Unexpected pressure spikes - why?

brotherjack

brotherjack

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I got a buddy with an NEF Handi-Rifle, and we are seeing some odd results indicating that the rifle makes way too much pressure, no matter what you do with it, and I wanna know why. This is the only rifle I've ever seen that doesn't behave more/less in-line with expectations.

Factory Winchester 180 grain 30-06 loads; primers come out flat, and chrony says velocity is around 2900FPS (!?!?!?!)

Handloads with 51 grains of W760 which should be a fairly light load (44,000PSI-ish according to QuickLoad) flatens the primers something wicked (like, WAY more than I have ever flatened a primer in my 308's, and I've played with some pretty hot loads before), and generates 2700FPS instead of the 2500FPS QuickLoad predicts.

He tried working up a while back with 4350 (didn't have the chrony that day), and by the time he got near max, the primers were spooky flat and the action popped open on him.

Seating depths are pretty short - OAL's for both the win factory and 760 hand-loads are 3.15.

So - question to all you more experienced guys, does anyone have any clue why a gun would across-the-board generate WAY too much pressure with whatever you feed it?

Thanks,
 
I would highly recommend sending the rifle to qualified technician, such as a factory warrantee rep, or well qualified gun smith.
I would not continue shooting it.
 
It's _possible_ that your chronograph is lying to you. Can you fire a .22 rimfire over it, or a different .30-06 with factory ammo, to rule this in or out?

Very flat primers are often an indication of high pressures, but that's not the only possible explanation (though to be safe you should assume that it is a high pressure indication until you determine otherwise).

You could try "slugging" the barrel. If you have a soft lead bullet that you can grease and gently hammer through the barrel (a pure lead .32 S&W target bullet works well), you can measure/mike it and see if your barrel is unusually tight)

Does an empty, brand new .30-06 case chamber fully and without effort? (just wondering if the mouth of the chamber might be pinching the bullet)

Were the primer pockets loose on the brass that had severely-flattened primers? (that would be an additional pressure sign that would indicate much too high pressures).
 
Tight bore? Tight Chamber? Perhaps headspace? perhaps loose chamber. The results are why you use a chronograph--that tells you what is safe in that particular rifle. Match the load to the appropriate velocity and don't go higher.
 
Oh, the chrony is mine, and it is accurate with 22, 308, 270WSM, etc. My buddy's rifle is the ONLY rifle I have ever seen come back with unexpected numbers from the chrony. Typically, I tell QuickLoad what my load is, and the chrony reads within a few FPS what QuickLoad said it would.

When I say very flat, I mean VERY flat -- as in, the back end of the case looks like a flat piece of brass; primer pushed out flat and tight, clear to the edges of the primer pocket.

Bore size would have to be WAY off to do that with the pressure -- I routinely shoot .312 bullets in my .309 (measured) bore mini-30, with zero change in velocity or apparent pressure over .308 bullets.

Hrmm.... I'm not aware that NEF does customer-service in Canada -- but I do tend to agree, would be nice to have a pro look at it.
 
Well in 2 cases of friends rifles, both new remingtons, one has I believe too large of head space and flattens primers of almost everything and tears brass in half if it is not just neck sized, this is a 22-250 vtr. And the other gave large pressure signs was a new remington semi 30-06 that was factory chambered with a 270 reamer(big opps). I would do as H4831 says and have it checked out by a qualified gunsmith.

My 2 cents
-Chad
 
It's not the rifle. It's the ammo. His charges are not 51 grains if you're getting 2900fps. Something is screwy with your buddy's powder thrower, his scale or how he's using either. A max charge of W760 is 55.5 grains. Gives 48,700 CUP at 2743fps for a 180 grain bullet.
 
"...FACTORY AMMO that's..." DOH!. Contact H&R for their Canadian repair people. Epp's is an H&R dealer too. They may be able to help.
Phone: (866) 776-9292
Fax: 336-548-7801
 
Check chamber length

My Dad was working up hand loads for .378 Weatherby. Chrony was reading wild velocities. He had a hell of a time running the bolt to chamber the next round. By the fifth shot he had to use a block of wood and hammer on the bolt to open it.

Findings were the brass after a few reloads had streched and when chambering the next round, he was forcing the brass into the bore slightly then there was no room for the brass to expand to launch the bullet. Pressures were off the chart and the shot was not a Boom, but almost a scream to it.

My point here is I understand you are using factory ammo, but the chamber may be a few thou short or have it freebored.

My $.02 for all its worth.
 
44Bore said:
Tight bore? Tight Chamber? Perhaps headspace? perhaps loose chamber. The results are why you use a chronograph--that tells you what is safe in that particular rifle. Match the load to the appropriate velocity and don't go higher.
Click to expand...

Yeper. Somethings tight and spiken your pressure. Ever read an article in handloader called "CHAMBER PRESSURE,FRIEND OR FOE" anyhoo it can go up not only by adding powder or changing types,theres unfriendly ways that will mimic those like chamber cut shallow or something trapped in chamber that wont allow brass to open naturally. When it does it creates far more pressure than the load should have. More FPS too but not the kind ya want. That thing needs the chamber cast. Also run a bore cleaner like wipeout through cause heavy fouling has also produced this
 
Coulod it be a rough chamber? I have heard of fresh chambers needing a good polish, as the rough areas were grabbing brass.

I'd contact the manufacturer and see if they can recommend a warranty depo.
 
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