DPMS style 6.5cm problems.

[jscb1b]

Good morning all!  I have a PSA-10 lower with a Davidson Defense upper in 6.5cm.  With one round in the magazine and the bolt locked back when hitting the bolt release the bolt will strip the round and fully chamber the round and lock the bolt. Upon firing the rifle, the bolt will extract and eject the case.  The bolt locks back too.

When trying to fire multiple rounds the bolt will strip the next round but the bullet gets jammed between the bolt and barrel extension.   This happens with either the left or right side of the magazine. 

The rifle did cycle and feed the next round 4 times.  After looking at the cases that cycled, 2 had split and 2 had pierced primers.

The rounds that split the case are seller and bellot 140gn FMJ.  The ones with the pierced primers are reloads.  Hornady brass 140gn ELD-M 43.8gn staball 6.5 powder.   

Am I over gassed and/or over pressure?

The barrel is 24" with a .093" gas port and a 15.5" gas tube.  The gas tube extends 3/4 of the way into the cam cut out. There is 10.75" of dwell. 

The bolt firing pin hole is .084" the firing pin is .065" and has .046" protrusion. 

The buffer weighs 3.8oz and is 2.503" long.  The extension is 7.135" deep.  The spring is 11.5" long and has 30 coils.

I am ordering a heavybuffer and spring.  2 quarters are going into the reciever extension.  An adjustable gas block is on order too.  

I loaded 5 rounds of staball 6.5 and 140gn Sierra boat tail lead tips at 37.5, 38, 38.5, 39, 39.5, 40, 40.5, 41, 41.5, and 42gn to test. 

Have I missed anything?  Thank you everyone for your time and help!  Scott. 

[jscb1b]

Headspace was checked with go no go gauges. 

[shooterrex]

Your buffer is too light. But you already figured that out.

Just change 1 thing as a time.

The 140gr Hornady American Gunner runs great in both my Creedmoors.

It also groups well.

Davidson doesn't have the best reputation for quality parts.

I would wait on changing the gas block till you try the heavier buffer and spring.

[jscb1b]

I went out and shot my reloads to day.  40gn of staball 6.5 ran the best.  41gn and above pierced one primer out of 15 rounds.  The rifle still will not feed from the right side of the magazine.  I'm going to polish the ejector.  

[Albroswift]

I am surprised the firing pin is so much smaller then the hole. You have the correct  0.065 firing pin, I don't have a HP bolt laying around to measure but 0.083 sounds like the bolt for a standard pressure pin. Big hole will cause problems. What do the primers look like after firing?

[shooterrex]

https://kakindustry.com/lr-308-bolt-carrier-group-ejector

 

This is what I put in my Creedmoor bolt.

Edited October 14 by shooterrex

[Albroswift]

Those are just fine, always have a couple spares laying around. I also just radius the square ones and polish. 

 

[jscb1b]

The KAK buffer is on it's way.   So is a sprinco orange spring.  I contacted Davidson Defense about the firing pin and firing pin hole in the bolt.  I gave them my measurements and am waiting for them to contact me.  The ejector face was square but I rounded it over.  Thanks to everyone who has replied. 

[Turd Furgeson]

jscb1b, I had the exact problem.  First, the S&B ammo is crap.  Second, the jam issue ended up being the PMAG magazines.  The mag wouldn't position the round high enough in the receiver, so sometimes it would strip the round out of the mag by the case body vs. the case head.  It would then wedge between the bolt and the barrel extension.  Used the Lancer L7-AWM mag so solve the issue.  Good luck.

[jscb1b]

The quarters are in.  The KAK buffer is in.  The sprinco orange spring is in.  I put 10 rounds of Hornady 140gn ELD-M through it. There was one failure to feed from the right side of the magazine.  The ejection pattern is 1 o'clock.  You can see on the shell deflector brass marks where the case is hitting.  What is a good adjustable gas block?  Thanks again for everyone's help!!!!!  Scott. 

[Albroswift]

1:00 ejection I would drill up one or 2 more sizes, pretty sure it takes more gas to go from 1:00 to 3:00-4:00. To answer your question, I like the Seekins Precision but there are a lot of good ones. An AGB won't help until you are gassed correctly/ little over. 

[Albroswift]

On 10/19/2024 at 8:14 AM, Turd Furgeson said:

jscb1b, I had the exact problem.  First, the S&B ammo is crap.  Second, the jam issue ended up being the PMAG magazines.  The mag wouldn't position the round high enough in the receiver, so sometimes it would strip the round out of the mag by the case body vs. the case head.  It would then wedge between the bolt and the barrel extension.  Used the Lancer L7-AWM mag so solve the issue.  Good luck.

AWM are good mags. I don't have problems with other mags either usually run the C-Products stainless steel, fits the budget and 100% reliable. 

