Modern Sporting Rifle Evolution
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GhostRider32

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Hi all,

I have my mongoose put together and am having some functioning issues. I have a Seekins adjustable gas block on a 22" 4T barrel. The Seekins is open close to 6 or 7 turns. It doesn't seem to have enough gas to cycle the action. Most of the time it will lock back on an empty mag but not always. It throws brass 3 or 4 feet at best. It will not load the next round in the mag. I have tried 2 different mags, same result. I used 3 different loads with 7 rounds each, fire formed brass, with the Speer 85gr SBT. IMR 8208, 26.0 gr, 26.5 gr, and 27.0 gr. CCI-450 primer. None will fully cycle the action.

The BCG and lower is Palmetto State Armory. I'm going to try my lower off of a well functioning Grendel and see if that works. I'm thinking maybe the buffer is to heavy or spring too strong but just guessing. Any suggestions are welcome. Thanks.
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GhostRider32

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Also, the barrel has rifle length gas.
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MDWS

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Sounds like a gas leak to me.... there are going to be a whole lot of suggestions thrown your way. Try to find a gas leak.
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RangerJoe

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Reply with quote  #4 
What length is the gas system?  Rifle?
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Reply with quote  #5 
Quote:
Originally Posted by RangerJoe
What length is the gas system?  Rifle?


22" are rifle gas.

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Reply with quote  #6 
Is the gas block fully open?


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BIGGDAWG

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Reply with quote  #7 
the mongoose doesn't need an adjustable gas block so if yours is not all the way open try it there first 

also is that one of the melonite barrels?  if so the chambers need polishing good on them. the melonite process makes them a bit rough causing the cases to drag in them.

just so you know about where your load is

goose 85 speer.jpg 


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GhostRider32

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Reply with quote  #8 
Thanks for all the help guys.

1. I will look for a leak.
2. It is not melonite.
2. I'm definitely too hot and should have plenty of gas. 
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bbbrownfield

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Don't forget to check your buffer and spring...
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ussrangersm3

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Reply with quote  #10 
I had the same problem with mine, opening up the gas port took care of it.
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Brunosplace

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Reply with quote  #11 
Is the gas block positioned properly, or maybe blocking the gas port?
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Crs89

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Reply with quote  #12 
Quote:
Originally Posted by GhostRider32
Thanks for all the help guys.

1. I will look for a leak.
2. It is not melonite.
2. I'm definitely too hot and should have plenty of gas. 


To much gas can also cause it to unlock early and can cause signs of not enough gas.
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GhostRider32

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Reply with quote  #13 
I think I just don't have enough gas. My wife says otherwise but that's another story.

I cannot find any gas leaks.


Todays load: W748 27.1 gr, Speer 85 SBT, CCI-450, fire formed case. Bigdawg, if you wouldn't mind running this load to see pressure I'd be grateful. 😉

I went and shot it again today with a different BCG and lower, same problem. The bolt actually catches on the magazine follower and stays open. It will always eject a fired case as long as there are no others in the magazine. If there are rounds in the magazine it's a crap shoot, most of the time the bolt will close but with no round chambered. Sometimes it will try to chamber a round and both the fired case and new case will be in the gun together. I also had this issue when the AGB was more closed but not fully closed. I've essentially tried from 2 turns open to 8 turns open on the block. At 9 turns open the adjustment screw comes out. Only one time in about 100 rounds has the gun fired the case and successfully reloaded the next one.

What size is the factory port hole and what size drill should I use?

Thanks for the help guys.
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Rifter

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Reply with quote  #14 
Quote:
Originally Posted by GhostRider32
I think I just don't have enough gas. My wife says otherwise but that's another story.

I cannot find any gas leaks.


Todays load: W748 27.1 gr, Speer 85 SBT, CCI-450, fire formed case. Bigdawg, if you wouldn't mind running this load to see pressure I'd be grateful. 😉

I went and shot it again today with a different BCG and lower, same problem. The bolt actually catches on the magazine follower and stays open. It will always eject a fired case as long as there are no others in the magazine. If there are rounds in the magazine it's a crap shoot, most of the time the bolt will close but with no round chambered. Sometimes it will try to chamber a round and both the fired case and new case will be in the gun together. I also had this issue when the AGB was more closed but not fully closed. I've essentially tried from 2 turns open to 8 turns open on the block. At 9 turns open the adjustment screw comes out. Only one time in about 100 rounds has the gun fired the case and successfully reloaded the next one.

What size is the factory port hole and what size drill should I use?

Thanks for the help guys.


Might be a good idea to just box the whole upper up and send it to Bruce.  Nobody knows these critters like he does.  Better that than drilling the gas port in the hopes that might work.

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wikster1983

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Reply with quote  #15 
I agree with Rifter, I and a friend both had undersized port issues in our 20" barrels. If you have a set of numbered drill bits, you can check port size yourself and confirm with BD. If that's not something you want to do, then by all means contact BD to send him your upper.
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MDWS

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Reply with quote  #16 
20" rifle gas Mongoose should be .091" port.  You can go to .093 if you think it will help.



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Drydock

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Reply with quote  #17 
I'd remove the gas block, check the port size, then replace with a standard gas block and see if that changes anything.
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GhostRider32

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Reply with quote  #18 
I have a regular gas block on order, will try it to make sure there's nothing wrong with the AGB and will proceed from there.
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BIGGDAWG

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Reply with quote  #19 
if ya have the drills go ahead and open to 093  -- a number 42 or a 3/32 drill and you will be good run that with your adjustable wide open and see what ya get.  just make sure to look into the gas block at the gas tube opening to see if it is all lined up i got a batch of tubes that partially obtructed the hole. i had to drill them out -- remove the rear set screw and use a .120 drill bit. 
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GhostRider32

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Reply with quote  #20 
Problem solved. Used a 3/32 bit to open the port. Now it functions flawlessly. I set the AGB to 5 turns out and I ran 30 rounds through it and it worked fine. I can probably close it down a little when I find a load I like. I shined a light through the barrel and did not see any burrs or anything and I ran an oiled swab down the barrel before shooting it to get any shavings out.

I'm not a machinist by any stretch but I'll tell everyone how I drilled it and maybe it will help someone else. I knew it was critical not to drill into the rifling so I took a smaller bit and hand inserted it into the port. Then I took a magic marker and made a mark where the bit and top of the barrel met. Then I took the 3/32" bit and used electrical tape and wrapped about a dozen rounds around the bit about 1/8" shorter than the mark on the test bit. If you wrap the tape tight, it will provide a shoulder to prevent the bit from contacting the bottom of the barrel rifling. 

Thanks for the help everyone.
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RangerJoe

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Reply with quote  #21 
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