7-08 overpressure problem

M

MrMagumba

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Jan 9, 2016
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Bummed that my new Weatherby Vanguard is not behaving. The short question is; How much space is needed between the shoulder of the case and the shoulder of the chamber for this hunting gun? I think I have about .007-.010 which should be plenty from what I have read, but maybe I'm wrong. So here is the background:
New PPU cases full length sized in Redding Series A die. Hornady 139gr interlock. .020 off the lands. Initial velocity ladder looking for nodes 37.7gr - 42.5gr Varget at .2 gr intervals. No problems.
Push it a little farther. Hornady manual max at 43.5, Hodgdon max at 41.5. Shoot 41.5 - 43.5. At 43.1 sticky bolt on ejection and velocity drop. Call it a day, go back and load groups at 42.0 node to see what she'll do.
Once fired cases now full length resized again. Easy chambering, but groups a bit sticky on the retraction. Not good for hunting. Primers a bit flat but not terrible. Bullets were moved up to .015 off lands to see if I could get an awesome group. .005 change causing problems? Hmmm. Cases stretching a bit more than I'm used to. (.005-.010) Some ending up over spec (2.035).
Resize again bullets back to .022 off the lands and trim all the way back to 2.025. Reshoot ladder 39.7 - 42.5. First few shots- sticky bolt. Something is up here!

Fired cases are not chambering smoothly. Let's do some measuring. Resized fired case loaded 1.615 on the .400 datum chambers smoothly.
Fired cases not resized 1.624 are sticky when chambering and ejecting. Could I possibly have a brand-new gun with headspace too short? Min chamber spec 1.630, length tolerance +.015 if I'm reading that correctly. Try a go gauge- darn $50 and wait for the mail or wait for day off and drive to far away gunsmith for gratuitous go gauge check. I'll make my own. 30-06 case reformed down to 7-08 and trim. Keep bumping until 1.630. Like hitting a brick wall when chambering- no go. Try again with another reform. Same result. Keep bumping until chambering correctly. At 1.622 it is working nicely.

So two things: 1) Original question: Should I be having problems with 1.615 ammo in a 1.622 chamber? 2) If my measurements are correct, I should probably have the gun fixed. How does a gunsmith fix this on a Vanguard?

Sorry so long, but want to understand where my thinking could be off. Don't want to just throw it at a gunsmith and say "make it shoot". or worse yet, have somebody tell me to just shoot factory ammo. Thanks for any insight on how to proceed.

p.s. Ammo is in spec for neck diameter, but haven't measured neck in chamber yet.
 
I used to try and push for velocity and almost max loads with Varget in my 7-08s. I never had a problem as far as extraction or flattened primer issues. One day I backed off the powder just because to starting load data and got the best groups I could ever ask for. That's my hunting load these days with BTs or SGKs. 2700 fps is just fine for a hunting load. Sticky extraction and not over max, could it be a tight chamber?
 
MrMagumba said:
New PPU cases
Click to expand...
Compare case volume/weight to other brands. Heavier brass with less volume will increase pressure.

You have high pressure signs.
MrMagumba said:
Hodgdon max at 41.5
Click to expand...
May be the rifles maximum, with your components.
MrMagumba said:
Fired cases not resized 1.624
Click to expand...
Bump back .004" for hunting. If still hard to chamber, extract, the area near the case head may be bulged some? The sizing die doesnt go there.

Pressure signs
 
^^^^^THIS^^^^

If you do not have a headspace gage, you need to get one.

www.youtube.com

Hornady HeadSpace Gauge

An examination of the Hornady Headspace GaugeExperience Level: Intermediate
www.youtube.com www.youtube.com

There are other manufacturers. Sinclair for one.

You mentioned .010 to shoulder. This would be way excessive. You need to find out exactly what that headspace is. If it's more than about .005, you need to call Weatherby.

I size hunting rounds for no more than .002 shoulder bump - that's what's being shown in the video.
 
