Stumped! Chamber pressure

[rcol317]

Thanks for the input. I measured the brass after the shot and I'm sure the bore and throat are fine. I'm pretty sure Coyboy is right, I think it's the cam on the bolt lift because there are no signs of pressure except stuck case, no stiff bolt or any marks on the case itself. We'll see what Cooper say's. I have 9 Coopers so I'll be disappointed if they don't attempt to resolve the issue.

 

[rcol317]

We'll update on my issue with the 6.5. I sent to Cooper and with the holidays and shot show they just sent the gun back last week. Wouldn't you know it, they couldn't duplicate the problem. While they were very nice and willing to address the problem on the phone, they claim they shot the rifle and didn't have an issue, did find it's a real shooter, I already knew that. I shot it again yesterday and same issue, as soon as I load any powder in the middle of published load data it's sticking the case. I even tried the load data they suggested, powder, bullet, primer, OAL brand new Lapua brass, and same issue. Guess I'll keep trying to figure it out. Maybe it only shots well in Montana. I like hunting Montana. Sure wish Cooper had tried a little harder!

 

[Lefty7mmstw]

I've had a couple of belted caliber rifles stick brass when pushed at all. The culprit has been a bit of burr at the back of the narrower part of the chamber. A bit of oiled 600 wet or dry and a brush/drill cured the problem in less than a minute. Be careful or you will be having it set back and re-chambered.
I also have a rifle that was shot with a VERY heavy load that put a notch in the extraction cam when they beat the rifle open. I simply stoned the cam with a diamond file and it's been stick free for hundreds of shots.

 

[rcol317]

Thanks Lefty for the suggestion, some else suggested I polish the chamber too. I'm a little afraid to use the 600 grit but I took your advise and polished it with a little JB compound with a drill. Looks like we're getting somewhere. I shot several powders today with 140 gr SMK's and 142 gr SMK up to Sierra max load data. With Lapua brass a only a few sticks at max pressure, with Hornady brass start to stick @ 1.5 grain under max. Going to try VLD's tomorrow. May go back and try polishing a little more with some lapping compound I have from Brownells.

Thanks again for the help from everyone looks like I'll be able to get past the stuck case issue. Sure thankful for the forum!

 

[rcol317]

Well I spoke to soon. Shot her a couple days ago and again ran into stuck cases again. Shot with a chrony and all of the stuck cases were at very low pressure/speeds. One stuck @ 2498 fps only 46 gr H4831 SC, another @ 2620 fps 47.5 gr H4831, Shot four rounds @ 48 gr and 48.5 gr no stuck case. Also had a couple stuck cases with RL 22 in mid range loads. I'm convinced that it's a cam issue on the bolt. A couple of my neck sized cases wont come out after you close the bolt. Not tight but just snug as a fire formed case should be, but still the bolt won't eject. Another thing I found is that the fired cases that ejected without a problem when fired that when you re-chamber them into the gun the bolt won't pull them out? Came out fine when shot but now won't eject? Go figure!

I ran several of the spent cases into three other 6.5X284 rifles I have, two of which are Coopers and one a Custom Surgeon, the rounds chamber without a problem as if they have been full resized although they've been fired in the rifle that won't eject them. This indicates to me that there isn't excessive pressure and the cases aren't swelled.

Cooper is convinced I don't know what I'm doing and there isn't anything wrong with the gun.

I'm convinced there is a problem. I'm going to buy some factory rounds and see what they do, if they stick I'm sending it back to Cooper!

 

[yawn]

Its possible this is a die-chamber relationship problem. The first thing I would try is to cover the case with a black marker and see where the case is sticking. I had the same problem with a cooper in 280ai. and the case was sticking just in front of the web. Running the cases through a small base body die fixed the problem.

 

[rcol317]

Great idea, thanks I'll see what that shows me. The cases show no indication of hanging up so that's a place to start.

 

[Frank B]

I would pull the firing pin assembly out of the bolt to see how easily it will close. I like my Rem BR bolt to drop on it's own weight. Some like a tiny bit of resistance. This test will tell you if the cases are properly re-sized. You need to look at the back side of the bolt lugs to make sure they are not galled. Hope not. Not an easy fix. Another thing that comes to mind is a short chamber neck. Later! Frank

 

[old_heli_logger]

You might try trimming a few cases shorter than normal. The bullet might be getting pinched in the throat.
Good luck!!

 

[old_heli_logger]

Did this issue get resolved? If so, how? Just curious...

 

[lever-hed]

I had a similar problem on a NEW gun except that I had primer blow-outs all the time even on factory loads. I swore it was the chamber. I even sent it back to Savage and of course there's never anything wrong with the rifle… they said stop loading hot rounds, even after my detailed explanation.

The comparison of those stuck cases to your other rifles does not compute, there is no corelation. Only that if you compared those other same caliber rifles' case dimensions before and after, to your Cooper it may help give you some insight.
What headspacing are you getting, before and after dims? What dies you using? Have you tried small base dies? Is it a custom chamber?
I may if I were you, send the gun to re-ream chamber or just rebarrel and then sell it, you might make up most of the cost, I know, I know, its hassle/money, but sometimes the chamber is not reamed exactly as one would want it, and a slightly 'bad' chamber is just a small % of thousands to a businessman. If he can sell it, he will. Imho. ..good luck.

 

[rcol317]

Still working on it, I've tried all the suggestions, no solution. Sent it away to one of the best smiths I know, an "OLD FASHIONED PROFESSIONAL", I'm confident he'll figure it out, he's been around! I didn't want to spend the money because thought Cooper should stand behind a $2,000 new rifle but they thought it was fine. It's not. I'll let everyone know what come's back from my smith and if it's solved be sure to let Cooper know about it.

 

[Freebore]

I hope your 'Smith does figure it out. I'd like to know 'why' too. I would have the 'Smith draft a letter on a letterhead with the results of findings. Then black out pertinent issue and send Cooper the letter.
If they want results of findings add up everything you and 'Smith have done and send then a billing to get results.
Good luck.

 

[azsugarbear]

Have your smith look at the bore with his scope. I had a custom .243 act the same way after 100 rounds. Turns out, in spite of my cleaning regimine, I had several layers of copper & carbon built up just past the throat area. I am meticulous with my cleaning, so I was very surprised. My gunsmith recommended a few passes (not more than 3 or 4) with JB's Bore Paste to loosen things up, then clean as before. My pressure problem went away. Just one more thing to check.