GAP-10 6.5 CM-- heavy cratering, heavy swipes, and 2 pierced primers with factory ammo

[msalm]

So, will an armalite let bolt work in a dpms carrier? Is this what I am gathering?

I built one on a DPMS upper but had to utilize the entire Armalite bolt carrier group. The Armalite bolt, due to the FP spring/FP will not fit in a DPMS carrier...at least that is what I remember from a project 2 years ago or so. I recognized I would rather just use Armalite bolts as I had a bunch at the time and just built off the Armalite platforms.

 

[JL]

Before Using Bartlein we used to use a lot of Obermeyer tubes, Boots uses a .298 bore but widens the groove to supside pressure, all the Mk11 Navy rifles use the Obermeyer barrels. a "tight" bore does not always spike pressure. And a lot of factory ammo is still too hot for Gas Guns.

There seems to be a misnomer that just because you buy "factory ammo" that that somehow means its 100% for sure solid perfect ammo. I could give countless stories where factory ammo is the culprit and to blame for some rifle problems.


Ill give you a couple. Large Government agency over 30 AR-10 rifles that we maintain and Re-barrel. they switched from one lot of ammo (big name factory ammo) to another and the rifles cease to function go back to the old lot back to running like champs.

A California Department was having problems with M-14 rifles we built started having erratic problems. They came out to the shop with their guns and ammo, again 2 different lots. I had a 3rd lot of the same brand. just for shits and giggles we pulled the bullets from this 3 different lots and not only was the charge all different they were 3 different types of powder. 2 of the lots worked great one would not function the rifles.

Now when I read my own posting- I see it can easily been understood as plain criticism.
As this was not my intention, will elaborate a bit:

Rifle was made perhaps 5-6 years ago, DPMS reciever. I recall barrel is Obermayer.
Occasional primer blow was with at least two Lapua Scenar factory loads, 155 and some other. Occational meaning perhaps 1/10 blown.
Velocities with any load were much higher than "they should have been". I recall he was getting 865mps (about 2840) with factory 155. I was able to get about 10mps (33fps) less with own 155 max book loads and 2" longer stainless match barrel.

Still, rifle worked and was accurate- which I think is whole point of making bit tight barrels.

 

[Dynamic Response]

My dad picked up a POF 308 and is having similar problems. He had pierced primers and huge ejector marks and extractor marks. These ejector marks where real bad tho. They made the brass stick up about 1/8in maybe a hair less. He was using federal gold medal match ammo.

Any ideas what is causing this?

 

[SharpsNitro]

My dad picked up a POF 308 and is having similar problems. He had pierced primers and huge ejector marks and extractor marks. These ejector marks where real bad tho. They made the brass stick up about 1/8in maybe a hair less. He was using federal gold medal match ammo.

Any ideas what is causing this?

It's a timing issue, the ammo he's shooting is causing the bolt to start unlocking while there is still too much pressure in the chamber. To continue using this ammo there are a few things that might help. An adjustable gas block to tune the gas system to the load and a heavier buffer and spring to slow down the unlocking process. Hand loads are the last (and best) option, choosing the right powder and primer combination for the rifle to avoid this.

 

[Irokcrawl]

My gap10 in 6mm Creedmoor Is doing this (heavy marks on the head) with every load, this is with everything 100% factory from gap and with with a Jp low mass bcg, enhanced bolt and captured buffer setup with all the springs swapped around as well. This is with copper Creek ammo as well as my handloads. I have a pri adjustable gas block on the way (I don't know why syrac doesn't make a 875 adjustable gas block, they would sell the hell out of them). The thing honestly should be gassed right from gap. I know there are variables in the ammo and I've tried quite a few combos as listed by George on another post as well as my loads, type of powder, type of primers etc with the same results. Hopefully this gas block will fix it because I have to put the brass on a belt sander to knock the burs off just to get it to fit in a shell holder. I went from all the way from 2815fps to 3100fps with the same results.. Other than that the gun shoots lights out. Any input on this George? Basically just a timing issue? The gun has a normal non adjustable gas block on it at the moment.

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[GlockandRoll]

I'm going to add weight to my DPMS buffer and put an adjustable gas block on it.
I've seen stock horny 140's flow primers in a bolt gun however, so not sure if it's the fault of the auto.

 

[Irokcrawl]

The guns need an adjustable gas block as a standard option. When you pay 3k plus bucks for a semi custom gun I would expect something that doesn't have these issues.

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[Irokcrawl]

Just put the pri adjustable gas block on and every single one of my issues went away. It was so overgassed that it broke the damn bolt catch off! That's ridiculous for a 3k plus dollar gun to do. Basically it runs ok now with the stock stuff and runs phenomenonal with all the Jp parts in it (low mass bcg, captured buffer setup with heavier spring installed and of course a new bolt catch

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[GlockandRoll]

I've been thinking about captured buffer setup with heavier spring but leaving the factory DPMS BCG in place, hoping that this and the adjust gas-port will fix it.
DO you forsee any problems with the factory BCG?