Thanks for the replies. So it seems that case fitment is not the problem. Just out of curiosity I did the home brew go gauge routine on my 260 and it behaved just like the 7-08. It started chambering at 1.620. So the method is flawed, but is evidence that the chamber is probably fine. So there is something about my recipe that is off unless there is a neck problem. So things to do are: try a proper go gauge, get a chamber mold, and try a different recipe. 7-08 brass is not exactly easy to find. The only other powders I have that would work are H4895 and H4350. Which do you think would be better behaved? I'll try to find some different brass and give it a try. I can revisit Varget after I confirm the gun will shoot something.
 
NMexJim, I am using the Hornady headspace/case comparator tool. Interesting point in the video is the caution to not use the tool to compare to SAAMI spec. Even though one of the inserts is .400 like the SAAMI spec, I can understand that this tool is only for relative measurements (comparator more than gauge). My loaded ammo is 1.615 and fired brass comes out about 1.623. So I could improve that by backing off the die, but I'm assuming that .008 slop is not causing the overpressure.
Couple pics. Velocities out of 20" barrel are unremarkable despite sticky bolt. 39.7 - 40.5 Varget at .2 increments. Primers on same 5 rounds.

7mm-08 vel.jpg primer pic.jpg
 
Plunk test seems to be ok. I do see that Sierra has quite a bit lower max for Varget. I'm starting to think that my chamber is on the lower side of spec (which is usually a good thing for accuracy) and my loads are ok for new brass, but too hot for fire formed brass. I'm going to try some H4895 and load it way down and see what happens. If that works I guess we can move to the reloading forum as there is likely not a gun problem. :)
 
No just made that one home brew go gauge out of the 30-06 case. The only stuff I have to shoot is the PPU 7-08 brass. I'd like to try something else as soon as I can find something. The brass is about .012-.013 thick on the neck for the PPU's. That is average to below average in my experience so the oversize neck theory is not high on my explanation list for overpressure. Neck OD of loaded case is about .308
 
MrMagumba said:
NMexJim, I am using the Hornady headspace/case comparator tool. Interesting point in the video is the caution to not use the tool to compare to SAAMI spec. Even though one of the inserts is .400 like the SAAMI spec, I can understand that this tool is only for relative measurements (comparator more than gauge). My loaded ammo is 1.615 and fired brass comes out about 1.623. So I could improve that by backing off the die, but I'm assuming that .008 slop is not causing the overpressure.
Couple pics. Velocities out of 20" barrel are unremarkable despite sticky bolt. 39.7 - 40.5 Varget at .2 increments. Primers on same 5 rounds.

View attachment 1168909View attachment 1168910
Click to expand...
Yep, manufacturer’s economies-of-scale would preclude holding to SAAMI specs, however Sinclair does provide steel bushing. Really, it’s a reference for your firearm only and not meant as a direct correlation to SAAMI. Even SAAMI gives a -.007 tolerance for cartridges and .010 for chamber cuts.
 
Yuck! Went to the range with H4895 35.0 - 39.5 gr in .5 increments. Average max as best as I could find is about 40 - 41 gr.
1st round not that smooth, 2nd round sticky, 3rd round ok with associated unflattened primer, the rest same sticky bolt retraction. I quit at 38.0 grains.
I tried letting the round cool in the chamber before ejecting-no help.
The bolt lift is really not that bad until getting to the detent where there is a mechanical bump. It jams there.
Looks like I'll have to open up the wallet and likely be shooting the 243 or 260 this deer season.
My list of potential culprits in order of least to highest probability looks like this:
Bore too small
Brass does not expand and contract correctly
Bolt has some part failing
Chamber Neck too small at some point in chamber
Chamber has tool marks or needs polishing for easier rotation

time for a nap
 
Have you put some factory ammo thru this gun? Similar issue?

1.615 brass in a 1.622 chamber will have no I’ll affect, other than wearing your brass out due to over working. That’s why we reload, so we can customize that length to suit the chamber.

Your primers and velocity looked fine, so I am not seeing a pressure related issue here, although your charge is at the higher end of things.

I would get Weatherby on the line and start running thru their prescribed troubleshooting sequence.
 