[Dewey Mack]

Ejecting at 1:00?....doesn't sound under-gassed to me. My rifle doesn't eject that far forward unless I have the suppressor on.

Sounds over-gassed and needing an AGB from my experience, not a larger gas port. I have used the Superlative Arms (clamp-on) with success.

0.020" slop around the firing pin sounds...VERY out of spec. It should be closer to 0.005" or less for precision shooting.  I'm running toolcraft "HP" double-ejector bolts in my rifles which fixed my cratering/punctures and launches the 308 brass about 10feet.

Gas tube extending 3/4 of the way into the cam cut out increases pressure time on the bolt = over-gas-like reaction.

Gas block journal size?

0.093" should be good enough. That's what my rifle-length 18" 308 is at, and it needs AGB full-open just to cycle the orange spring + 5.6oz buffer, granted it's a much shorter barrel. I stepped down in spring and changed to A5 tube setup. It still fits my PRS Lite stock and many more spring/buffer options to play with. It also cycled fine with KVP 2.5" buffer and KVP AR10 carbine spring in the 7" buffer tube.

Hint: check out my new post about spring data.

I HIGHLY recommend you get the rifle running correctly (without primer cratering/punctures) with good basic (not cheapest) factory ammo before working on reloads. Otherwise you don't have a baseline to know what exactly is causing a problem. You're changing too many variables at once.  Fixing your rifle should be methodical, just like reloading.

[jscb1b]

Yesterday I installed an Odin AGB.  I shot it with 140gn remington cor-lock.  It is set to where the bolt locked open on an empty magazine then I gave it 5 clicks.  The rifle cycled 5 rounds with no problems.  The Remington primers are still cratered but not as bad.  

[Albroswift]

1 hour ago, jscb1b said:

Yesterday I installed an Odin AGB.  I shot it with 140gn remington cor-lock.  It is set to where the bolt locked open on an empty magazine then I gave it 5 clicks.  The rifle cycled 5 rounds with no problems.  The Remington primers are still cratered but not as bad.  

That's good! @Dewey Mack makes some good points, I may have been backwards on the ejection pattern but would swear that more pressure brings my rounds back. Also agree about the gas tube location and the bolt firing pin hole. Brother was having cratering problems/ pierced primers/ stuck pin due to primer debris, gave him  a dual ejector SRC high pressure I had extra really made a difference. 

This is what the gas tube should look like.

Edited October 24 by Albroswift

[jscb1b]

[jscb1b]

It gets a lot of gas.🤣🤣🤣🤣

[Dewey Mack]

Good to hear!

My 15.5" gas tube is about 1/8" too deep on my Wilson Combat barrel because I'm lazy and didn't order a custom tube from WOA. Even the tubes WC sells are too long (f- wilson combat barrels). As long as you control it with the AGB like you did, you should be fine.  If you ever want to go to a fixed gas block, you'll probably need to order a custom tube.

How's the ejection pattern?

If it's between 2:00-4:00 you should probably just run it. I have mine ejecting at 4:30 on weakest ammo but cycling fine, and about 1:30 with suppressor. I use my rifle in 110F in Phoenix to -20F in Wisconsin. Temperature changes ejection pattern too. I'm actually looking at getting the $200 Riflespeed for my setup because I'm about 50/50 with my suppressor use and it's annoying. I even broke the bolt catch [strike industries] the first time I used the suppressor. 🤬 The SA AGB works great but it's less-than-ideal to adjust on the fly.

[jscb1b]

It is still ejecting to the 1o'clock position.  I'm going to run it some more to break it in better.  I will get a high pressure bolt when the funding is available. 

[Dewey Mack]

This has some good information on it for ejection patterns....
Sprinco USA -- Recoil Solutions

[jscb1b]

I read that stuff and watched the video.  Why are the Odin works AGB not meant for high pressure rounds?

[Dewey Mack]

Don't know, but my guess is that the high pressure at pistol-length might be enough to blow the adjustment screw right out of the gas block. It is pretty small threads in there. They don't define "high pressure" on their website, but if you're running 308 carbine to rifle length, I would think it would work. If that's the block you're getting, call Odin before you purchase.

[jscb1b]

I had the Odin block on hand so I installed it.  The problem now is finding a firing pin in stock.  

[jscb1b]

Just an update, I replaced the gas block with an adjustable one.  Then I replaced the buffer and spring with a KAK  buffer and sprinco orange spring.  Two quarters have been placed in the back of the reciever extension.  The Davidson Defense bcg has been replaced with a PSA 6.5cm double ejector bcg.  The bcg has been liberally oiled with 0w15 full synthetic motor oil.  The rifle functioned flawlessly for 50 rounds with 3:30 ejection this morning.  Thank you to everyone who helped!!!!!  Scott. 

[shooterrex]

Happy it's working well now.