Home Forums Reloading Big Game Rifles Hot Loads? - I really need to get a chonograph

I purchased a Model 600 .308 Win a few months ago for use as a "donor" action. However, it shot so well with factory loads I decided to keep her as is.

After getting new Lapua Brass and Redding dies I decided to go with the 168 grain TSX and H4895 for starters.

I'm currently 10% off Barnes Manual max with a standard X bullet but every primer has been pretty flat and I'm worried this is an excessive pressure sign.

The factory loads I shot were Lapua as well because I wanted the brass. They were accurate but the primers seemed really flat on these also.

I've been considering that the new lapua brass is thick, thus reducing case capacity causing higher pressures than normal. I am hoping that the second loading of these cases might reduce pressure as case capacity increases slightly from fire-forming but I'm also planning on dropping down to 38-39 grains of H4895 (seems excessively low to be getting high pressure in the .308).

The only round I fired out of my 30 loads that did not have a flat primer was shot 26 (after firing 25 TSXs) which was a 165 Grain Hornady Interbond. The other 4 Interbonds showed the same flat primers as the TSX loads.

The bullets are well off the lands to allow for short magazine length, the bolt works fine, cases extract smoothly, no excessive blackening and there are no extrator marks on the case head. Accuracy has been great for all 30 reloads as well as the 20 factory loads.

Assuming pressure is high, what things could cause this. Tight chamber? Thick Brass? Tight Bore?

This is a new occurace for me since I can always get my other loads to at least within a grain of book max w/o seeing primer flattening.

7- sounds like excessive headspace to me. I had the same thing you described happen in a .308 Win. this Spring. My starting loads were showing flattened primers no matter what powder, bullet, or primer combo I tried. So I bought a box of Winchester factory ammo and the first shot showed a flat primer as well. I had a gunsmith verify my suspicion of headspace with a go/no-go gauge. I bought a neck-size die to use on brass for this rifle so the shoulder won't be set back at all.

Dale

Second vote for headspacing, had the same thing happen. Confirmed it when switching ammo between two .308 bolt guns. Ammo set up for one rifle would actually go in deep enough that I could not extractl live ammo.

What you are seeing is likely the primer backing out and hitting the bolt face, gas leaks around the primer leaving the black soot and then the case slams back into the bolt face, reseats and flattens the primer.

The simplest solution is to pull the barrel and have a thread or two taken off and rechamber. If you have a RCBS casemaster (im sure there are other tools) check for casehead seperation. I had several cases that would not have survived a second shot.

These were all brand new cases, so in theory if I don't bump my shoulders back when resizing the next batch pressures should return to expected levels.



I realize factory loads still might be "hot" under this scenario. However, I very rarely use factory ammo and only did so in this case to test the gun to see if it was a keeper before investing in dies and brass.



To clarify, there was no excessive blackening with these rounds.

You have it right but you should understand that you most likely don't have a "hot" condition. Your chamber probably has a little excess space so the cartridge moves ahead slightly at the strike of the firing pin. The case grabs the chamber walls during the explosion and the primer possibly backs out ever so slightly, then the pressure forces the case back towards the bolt face flattening the slightly protruding primer. Bottom line is they "look hot" but you could easily be running 10K under max pressure and get "the look".

Reading pressure by primer apperance is not a good idea. Better bet is to use case head or pressure ring expansion as a guage. You are right to assume that a chronograph would tell you if you are approaching unsafe pressure levels. IF you know how to interpret the readings the chronograph is giving you.

During load developement, you should see an even ammount of gain in velocity for each even increment in powder charge increase. When approaching max, the gain slows down, it can even decrease!

I've since fired some loads using 1 fired cases that were formed for my chamber. I also backed off 1/2 grain of powder.

I fired 5 rounds with 2 primers being completely rounded (shots 2 and 4) but 3 were less rounded but not as flat as the loads I was getting with brand new cases. The group was very accurate.

Does this still appear to be a headspace issue?

What would cause the apparent differences in pressure for each round. All charges were measured with a scale, OAL was precise and cases were all in spec.

I'm inclined to think you have varying primer hardness rather than seeing signs of excessive pressure or a headspace problem. If it hasn't blown or the pocket hasn't expanded enough to let some gas escape around the primer, trying to determine anything about pressure from the primer's appearance is an iffy proposition. It is equally iffy trying to determine pressure from case head measurement -- especially with new brass.



