I recently got a new 6.5 creedmoor built on the AR-10 platform. I've put a little over 200 rounds though it and had no issues with Hornady or Norma's ammo but have experienced blown primers with Winchester and now today with Federal.

I want to make sure the rifle is safe to shoot considering this is occurring with two ammo manufactures. Could this be a problem with to much headspace or overpressure? (I'm going to try to turn down my gas block). I don't own any headspace gauges but might get some to check it.

Links below to pictures.

Picture of Winchester 140 grain


Picture of Federal Fusion 140 grain


Picture of Bolt Face

What barrel?

What gas length?

How many rounds since the last time you cleaned the chamber and barrel?

Haven’t shot the Norma, but the FGMM is known to be on the warm side. That said, I ran it in my rifle length gas 6.5 creed today, at 40F, with no issues.

24” barrel by unknown manufacturer. I won the gun in a raffle and don’t see any markings visable. Riddle length and just recently cleaned it. (Not real bad)

You have a pretty good primer swipe on some of those cases also.

Was the gun a put together by someone or was it a company / manufacturer assembled?

Large frames don't have the standard specs akin to a AR15, so they can be finicky. I have a 6.5CM and .260 gassers, each with a +2 gas system as those cartridges have higher gas port pressures. I had blown primers with FGMM even with a heavier buffer and spring so, I moved the FGMM to only fire in my bolt gun. I've had real success with factory Hornady 130gr ELD-M stuff. The heavier 140gr class also works, but it needs to be a lower / slower load in a gasser.

OP - I wouldn't worry about the headspace at this point, particularly if the Hornady was shooting.  You may want to include an HP bolt (JP makes one), this adds support to the primer cup as opposed to having a gap that allows the primer material to "flow" into that channel. When that flow becomes too much, you start piercing primers.

It's not all that uncommon with these 6/6.5 caliber AR's for these issues.  Have you tried the American Eagle 140gr OTM?  I thought it was going to shoot like shit out of my rifle, but it shot way better than the Hornady Match, 5 rounds in .3" at 100.

It was put together by a local shop. They milled the upper/lower and rail and outsourced the rest of the parts. Overall the quality seems good and I’m not complaining since I won it for free.

Thanks for the good info. I’m new to 6.5 and AR-10. Do you think the swipe marks just mean I need to turn the gas down some (on the working ammo).

Here is a pic of the rifle

Yes, I’ve had good luck with American Eagle, and it’s cheaper too

I’ll check out those bolts I was reading about them and that sounds like a good idea.

It has an adjustable gas block?  If so, yes, turn it down a bit.

Two articles others might find helpful for this issue

https://www.shootingillustrated.com/articles/2011/4/12/case-head-swipe/

http://www.massreloading.com/reading_pressure_signs.html

Safety first...

Get rid of the firing pin that you kept abusing.

Get a handful of firing pins.

I am going to guess you are over gassed and that is unlocking the bolt too early and blowing primers.

If it keeps blowing them you will eventually have a serious stoppage due to a feral primer being where it shouldn’t.

OP, I'm afraid the bulk of the responses above are appropriate for the .223 and even a normal .308, but not the 6.5CM.

All you need is the high pressure bolt.  And you need it right away.  I have been down this road for a few years now and put together my first 6.5CM before JP even made their HP bolt, things were tough back then.  It will solve the blown primers and ejector swipes.  And adjustable block will somewhat help slow down your unlock timing, but won't do a thing to reduce max pressure.

I agree with SCV and the others, a high pressure bolt is a requirement.

Other suggestions:

1) slow unlocking time by adjusting gas and/or adding weight behind the bolt.  A heavier buffer and/or full mass carrier will help with the brass abuse

2) Federal brass is soft.  So soft, I don't reload it.  It's a warm load, but I've exceeded the FGMM 130 factory load velocity in Hornady brass using the 130gr Berger hybrid and haven't seen the same pressure signs.

3) You'll need to do some tweaking.  Semi-auto creedmoors need finesse, but they're fun to shoot once dialed in.

Read and ask questions.

I turned down the gas which really helped with the swipe marks. Staying away from the hot ammo and looking to buy an HP bolt.

Shot some more Hornady 140 ELD which it seems to like best.

Thanks all for the great info!

Gotcha, I appreciate the valid concern. I found the barrel is a Faxon match grade. I’ve got some gauges in route to double check the chamber specs.

http://faxonfirearms.com/match-series-22-heavy-fluted-6-5-creedmoor-5r-416r-nitride-nickel-teflon-extension/

It does.  Everytime in a 6.5CM.

Check for a short throat too.  If the bullet is being jammed into the lands it increases pressure.

I believe that is why my 22” rifle length gas Mega barrel blows primers with AE 140 gr OTM and Win 140 gr Match.  The ogives are fat and are pushed into the rifling when chambered.

