Help with .308 OAL

[jray57]

Recently got my son a model 14 Classic in .308. Figured it was time to get back into reloading after a 20 year hiatus. Got a new Sierra manual, some Varget, Federal 210M primers, and 165 gr Sierra bthp. Figured I would fireform the new WW brass with a moderate load. Used 42gr and got cratered primers?! This was with a COAL of 2.750 well under the max Sierra stated of 2.810. I was aiming to get the top of the boattail at the base of the neck, not yet knowing what the max length of seated against the lands would be. And not really concerned at this point, just wanted to be short at this point to get a few rounds through it. So I figured I would do what I probably should have done to begin with and started at the minimum (38.5) and loaded 5 rounds each at .5 grain increments up to 41.5. Again cratered primers at the minimum load, this time in once fired, neck-sized cases. My reading on this forum made me think that maybe the slop in the firing pin/bolt face might be causing the primers to be cratered but not due to high pressure. well this morning I figured I would find out what the COAL would be with the bullet .005 short of the lands. I seated a 165gr Sierra long and started tring to close the bolt on shorter and shorter lengths. I could not close the bolt on anything longer than 2.750 (go figure). Upon extracting the case I measured it at 2.745. The cases had been sized with a collet neck sizing die so I figured (again) that the bolt closing was seating the bullet deeper to a point jammed against the lands. I smoked the bullet with a lighter (no powder or primer) and continued seating the bullet deeper in .005 increments until I could no longer see the lands on the bullet. That COAL ended up being 2.720. A rough measurement from the base to the lands looks like 2.285.

[jray57]

Does this seem normal (acceptable) to you? I am assuming this may have been the reason for the primers cratering. Just wondering what those in the know think about the load(s) used, the seating depth and the length of the chamber to the lands. Need some input before I go load some more.

[sharpshooter]

Cratered primers are nothing more than a visual annoyance. As long as they are not blanking it's nothing to lose sleep over. Just because they crater is not neccesarily a sign of pressure. Most of the time it is caused by the contour of the firing pin tip. Most firing pin tips are .068" in diameter and have a full radius. The tip of the pin will never penetrate the primer cup more than .025", and if the radius of the pin is .034", the tangent of the radius is blow the bolt face. This leaves an area unsupported and gives the primer somewhere to flow. You can re-contour the firing pin tip with a .020" radius and pretty much eliminate the problem.
http://i2.photobucket.com/albums/y48/sharp-shooter/firingpintip.jpg

[jray57]

Thats kind of where I was at with the cratering issue until I checked the seating depth-distance between bolt face and lands. The Lee manual even lists a minimum COAL of 2.750. I'm at 2.720 to just clear the lands by .005.

[r0ttie1]

Thats kind of where I was at with the cratering issue until I checked the seating depth-distance between bolt face and lands. The Lee manual even lists a minimum COAL of 2.750. I'm at 2.720 to just clear the lands by .005.

I might be having the same issues as you are. I haven't reduced the OAL to the point to have though.

[tammons]

Sounds like a pretty short throat.
I have not shot that bullet but my 308 with a 130 gr barnes TTSX loaded 20 of the lands COL = 2.865.

I don't pay attention that much to primers until they really flatten out then I start looking for brass flow and
measure the case head.

That said I have shot various factory loads that the primers were so flattened you would think you were 6-7k over.

I would say the cratered primer was because the bullet was jammed.
That load in QL is running at about 52K.

Did you check and trim the brass ??

You have any brass flow or case head expansion ??

[jray57]

I trim and chamfer every time after neck sizing only with a Lee collet die. Where should I measure for case head expansion and what are acceptable limits? Ther is a faint "line" about .285 from base of case - at this point the case measures .470 which according to Sierra specs is correct. FWIW the Sierra 150gr SPBT jammed measures 2.815 OAL

[tammons]

What was the brass type ??

The line you see is where the case halves are joined.
When you see a line or a ridge its time to stop and check it out.

If you see a distinct ridge you can feel with your fingernail then you have have high pressure
but that might depend on the brass, IE Remington brass is soft IMO.

About half of my 6.8 SPC brass ends up over expanded and I trash it, but I am running them very hot.

I usually see very flattened primers, brass flow and case head expansion together.
Never have blown or pierced a primer though.

Measure it on the ridge.

I think the typical accepted expansion is about .002 maybe.
.005 is too much. From what I have seen that is where a ridge starts to show up.

That said I have some WSSM brass that was expanded .008 which is a lot, and it is super hard brass,
but it only had some primer flattening and no crater. The WSSM brass is really too hard to read though.

[jray57]

It is WW brass that I bought new unprimed. The "hottest" load I have shot in these cases is 43 gr Varget. This is still well below max according to Hodgdon's data. Is this "line" where I would measure for excessive case head expansion? Any expansion I should be worried about would be over .470 correct?