For those who don't have access to pressure measuring equipment, a chronograph is the second best method. There is nothing mysterious about either using one or qualitatively interpreting the probable pressure level.

7mmsaum,

Ran Quickload using Barnes recommended load of 43.5 grains H4895 in a 308 Winny using the standard Barnes X 165 grain Flat base (Barnes item# 30825) and got 67647 psi which is an overload.

Subsituting a 165 XLC (Barnes #30857) and the same 43.5 grains I got 64975 psi, which is also an overload, but 65k psi is ok for good brass in a good rifle.

Backing up I got a "safe load" at 41.5 grains with the regular 165 X @ 59185 psi.

No 165 grain TSX's are listed in my version of Quickload.

Overloads as shown by quickload is common using Barnes #3 data.

Quickload is a good tool, and a chrono is even better.

Good luck,

Bob

Shadow,

I appreciate that information. I started at 40.0 grains and only went up to 40.3, so I wasn't that far off from the 41.5 max that QL gave you. I had 43.5 as the book max so that was strange to be seeing flattened primers at close to 10% off of book max.

When I dropped down to 39.5 the primers looked better. I'm going to have access to a chrony on Sunday and that should give me an idea where I stand.

I had access to to a chonograph (thanks to member John Frazer) this weekend and was getting between 2325 and 2375 fps with 39.5 and 39.7 grains of H4895 (168 TSX in .308 Win).



That is probably the expected velocity from this charge after I deduct 200 fps for the 18 inch barrel.



After seeing this, I feel like there is certainly room to work the loads up another 150-200 fps. I'm also going to try to shoot some factory loads through the chrony to get a ballpark on what the short barrel does to published velocities of the .308.



Another guess on the primers being flatter than normal could be that they seat slightly deeper when using my RCBS hand priming tool than most of my other cartridges. Since they had a little bit more of a running start before hitting the bolt face, they might flatten a little more than expected.

I put that load into quickload using a nosler ballistic tip. Everything I read about the tsx is it definately makes less pressure than the regular barnes because of reduced brg area. Everthing I read seems to indicate that it is safe to use normal "for wt" load data with other bullets with the tsx. Some people are even approaching the xlc data from what I'm reading. (But do not take my word for it). Anyhow with the 18" barrel it predicts a velocity of 2350 at 48,000 psi. (Which is sure "on the numbers" with your experience.) I kept bumping the loads up to 42.0 on QC and it shows 2483 fps @ 56,000psi. Saami is just over 60,000psi. So IMHO you can probably start working TOWARDS THAT LOAD CAREFULLY.
AGAIN--I claim no responsibility for your work or results but I am using quickload the very same way I would research a load for myself. And remember that all lots of powders are a little different and different guns of the same brand and model can run 150fps less or more than the next with the same ammo. Don't know if I've helped but this is the way that I would use the information.

Got to the range this weekend and tested some more loads with my .308 600 and borrowed chronograph.

I wanted to get a factory velocity to see if my gun trended towards higher pressure loads so I picked up some Core Lokt 150s because I couldn't find 165s.

Out of my 18 inch barrel I was getting 2658-2683. This was about what I expected with 2800 being the published velocity from a 24 inch barrel.

The strange thing now is my 168 TSX loads now show normal looking primers for H4895 with both 40.3 and 40.8. (They were flattening a good bit with only 39.5 grains of powder last week)

The 40.8 pushed me slightly over the 2400 mark but I really believe I have more room to work up and think 2475-2525 is about what I should expect. With 43.5 being book max and 41.5-42.0 being QL maxes.

My question is, what could suddenly cause primers to be more rounded after increasing the powder charge? Was my initial load too LIGHT and possibly caused some wierd pressure signs? Could fouling the barrel with Core-Lokts somehow change the pressure of the TSXs on subsequent shots.

Other than the primer thing causing me to be extra careful in working up loads for this gun, I'm extremely pleased with results on paper. This is an unbedded 600 with the original stock, plastic bottom and no bedding and groups have always been good (.75 - 1.25 inches). Actually, the 40.3 - 3 shot group at 100 gave me a single hole that looked like a single .338 or .358 caliber bullet made it. Probably a fluke but flukes like that can't happen unless things are pretty good to begin with....................