I can push either one of those rounds into the chamber by finger and they jam in there before bottoming out on the case shoulder.  Tap them back out with a cleaning rod and they have engraving on the bullets from the rifling.

It’s not the gas port size, buffer, spring, etc causing the blown primers.  I think it’s the short throat.

I will and plan on shooting lighter faster bullets that fit to wear the throat in some.  Then I bet the 140 gr will shoot real good.  Might take a while with the nitride finish.

Just as an update.  I bought some Winchester Deer Season XP 125 gr. 6.5 Creedmoor and they drop right into the chamber to the case shoulder and fall right back out.

The bullets are narrower/pointier than the 140 gr. OTM and 140 gr. Winchester Match discussed above that push into the rifling lands.  The 125 gr. XP are also have a shorter OAL.

I'm going to try to get to the range Saturday to see if they work.  I already feel a lot better about this gun.

If it were overgassed and your were right up on the lands when chambered, that could be some of the pressure indications.

If it were me and I had an adjustable gas block, I'd shut the gas completely off and shoot a round or three checking each casing afterwards for signs.

I’ve tried that and changing buffer weights and buffer springs around.

Shutting the gas block off completely seemed to stop the primer cups from blowing out of the cases but when opened up just barely enough to cycle the gun, lost primer cups and huge ejector swipes would happen again.

It wouldn’t happen every round.  Maybe 4 out of ten rounds would have a blown out primer cup and/or have a deep ejector swipe.  Strangely, every once and a while a fired case would come out with no damage at all.  Not even a flattened primer.  Could it have been slight differences in seating depths in that factory ammo that was making the difference.  Some rounds squished into the lands causing high pressure and some not.

No combination of buffer weights (car, h2, h3) or springs I tried seemed to make any difference on controlling the blown out primers or case damage.  Though I didn’t try a Tubbs flatwire spring or red Springco.

Yeah, what I think's happening is that the gun begins unlocking under pressure, which allows the primer to unseat and swell, and then the case is forced back down on top of the primer when it squirts out of the chamber.

Mostly. Sometimes it misses and drops the primer completely out.

ARs don't treat primers the same way a bolt gun will. Trying to read them is somewhat futile.

H4350 is a standard powder for 6.5 Creedmoor, excessive port pressure is common. The action is getting too much gas too early in the cycle.

Hand loadiing with Varget or RE-15 can slow the bolt speed down.

Heavier buffers, stiffer springs and an adjustable gas system can all be employed to delay or slow the action down.

I'm running Slash's heavy buffers in .308 AR's with total reliability, I'm pretty sure a 6.5 will need it way before my .308 did.

The cheapest and most flexible option is an adjustable gas block. Do you have any way to measure your headspace?

The fired cases can be measured with a RCBS, Mo DeFina or Hornady headspace gage. Blown and/or flattened primers can be a sign of excessive headspace.

With only 200+/- rounds down the tube the bolt should be like new. The chances that you got two different lots if over pressure ammo from two different commercial sources at the same time is probably close to zero.

Something is wrong with the rifle, either headspace or too much gas.

I shot the Winchester Deer Season XP (125 gr.), Hornady Match ELD (120 gr) and Hornady Interbond (129 gr.) "American Whitetail" load over the weekend.

I started with the XP and opened the gas block one click per round at a time until the bolt began locking back on the empty mag.  After several rounds/clicks, I got it adjusted.

I got through a box of Deer Season XP 125 gr. with no issues.  No blown primers.  Light ejector swipes on a few cases.  Most fired cases looked good.  Accuracy so, so.  Maybe 1.5" groups at 100 yds.

The Hornady Match ELD also ran well, but I could see a little bit of primer flow on a couple of rounds.  Also, light ejector swipes on half of the fired cases.  Great accuracy.  1" groups and smaller at 100 yds.

I got through about 10 rounds of Hornady Interbond 129 gr. with one primer cup falling out and jamming in the star chamber (had to mortar to get the bolt to unlock).  Deeper ejector swipes.  This one appeared overpressure.  I only shot half the box.  Super accuracy though.  This one shot the tightest groups of the day.

I shot with both a CAR buffer and H2 buffer (VLTOR A5 receiver extension on it).  No difference in gas block adjustment was needed between the two buffers.  The H2 buffer slowed the action down noticeably and increased recoil.  Buffer weight didn't seem to make a difference on the ejector swipes or condition of fired cases.

I also had a couple rounds where the extractor didn't engage the rim when it chambered resulting in the hammer falling on the bcg out of battery and not firing.  Pulling the charging handle back and letting the bolt fly gave it enough force to push the extractor over the case rim of the round in the chamber, allowing it to go into battery and then fire.  This happened once with the CAR buffer and the H2 buffer.  Maybe putting in a stronger buffer spring might help alleviate that.