[tammons]

Well I have my terminology wrong.
It is PRE expansion or something like that.
You may want to ask SSS the proper terminology.

Case head expansion is right at the end of the case where it is thickest right at the groove and measured in .0001 increments.

What I measure is up the case where the case halves are fused together so yes where it is bulged out the most.
If you have ever seen a picture of a case that has split apart from high pressure that is where it happens.

Go down the page where he is holding the shell in his hand. Luckily he still has his hand.
http://www.ar15.com/forums/topic.html?b=3&f=121&t=494141&page=1

I usually measure at the case head and at the bulge, but if you want to know exactly, then measure a new case at that point and your bulged out case.
I have read that in a lot of cases WW cases have problems, thin, undersized etc.

If the brass is undersized from the factory then measuring a bulge wont tell you much.

Its a sort of difficult thing to figure out. I just got into a thread at arfcom, where a guys new 6.8
rifle blew up on his 3rd shot with some hot factory ammo.
It turned out it was some oddball bad chamber design error combined with the bullet/ammo.
Everytime a round chambered, it would shave off a thin copper ring. by the 3rd shot they had fudsed together to
wedge the bullet in.

We all speculated on chamber ammo, bad ammo, but it was a combination of a bad chamber and hot ammo with a certain bullet that did not work in that chamber.

So if your powder is good, I would guess something is causing your rifle to spike up maybe about 7-8k psi. Quickload says you should be at 53k but if you are getting a lot of case expansion it sounds like you could be at max like 60-62k +-

Are you getting any ejector brass floe on the face of the case ??

[tammons]

Did you try any factory ammo in it.

Is it a new or used barrel/rifle and did you give the barrel and chamber a good cleaning ??

Some things I have had happen to me that caused high pressure that caught me by surprise.

Case that measured less capacity. Probably a 2-4k over a few times

Oil or gunk in the barrel or chamber.
I picked up a rifle one time that had been cleaned and oiled but the chamber had not been
thoroughly cleaned and it still had some wipe out residue around the shoulder area. It caused the bolt to lock on a normal load.
I usually clean my rifle barrels and spray them out with brake cleaner then give them a very light oil patch
follow by 2 dry patches. I would guess that one was about 5-7k over.

Another one that got me was I was using load data for a 338 210 Gr TSX and loading a longer 210 grTTSX (tipped)
My chrono jumped up 100 fps and bolt lift was very hard.

So now what I do is start off in quickload.
If its iffy, I measure the actual case capacity, measure the bullet length
and go from there.

A carbon ring can cause high pressure.

Jammed bullet, but I have never reduced a load going from jumped to jammed much more than about 1/2 grain.

Not enough head space. Have you checked that ??

Something different in your setup than the speer manual could cause higher pressure, powder, bad powder, different primer, different brass, different bullet, chamber, fast twist.

Edit: I just ran your load again and at 43gr of varget it came back at 50.5K so you must have some other issue.
Hodgdon site says 46gr is a max load at 2.75
QL returns 62k at 46gr.

[tammons]

Measuring case expansion....

http://www.reloadingroom.com/index_files/Measure%20Pressure.htm

[jray57]

It is a new gun. I cleaned the chamber/barrel thoroughly with shooter's choice solvent prior to shooting it for the first time. I have seen no sign of pressure in the way of plunger/extractor marks on the case head. Also have never experienced hard or sticky bolt lift after firing. Not really sure how I would check headspace-I don't have headspace guage. I think next step will be to try some factory ammo using method in article you linked. Measuring case expansion as well as chronographing the load to compare to velocities I am getting with my loads, which incidently were about 2650 fps for the 43 gr. load.

[tammons]

Maybe you just have a sloppy bolt head, pin and or soft primers.
Maybe try some CCI BR primers. I really like them but they are hard primers.

http://6mmbr.websitetoolbox.com/post?id=2741414

A digital caliper is the easiest way.
I also use one to sort cases as to which ones need to be trimmed, measure COL etc.
Good to have if you fiddle around with reloading.

http://www.harborfreight.com/6-inch-digital-caliper-47257.html

In general .002-.003 is probably about max case expansion at the seam, so you can just measure at the
largest part of the base where it is thickest and at the seam.

With a 22" barrel 165 gr SHBT and 43 gr varget Quickload says you should be at about 2575.

I think I would shoot one 43 gr shot through a chromo and see what you get.

So if you are close to that,
no ejector marks, IE no brass flow
no severely flattened primers
the case expansion is normal
no heavy bolt lift

I would say your load is normal and the cratering is as explained above by SSS and or the link.

I just looked through all of my brass, in 308 338/284 and some 375 Ruger, all savage and also 270 weatherby magnum hand loads and I don't have any cratering. Actually I don't think I have ever seen any at all except maybe an AR and factory ammo, but I use CCI BR primers.