Help diagnose a .308 Win problem

[mtnman31]

I've got a rifle that has really tested my patience and has exceeded my experience level. It is a Remington VTR in .308. I got it for my kids to use as a hunting rifle. Last year I tried working up some loads for a lead free hunting bullet. Everything was pushing pressure limits and velocities were too low for the bullet to work. I just assumed it was the difference in bullet construction that was driving up pressures. I put it on the back burner for a while and have re-started load development again. Like last year, everything I put into it is producing really high pressures while velocities are low. I've changed my efforts to conventional bullet construction. Starting level loads are flattening and backing out primers. While it isn't a fair comparison, I can put the same loads into my FAL and don't see any issues.

I checked headspace. Using Forster gauges, bolt closes on "go" will not close on "no go". The chamber is clean, no carbon or other obstructions. Freebore is not an issue since these bullets would be all the way out of the case if they were to touch the lands. I've tried different powders, brass, and bullet designs.

As an example, my load from yesterday's short session.
WW Brass, trimmed to 2.005"
Fed Large Rifle primers
46.0 gr Win 748
Speer 150gr PSP BT bullets
COL 2.750"
Avg Velocity: 2606fps 13.6 SD 36 ES
Primers were flat and backing out of brass. Bolt was starting to get hard to lift.
Fired brass shows no measurable increase in diameter around the case head.

I've reloaded for many years and never had any problems like this that I've just spun my wheels with. I don't think it is a load issue. I mean .308 is relatively easy to load for and I'm not pushing the envelope. What am I missing? What should I be looking at?

 

[284winner]

Certainly low velocities for a 150 psp with signs of pressure. The 2.750 seems low at first but saami max is 2.8 so I'm assuming 2.70 is not unheard of for lighter bullets. My typical load is 2.8 regardless of the bullet. The 2.750 seems reasonable so I'm about as puzzled as you are. I'm curious with what responses you will receive on this issue. I will be watching. You sure have a great experienced group of guys here to get your solution.

 

[Fred B.]

If it was mine, I would try some off the shelf Remington ammo in it and if they show the same symptoms; call Remington and tell them the barrel is bad and needs to be replaced.

 

[Crosshair1]

Primers backing out are not a sign of excess pressure.
If the load is light the primers will back out and the case head does not stretch back to meet the bolt face.
If the primers are not cratering then the most consistent measure of overpressure I have found in my rem700s is heavy bolt lift and ejector mark on case head.

 

[olddav]

Perhaps check to see if you are under sizing your brass, (bumping the shoulder to far back). Just offering suggestion while we wait on the experts to show up.

 

[284winner]

I think one arrived. Crosshair1 is on to something. Right in the money. Primers do crater when pressure is up. Never heard of them backing out when undercharged but he must have. 46 grains seems about right with the load. Certainly low velocity for that charge IMO.

 

[Bc'z]

Keep in mind the Remington VTR claims to have a 22" barrel, when in reality its actually 20" due to muzzle brake.
Velocity will be lower.
Wife's 260 VTR I had the same problems running 140's, it would shoot good one day then not the next.
Wound up switching to lighter bullet for velocity and group improvements.

 

[rammac]

QuickLoad estimates that a muzzle velocity of 2606 fps would correspond with about 41,700 PSI chamber pressure, that would be low enough chamber pressure to not expand the case and cause the primers to be backed out. I'd say that there is a problem with the powder or your powder charge. Maybe your scale is off or if you are using a volumetric powder dropper then you might have the wrong setting.

 

[mtnman31]

This round of testing (w/ the 748) had 2 out of 5 primers backing out. The other 3 cartridges had flat primers that were just starting to flow around the firing pin indentation. The previous attempt at starting loads using both Varget and RL15 had flattened and cratered primers and ejector marks on the cartridge bases. Other symptoms were similar, starting to get heavy bolt lift and again, no increased case head diameter.

I have not fired factory ammo through it. I haven't purchased factory ammo in .308 in over 20 years. I'll have to buy some.

I will have to double check my sizing die to ensure that I'm not forcing the shoulders back excessively.

My powder is performing as expected in other cartridges I use it with. My scale is an FX-120i. I don't think either of those are at issue.

 

[rammac]

There is too much velocity drop for a 2 inch barrel length difference. If you can't get a 150 grain bullet to work in a .308 going to a lighter bullet wont help.

 

[shoot4fun]

I had a R70 in 220 Swift. It seemed to show excessive pressure no matter what load, hand load or factory.
I sent it back to Remington and they said there was nothing wrong with it. Trouble turned out to be with the firing pin hole. It was way over size and mimicked a pressure issue. If you're trying to get a good read on pressure you will likely need to measure case heads with a blade mic instead of "reading" the primers and ejector swipe on brass. Remington's "quality" makes that dang near impossible to do.

 

[D-4297]

From the "for what it's worth" crowd .....I would be real tempted to Slug the barrel . Under-sized barrels are possible in a factory rifle , and it would create exactly the situation you are describing . If it does come out to be under-sized , I'd slug it twice , and send one of the slugs back with the rifle , and a note sayin , "Don't tell me there's nothin wrong with this rifle" .

 

[Fred B.]

I don’t believe primer backing out would cause heavy bolt lift by itself.

 

[Coyotefurharvester]

Second vote for factory rem ammo trial, if same primer movement contact Rem.

 

[spclark]

From the "for what it's worth" crowd .....I would be real tempted to Slug the barrel . Under-sized barrels are possible in a factory rifle , and it would create exactly the situation you are describing.

I was gonna post this too, thinking an underbore barrel’d be acting just like this one seems to be.

But D-4297 saved me the trouble. Slug that bore, find out what you’re forcing .308 bullets into.

 

[Darrel Martin]

I'M not sure about the primer signs, such as backing out, as indicators of excess pressure..Does it seem to have bolt timing and primary extraction problems? That can cause difficult extraction not related to excess pressure.

 

[lb-ft]

Third vote for Remington factory ammo trial. It will cost $18 and next to no time.

Do it

 

[JFrank]

^^^^
They all shoot Federal Gold Medal Ammunition last I heard.

 

[mtnman31]

Thank you for the assistance and suggestions. I burned a little midnight oil last night and figured out part of the problem. I'm embarrassed at what I discovered. I have more than one reloading press. Last time I switched between presses, I left my sizing die set up for the JR press and never checked it when I changed over to the RC press. I was bumping the shoulder back .025"! I guess I was subconsciously attempting to make a new wildcat cartridge. The embarrassing part is that I have multiple tools on my bench that would have shown my error, had I just used them. I've got a ammo checker gauge and two different tools that measure cartridge headspace/shoulder length. I was just being complacent and never used them. That explains the backed out primers, but not the flattened primers and heavy bolt lift.

That being said. I know that properly resetting my sizing operation won't solve all the issues with this rifle because looking at the ammo I tried to work up last year, it was sized properly and I was definitely not getting acceptable results then. I think my next step will be to slug the bore and measure my lands/grooves. I'll also get a box of factory ammo and see how it performs.

Today's reloading lesson, don't be lazy and/or complacent.

 

[JFrank]

You knucklehead..
We were worried sick over this, thank goodness you have it figured out now get outside and shoot somethin...
Smiles
J