starting load with pressure signs?

[riverratt]

I wanted to go with a faster powder than imr 4350 for the 7mm-08 ( I just don't like compressing powder that much) so I thought I'd try imr 8208 xbr. I called a barnes tech and got some data for the 120gr ttsx, min charge 40gr max charge 42.5gr. I loaded 5 rounds each from minimum to maximum charge in .5gr increments.

At the range the 40gr charge had a cratered primer. I thought it could be just a low charge so i went on to the 40.5gr charge, the results stopped me there and sent me home. Cratered primer sticky bolt and flowing brass!!

Now I do have load data from hornady that is for cup and core bullets that is lower than what barnes starting load is. Should I neglect the barnes data for there bullet and use data that I have from hornady or just call it a lost cause?

BTW I am seating my bullets .040 off the lands as per a barnes tech suggested.

[jdscholer]

Are your cases trimmed within specs? jd

[riverratt]

[QUOTE Are your cases trimmed within specs?-CENSORED-/QUOTE]

Yes all cases are trimmed 10 thousands below max case length. I am using necked down .308 brass that was FL sized fired then I set the die to bump the shoulder back 3 thousands. The bolt closes without any resistance. I have had no issues with pressure wile using imr 4350, imr 4064 or imr 3031 within load specs using the same brass prepared the same way.

With the 4350 powder I can't seat the bullet deep enough (barnes bullets like a jump) to achieve the accuracy potential of the gun. The gun don't like the other two powders with that bullet. I'm just trying to find that magic combo with good velocity and accuracy. I'd like to see a velocity around 2900 fps give or take 100fps.

[Clark]

I am calculating that with 8202 xbr 40.5 gr 120 gr TSX 7mm-08, we could get a sticky bolt if the over all length were 2.3" instead of 2.8".

[Snyper]

I called a barnes tech and got some data

I'd stick to what's published rather than word of mouth over the phone

[PA-Joe]

You can also use IMR 4064 or Win 748

[steve4102]

I am using necked down .308 brass

What brass? Is it Military 308 brass?

How far off the lands are you with your TTSX?

I ran your load through Quickload. Matching Hodgdon data with the 120gr Ballistic tip, switching over to the 120gr TTSX pressure increased by just over 4K and no where near an over pressure Max.

This tells me something else is amiss here.

Military brass?

Into the lands?

Scale off?

Mixed up the loads in the loading block, as in max is now Min and Min is Now Max.

Wrong Powder?

Just my .02.

[James K]

When necking down any case, or using a case for a shorter round (like re-forming .30-'06 to .308), don't overlook the neck thickness. When a round is fired, the case neck has to have room to expand and release the bullet or pressure goes pretty high. While .30 to 7mm should not be that much, if the chamber neck is already tight, there could be a problem.

So ream the case necks to 7mm (or alternatively, turn the necks on the outside, but that is trickier) and see if that helps.

Jim

[Metal god]

FWIW , I have 3 manuals -Sierra , Lyman and Hornady . None of them have the 120gr 7mm-08 min charge that high . all in the upper 30s . They all how ever have the max well over Barnes 42.5gr . All were in the 44 to 45gr range ,

What were your velocities ? Were they higher then what the charge should have given you ?

[riverratt]

[QUOTE What brass? Is it Military 308 brass?

How far off the lands are you with your TTSX?

I ran your load through Quickload. Matching Hodgdon data with the 120gr Ballistic tip, switching over to the 120gr TTSX pressure increased by just over 4K and no where near an over pressure Max.

This tells me something else is amiss here.

Military brass?

Into the lands?

Scale off?

Mixed up the loads in the loading block, as in max is now Min and Min is Now Max.

Wrong Powder?

Just my .02/QUOTE]

Hornady match brass

Aprox .05 off the lands. I do not use any precise way of measuring this I just blacken the bullet and chamber eject and look for the rifling marks. Seat the bullet deeper and repeat until I don't have the marks, get my OAL and seat the bullet down to where I want.

Cross checked my scale with my grandpa's Dillon, good there.

Don't use a loading block for that reason one at a time.

Definitely not the wrong powder.

[riverratt]

[QUOTE
What were your velocities ? Were they higher then what the charge should have given you ?/QUOTE]

Can't tell you I don't have a chronograph (on my wish list). One of the ranges I go to rents them but I wasn't at that range.

That's what's got me confused, why would barnes have there starting load at 40gr wile hornady starts with 37.6gr? Shouldn't the mono bullet produce higher pressures than a traditional lead bullet?

BTW I did notice that I had made a typo mistake in the op the powder is imr 8208 xbr. Sorry about that I was on break at work and was in a hurry.

[tobnpr]

Aprox .05 off the lands. I do not use any precise way of measuring this I just blacken the bullet and chamber eject and look for the rifling marks. Seat the bullet deeper and repeat until I don't have the marks, get my OAL and seat the bullet down to where I want.

FWIW, I use data right off Hodgdon's site- they're the powder manufacturer. In this case it agrees with what the bullet manuf. provided, but that's not always the case.

Get yourself an OAL gauge and bullet comparator from Hornady. IMO, these are as essential as a scale for serious reloading.

Info on the rig? Barrel make and length?
You should easily be able to get 2900 with 120's, with either H4350 or IMR 4350. I was getting 2730 with H4350 with 162 heavies- and 2800 with IMR 4350.

You mentioned cratered primers, but were there any other overpressure signs- like hard bolt lift/extraction? I suspect there is another issue, not overpressure.

Steve is right- doesn't make sense.

