having some issues with my 300 BLK

champ198

champ198

Member
Having some accuracy issues with my 300 Blk.
have shot 150gr and 120gr out of it and at 75 yards it seems to be right on. In shooting yesterday with the 120s at 75 yards i was dead in line, right and left and 3/4" high.
Stepping out to 100 yards it is all over the place...3" left, 2" low, 2" right. its all over and I cant figure it out.
I dont think its me as at the same range time was shooting 2 of my other rifles, a 270win and 6.5 CM and both of those were shooting within .5. So i dont think its me.
Just not sure what the issue is.

The other problem I had with it was at the end after shooting roughly 15 rounds flawless the last 3 rounds it had a light primer hit and would not fire off. One round it did it twice on the same round, Could see the firing pin hit but was light. It would almost jam up and was a bear to get the charging handle pulled.
Not sure if maybe the bolt might be dirty? any ideas would be a huge help.
Mainly got this thing as it would be easier for my young kids to shoot as typical AR I can shorten it down. But now its got me wondering what is going on with this thing.

Could use some help from the AR pros here.
 
What length barrel?

What twist rate?

What gas system?

What brand barrel?

What type of ammo?

Factory or handloads?

What type of trigger?



You have presented a number of issues with a number of potential causes. I can help you "identify" the problem but I need more deetz.

TC
 
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16" Barrel
1/8 twist
all factory gas system nothing has been altered on the gun other than the handguard
Its a Diamond Back brand
ammo was Sig Sauer 120 grain
factory rounds
factory trigger.

It really threw me as at 75 yards i got it lined up but were all high. I brought it down to about 3/4" high at 75 yards. So i would have thought it would have been fairly close at 100.
If I would have taken just this rifel to the range I would have swore that it was jsut me jerking the trigger. But i had my other 2 rifles there a 270 win and 6.5 CM and was shooting dime size groups at 100 with both of them.
Was also shooting off of a led sled.
I took the 300 home and took the bolt carrier group out and cleaned the bolt, carrier and took the firing pin out and cleaned it also.

I dont expect dime size groups out of it, but i would have thought it would group better than this really.
 
Issue 1:

I had a 300 blk upper from Saturn (circa 2012). It was 16" and 1/8 twist. I shot handloads with Hornady 125 grain bullets and they grouped about 8" at 100 yds. I could not believe how poorly they grouped. Some flyers even spread out to about 12" at 100 yds.

So I moved to a SMK 125 gr and they grouped about 1" at 100 yards. Some bullets do not group well and that's how it goes.

Do you have access to any handloads?

Issue 2:

Light primer strikes or misfires can be due to headspace or trigger pull weight. Jamming part makes me think of your chamber and or the extractor ring (otherwise called a donut). That could be due to your mags, too.

1. Take a chamber brush and thoroughly clean that area. Then, you can pull the extractor from your bolt and see if there is a "ring" which is otherwise known as a donut. If that is missing, and believe me many are, that can cause failure to extract and some other issues.

2. 223 mags can be 300 blk unfriendly. There are ribs on the inside of the mag. What mags are you running? Pmag makes an amazing 300blk mag if you don't already own some. I have field tested these mags and they are GREAT. Lancer makes good ones, too.

3. Your factory Sig ammo should be to spec so I would rule out headspace unless you have a comparator gauge. I have had factory ammo with headspace issues (recently, too).

4. Last, do you have access to a trigger pull measure?

TC



 
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I can check the bolt extractor. I did pull the bolt and firing pin and clean them but did not pull the extractor apart.
I dont have access to any handloads yet as I jsut got the gun from a friend not long ago and havent really done much with it yet till now.
I have the ability to handload just not the components and materials for the 300 Blk.
The mag i have is a 223/5.56 10 round Magpul mag
I dont have access to a trigger pull guage
I did think about putting a drop in trigger in it. We have a local shop that I am pretty good frineds with the guy and was up there the other day to get a different charging handle for it that has a bigger latch so I could get ahold of it easier.
He did have a single stage drop in trigger kit there for like $135 but I cant remember the brand. I jsut dont know if i need a single stage or dual stage...a little fuzzy on the big difference.
 
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Originally Posted By: champ198Stepping out to 100 yards it is all over the place...3" left, 2" low, 2" right. its all over and I cant figure it out.
I dont think its me as at the same range time was shooting 2 of my other rifles, a 270win and 6.5 CM and both of those were shooting within .5. So i dont think its me.
Just not sure what the issue is.

This much variation in POI makes me think it might be your optic. I would check your mount and rings to make sure everything is torqued properly and maybe even try a different optic to make sure there are no internal issues with your reticle.

You might also verify the barrel nut is torqued properly. Sounds like something is inducing a lot of POI movement. It's possible there is a lot of slop between the barrel and the upper and the barrel nut is not able keep the barrel seated. I have had to ship some barrels to have them fitted with factory uppers to get a good tight fit.

.


 
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For the jamming issue: check on the extractor ring (donut) and buy a Pmag stamped 300blk. Check those two things and report back, please.

The image below shows the ribs and why they matter:

33mByNBl.jpg
 
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I will have to take a look at the magazine when I get home and see.
Do you know of a 300Blk 10 round mag?
All i have found are large capacity mags for the 300 Blk
 
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