The closer you seat the bullets to the lands ... the higher the pressure will spike .
Drop back your load any time you get "sticky" bolt lift and / or extraction ... and drop back your cahrge any time you seat the bullets closer to the lands .
Do not seat the bullets touching the lands unless you drop back and work load back up slowly .
And dont over resize cases ... try neck sizing only and see if that helps .
Load Safe .
Gary
 
I know I will probably have to eventually drop $50 on box of factory ammo to prove a point, but the likely outcome is that it will function just fine. This is because the factory ammo is built so far below spec so that it will function in guns with poor chambers, like mine perhaps. Unless I get some custom dies that take it way down, the reloads won't work that well. I think the problem is that the neck is too narrow just near the front. As the better fitting once fired cases expand, the neck flows forward into this narrow area and spikes the pressure just enough to be a nuisance. Need to get the chamber mold to know for sure. In the mean time I found some Starline brass at Graf and Sons and will shoot a few new brass with the bullet seated back .050 and cases trimmed well below book. This might keep the pressure low enough to support my theory. Also ordered a neck reamer as this gun might be like loading for a wildcat for the most part.
Called Weatherby and they will guarantee that the gun shoots factory ammo, and has a certain accuracy. When asked if they would repair the gun if the chamber was below SAAMI spec, I was not given a clear answer. Their techs would "have to evaluate it."

From today's shoot: notice the third round. It was the only round that functioned normally. I don't know why the pressure was lower on that round but it was the only one to function well. Also that case shortened after shooting from 2.025 to 2.020. The rest lengthened by at least .005 to greater than 2.030. These were pretty tame loads only possible because of the ability to download H4895 to 60% of max per Hodgdon website.

Chrono 4895.jpg primer pic2.jpg
 
Thanks for the reply Gary. Yes, I will be backing the bullets off and paying closer attention to the neck as I move forward with the investigation. I followed the rules initially, starting low and working up slowly. Didn't think the picture would change so much just because I continued with previously fired brass.
 
Least expensive diagnostic option at this point is a chamber cast with Cerrosafe. That will tell you exactly what is going on with your chamber. If the chamber is too small a touch up with a finish reamer should do the trick. Same with the throat.
A soft lead slug can be pushed through the bore and measured to verify bore diameter.
 
Use 41.5 grs of Varget as your maximum with 139 gr bullet in the new Starline brass.

Measure the web area before & after firing. It will grow larger, but should not be larger then .470"

Minimum trim length is 2.015" (SAAMI)
Screenshot_20230831-065906_Drive.jpg
 
Yes chamber cast is on the short list. The 41.5 gr max sounds good, and I'll take all the measurements I can with the new brass for more clues. I am tentatively scrapping the chamber neck problem. Just so happens a 2018E aluminum arrow has a diameter of .315 - same diameter as min chamber neck. This inserts into the chamber neck without binding. So the hit list is now:
Bore too small
Brass does not expand and contract correctly
Bolt has some part failing
Chamber has tool marks or needs polishing for easier rotation

Pics of chamber neck
1. Aluminum arrow just shy of chamber mouth
2. Arrow flush with mouth
3. Slightly overlength (2.038) case fully chambered

WIN_20230830_23_29_09_Pro.jpg WIN_20230830_23_29_48_Pro.jpg WIN_20230830_23_31_57_Pro.jpg

Thanks for following along. I know this is dragging out. I'm thinking it will probably work after "polishing/sanding/refinishing" the chamber.
 
Thanks for pointing out that trim length. Load manual recommends 2.025, but I see I have more to work with now.
 
The chamber length can be measured. Link Standard trim is .010" below maximum. Or 2.025"

If the reduced 41.5 powder charge & new brass doesnt fix hard bolt lift, see below.

Hard bolt lift may be caused by 2 things.
1. Bolt timing.
2. Cock on open
Lube- Break Free CLP- 1 drop on each lug & bolt cam.

Something to ask a gunsmith about. I am not one.

Or return to manufacture.
 
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