Author Topic: Throat burnout (Read 900 times)

Nobody · « **on:** March 31, 2004, 05:46:40 AM »

I have a Remington PSS in 308. It has a 24" Mike Rock barrel. I've been getting flattened primers and primers that are being pushed out the back of the case. I've read, and been told that instead of being a sign of excess pressure, that this can be a sign of low pressure. Now I've never shot hot loads, 42.0g of 4895 under Hornady 168s. I have no signs of cracked necks or bulged case bodies. Haven't chronoed this load. It shot sub 1/2 minute.

I've tried different methods of determing the proper OAL for this rifle. Used a Stoney Point OAL gauge and comparator. Kept getting different readings. From 2.171 to 2.388. Then, tried seating the bullet really long in a slightly necked case and then closing the bolt thus allowing the lands and grooves to push the bullet back in (got a reading of 2.412). Had to try this with a 190g SMK because the 168s were simply falling out of the neck.

I have less than 2000 rounds through this gun. I know it's POSSIBLE that the throat is burned out but is it probable? This was a factory built gun (just got lucky with the Rock barrel) and so it could have been throated long to begin with.

Any advice would be MUCH appreciated.

palgeno · « **Reply #1 on:** March 31, 2004, 11:17:08 AM »

I have the same gun----Mike Rock barrel also----mine has a slightly longer throat than my .308 Encore barrel!-I was mildly perplexed by this finding. I used a Stoney Point oal gauge and loaded rounds copying Federal 165gr Gold Medal from .020 OFF the lands down to factory load length . Ignoring the magazine and loading as a single shot, I fired groups to check accuracy at 100 yd----virtually no difference in accuracy----for most barrels this would likely not be the usual result. No pressure or other problems----but no loads were assembled with the bullet in contact with the lands. pg[/b]

Jose Grande · « **Reply #2 on:** March 31, 2004, 12:20:55 PM »

I wouldn't expect a 308 barrel to burn before 8000 rds., maybe even more. So it's not likely yours is.

Nobody · « **Reply #3 on:** March 31, 2004, 03:46:06 PM »

Palgeno - what was your OAL? Not that I'm going to load mine to your dimensions I'm just wondering. I only contacted the lands and grooves to see how long the throat was. Backed off .010 and started testing there.

I talked to a guy who owned a 40xb, I believe it was a 308 and he burned his out in 1100 rounds.

Gees, if it's not burned out what could be causing these problems? I'm absolutely bewildered. I tried different primers (Federal Match - I thought the Winchesters I was using might be burning hot). Tried going to 42.5grs of 4064. Tried using never-fired-factory-primed brass.

Jose Grande · « **Reply #4 on:** March 31, 2004, 07:01:44 PM »

That is the first time I ever heard a claim (second hand I admit) of a 308 burning that fast. We shoot 30-06 from 8-10,000 before replacement of the barrel. I know 308 should last as long. It's a very efficient cartridge. And not overbore at all. I'd like to hear more. God knows I don't know everything.

palgeno · « **Reply #5 on:** April 01, 2004, 05:51:10 AM »

Don't have notes on max oal for my gun because after the expereiment, I just decided to load the same Sierra 168gr match bullet to Federal factory match load length ---since accuracy was just fine at that oal. Also I could not use the magazine at the max length ----cartridges were too long to fit. Gene

yankee · « **Reply #6 on:** April 02, 2004, 06:20:11 PM »

Here are some questions that may help you get some answers.
Has this rifle always done this? Or just recently?
Does it do it with factory loads or just your reloads?
Are you full length sizing or neck sizing?
Have you changed or adjusted your sizing die?
Primers slide out of the case because they can. Meaning the case has been pushed forward by the firing pin-the case expands and grips the chamber and the primer backs up and fills the void. Sometimes the case does not grip the chamber and slids back and mashes the primer flatter yet. Possible reasons for this are the cases being resized to short or the head space is to long for the cases. This is the same thing just stated different.
Suggestions
1. is the barrel still screwed in tight
2. back the load down to 39 or 40 grains
3. if that does not help you want to fire form some cases to your chamber and see if that helps. To do this drop a couple grains of powder and seat the bullets to touching the lands and shoot. Next reload these cases with your sizing die backed out till 1/2 the neck is being sized, load and shoot .020 or .040 off the lands or what ever you want.
Let us know what you find out.

Nobody · « **Reply #7 on:** April 03, 2004, 06:58:09 AM »

Yankee, Jose and Palgeno

Took the stick to the gunsmith today and the first thing he did was check the headspace, whereupon he immediately declared it excessive.