[DAVID NANCARROW]

Assuming the neck thickness is within spec and the cases are sized properly, I would back down several grains (maybe the start load on cup and core that you have already looked up) and work them back up in .5 grain increments.
Something else would be to have a chamber casting done to make sure you aren't running an exceptionally tight chamber.

[riverratt]

[QUOTE]
You mentioned cratered primers, but were there any-CENSORED-other-CENSORED-overpressure signs- like hard bolt lift/extraction? I suspect there is another issue, not overpressure./QUOTE]

All I had at the 40gr mark was a slightly cratered primer, barley visible but you could feel the raised portion with your thumbnail. Primer was flat with no sign of gases leaking around it. The bolt opened easily.

When I stepped up the charge to 40.5gr the bolt was sticky, not hard by any means just harder than normal. The primer was completely flat filling the pocket and the cratering was more visible. On the headstamp there was a nice shiny spot where the brass was beginning to flow into the extractor.

When I was using imr 4350 I started with my data, I forgot which book whatever was lowest, of 47gr. That charge filled the case up to the neck. Fired some test loads and had a cratered primer. I called barnes and they informed me that I was at there max load and that I needed to back off the lands to around .050 for best accuracy with there bullets. I backed off the charge to 46gr, no signs of pressure there. Accuracy is ok with that load but I can only seat the bullet around .02 off, completely compressed load.

I have an axis II with a 22in barrel.

[243winxb]

The loaded rounds neck diameter should not be larger than .315" You have found your maximum load. Now work down till you find accuracy you like.

[steve4102]

Don't use a loading block for that reason one at a time.

What I meant was how the completed rounds were marked with various charges? Sharpie? Or did you just place them in order in a box or block?

Is it possible the completed rounds were mis-marked or mixed up?

[Unclenick]

Originally Posted by riverratt

That's what's got me confused, why would barnes have there starting load at 40gr wile hornady starts with 37.6gr? Shouldn't the mono bullet produce higher pressures than a traditional lead bullet?

It will. But Hornady data is well known for usually being conservative. From the guns they describe developing the loads in, I don't believe they pressure test, so they tend to make an extra safety allowance. So does Sierra.

Your best bet is to look at Hodgdon's site. They distribute the powder and maintain a reference lot that is exactly average in behavior and they measure pressure. Their starting load for a Nosler 120 grain BT bullet seated to 2.800" in Remington brass with a Remington 9½ primer is 40.1 grains. I would put that bullet and charge weight and COL into QuickLOAD with your case water overflow capacity and note the peak pressure, whatever it is. Then swap in the Barnes bullet as you did before, but adjust the powder charge down until you get a pressure match to what you wrote down. Take your Barnes starting load down to that number for your gun.

Unless I missed it, you didn't say what primer you are using. Pressure signs on a primer tell you that primer is having trouble with the pressure, but little about how it is for the bras or the gun. Winchester primers became notorious for showing pressure signs and piercing early, ever since they stopped nickel plating them (a move they made in response to complaints about inadequate sensitivity). If you aren't using them already, try getting some 9½ primers to copy Hodgdon's load. See if the pressure sign issue changes for you.

[Clark]

~ 13 years ago, I necked down 308 brass to 243, loaded to between 70k and 80 kpsi, but some had even higher pressure. The three above all had the same bullet and powder charge.

It took a while to figure out that when it takes 100 pounds on the bolt knob to close the bolt, the neck might be getting pinched. That was with a standard SAAMI 243 reamer and LC 308 brass.

Since then I have done some careful measuring of RP and Win 308 brass necked down to 260 Remington SAAMI chamber. About 10% of the necks will be too thick.

Based on that, 308 brass necked down to 7mm-08 with a standard 7mm-08 SAAMI chamber, should be no problem.

I suggest measuring the chamber neck with pin gauges and measure the cartridge neck with dial calipers that are checked with the pin gauges.

[riverratt]

Steve, I load 5 rounds of xxgr of powder place in a small freezer bag and label the outside of the bag as well as a piece of paper inside the bag. I then move on to loading xx.ygr of powder and repeat. At the range I check the bags place in order from lowest to highest crosscheck with the paper and only those 5 rounds are put on the table to be shot.

[F. Guffey]

It took a while to figure out that when it takes 100 pounds on the bolt knob to close the bolt, the neck might be getting pinched. That was with a standard SAAMI 243 reamer and LC 308 brass.

It never made sense, some choose to close the bolt with slight resistance to closing. Even when they did not know the cause. There are methods and techniques a reloader could use to determine the cause. I have not determined how to measure neck tensions so I have to settle for pounds.

F. Guffey

[Longshot4]

You were working up loads and found primers or even one primer cratered. I don't see any reason to be alarmed. The clue has been seen. Now back off. It is as simple as that. You knew to be cautious but you went on because you were curious. I hate to say it but I have been there. I understand but we know better.
Back off .5 or 1.0 and then finish.
Now sure you seen signs or higher pressures so after you finish firing the safe loads. Assuming that the bullet is not too deep, the powder is stable... Inspect everything I would start with case necks. I have seen after trimming and before chamfering the case thickness by just looking at the mouth. I have heard that the seating die seating piston can be the wrong type causing the bullet to get pressed by the tip deforming the bullet. Redding just came out with replaceable pistons (that may not be the right word) to adapt to the different bullet shapes. Good luck and stop when you find some thing wrong and prevent problems.

[Bart B.]

A weak firing pin spring and/or an undersize pin tip allows primer cratering with normal, safe, maximum loads. If the primer dimple depth is shallow, that's usually a sign of a weak spring.

Too short of pin tips that don't stick out of the bolt face enough also causes shallow dimples and cratering. Tip should stick out past the bolt face at least .050".