 

[Irokcrawl]

No that works just fine actually. I tested all combos and while there is some benifits to the lowmass bcg it may not be worth the price. The adjustable gas block and captured buffer setup is imo the two best things you can put on it. No more spring sound, less recoil and gassed just the way your ammo likes it. I did drill a hole in my handguard so I didn't have to take the thing off to swap the gas blocks and also so I could adjust it. It's very clean and I'll get a little paint out to cover the bare aluminum. Syrac said a few months on there setup but you have to make sure to move the adjustment around and then back or it will lock up due to all the build up. The pri and jp gas block (it's a 936 but uses a spacer which works good) work just fine. Put some mild loctite on the set screw and your good to go!

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[GlockandRoll]

Good to know man, thanks!

 

[Irokcrawl]

Here is the difference in the brass. The silver primer is actually a cci 250 Magnum primer. The bronze color primer is a wolf non Magnum primers (actually very good primers) . Basically the wolf primers load was a good bit lower as far as powder charge as well as the non Magnum primer. The cci 250 was/is now my match load which is moving pretty fast for a gasser, around 3120fps. All are Bn coated 105gn hybrids..

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[Irokcrawl]

And that piece of brass (wolf primer one) is actually one of the better looking ones. The others had to be hit very quickly with a belt sander to get the thing in the shell holder! The gun obviously was not tested when it left and if it was their standard of quality is not where mine is. It now shoots lights out, cycles perfectly, has at least 1/2 of the recoil and is a much smoother shooting gun. An adjustable gas block should be standard as well as the captured buffer setup or something similar even though I understand jp and gap are competitors. Still if you want to have the best product you need to use the best parts. Half way decent products at a premium price is not acceptable by me in any form or fashion.

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[GlockandRoll]

Cool, I'm hoping to use factory Horny 140s in my DPMS, as that was the reason I got it - was to have a turn-key match rig for PRS/Precision multi-gun.

 

[Irokcrawl]

Mine will be used this week was pts so I'll see how it does. It will be my first match with a semi. I'm still reaching for the bolt knob befor moving to a new position!

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[STLSteve86]

Irokcrawl all in all how do you like the 6mm creedmoor? I think the gap 10 is going to be my next rifle. Just can't figure out what to chamber it in. I was thinking 243, 6mm or 6.5.

 

[Irokcrawl]

6 Creedmoor is a great round. It's short enough to have tons of room to play with the seating depth and fit in the pmags. I only run the 105gn hybrids since imo nothing can touch them, especially after pointing them. I don't know if I would go 243 in a gasser. Might not be able to find the right seating depth and still have room in the mags. In a bolt gun sure it's great but I think a 6SLR is a much better choice due to the improved shoulder angle and all it requires is sizing 243 brass down which has to be done ways. I'll snap a picture here in a second of a 243, 6slr and then the 6mm Creedmoor cases. Also a whole lot less trimming with the slr and Creedmoor!

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[Irokcrawl]

Here is a picture of a 6.5x47l, 6mm Creedmoor, 6slr and last on the far right a 243. As you can see the 243 and slr are a good bit longer than the 6mm Creedmoor and the slr has a better shoulder angle. That was just thrown in the press with a slr bushing die and sized from 243 Winchester brass right before I took the picture. The slr is intended for a no neck turn no trim setup from get go with domestic brass. Also you can use h1000 with the slr and still pull the velocities with less wear on the throat since it's no where near as fast/hot as h4350, h100v, r17 etc.. That's what the 6cm (competition match) is designed to use and there are a few slight differences between the slr and the comp match, shoulder angle being one.. The guys running the 6cm are claiming 4k rounds..

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[oubeta]

My GAP-10 in 6.5 Creedmoor is blowing primers with factory 140. I'm having about two blown primers per magazine with factory 140. My buddies rifle was built the same time mine was and is having the exact same issue.
I've tried three different lots of factory 140 and getting blown primers with all three
The gun is at gap right now being looked at. Of course it's not blowing any primers when they shoot it.
They can't find anything wrong with the gun. I'm sending them some of my ammo from the three lots that I'm having blown primers from to them for testing. I'll let you know what they find out.

 

[WyGuy]

Here's a picture of fired brass from my last range trip. Shooting factory Hornady 140gr amax out of my gap10. I've never experienced any pierced primers but have always had some mild cratering. Does this brass show anything I should be concerned with?

 

[Curt1521]

Here's a picture of fired brass from my last range trip. Shooting factory Hornady 140gr amax out of my gap10. I've never experienced any pierced primers but have always had some mild cratering. Does this brass show anything I should be concerned with?

I definitely see some cratering, but that's all I see at a quick glance.

 

[MSTN]

Here's a picture of fired brass from my last range trip. Shooting factory Hornady 140gr amax out of my gap10. I've never experienced any pierced primers but have always had some mild cratering. Does this brass show anything I should be concerned with?

If you had pressure issues, your primers would be flattened on the edges. You'd also probably be seeing some heavy ejector swipes from the gun unlocking prematurely.

I'm of the opinion that your primers look like any commercial primer suitably ignited by a mil-spec diameter 0.080" firing pin.

 

[KULT]

No you need to get either an complete ARmalite bcg or JP HP bolt that just came out if you want to use your existing dpms carrier. Don't mix and match bolts and carriers

So, will an armalite let bolt work in a dpms carrier? Is this what I am gathering?