Yes, I could have the barrel cut back. No, I'm not going to. New Mike Rock barrel, and oh while you're at it Mr. Gunsmith, true the action and lap the lugs. Thank you very much. What's that sound I hear? cha-CHING. :-)

Just answer me one more question (hopefully). How do headspace problems develop RELATIVELY SUDDENLY ?
Yankee to answer your very wise questions:

Has this rifle always done this? Or just recently?
- Only just started in the last 500 rounds.

Does it do it with factory loads or just your reloads?
- Never shoot factory so it's just my reloads.

Are you full length sizing or neck sizing?
- Currently full-length but am going to begin neck sizing only.

Have you changed or adjusted your sizing die?
- Yes, I did go to a RCBS competition die set. Set it up per instructions (I think.) Suspected I might be pushing the shoulder back and have taken steps to doublecheck this theory.

Many thanks.

yankee · « **Reply #8 on:** April 03, 2004, 10:32:06 AM »

OK - Here is my idea. The headspace may have been a bit on the long side all along. Head space does not change without a reamer or maybe, maybe a very , very ,very agressive use of a oversize stainless brush on a high speed drill motor. I would guess the problem started when you started using the new die which may have been a bit on the short side. The combination of both gave you the extra room and problems. With a bolt gun the idea is to resize just enough so the case fits into the chamber but not to much more. good luck with the new barrel.

m14dan · « **Reply #9 on:** April 09, 2004, 05:40:06 PM »

I am using the same load almost in my m-14 with a heavy douglas match barrel. I use a LC-91 case, coated barnes 168, win primer, 42 grains of 4895.
One thing I have noticed, I didn't see where you mentioned the type of brass you use, with LC brass I never have any problems. With federal I get 2 to 4 loads max before primers start leaking and backing out. With winchester brass I am lucky to get 3 loads. LC goes 6 easily.
I don't blame anythng anymore on low pressure. If I can shoot cast bullets in the same gun with the same powder, case and primer all day long with nothing out of the ordinary than a sooty neck from the case not expanding as much then low pressure is a non issue. Well within reason. I run the 4895 down as much as 28 grains and as high as 42.5.
I think you may have wanted to get a second opinion on your headspace too. That just doesn't sound right to me about it being long already. Not with your load. That is not a hot one! In my rifle it is a little on the stiff side at 2600 fps but not in your PSS bolt rifle.
Have you looked in the throat with a strong light? you will sometimes see flaking or rough lead area if the throat is blown. Mine is only measuring a 3 right now and I am past 5000 rounds that I have put on it. When I bought the barrel it came with the front half of a military m-14 attached to it and torched right in the middle. I assume it was a military match rifle and well used. It get's a 3/8 inch 5 shot group for me at 100 yards so I am not complaining!

Nobody · « **Reply #10 on:** April 09, 2004, 06:07:11 PM »

Almost always Winchester brass. Since this problem has developed, I've conducted various experiments. Most experimentation was with Winchester brass, though I did one batch that was LC brass. I used Win brass that had been fired 1 or 2 times and brass that was new, factory-primed. I also used Georgia Arms "factory" loaded LC brass. ALL had flattened primers.

It's out of my hands now though. Shipped the stick to Mike Rock in Wisconsin. If necessary (and I'm thinkin it will be) he'll re-barrel it. Cha CHING. Yeah, I know, if it is headspace he could cut it back but from what I've read/heard doing so is a 50/50 proposition.

That's very interesting to me that you get 2-4 loads before primers start leaking or backing out. And with Winchester only 3 max. Learn something new everyday.

Thanks

m14dan · « **Reply #11 on:** April 10, 2004, 02:52:20 AM »

Did you ask him to ship your barrel back to you when he's done. It may be a good candidate for a wildcat or a 30-06 or something in the future. If it gets requalified and reamed deeper the throat on it now is irrelavent.
Oh is that georgia arms ammo already once fired reman ammo? I only buy new pulldown LC.
As for the flattened primers, That in itself isn't always a problem. When they are flat and you are getting metal flow of the primer into the firing pin hole or anywhere else then THAT is a problem. My m14 is tight chambered and the brass doesn't have any excess room to move and it generally flattens them at loads above 41 grains. I rarely go over 42.5. 42 is enough to get a 168 to 1000 yards so theres no need. I have a chrono and a pressure tester so I know my pressure isn't excessive.

Nobody · « **Reply #12 on:** April 10, 2004, 07:05:03 AM »

Haven't done it but I do need to ask him to return the old barrel. Somebody might want it for a 20" or 22" barrel job. Me, I go with longer barrels.

Georgia Arms - I honestly don't know if they're "new" or remanufactured using different components. I've seen their stuff work pretty good through some rifles.

I have a buddy who shoots M14 stuff. I'll make sure I refer your site to him.