ring. They will run dirty. They do not like to run dry.

M1key
March 12, 2011, 09:58 PM
^^^what he said.

Sorry I missed the XM193 comment...Glad you're up and running again.

Interestingly, my step-son is currently with the Marine Corps EOD over in Afghanistan and he tells me they all run their M4s dry. :confused: Claims the sand over there mixed with oil turns to something like cement.

M

HOLY DIVER
March 13, 2011, 12:12 PM
well i had it lubed before i cleaned it i'm going with something gummed it up

jerkface11
March 13, 2011, 12:14 PM
anyway i took the bolt down......3 of the gas rings were perfectly lined up i'm almost %100 sure i off sett them last time i cleaned it

They are free to rotate as the gun cycles.

Jaybird78
March 13, 2011, 03:03 PM
I am not a AR expert by any means. I do have a BCM middy.

FWIW I am running a H buffer with the BCM Carrier group. I don't remember where on the NET I found/saw it but an H was reccommended by someone/others. :confused:

The rings lined up should not matter.

I oil/clean after every range outing and I usually shoot 90-200 rounds on trips. All I have shot are reloads with 55 fmj and 62 fmj with W746.

Good luck and you may want to check out m4carbine.com for more answers from people you seem to know more. :)

HOLY DIVER
March 13, 2011, 09:45 PM
well upon closer inspection i think i know what gummed it up inside the bcg was full of unburnt powder last time i shot it i figured i'd get rid of some steel cased stuff i had. the unburnt powder and tetra gun lube mixed together and made a gummy mess also felt very gritty. i just got done doing a very extensive clean and relubed with slip2000 and trust me i'll never ever shot that crap in my rifle again

taliv
March 13, 2011, 09:57 PM
i could be wrong, as i often am, but i believe 4198 is mostly for 223 in bolt guns, and not recommended in gas guns due to the burn rate. might be worth checking into. not saying it won't work, but it may be marginal

HOLY DIVER
March 13, 2011, 10:29 PM
taliv fixing 2 order a keg of varget i've allways used imr powder but everyone seems to love varget when loading for an AR so think i'll make the switch

Quentin
March 14, 2011, 09:39 AM
well upon closer inspection i think i know what gummed it up inside the bcg was full of unburnt powder last time i shot it i figured i'd get rid of some steel cased stuff i had. the unburnt powder and tetra gun lube mixed together and made a gummy mess also felt very gritty. i just got done doing a very extensive clean and relubed with slip2000 and trust me i'll never ever shot that crap in my rifle again
If a BCM truly can't handle a little extra gunk from steel case then you'd better rip those fine letters off the receiver. I shoot it all the time in my two ARs. I'm sure most of us have read the story of Pat Rogers' Filthy 14 BCM. For those who haven't it's an eyeopener.

Anyway, glad you found your problem but don't fear the cheap stuff, it's good to have around. Besides it would be a great test to prove what went wrong when you try the new powder.

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